Atomic spectrometry update: review of advances in the analysis of clinical and biological materials, foods and beverages

Contents

• 1 Reviews

• 2 Metrology, interlaboratory studies, reference materials and reference ranges

• 3 Sample collection and preparation
  • 3.1 Collection, storage and preliminary preparation
  • 3.2 Digestion, extraction and preconcentration

• 4 Progress with analytical techniques
  • 4.1 Mass spectrometry
  • 4.2 Atomic absorption spectrometry
  • 4.3 Atomic emission spectrometry and laser induced breakdown spectroscopy
  • 4.4 Atomic fluorescence spectrometry and vapour generation procedures
  • 4.5 X-ray spectrometry

• 5 Applications: clinical and biological materials
  • 5.1 Metallomics and elemental speciation
  • 5.2 Imaging with MS and X-rays
  • 5.3 Multielement applications
  • 5.4 Progress for individual elements

• 6 Applications: drugs and pharmaceuticals, traditional medicines and supplements

• 7 Applications: foods and beverages
  • 7.1 Single and multielement applications in food and beverages

• Abbreviations

• References

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Abstract

A theme that emerges from this year's Update is that of ‘green’ chemistry. This, in part, explains the larger than usual number of publications focussing on sample preparation, especially those concerned with the analysis of foods. Procedures that involved dilute acids while still achieving digestion of the specimens were reported by various workers. Meanwhile the trend towards smaller and smaller volumes continues with developments on the micro-scale. These aspects were noted in both the original work and in reviews. Last year saw the large number of papers concerned with metallic prostheses and this topic continues to attract interest. In possibly the first publication in which ICP-MS/MS was used for a clinical application, concentrations of Ti were determined in serum from healthy subjects and patients with hip implants. Concern is evident over the toxicological implications of consumption of rice grown in regions where water is contaminated with As. This has led to several reports of analytical methods and of concentrations in foods and total diets. Localisation of the As into different parts of the plant and the rice was also investigated and, in some reports this included speciation as well as the total As concentrations. Compared with the last few years, Se longer dominates the speciation work reported in this Update and there are more reports relating to As and Hg. A new class of arsenolipids, cationic trimethylarsenio fatty alcohols, were discovered in Capelin Oil. The number of publications applying XRF spectrometry to imaging elements within tissues appears to be increasing with localisation in bone of particular interest. Laser ablation ICP-MS in combination with other techniques, TOF-SIMS, XRD or XPS was also noted, to increase the information obtained.

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1 Reviews

This latest Update adds to that from last year¹ and complements other reviews of analytical techniques in the series of Atomic Spectrometry Updates also from the previous year.^2–6Table 1 and 2 summarise details of the publications used during the preparation of this Update.

Advances in sample preparation were covered in four reviews during the past year and the focus in all these was on pre-concentration. Lum et al.⁷ discussed the use of ionic liquids, sorption by nanomaterials, surfactants and automation, as applied to clinical specimens, pointing out the shorter preparation time and reduced consumption of chemicals when analytical procedures can be reduced to the microlevel. The two other reviews dealt exclusively with ionic liquids. The positive features of the solvents were noted by Escudero et al.⁸ who contrasted the negligible vapour pressure, thermal stability, miscibility with water and organic solvents, with environmentally unfriendly organic solvents. This review covered dispersive liquid–liquid microextraction and single drop microextraction techniques, with a comparison of LODs and environmental compatibility, and discussed critical issues and challenges associated with their use. Saraji et al.⁹ restricted their interest to dispersive liquid–liquid microextraction with an extensive discussion of the extraction and disperser solvents, combination with other extraction methods, automation of procedures, derivatisation reactions and application to extractions of metals. Again, the rapidity, low cost and low consumption of solvents and other reagents associated with the technique was emphasised. These reviews illustrate the trend towards “green” chemistry, a feature observed elsewhere in this Update. Research published during the last 20 years, from Latin America, relating to preconcentration, speciation and determination of elements in biological specimens, was reviewed by Pacheco et al.¹⁰

In a review of the analytical techniques, Gao et al.¹¹ discussed HG, cold vapour, photochemical and electrochemical VG as applied to ICP-MS. The authors also included alkylation and ID calibration protocols. Reflecting work included in our recent Updates, reviews of continuum source AAS and imaging by LA-ICP-MS have been published. Bernhard Welz (an AAS patriarch!) and colleagues¹² presented a critical review of the past, present and thoughts about the future aspects of continuum source AAS. Similarly, Becker et al.¹³ bring their experience with LA-ICP-MS to a review this technique for quantifying trace elements and isotopes within tissue sections with recent improvements in ablation systems, operation and cell design providing progressively better spatial resolutions down to 1 mm.

Reviews devoted to the measurement of specific elements featured As speciation, halogens in a range of specimen types and Sb in blood. Chen et al.¹⁴ described methods developed during the last five years for speciation of As. Approaches to preparation of specimens and the measurement techniques were discussed and HPLC-HG-ICP-MS was proposed as the most powerful procedure. Mello et al.¹⁵ reviewed work published in the last 20 years on the measurement of halogens in biological samples, food, drugs and plants. Sample preparation, analytical methods and the availability of CRMs for the determination of Br, Cl, F and I were discussed. Human exposure to Sb has been the subject of a series of reviews in recent years and concentrations in whole blood and serum/plasma of non-exposed subjects were presented in the last of these.¹⁶ In addition to a compilation of results from published reports, the authors discussed problems associated with measurements in these samples.

2 Metrology, interlaboratory studies, reference materials and reference ranges

The reliability of analytical results, including their traceability to international units, provides the basis for progress in science, accurate diagnosis and correct implementation of legislation for the protection of workers, consumers and the general population. Reference materials and reference methods are the pillars on which such confidence is built. A few reports have appeared in this review period, dealing with these issues. Turk et al.¹⁷ reported the certification of a tablet RM (NIST SRM 3280), for the content of 26 elements, 13 vitamins and two carotenoids. A further paper by Christopher and Thompson¹⁸ provided details of the quantification of Cd in this SRM. After sample pretreatment involving both precipitation and solid phase extraction, the authors were able to determine the Cd mass fraction as 80.15 ± 0.86 ng g⁻¹ (mean ± 95% expanded uncertainty) by means of ID using both Q-ICP-MS with a collision cell and SF-ICP-MS. In an attempt to maximise the value of existing multilevel SRMs for trace elements in blood (SRM 955c) and urine (SRM 2668), the mass concentration values of As were determined by RNAA and ICP-MS. The certified values were 10.81 ± 0.54 μg L⁻¹ and 213.1 ± 0.73 μg L⁻¹ in urine; 21.66 ± 0.73 μg L⁻¹, 52.7 ± 1.1 μg L⁻¹ and 78.8 ± 4.9 μg L⁻¹ in blood, Levels II–IV. The As mass concentration in blood, Level I, could not be assigned, due to discrepancies between the results of the methods applied.

Reference materials for elemental species are scarce. The accurate determination of MeHg is of particular interest, due to the growing concern for its potential toxicity for vulnerable population groups exposed through the diet. Ulrich and Sarkis¹⁹ reported the preparation and certification of a fish based RM for the content of Hg (0.271 ± 0.059 μg g⁻¹) and MeHg (0.245 ± 0.053 μg g⁻¹). Both FI-CVAAS and ID-ICP-MS were applied to determine the certified values.

The accuracy of the determination of the concentrations of electrolytes in serum is a critical issue, owing to the importance of even small variations of such values for the diagnosis and monitoring of diseases. Two groups of researchers reported improvements of reference methods in this area. Yu et al.²⁰ at NIST described a faster method, as compared to the tedious preparation required by TIMS, for the determination of Ca, K and Mg after a simple dilution of serum samples. Measurements were carried out by SF-ICP-MS, using ⁴⁴Ca, ²⁶Mg and ⁴¹K for ID. Polyatomic interferences on the measurements of the ⁴²Ca : ⁴⁴Ca and ²⁴Mg : ²⁶Mg were substantially resolved at medium resolution, whereas residual interferences on the ratio ³⁹K : ⁴¹K could not be eliminated completely at levels below 100 ng g⁻¹ even using the high resolution mode. The analysis of NIST SRM 956 provided values (mean ± expanded uncertainty) comparable to the certified ones (obtained values vs. certified ones, respectively: Ca, 10.14 ± 0.13 vs. 10.17 ± 0.06 mg dL⁻¹; Mg, 2.093 ± 0.008 vs. 2.084 ± 0.023 mg dL⁻¹; K, 15.48 ± 0.11 vs. 15.55 ± 0.13 mg dL⁻¹). Comparable results were obtained by a separate group in Germany,²¹ using the same technique for the simultaneous determination of a wider panel of elements (Ca, Cl, K, Li, Mg and Na) after dilution of the serum samples with 4 mmol L⁻¹ HNO₃. Coefficients of variations ranged from 0.46% for K to 0.78% for Mg and the analysis of NIST SRMs gave mean biases between −0.46% (K) and 0.85% (Cl). The results were also comparable to those obtained with reference methods based on different analytical principles (AAS, FAES and coulometry).

The first step to ensure the traceability of analytical results is the calibration of analytical instruments, in order to establish a meaningful relationship between instrumental signals and concentrations or mass fractions. The availability of appropriate materials, representing known values of the quantities to be measured, is therefore essential. In many cases, these will be solutions, accurately prepared from pure metals or other compounds. Other techniques, among which XRF and LA-ICP-MS, require more complex strategies to produce reliable calibrating materials. Inui et al.²² devised a clever approach to this problem for the determination of Cd in rice by XRF, by producing rice grains with a known amount of Cd embedded. This was achieved by soaking the rice grains in MeOH containing a stated amount of Cd, followed by heating and cooling. The materials could be produced at different Cd mass fractions, determined via AAS, and stored in appropriate plastic containers.

The last but not least step when reporting a measurement results is the assessment of its uncertainty. Due to the complexity of analytical measurements, this is not a straightforward task. Coelho et al.²³ undertook the task to compare the outcomes of two different approaches (modelling vs. using data from method validation and participation in PT) applied to the estimate of the uncertainty of measurements of As, Cd, Cr and Pb performed by ICP-MS in several food matrices. They concluded that similar results were obtained with either approach when the expanded uncertainty was less than 20%.

Interpreting the results of clinical and other studies requires knowledge of reliably produced reference ranges, determined in appropriate specimens. Several useful reports have been presented during this review period. Those noted here are for studies where the authors have included sufficient information concerning specimen collection and analytical quality assurance for the results to be accepted with reasonable confidence and/or where the data refer to examples where there are few other reports.

In an excellent multi-element study, Cesbron et al.²⁴ determined the concentrations of 27 elements in blood and plasma samples, collected in 2012, from 106 healthy adult French subjects. None were occupationally exposed to metals, receiving any medication or supplements and had no metal prostheses. Tobacco use and the number of dental amalgams were noted. Results were presented as the median and 5^th to 95^th percentile range. Differences between male and female subjects were seen for Cu and Zn while Cd and Pb concentrations were higher in smokers. Concentrations of 16 elements were measured by Liu et al.²⁵ in 440 plasma specimens collected from children aged 3–12 years, as part of the Chinese National Nutrition and Health Survey Project 2002. The cohort were from economically developed rural areas. Results were presented by age groups and gender. X-ray fluorescence spectrometry was used by Redigolo et al.²⁶ to measure the concentrations of Ca, Cl, Cu, Fe, K, Mg, Na, P, S and Zn in blood samples from Brazilian adults. Brodzka et al.²⁷ analysed urine samples from 16 Polish subjects. The ICP-MS procedure was fully described and results obtained for CRMs and performance in the German proficiency testing scheme were presented. Results, as the geometric mean ± geometric SD, for 11 elements were reported as μg g⁻¹ creatinine and as μg L⁻¹. In one other multi-element report, Mikulewicz et al.²⁸ presented a systematic review of published reference ranges for trace elements in hair. From 52 papers identified by a literature search, 47 were rejected because of insufficient detail. Data from the remaining five were combined and provided the raw material for the review which showed the methods used for sample preparation and tabulated ranges for 24 elements, presented as macro-elements, essential trace elements, toxic elements and ‘other’ trace elements (Li, Sr, V).

Single element reference ranges were reported for Hg species in urine, Sb in serum and plasma, Se in blood and serum and Tl in urine. Leese et al.²⁹ found that the 95^th percentiles for As^III, As^V, MMA, DMA and AB in urine specimens from 95 non-occupationally exposed adults were 0.99, 0.35, 3.08, 16.08 and 174.7 μmol mol⁻¹ creatinine, respectively. The review by Filella et al.¹⁶ tabulates ranges from more than 30 publications referring to various study groups such as health subjects, patients with hypertension, kidney disease, newborn infants. Selenium concentrations were measured in specimens of serum for premature infants by Peirovifar et al.³⁰ Cord blood samples were collected from 54 babies born at less than 30 weeks gestation and Se concentrations were 64.78 ± 20.73 μg L⁻¹ in blood and 60.33 ± 26.62 μg L⁻¹ in the serum. Urine specimens from 113 non-occupationally exposed healthy adults were analysed by Staff et al.³¹ to define a reference range for concentrations of Tl. The median value was 0.11, with an upper concentration of 0.27 μmol mol⁻¹ creatinine.

A further series of papers provide details of the reference ranges for elements of interest in patients with metal implants. In an extensive systematic review Matusiewicz,³² tabulated concentrations of Co, Cr, Mo, Ni and Ti in blood, serum, urine and synovial fluid specimens from patients with metallic implants (knee, hip and orthodontic). Results from more than 60 studies were shown and in addition to concentrations found in the patients the tables also included the control values reported. In an original publication, Savarino et al.³³ determined the concentrations of Cr, Co, Mo and Ni in serum specimens from patients with metal hip prostheses and from 48 healthy control subjects. The reference ranges obtained were 0.06–0.67, 0.08–0.53, <LOD and 0.10–0.81 μg L⁻¹, for Cr, Co, Mo and Ni, respectively. As part of a study to develop a highly sensitive and accurate procedure for measuring concentrations of Ti in serum, Balcaen et al.³⁴ analysed specimens from four healthy subjects. Careful attention was paid to contamination control throughout the study and the results obtained were; 0.27, 0.29, 0.32 and 0.80 μg L⁻¹.

3 Sample collection and preparation

3.1 Collection, storage and preliminary preparation

The title of a publication by Ichou et al.³⁵ hints at the notion that parenteral nutrition fluids may be contaminated with Al from containers. These authors measured concentrations of Al in prepared fluids and their individual components and found levels that implied many patients would receive more than 2 μg per kg per day, the upper limit recommended by the American Society of Parenteral and Enteral Nutrition. While this observation raises concern, the results do not confirm that materials were contaminated from containers as opposed to other sources during manufacture and storage.

The initial preparation for hair and nail specimens involves a washing procedure in an attempt to remove exogenous contamination. Tipple et al.³⁶ were interested in measuring Sr isotope ratios in hair using MC-ICP-MS and investigated five washing protocols of varying aggressiveness. Different isotope ratios were found in leachates and in treated hair and it was inferred that Sr incorporated into hair or as surface contamination could therefore be discriminated. From this experiment, it was concluded that the most aggressive washing procedure best allowed determination of internal and external hair Sr concentrations. In their study, Gherase et al.³⁷ however, do not indicate whether nail specimens analysed to determine the distribution of As were subjected to a specific cleaning protocol. Finger and toe nail clippings were embedded in polyester resin and cut into 270 μm sections for measurement by XRF spectrometry.

3.2 Digestion, extraction and preconcentration

Table 1 Clinical and biological materials

Element	Matrix	Technique	Sample treatment/comments	Ref.
Al	Parenteral nutrition compounds and solutions	ETAAS	A survey of parenteral nutrition compounds and solutions revealed Al content exceeding the maximum allowable level of 25 μg L^−1, leading to potential excessive Al exposure of patients	35
As	Blood, urine	RNAA, ICP-MS	The RNAA method applied for the certification of As content at three levels in blood (SRM 955c) and two levels in urine (SRM 2668) RMs was reported. Certified values, obtained combining both RNAA and ICP-MS results provided by NIST and other collaborating laboratories, were 10.81 ± 0.54 and 213.1 ± 0.73 μg L^−1 for urine and 21.66 ± 0.73, 52.7 ± 1.1, and 78.8 ± 4.9 μg L^−1 for blood CRMs, respectively	161
As	Cells	LC-ICP-MS	The in vitro toxicological characterization of two arsenosugars and six of their metabolites was reported. Whereas DMA^V–sugar–glycerol and DMA^V–sugar–sulfate, as well as four of their metabolites (oxo-dimethylarsenoacetic acid, oxo-dimethylarsenoethanol, thio-dimethylarsenoacetic acid and thio-dimethylarsenoethanol), showed no toxic effect, two others (dimethyl-arsenic acid and thio-dimethylarsinic acid) did. Additionally, bioavailability of the arsenosugars and their metabolites was tested on the Caco-2 intestinal barrier model	129 and 130
As	Nails	SR-XRF	As distribution in nail clippings from 3 healthy human subjects was investigated using the microbeam experimental setup of the hard X-ray micro-analysis beamline from the Canadian light source synchrotron	37
As	Urine	LC-ICP-MS	The concentrations of five As species (AB, As^III, As^V, MMA^V and DMA^V) were determined in urine samples from 95 non-occupationally exposed volunteers, following an anion exchange separation on a micro LC system coupled to ICP-MS. Consumption of fish, shellfish and red wine, but not smoking, significantly increased AB, DMA and MMA urinary concentrations	29
As	Urine		In a study of As species in urine samples from children chronically exposed to As in drinking water, special precautions were taken to preserve MMA^III during collection, storage and analysis. However, MMA^III was detected in only 41 out of 643 urine samples stored deep frozen for 3–6 months, and only in two samples the MMA^III level was >1 μg L^−1. It was concluded that MMA^III may have limited value as an epidemiological biomarker	128
Au	Tissues	MALDI-Q-TOF-MS	DDC was added to wet-ashed tissue samples to form the Au and Pt chelate complexes, which were then detected by MALDI-Q-TOF-MS, with LODs of 0.8 ng g^−1 (Au) and 6 ng g^−1 (Pt)	71
Be	Tonsils	ICP-AES	As a potential biomarker of exposure to environmental pollution, Be concentrations were determined in 379 tonsil samples, after acid digestion with HNO3. A reference range (0.02–0.04 μg g^−1) was proposed for the concentration of Be in pharyngeal tonsils of children	162
Ca	Bone	SIMS	TOF-SIMS was applied to mapping the distribution of Ca in bones, with a lateral resolution of up to 1 μm. For calibration, Ca hydroxyapatite collagen scaffolds were synthesized and characterised	72
Ca	Serum	SF-ICP-MS	A reference method was developed for the determination of Ca, K and Mg in serum by ID with SF-ICP-MS, after spiking with a mixture of isotopically enriched elements (^44Ca, ^41K and ^26Mg). The ratios ^42Ca : ^44Ca and ^24Mg : ^26Mg could be measured at medium resolution, whereas, at levels below 100 ng g^−1, the ^39K : ^41K ratio remained affected by the presence of ArH, even at high resolution	20
Ca	Urine	AMS	The reliability of determinations of ^41Ca in urine by AMS was demonstrated by a comparison between two facilities (the Lawrence Livermore National Laboratory and the Purdue Rare Isotope Laboratory)	163
Cd	Hair	AFS	The simultaneous determination of Cd and Pb concentrations in digested single human hairs was achieved by coupling tungsten coil electrothermal vaporization with Ar–H2 flame AFS	89
Cd	Tablet CRM	ID-ICP-MS	The certification of a tablet CRM (NIST SRM 3280) for the content of 13 vitamins, 26 elements and two carotenoids was reported. Extensive sample pretreatment was necessary to separate Cd from interfering ions (Sn and Mo). A desolvating nebulizer system reduced the remaining interference from MoO, allowing the measurement of both the ^111Cd : ^113Cd and ^111Cd : ^114Cd isotope ratios by either Q-ICP-MS or SF-ICP-MS. Cd mass fraction was quantified as 80.15 ± 0.86 ng g^−1 (mean ± 95% expanded uncertainty)	17 and 18
Co	Biological and water samples	ICP-AES	Predictions from an artificial neural network approach were applied to the extraction efficiency of Co from biological and water samples using magnetic nanoparticles. Determinations of Co concentrations were performed after batch solid-phase extraction, carried out with 0.75 mg L^−1 of complexing agent (1-(2-pyridylazo)-2-naphthol), 125 mg L^−1 of nanoparticles, at an initial pH 11.0 and an extraction time of 12.5 min. The LOD was 7.0 ng L^−1and the RSD% at 10 μg L^−1 was 2.1%	164
Co	Blood, serum	ICP-MS	The levels of Co and Cr in blood of 40 patients with hip prostheses with metal-on-metal coupling were compared with the amount of debris in the synovial fluid, determined by SEM-EDX, to assess the value of measurements of Co and Cr in serum and/or blood for monitoring the wear process of these prostheses	113
Co	Synovial fluid, blood, serum	ICP-MS	Co levels were significantly higher in blood, serum and synovial fluid samples from 32 subjects with metal-on-metal hip prosthesis than in the corresponding samples from 22 controls. Co concentrations in blood were higher than in serum, but both were strongly correlated with those in synovial fluid	112
Cr	Blood, serum	ICP-MS	See Co, ref. 113	113
Cr	Urine	ICP-MS	The capabilities of Q-ICP-MS with universal cell technology for the determination of the concentrations of Cr and Ni in urine for biomonitoring purposes were explored. Using He at 6.0 mL min^−1 as the collision gas and the kinetic energy discrimination mode, polyatomic interferences on ^52Cr and ^60Ni were removed and LODs of 0.162 μg L^−1 (Cr) and 0.248 μg L^−1 (Ni) were achieved, which compared well with those attained by SF-ICP-MS. RSDs were <10% and analysis of NIST SRM 2668 provided values within the 95% confidence intervals for the certified values	64
Cu	Blood	MC-ICP-MS	To assess the relevance of menstruation on the observed difference between the isotopic composition of Cu and Fe in whole blood in men and women, Cu, Fe and Zn isotopic concentrations were determined in whole blood samples from non-menstruating women, either in their menopause or carrying an intra-uterine device. No difference associated with menstruation or age was observed in comparison with a male reference population, but, for Zn only, a significant difference was reported between the two groups of women studied	116
Cu	Blood	MC-ICP-MS	Cu, Fe and Zn isotope ratios were determined by MC-ICP-MS after LC on an ion exchange resin in blood samples from 39 Yakut volunteers from Sakha Republic, Russia. Increasing age affected the ^66Zn : ^64Zn ratio (increased) and the ^65Cu : ^63Cu ratio (decreased), but not the Fe isotopic composition. Both Cu and Zn isotope ratios were significantly different from those observed in European and Japanese populations	115
Cu	Liver	LIBS	A novel application of LIBS was reported, aimed to detect Cu concentrations in human liver for the diagnosis of Wilson's disease. For these measurements, a Nd : YAG laser at 532 nm and an echelle type spectrometer were used	85
Eu	Organs	ICP-MS	The fate of Eu-doped Ga2O3 nanoparticles, intratracheally instilled into mouse lung, was investigated by collection, acid digestion and analysis of the target organs 24 h after treatment. The assumption that intact nanoparticles were measured was based on experimental evidence of a protein corona coating the nanoparticles, poor solubility in biological fluid surrogates and an elemental ratio corresponding to that of the nanoparticle constituents. Most of the dose was found in the lung or was excreted in faeces, with traces present in all the studied organs	136
Fe	Blood	MC-ICP-MS	See Cu, ref. 116	116
Fe	Blood	MC-ICP-MS	See Cu, ref. 115	115
Fe	Brain	ETAAS	Fe levels were determined, after microwave-assisted acid digestion, in post-mortem samples from 14 different areas of the brain collected from 42 subjects, aged from 53 to 101 years. Globally, Fe levels increased with age, but the Fe distribution in the different areas was highly variable	133
Fe	Diet	MC-ICP-MS	The accurate determination of Fe isotopic composition in 60 food products representative of the German diet highlighted differences between vegetables, crop food and food of animal origin. This information was used to determine fractionation factors for Fe intestinal absorption in vegetarians and omnivores	165
Fe	Exhaled air	ICP-MS	As part of an investigation of potential biomarkers of exposure to welding fumes, the content of Fe and Mn in endogenous particles in exhaled air was determined by ICP-MS in samples collected from 9 individuals, experimentally exposed to welding fumes, revealing increased mean concentrations of Mn (82–84 pg L^−1) and Fe (2600 pg L^−1) in exhaled air	119
Fe	Serum	ICP-MS, LC-MS/MS	In an attempt to improve the comparability of determinations of the clinical biomarker carbohydrate-deficient transferrin, the separation and quantification of the transferrin sialoforms in human serum was achieved by anion exchange chromatography coupled with ICP-MS. The identity of the separated species was confirmed by LC-MS/MS. Three IDA methods were applied to CRMs to determine both the concentration of each sialoform and the total content of transferrin	135
Ga	Organs	ICP-MS	See Eu, ref. 166	136
Hg	Blood	GC-ICP-MS	A novel methodology was described for the quantification of three Hg species (Hg, MeHg^+, and EtHg^+) in whole blood, using the isotopically enriched species ^199Hg^2+, Me^200Hg^+ and Et^201Hg^+ for ID. After spiking with the isotopically enriched species, sample pretreatment involved microwave-aided digestion with 2.0 mol L^−1 HNO3, treatment with 1% (w/v) sodium tetrapropylborate (at pH 5.2) and extraction of the propylated Hg species in the headspace using a carboxen/polydimethylsiloxane-coated SPME fibre followed by thermal desorption and determination by GC-ICP-MS. The method was validated using mass balance of the species involved and analysis of the NIST SRM 966, Level 2. An LOD of 30 pg g^−1 was reported	95
Hg	Blood, plasma surrogate samples	ICP-AES, ICP-MS, LC-ESI-TOF-MS	A combination of analytical techniques was applied to investigate the behaviour and binding partners of EtHg^+, resulting from the decomposition of thimerosal, in human whole blood and plasma surrogate samples	167
Hg	Hair	LA-ICP-MS	The determination of Hg concentrations in hair from captive and wild grizzly bears allowed to assess their exposure to Hg through the diet	105
Hg	Plasma proteins	ICP-MS	Hg-containing proteins from human plasma were separated by on-line 2D-HPLC, based on SEC followed by weak anion exchange LC. The fractions were analysed by both UV and ICP-MS. Human serum albumin was identified as the major carrier for Hg	168
Hg	Water, CRMs (dogfish muscle and human hair)	FI-CV-AAS	Coating the inner wall of a quartz tube atomizer with gold nanoparticles provided an effective in situ trapping method for enhanced Hg determination by means of FI-CV-AAS. Hg desorption was achieved by increasing the voltage (thus the temperature) to 30 V. With 5 mL sampling volume, an LOD of 0.01 μg L^−1 was achieved. The RSD was <4.0% at 0.5 μg L^−1	79
I	Hair	ICP-MS	Hair I was investigated as a potential biomarker of I status in an epidemiological study involving 870 subjects. The median I value was 0.499 μg g^−1 and no sex-related differences were observed. Levels of I between 0.565 and 0.739 μg g^−1 were proposed to correspond to an adequate I status	131 and 169
I	Human milk, urine, kitchen salt	ICP-MS, titrimetry	Elevated I levels in urine (median: 293 μg L^−1) of a sample of 33 infants in Brazil were positively correlated with high I levels in maternal milk (mean: 206 μg L^−1), both measured by ICP-MS. This was considered to be related to a high I concentration in the kitchen salt used by the mothers, with a mean value, assessed by titrimetry, of 39.9 mg kg^−1	132
I	Urine	HPLC-ICP-MS	The speciation of I in urine was achieved in 7 min by ion-pair RP LC coupled with ICP-MS, using a 12.5 mm C18 guard column, gradient elution and aqueous mobile phases containing tetrabutylammonium hydroxide, as the ion pair reagent, and either NH4Cl, L-phenylalanine or deoxycholic acid. Seven I species (I^−, IO3^−, mono-iodotyrosine, di-iodotyrosine, tri-iodothyronine, reversed tri-iodothyronine and thyroxine) were determined with LODs of 0.046, 0.047, 0.057, 0.072, 0.093, 0.094 and 0.081 μg L^−1, respectively. Recoveries ranged from 93 to 106%	97
I	Urine	ICP-MS	Excessive I intake was reported for 66.4% of the 611 Korean preschool children (aged from 2 to 7 years) involved in a cross-sectional study. I status was assessed from urine I, for which a median concentration of 438.8 μg L^−1 was observed	170
K	Serum	SF-ICP-MS	See Ca, ref. 20	20
Mg	Serum	SF-ICP-MS	See Ca, ref. 20	20
Mn	Blood, plasma	ICP-MS	Mn concentrations were determined in blood and serum samples after dilution with a solution of 0.005% Triton X-100–0.2% propan-2-ol–0.2% butan-1-ol–1% HNO3 and addition of Ga as the internal standard. The polyatomic interference from FeH on ^55Mn was successfully removed using modified (Xt) skimmer cones, whereas the collision cell with 7% H2 in He and flow rates between 4 and 7 mL min^−1 was ineffective	67
Mn	C. elegans	LA-ICP-MS	The uptake of Mn in Caenorhabditis elegans, a model organism extensively used in relation with heavy metal induced toxicity, was studied by elemental bioimaging using LA-ICP-MS. The optimization of analytical parameters allowed to achieve intense Mn signals at a spatial resolution of 4 μm	106
Mn	Exhaled air	ICP-MS	See Fe, ref. 119	119
Mn	Placenta	ICP-MS	To assess a possible association between exposure to Mn and the risk of foetal neural tube defects, the concentrations of Mn (and other 4 elements: Cu, Fe, Se and Zn) were determined in placental tissue from 80 cases and 50 controls. The median Mn concentration was significantly higher in case placentas than in controls (131.60 ng g^−1vs.101.54 ng g^−1) and elevated Mn levels were associated with increased risk for foetal malformations	121
Ni	Urine	ICP-MS	See Cr, ref. 64	64
Pb	Bone	SR-XRF	Analysis of 14 human bone samples by SR-μXRF in combination with quantitative backscattered electron imaging allowed sufficient resolution to identify differential accumulation of Pb, Sr and Zn in bone structural units	109
Pb	Hair	AFS	See Fe, ref. 89	89
Pt	Phantoms	XRF	The potential of L-shell vs. K-shell XRF computed tomography for the imaging of cisplatin was investigated using a Monte Carlo simulation to compare their performance	139
Pt	Serum	ICP-MS	A procedure based on conjoint liquid chromatography on monolithic convective interaction media discs coupled on-line to UV and ICP-MS detectors was applied to the speciation of Pt in human serum incubated with Pt-based anticancer drugs	92
Pt	Serum, albumin	ICP-MS	As part of the development of new anticancer metallodrugs, an investigation of the albumin binding capacity and serum distribution of cis- and trans-isomeric Pt^II complexes was investigated	171
Pt	Tissues	LA-ICP-MS	Tissue embedding in cold-curing resins improved the standardization of measurements of spatial distribution of Pt in tissues, offering an LOD of 8 μg kg^−1	101
Pt	Tissues	MALDI-Q-TOF-MS	See Au, ref. 71	71
Sb	Erythrocytes	HPLC-HG-AFS	A procedure consisting of protein precipitation, followed by C18 SPE, EDTA elution, anion-exchange chromatography on a (100 mm × 4.1 mm) PRPX-100 column with 20 mmol L^−1 EDTA as the mobile phase, followed by HG-AFS allowed the separation of Sb species from human erythrocyte fractions with recoveries of 90% (Sb^V) and 55–75% (Sb^III). Factors affecting the distribution of Sb species were investigated	127
Se	Blood serum, urine	ICP-MS	Low Mr Se species were separated from human serum and urine using RP and anion exchange chromatography, whereas double column affinity HPLC achieved the separation of selenoproteins and RP-HPLC of the enzymatically hydrolysed fractions allowed to investigate selenoaminoacids. All Se species were detected, after post column spiking with ^78Se, by ID-ICP-MS, using 4 mL min^−1 H2 as the reaction gas in an octopole reaction cell	99
Se	Serum	ICP-MS	3 instrumental set-ups (standard mode; collision cell mode using either a H2–He mixture or H2) were compared with respect to the Gd (from MRI contrast agents) interference on the determination of Se in serum by ICP-MS. Only with the collision cell with H2 accurate results were obtained. The method was tested on both CRMs and PT samples spiked with Gd and patients' samples known to contain the Gd contrast agent	35, 63
Sn	Urine	GC	The simultaneous determination of 11 organoSn compounds, including methyl-, butyl-, phenyl- and octyltin derivates, in human urine was achieved using headspace-SPME followed by GC with pulsed flame photometric detection. Recovery of spiked amounts of all analytes at different concentration levels was >87% and RSDs were between 2% and 7%. Care was required to avoid degradation of organoSn compounds in human urine. Satisfactory storage conditions over the first 4 days from collection were found to be at 4 °C and pH 4. The method was applied to the biomonitoring of harbour workers exposed to antifouling paints, confirming the presence of MeSn and BuSn	172
Sr	Bone	SR-XRF	See Pb, ref. 109	109
Sr	Bone	XAS, ICP-MS	Following the introduction of Sr supplements for the treatment and prevention of osteoporosis, Sr localization in bone tissue was studied in dogs treated with Sr malonate	91
Sr	Bones	XRF	Non-invasive in vivo^125I based XRF measurements were used to monitor, over 5 years, bone Sr levels in 10 female volunteers using Sr citrate as a supplement, nine of which were suffering from osteopenia and/or osteoporosis. For analysis, the 14.2 keV Sr K-alpha peak normalized to the coherent peak at 35.5 keV was used	173
Sr	Hair	MC-ICP-MS	High precision measurements of Sr isotopic ratios allowed to address variation caused by aggressive washing treatments and to distinguish internal Sr content from environmental contamination	36
Ti	Blood serum	ICP-MS/MS	ICP-MS/MS was applied to the determination of Ti levels in serum, using a mixture of NH3–He as reaction gas, with an instrumental LOD of 3 ng L^−1. A comparison with SF-ICP-MS was carried out on both an RM and human serum samples. Ti levels were typically <1 μg L^−1, rising to 2–6 μg L^−1 in individuals with Ti-based implants	34
Ti	Tissues	ICP-MS	Tissues of rats exposed to TiO2 nanoparticles were digested with a HNO3–HF mixture prior to determination of the total Ti content by ICP-MS. A comparison of the results obtained on the same samples by 4 laboratories demonstrated good agreement for Ti concentrations >4 μg g^−1	141
Tl	Urine	ICP-MS	Tl levels were measured in urine of 113 non-occupationally exposed people and 447 workers. The reference value, set as the 95^th percentile value of a non-occupationally exposed population, was found as 0.27 μmol mol^−1 creatinine or 0.40 μg L^−1. Median values were 0.11 μmol mol^−1 creatinine (0.17 μg L^−1) for non-occupationally exposed people, 0.12 μmol mol^−1 creatinine (0.20 μg L^−1) for general workers and 0.19 μmol mol^−1 creatinine (0.41 μg L^−1) for thallium workers	31
V	Blood, serum, urine	ICP-MS	V release in whole blood, serum and urine of 129 patients implanted with a titanium alloy hip prosthesis was assessed. 42% of the patients showed serum V values above the reference interval, as compared to 29% in urine and 13% in whole blood. Patients experiencing pain or other problems with the prosthesis also showed a significantly higher excretion of V in urine, as compared with that in asymptomatic patients (p < 0.001). In the remaining group of patients, V values (95^th percentile) of 0.3 μg L^−1 (whole blood), 0.5 μg L^−1 (serum) and 2.8 μg L^−1 (urine) were observed	114
Zn	Blood	MC-ICP-MS	The reliability of a previously described method to identify Zn from ZnO nanoparticles in blood of women after dermal exposure to ZnO nanoparticles contained in a sunscreen was confirmed by independent analysis carried out in a different laboratory	142
Zn	Blood	MC-ICP-MS	See Cu, ref. 116	116
Zn	Blood	MC-ICP-MS	See Cu, ref. 115	115
Zn	Bone	SR-XRF	See Pb, ref. 109	109
Various	Eye lenses and aqueous humour	TXRF	Aqueous humour and lens samples, collected from 14 cataract patients, were analysed for the content of selected chemical elements by TXRF after dilution and addition of an internal standard. A high variability was observed. Cr and Mn were present in both media, whereas Ba was found only in the lens and Ni only in the aqueous humour	122
Various	Retina, cornea	PIXE, RBS	Non homogeneous distributions were reported for trace elements in retina and cornea samples from Wistar rats, assessed by PIXE in combination with 3D depth profiling with RBS	111
Various	Bones	XRF	In an investigation of the mechanisms of bone healing in vertebrates, synchrotron rapid scanning XRF was applied, combined with microfocus elemental mapping, to determine the distribution and concentration of trace elements within pathological and normal bone of both extant and extinct archosaurs (Cathartes aura and Allosaurus fragilis)	110
Various	Bones	XRF	The determination of chemical elements together with chemometric analysis was applied to identify the remains of different individuals from common graves	123
Various	Bone implants	XRF, LA-ICP-MS	Combined measurements carried out by XRF and LA-ICP-MS allowed to map the elemental distribution in a nanosilver-coated bone implant	108
Various	Brain	PIXE, RBS	The results obtained with 3 MeV proton and 36 MeV carbon ion beams, applied to 7 μm thick mouse brain sections, were compared	90
Various	Organs	LIBS, ICP-AES	LIBS was investigated as a technique for mapping nanoparticles and trace elements in tissues. Experiments involved mapping Ca, Fe, Gd and Si in mouse kidney slices, after intravenous injection of Gd-based nanoparticles and a comparison with ICP-AES	86
Various	Tissue	LA-ICP-MS	A novel approach combining a UV LA system coupled in parallel with both elemental and molecular MS was described and applied to spatially resolved analysis of the distribution of chemical elements in tissue sections	107
Various (4)	Biological marine samples	ICP-AES	A fast and “green” procedure was proposed for the pretreatment of marine samples prior to the determination of Cu, Fe, Ni, and Zn by ICP-AES. Fish (muscle and liver) tissues and macroalgae were digested using a 20 s microwave-assisted dissolution in choline chloride–oxalic acid, at atmospheric pressure, followed by cooling, addition of 7.0 mL of 2.0 M HNO3, centrifugation, filtration and dilution to a known volume. A comparison with a conventional acid digestion method was carried out and analysis of a CRM (DORM-3) showed recoveries >96.1% for all elements	44
Various (4)	Clay	ICP-MS	The levels of As, Cd, Hg and Pb in clay products, consumed according to local traditions or for health purposes, were assessed. In a total of 63 clay products, sampled from the Dutch market, maximum levels of 45.1 (As), 0.75 (Cd), 2.2 (Hg) and 99.7 (Pb) mg kg^−1 were observed. These data, combined with estimated daily use and bioaccessibility, were used to assess the potential risk associated with consumption of these products	143
Various (4)	Sputum	ICP-MS	Metal concentrations measured in sputum samples from 45 subjects with cystic fibrosis (CF), 8 with non-CF bronchiectasis and 8 healthy controls were compared with biomarkers of cellular injury and disease severity. Elevated concentrations of Ca, Mg, Mo and Zn were considered as potential biomarkers	120
Various (4)	CRMs (human hair, stream sediment)	AES	Improved sensitivity (from 2.1- to 6.6-fold) for the determination of the concentrations of Cd, Cr, Hg and Pb by solution cathode GD-AES was achieved by addition to the samples of 0.15% of the ionic surfactant cetyltrimethylammoniumchloride. LODs of 1.0 (Cd), 42 (Cr), 7.0 (Hg) and 2.0 (Pb) ng mL^−1, respectively, were achieved. The method was tested on CRMs	84
Various (4)	Liver	LA-ICP-MS	LA-ICP-MS was applied to determine the distribution of 4 elements (Cu, Fe, Mn and Zn) in mouse liver tissue as a model for Wilson's disease. Quantification was based on in-house produced standards. Significant differences were noted for Cu, Fe and Zn, but not Mn, concentrations	102
Various (4)	Serum	ETAAS	Levels of Co, Cr, Mo and Ni were measured in serum of two groups of patients, who had received metal-on-metal hip resurfacing arthroplasty or traditional metal-on-metal total hip arthroplasty	33
Various (5)	Toenails	ICP-MS	The mass fractions of As, Cd, Mn, Ni and Pb in toenail samples from 48 welders were determined as part of an investigation of their potential value as biomarkers of exposure to welding fumes. After adjustment for potentially confounding variables, significant correlations were observed for past (from 7 to 12 months) exposure to Cd, Mn and Pb, but not with years as a welder	174
Various (6)	Exhaled breath condensate	XRF, ICP-MS	The performances of XRF and ICP-MS based methods for the determination of Cd, Cu, K, Mn, Pb and Sb in exhaled breath condensate were evaluated. Recovery of added amounts of the elements studied was the most significant contribution to total uncertainty. The overall uncertainties obtained for ICP-MS enabled to discriminate between groups of individuals exposed to different levels of contaminants	118
Various (6)	Serum	SF-ICP-MS	Candidate reference methods for the determination of electrolytes (Ca^2+, Cl^−, K^+, Li^+, Mg^2+ and Na^+) in serum were presented, based on ID-SF-ICP-MS after dilution of the serum samples with 4 mmol L^−1 HNO3. Comparisons with AAS, FAES and coulometry were carried out. Mean coefficients of variation ranged from 0.46% (K^+) to 0.78% (Mg^2+) and mean biases from the analysis of NIST CRMs varied between −0.46% (K^+) and +0.85% (Cl^−)	21
Various (9)	Tissue	LA-ICP-MS	LA-ICP-MS was applied to map the spatial distribution of inhaled CdSe quantum dots in mouse lung slices, to support their application as drug delivery carriers and fluorescent markers in bioimaging. Several isotopes were monitored simultaneously (^13C, ^111Cd, ^112Cd, ^114Cd, ^63Cu, ^56Fe, ^57Fe, ^31P, ^34S, ^82Se, ^125Te and ^66Zn) and the results were combined with hematoxylin and eosin stained images. Evidence was reported for the accumulation of CdSe quantum dots in the bronchiolar area, with no degradation over 17 days, and consequent inflammation and immune responses	103
Various (10)	Blood	EDXRF, INAA	Reference values for Ca, Cl, Cu, Fe, K, Mg, Na, P, S and Zn in human and animal blood were determined. A comparison with INAA showed comparability of results within statistical limits (alpha = 0.05)	26
Various (11)	Urine	DRC-ICP-MS	The concentrations of 11 elements (As, Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in human urine were determined after a 10-fold dilution with 0.1% HNO3 and addition of Rh as an internal standard. The DRC with CH4 was used to remove interferences on Cd, Co, Cr, Cu, Fe, Mn, Ni and Rh, whereas O2 was applied for the determination of As. LODs were 0.025 (Al), 0.007 (As), 0.002 (Cd), 0.004 (Co), 0.004 (Cr), 0.086 (Cu), 0.037 (Fe), 0.009 (Mn), 0.016 (Ni), 0.008 (Pb), 0.064 (Zn) μg L^−1. The method performance was confirmed by participation in a PT scheme	27
Various (16)	Plasma	SF-ICP-MS	As part of the Chinese National Nutrition and Health Survey Project 2002, the concentrations of 16 elements were determined in plasma samples from 440 children, aged 3–12 years, by SF-ICP-MS. The LOQs ranged from 0.02 μg L^−1 (Rb) to 1.89 μg L^−1 (Se), between-day RSDs varied from 3.7% (Fe) to 12.7% (Al) and recoveries spanned from 89.82% (Al) to 119.15% (Se)	25
Various (18)	Tablets	ICP-AES	A method was developed and validated to comply with new US Pharmacopeia regulations on elemental impurities. Several elements (As, Cd, Cu, Cr, Fe, Hg, It, Mn, Mo, Ni, Os, Pb, Pd, Pt, Rh, Ru, V and Zn) were determined in tablets by ICP-AES after microwave-assisted acid digestion with a 3 : 1 v/v mixture of 65% HNO3–37% HCl. Overall, the method was fit for the purpose, but a few issues remained to be solved, i.e. memory effects affecting Os determination and potential spectral interferences for It, Os, Pb, Pt and Rh	82
Various (20)	Blood, urine	SF-ICP-MS	Twenty elements were determined, with LODs ranging from 0.02 to 27 ng L^−1, in blood and urine samples from occupationally exposed workers. Sample pretreatment required microwave-aided acid digestion with HNO3 for blood, whereas urine samples were diluted 1 + 49 with 5% v/v HNO3. In the concentration range from 0.01 to 1.0 μg L^−1, RSDs between 5 and 10% were achieved, further reduced to <3% for concentrations above 1.0 μg L^−1	117
Various (27)	Blood and plasma	ICP-MS, collision cell-ICP-MS	As a follow-up of a previously reported survey, the concentrations of 27 elements in whole blood and plasma from 106 volunteers with no known professional or medical exposure was determined. Taking into account tobacco consumption and the number of dental amalgams, no significant differences were observed compared to the previous study, except for blood Pb (12.5 vs. 26.3 μg L^−1, p = 0.0001)	24

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Whilst the same or very similar procedures may be applied to all sample types included in this Update, as there has been much more innovative and interesting developments associated with foods and beverages, we have separated this work from that involving other specimens.

3.2.1 Clinical and biological materials. The first step of a method developed by Liu et al.³⁸ was to solubilise biological tissues using HCOOH. The solutions thus formed were taken for photochemical generation of Hg vapour with concentrations determined by ID-ICP-MS. The HCOOH served as the solubilisation agent and also as reductant for the VG.

Several approaches for the extraction of Hg from biological samples were reported during the last year. Cavalheiro and colleagues³⁹ used TMAH with microwave heating for tissue specimens, prior to derivatisation and measurement of iHg and MeHg using GC-MS and GC-ICP-MS. The method also determined organoSn compounds. Lower LOQs were obtained when the concentrations of the products were measured by GC-ICP-MS. A preparation method for selective extraction of MeHg from specimens was developed and validated by Masbou et al.⁴⁰ A two-step extraction/back extraction procedure was employed which provided MeHg yields of greater than 97%. The MeHg was extracted with 3% NaBr : 2.5% CuSO₄ in toluene and mixed for 1 h. The MeHgBr thus formed in the toluene layer was then back extracted into 0.005 M Na₂S₂O₃ solution as a MeHg–thiosulfate complex. For ID-GC-ICP-MS, the thiosulfate fraction was diluted 10-fold in 0.05% HCl, mixed with isotopically-enriched Hg species and extracted into benzene for analysis. For CV-AFS, the thiosulfate fraction was again diluted with HCl and Hg quantitatively determined following the EPA 1031 protocol using a custom-made gold amalgamation system. The method was validated by analysing MeHg in seven selected biological CRMs. A much simpler protocol was reported by D'Ulivo et al.⁴¹ who showed that MeHg would extract from samples using methanesulfonic acid, a reagent widely used for amino acid extraction.

Two reports which proclaim green approaches for specimen preparation may be mentioned. Matusiewicz and Ślachciński⁴² used 0.1 g sample, extracted with dilute (1%) HNO₃ in a 90 bar pressurised system at 280 °C for 10 min. Ten elements were then determined by MIP-OES. Bizzi et al.⁴³ chose to digest powdered samples to eliminate potential matrix effects during the measurements by ICP-MS and ICP-OES. Up to 500 mg of sample was digested in a closed microwave digestion system with 1 mol L⁻¹ HNO₃ and 30% m/m H₂O₂, typically 1.5 and 2.5 mL, respectively. The effectiveness was assessed by analysis of CRMs and determination of residual carbon content. These reports demonstrated that, in addition to reducing the amounts of toxic and hazardous agents entering the environment, low blank values may be obtained with, therefore, improved LODs and RSDs while maintaining the accuracy of the analysis.

3.2.2 Foods and beverages.
3.2.2.1 Digestion. The drive to improve the ‘green’ aspects of acid digestion has motivated several authors to study reducing acid volume or strength. Despite the widespread use of H₂O₂, as well as pressurised O₂ gas, as auxiliary oxidants with HNO₃, their reaction mechanisms have not been fully elucidated. Bizzi et al.⁴³ optimised concentrations of HNO₃ and H₂O₂ to obviate the need to use pressurised O₂. From starting conditions which completely digested 500 mg of sample (whole milk powder or bovine liver) using dilute HNO₃ and O₂ (7.5 or 5.0 bar), the authors optimised concentrations to give minimal residual carbon content (RCC) and residual acid (RA). Increasing the amount of H₂O₂, without the use of pressurised O₂ gas, produced a digestion efficiency that was identical to that when pressurised O₂ was used. However, the RA increased with increasing H₂O₂ concentration leading the authors to postulate that HNO₃ is being regenerated from the O₂ produced in situ by H₂O₂ decomposition. This allowed for a reduction in acid concentration to 1 and 1.5 mol L⁻¹. Determination of minor and trace elements was carried out using ICP-AES and ICP-MS, respectively, and gave better than 95% agreement with certified values. Matusiewicz and Ślachciński⁴² took a similar approach but used pressurised sub-critical water extraction using only dilute HNO₃. Samples (0.1 g) were sealed in a microwave digestion vessel with aqueous HNO₃ and held at 280 °C and 90 bar for 10 min. Trace element (Ba, Ca, Cu, Fe, Mg, Mn, Na, Pb, Sr and Zn) determination was by MIP-AES after optimisation of an in-house micro-USN and calibration against aqueous standards. The method gave good agreement with several CRMs.

Deep eutectic solvents (DES) appear to be a very suitable solid sample digestion media because, as ionic liquids, they interact with microwave energy and having very low vapour pressure, they present as much safer than hot concentrated acids and oxidising agents. Ghanemi et al.⁴⁴ proposed for the first time the microwave-assisted digestion of fish muscle samples with the DES choline chloride–oxalic acid. The optimum molar composition of the two components was determined as 1 : 2 since this mixture gave >96% recovery of the metals studied (Cu, Fe, Ni and Zn) measured with ICP-AES. The sample (0.1 g) was mixed with the DES (prepared by combining the components and microwave heating), then microwave heated to 150 °C for 5 min, cooled before addition of dilute HNO₃ and centrifugation. Method validation was determined using the CRM DORM-3 and indicated full agreement on accuracy at 95% confidence limit while LODs were 0.08, 0.56, 0.04 and 0.23 μg g⁻¹, respectively. Digestion times were considerably faster than conventional acid digestion and this method can boast safer and more environmentally-friendly credentials.

3.2.2.2 Preconcentration. Improvements that minimise environmental impact continue to make liquid–liquid extraction a relevant technique. The use of Victoria pure blue as a new CPE ion-pairing agent in the presence of excess SCN⁻ was proposed as a good method for the determination of Mo in HNO₃-digested foodstuffs for determination with FAAS.⁴⁵ After optimisation, the authors settled on Triton X-114 as surfactant and cetylpyridinium chloride at pH 2.0 with HNO₃ in methanol as diluent for the surfactant-rich phase. An enrichment factor of 32 was achieved with figures of merit including an LOD of 2.18 μg L⁻¹, accuracy (relative error) of 3.25%, RSD of 2.36% and a wide linear range 7.5–1800 μg L⁻¹. Ionic liquids (IL) have been reported as extraction solvents in this review over the past few years, and their use equally confers ‘green’ credentials to extraction and preconcentration methods involving them. Two such methods, IL-DLLME and cold-induced aggregation microextraction, were combined and improved by Zeeb et al.⁴⁶ for the FAAS determination of Cr. Given that the solubility of ILs increases with increasing ionic strength, the authors used a common ion (NaPF₆) for the IL (1-hexyl-3-methylimmidazolium hexafluorophosphate) and the chelating ligand bis(2-methoxybenzaldehyde) ethylene diimine hexafluorophosphate that forms a complex with Cr^III. After optimisation of reagent concentrations, pH, temperature and diluting agent, the proposed method was shown to have an LOD of 0.7 μg L⁻¹, which compared favourably with other similar techniques but was 10–200 times less sensitive than ETAAS.

Further improvements to DLLME methodology proposed by Liang et al.⁴⁷ involved (i) ultrasound to improve the emulsification of the extractant into the aqueous sample instead of using an organic dispersant, (ii) the use of a surfactant, (iii) a combination of the two. The authors used these combined improvements for the first time in a metal ion preconcentration application. They preconcentrated metals in water and food samples digested with HNO₃ and determined Co by ETAAS. Optimisation of appropriate parameters determined DDC as chelating agent at pH 7.0 with CHCl₃ as extraction solvent and SDS as the emulsifier. An enrichment factor of 58 was achieved with an LOD of 15.6 ng L⁻¹ from a sample of 5 mL and the RSD was 4.3% at 1.0 ng mL⁻¹; good accuracy was demonstrated by agreement with two CRMs (tea leaf and spinach). Notwithstanding the improvements to DLLME such as those mentioned above, a standard application of the preconcentration methodology was applied for the determination of Cu^II in drinking water by microsample introduction FAAS.⁴⁸ The complexing agent was 1-nitroso-2-naphthol and EtOH and CHCl₃ were used as dispersion and extraction solvents, respectively. The LOD was 0.95 μg L⁻¹, and the relative error and RSD were −3.3% and 1.9%.

Standard liquid–liquid extraction techniques continue to be modified, optimised and improved despite being one of the earliest and simplest forms of analyte preconcentration for many analytical techniques. Another old extraction variant is homogeneous liquid–liquid extraction (HLLE), in which the analyte and complexing agent in aqueous phase are soluble in the solvent until conditions are modified such that phase separation occurs. This has been adapted for FAAS determination of Pb and Cd in beverages.⁴⁹ The authors used Na-DDC in acetone and acetate buffer at pH 4 to complex the analytes from the sample (50 mL) which were then extracted into the same volume of perfluorooctanoate dissolved in acidified LiOH. This caused a turbid solution on standing for 5 min, which, after centrifugation, formed into a 100 μL droplet which was subsequently dissolved for FAAS. The enrichment factor was 50 and recoveries were >85% for both analytes and samples of drinking water and wine, however the authors' choice of hotplate acid digestion with HNO₃, and H₂O₂ may not have been the most judicious for such volatile analytes.

Some novel developments involving SPE were seen during this review period. Complex element-specific ligands typically adsorbed onto specific polymer supports have the ability to complex and preconcentrate important analytes. The health impact assessment of the naturally-occurring radionuclides ²¹⁰Po, ²³⁴U, ²³⁵U, and ²³⁸U, is impaired by difficult sample preparation and poor sensitivity of alpha spectrometry. Having recently proposed the suitability of using polymer-immobilised 1,3,5-OCH₃-2,4,6-OCH₂COOH-p-tert-butylcalix[6]arene (called AQUALIX tubes) to isolate and preconcentrate Po and U in water samples, Bouvier-Capely et al.⁵⁰ further optimised their use when paired with determination by ICP-MS. Sample acidification to pH 0.5 ± 0.1 is necessary to eliminate bicarbonate competition and elution is best carried out using dilute HNO₃; degassing under vacuum is also necessary for sparkling waters. When ²¹⁰Po is also present in the sample (e.g. from tracer studies) this has to be removed by deposition onto a Ag disc prior to loading the AQUALIX tubes. From a sample size of 500 mL reported LODs for ²³⁴U, ²³⁵U, ²³⁸U were 0.0006 ng L⁻¹, 0.002 ng L⁻¹ and 0.03 ng L⁻¹, respectively. Another complex ligand ({4-⁵¹ amino}-1H-pyrazol-4-yl)diazenyl benzoic acid (AHPMAPDAB), previously synthesised by the authors, was used for determination of Al and Pb by HR-CS-FAAS, after conditions were optimised for analysis of waters and beverages.⁵¹ The technique involved mixing ligand with sample, at pH 7, which were adsorbed onto poly(ethyl methacrylates-co-polystyrene) (poly S₁₅-g-EMA₁₂₀) in a 10.0 × 0.8 cm glass column; the analytes were eluted with dilute HCl with a low flow rate. The Langmuir capacity (q_max) of the sorbent material was 14.6 and 18.4 mg g⁻¹, for Al and Pb respectively which was shown to remain stable for up to 80 adsorption–desorption cycles. Recovery was >95% for both analytes and the relative error against a CRM (trace elements in water NIST1643e) was −2.5% and −2.6%, while respectable LODs of 0.32 and 0.24 μg L⁻¹, respectively, were achieved.

Carbon nano-tubes and particles provide the support for chelating ligands, some new and others more traditional. Functionalised graphene oxide nano-sheets were used as an SPE sorbent in the determination of Cd in seafood samples by FAAS.⁵² These are sp²-bonded carbon atom monolayers produced from graphite powder and suspended in a mixture of HNO₃ and H₂SO₄ (3 : 70 v/v) to which KMnO₄ was added, then stirred overnight. The product was washed with H₂O then H₂O₂ after which it was ‘exfoliated’ (sic) by sonication to produce the graphene nano-sheets. These were functionalised with dipyridyl groups using triethylamine and dipyridylamine in dried EtOH. The sample was loaded and Cd^II ions eluted with thiourea in HCl. The maximum Cd^II adsorption capacity was 392 mg g⁻¹ with an enrichment factor of 416 and recovery >99%. No interference was found from common concomitant cations in seafood samples (As and Hg were not studied). The LOD using FAAS was 0.19 ng mL⁻¹ and the RSD was 1.6% for five replicates. A similar technique allowed Taher et al.⁵³ to propose the preconcentration of Ni from various food matrices and water samples using carbon nano-tubes functionalised with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol. Analyte ions were adsorbed in the pH range 6.5–8.5 and were desorbed with HNO₃. After appropriate optimisation of experimental parameters, the enrichment factor was 180 and, with determination by ETAAS, the LOD was 4.9 ng L⁻¹.

Metal oxide particles can be equally used to immobilise more traditional chelating agents. Magnetic Fe₃O₄ nanoparticles were functionalised with dithizone (DT) as a new sorbent for the preconcentration of Hg in various foods (green tea, table salt, vegetables), water and toothpaste.⁵⁴ The sorbent was prepared by refluxing for 24 h an excess of DT added to chloro-functionalised Fe₃O₄ nanoparticles dispersed in toluene. Samples, appropriately digested if necessary, were adjusted to pH 8.5 and stirred with the magnetic DT-nanoparticles in a beaker for 5 min. A strong magnet was used to retain them in the beaker prior to washing with H₂O and Hg was ‘eluted’ with dilute HCl containing thiourea, prior to determination with CF-CV-AAS. For a more conventional in-line implementation of the DT-mediated preconcentration of Hg with CF-CV-AAS determination, Chandio et al.⁵⁵ immobilised DT on a cartridge of ammonium lauryl sulfate coated alumina particles. The sorbent was prepared by adding ammonium lauryl sulfate and DT (5 mg) to NH₄OH into which alumina was added, the suspension acidified to pH 2 with HCl and briefly shaken. The washed and dried sorbent was packed into a cartridge column and sample solution was slowly pumped and then Hg eluted with HCl, for CV-AAS determination. The preconcentration factor was 125 and the LOD was 0.12 μg L⁻¹. The more adsorptive form of alumina, nano γ-alumina, was used with DDC for the preconcentration and subsequent speciation of Sb by FI-SPE-FAAS with a slotted tube atom trap (STAT).⁵⁶ The dried nano γ-alumina (20 mg), prepared by the citrate sol–gel method from Al(NO₃)₃, was packed into a PTFE microcolumn. The sample, adjusted to pH 8, and DDC were pumped synchronously through the minicolumn where the Sb^III–DDC complex, formed in situ, was adsorbed onto the γ-alumina nanoparticles; the Sb^V remained in solution. The Sb^III was then eluted with HNO₃ in MeOH into the STAT-FAAS. Total inorganic Sb was measured after reduction with acidified thiourea. With a measured γ-alumina surface area of 387.2 m² g⁻¹ and adsorption capacity of 21.5 mg Sb^III, the enrichment factor was 56.5; the LOD for this technique was 6.0 ng L⁻¹ for Sb^III and 8.2 ng L⁻¹ for Sb^V with RSDs of 2.8% and 3.5%, respectively. A chelating agent for Cd^II and Pb^II, Alizarin red S (ARS), was adsorbed onto TiO₂ nanoparticles, for the first time, to increase sorption capacity.⁵⁷ Glass beads were mixed with the ARS–TiO₂ nanoparticles and packed into a microcolumn. Elution into the FAAS was carried out with dilute HCl. A sample volume of 200 mL yielded a preconcentration factor of 100 and LODs were 0.11 and 0.3 ng mL⁻¹ for Cd^II and Pb^II, respectively. By layering together different SPE sorbent disks (47 mm diameter), including activated carbon as the middle layer, Hagiwara et al.⁵⁸ were able to separately determine diphenylarsinic acid, phenylarsonic acid and iAs. Water samples (200 mL) were passed through the stack of discs that were then separated and each species eluted separately before determination with ETAAS.

By far the most intriguing SPE sorbent proposed was the use of mandarin peel (Citrus reticulata) for the preconcentration of Ni in alcoholic beverages for determination by FAAS.⁵⁹ Peel was prepared from fresh fruit, ground and sieved though 850 μm screens, and washed with dilute NaOH before being packed into a microcolumn. A preconcentration factor of 12 was obtained; LOD and LOQ were 3.1 and 10.3 μg L⁻¹, respectively, and the RSD was 0.9% at 30 μg L⁻¹. A single column was used for 40 successive cycles of preconcentration and elution without loss of stability.

An electrochemical flow cell was used to reduce matrix interferences and improve the LOD of Se speciation with determination by ETAAS.⁶⁰ A low-volume (3 μL) commercial three-electrode FI measuring cell was coupled to the sample delivery system for the ETA; the working porous carbon electrode was coated at −2000 mV using HAuCl₄ and KSCN; the auxiliary electrode was made from Pt wire. During operation, Se⁰ was accumulated on the working electrode with a current of −1.5 mA and then stripped at +120 mA into a stream of HNO₃. This was then delivered into the atomiser. The only interference, from a 50-fold excess of PO₄³⁻, reduced the response by 10%.

3.2.2.3 Solid sample introduction. Nischkauer et al.⁶¹ showed solid sampling of plant material for PGE determination by ETV-ICP-AES was preferential to digestion, because sensitivity is not lost through dilution and also by allowing spatial distribution to be determined in one plant. Milled samples were placed in a graphite boat and carbonised in a muffle furnace before transfer by ceramic tweezers, for ETV. The authors demonstrated that, in order to avoid memory effects, aqueous external calibration solutions, pipetted onto filter paper strips, had to be dried before placing in the graphite boats. The LODs for Pd, Pt and Rh were 0.14, 0.38 and 0.13 μg g⁻¹, respectively for a 5 mg sample and the RSDs ranged from 4.7% (Pd) to 7.1% (Rh) for 25 ng of analyte. Slurry sampling of honey for ETAAS determination of Cd, Cr and Pb was described as a simple and low cost method.⁶² Honey was sonicated with HNO₃ and H₂O₂ then injected into a pyrolytic graphite tube (Pd–Mg modifier was used for Cd determination). External calibration using aqueous standard was possible with the addition of fructose for Cd determinations. The LOQs were 2.0, 9.4 and 5.4 ng g⁻¹, respectively.

4 Progress with analytical techniques

4.1 Mass spectrometry

4.1.1 Inductively coupled plasma mass spectrometry. The use of collision reaction cell with ICP-MS is well established and has been used to solve a number of challenges. Harrington et al.⁶³ reported the difficulty of Se determination in serum of patients administered Gd-based contrast agents. The doubly-charged Gd ions produced a positive bias for Se isotopes, up to 29 000% based on spiked sample recoveries. However, the use of H₂ cell gas removed the interference resulting in excellent recoveries for Se (99–103%). Quarles et al.⁶⁴ demonstrated improvements with Cr and Ni analysis in urine when using collision cell Q-ICP-MS when compared with SF-ICP-MS. After testing various cell gases, He was found to be best for Cr and Ni based on interference reduction. Overall, accuracy and LODs were similar between the two instruments but precision was improved with collision cell Q-ICP-MS. It offered a more robust, higher throughput alternative to SF-ICP-MS. Brodzka et al.²⁷ reported the development of a DRC-based ICP-MS method for the determination of Al, As, Cd, Cr, Co, Cu, Fe, Mn, Ni, Pb and Zn in urine. The group demonstrated that CH₄ as the cell gas was optimal for Cd, Co, Cr, Cu, Fe, Mn, Ni and Rh whereas O₂ mode was superior for As. The reported LODs and method performance characteristics were described and the validated procedure was applied to an occupational exposure monitoring study for copper smelter workers. Döker and Uslu⁶⁵ used He mode collision cell ICP-MS to measure the trace element content of edible salt with simple sample preparation. Solutions of 0.5% NaCl were aspirated in aerosol dilution mode to minimise the effect of such a high salt content. Good recoveries of spiked salt solutions at 0.2 and 1.0 μg L⁻¹ were presented and LODs which were comparable or superior than previously reported. Lee and co-workers⁶⁶ described the use of collision reaction interface ICP-MS to accurately quantify Cr in foodstuffs. The interface region employed specially designed cones which enabled gases, such as He, to be added to the plasma region which induced collisions and/or reactions to remove interferences. Although not widely available, the technique demonstrated good results for Cr in complex matrices such as food products. In an interesting study, Richardson et al.⁶⁷ accurately determined Mn in whole blood and plasma without using collision cell technology. The use of a modified skimmer cone enabled removal of the major interference, FeH, which performed better than with 7% H₂ in He as the collision cell gas.

The coupling of ICP-MS to CE can be challenging to maintain steady flow rates without impacting peak profiles and with a minimum dead volume. Liu et al.⁶⁸ described the successful use of a commercial interface kit designed for ESI-MS for this purpose. With optimised conditions, they demonstrated the separation of 10 As species in a number of food and environmental samples, achieving baseline resolution within 30 min.

A review of vapour generation techniques for ICP-MS was published by Gao et al.¹¹ covering recent developments in the field. It included HG, cold vapour, photochemical VG, electrochemical hydride, alkylation and other approaches such as volatile metal chelates and halide generation. In order to improve LODs, photochemical VG was combined with ICP-MS and applied to beverages⁶⁹ and biological samples.³⁸ Volatile species of Co, Ni and Te were generated from alcoholic beverages after treatment with formic and acetic acids and a UV source to allow direct determination by ICP-MS.⁶⁹ Improvements in the LODs using the VG approach were observed when compared to conventional pneumatic nebulisation. Liu et al.³⁸ also applied photochemical VG with formic acid and UV for the analysis of total Hg in biological tissues. Additionally, the group applied ID as the calibration approach and demonstrated the optimised methodology with CRMs. The LOD for Hg was 0.5 pg g⁻¹ which represented a 350-fold improvement compared with pneumatic nebulisation. For the determination of As, Cu, Hg and Pb in vegetable oils, Hsu et al.⁷⁰ employed ETV-ICP-MS. The samples were emulsified using a solution of 1.5% Triton X-100 and 50 μg mL⁻¹ ascorbic acid and injected into the furnace with Pd nanoparticles as a modifier. Subsequent detection utilised DRC-ICP-MS with calibration by standard additions and ID. The results were compared against total acid digestion with pneumatic nebulisation ICP-MS. Overall, good agreement was found demonstrating that a straightforward sample preparation approach can be applied for ETV-ICP-MS measurements.

The use of GC for speciation purposes of Hg and Sn is well known. Cavalheiro et al.³⁹ considered the determination of MeHg, iHg, butyl tin and phenyl tin compounds in biological samples by comparing GC-MS and GC-ICP-MS. Using ID as the calibration approach helped to overcome issues from losses during the derivatisation stages. In general, both techniques compared well in terms of precision and recovery of CRMs. However, GC-ICP-MS had better LODs by a factor of approximately 9.

4.1.2 Other mass spectrometry techniques. The use of other MS instrumentation for the analysis of biological tissues was demonstrated in three reports.^71–73 Minakata et al.⁷¹ applied MALDI-Q-TOF to quantify Au and Pt in tissues after complexation with DDC. An optimised method was presented and tested on tissues removed from 3 control individuals and 1 patient exposed to an accidental overdose of cisplatin. Good LODs were found for Au (0.8 ng g⁻¹) and Pt (6 ng g⁻¹) in the tissues. Additionally, the MALDI-Q-TOF results were compared against ESI-MS, as described and measured in earlier published work, with little difference observed despite the MALDI method using 10 times less tissue In a study by Henss et al.,⁷² TOF-SIMS was used to determine the Ca content in bone to aid research into bone disease, bone remodelling and the interface with implants. Matrix matched calibration standards were prepared and characterised in-house to enable quantification. When comparing the results of TOF-SIMS against XPS, good agreement was observed but TOF-SIMS was able to provide much higher spatial resolution. The accurate quantification of AB is a challenge in fish tissues, but Lee et al.⁷³ developed an approach utilising ID with LC-MS-MS. A ¹³C₂-AB standard was used as the enriched spike. The optimised method was used to certify a new shellfish CRM, with accuracy demonstrated with a codfish CRM.

4.2 Atomic absorption spectrometry

The use of FAAS for speciation analysis was demonstrated by Tian et al.⁵⁶ for Sb in food and water samples. They combined on-line FI with a γ-alumina SPE micro-column, which was synthesised to provide a very high surface area, with slotted tube atom trapping FAAS. This approach enabled separation of Sb^III and Sb^V using DDC, which only formed complexes with Sb^III, and sample pre-concentration. The optimised method significantly enhanced the sensitivity, with LODs of 6.0 and 8.2 ng L⁻¹ for Sb^III and Sb^V respectively, gave good spike recoveries for both species in real samples and had an analysis time of 145 s.

In the past year, a number of works have applied GF-AAS for food analysis. Sun et al.⁷⁴ focussed on Se species in rice The inorganic and organic Se species were extracted using CPE with analysis by GF-AAS. An LOD of 0.08 μg L⁻¹ and good precision were demonstrated, with confirmation of the method accuracy by comparison with ICP-MS. Silvestre and Nomura⁷⁵ also analysed rice for Al, Cd and Pb with GF-AAS but applied a solid sampling approach. A Pd–Mg modifier was used to enable calibration with aqueous standards. With the optimised procedure, a number of commercially available rice samples were measured whilst the effects of washing and cooking were also investigated. Slurry sampling allowed de Andrade et al.⁶² to quantify Cd, Cr and Pb in honey with minimal sample pre-treatment. Nitric acid and H₂O₂ were used to create the slurry which was directly injected into the graphite furnace. Cadmium required the use of a modifier, namely Pd–Mg, and addition of fructose to the aqueous calibration standards. The LODs were 2.0, 9.4 and 5.4 ng g⁻¹ for Cd, Cr and Pb respectively, with honey samples from Brazil containing <2.0–8 ng g⁻¹ Cd, 83–94 ng g⁻¹ Cr and 141–228 ng g⁻¹ Pb. Moraes et al.⁷⁶ presented a method to determine Hg in fish with GF-AAS following acid mineralisation. A combination of tungsten-carbide pyrolysis tubes and Cu(II) nitrate were used as modifiers for GF-AAS. The instrumental LOD and LOQ was 27 and 89 ng L⁻¹ and accuracy was demonstrated through spiked samples and use of DORM-4 fish protein CRM. The method was applied to dourada, pacu and jaraqui fish from the Brazilian Amazon with concentrations ranging from 0.081 to 0.331 mg kg⁻¹ Hg.

The determination of toxic elements in waters by GF-AAS was the subject of research for two works.^60,77 Cacho et al.⁶⁰ described the unique use of an electrochemical flow through cell for the on-line pre-concentration of Se in water samples. The cell contained a gold-plated porous carbon working electrode with a Pt auxiliary electrode and was connected to the GF-AAS system through a 6 port valve and sampling loop. The procedure had an LOD of 0.01 μg L⁻¹ and accuracy was demonstrated using a number of CRMs and comparison against results by ICP-MS. It was also possible to determine Se^IV or total Se if the sample was pre-treated with HCl and heated. Ajtony et al.⁷⁷ developed a method for the measurement of As, Cd, Cr, Cu, Pb, and Se in various water samples (snow, tap and well). Simultaneous detection of As, Cd, Pb and Se was possible using end-capped graphite tubes whilst Cr and Cu required the use of graphite tubes with L'vov platforms. The influence of chemical modifiers and interferences from Cl⁻ and SO₄²⁻ were investigated. However, at high levels, the effect of Cl⁻ and/or SO₄²⁻ could not be overcome which could lead to falsely low results, particularly for Se. This, combined with the use of 2 types of graphite tubes, limited the benefits and usefulness as a ‘simultaneous’ method.

Cold vapour generation for the determination of Hg was combined with AAS with some novel advances. Chandio et al.⁵⁵ described the use of an on-line pre-concentration procedure with a modified alumina adsorbent for the measurement of Hg in water and foodstuffs. Alumina was used as a cheaper alternative for SPE and was treated with ammonium lauryl sulfate and dithizone to improve adsorption characteristics. Hydrochloric acid was used as the eluent for Hg which was directly mixed with NaBH₄ to generate the Hg vapour. With optimised conditions, the enrichment factor was 125, LOD was 0.12 ng mL⁻¹ and recoveries between 97–99% were obtained from spiked samples and NIST SRM 1570a. Lemos et al.⁷⁸ also reported an on-line pre-concentration approach for Hg CV-AAS. In this work, Amberlite XAD-4 was treated with 2-(2′-benzothiazolylazo)-p-cresol as the adsorbent. The LOD obtained with this method was 0.011 μg L⁻¹ and was applied to human saliva samples (0.055–0.200 μg L⁻¹), fish (0.043–0.361 μg g⁻¹) and shellfish (0.075–0.397 μg g⁻¹). A novel development by Peng et al.⁷⁹ utilised gold nanoparticles to coat the surface of a quartz tube atomiser for Hg determination with AAS. The in-atomiser trapping was successfully demonstrated for spiked water samples and 2 matrix CRMs (GBW07601a and DORM-4), with an instrumental LOD of 0.01 ng mL⁻¹.

The history, background and use of continuum source AAS were highlighted in a review by Welz et al.¹² covering the past, present and future of the technique. The article included the development of the technique, which emerged over 150 years ago, the current state of the field with examples, the challenges that remain and the future direction. Çiftçi et al.⁵¹ presented the use of HR-CS-AAS for the determination of Al and Pb in water and beverages. A complex ligand was used to chelate Al and Pb, followed by selective absorption and pre-concentration using a polystyrene based substrate. The method was optimised and validated, achieving LODs of 0.32 μg L⁻¹ Al and 0.24 μg L⁻¹ Pb. Santos et al.⁸⁰ applied HR-CS-AAS for the analysis of Ca, Cu, Fe, K, Mg, Mn, Na and Zn in ‘baby leaf’ salad leaves. After acid digestion, the elemental content of the salad leaves was determined using both flame and electrothermal atomisation HR-CS-AAS, with accuracy checked using a CRM. The results showed that the main constituents were Fe, K and Ca, and LDA could discriminate between the different families of leaves.

4.3 Atomic emission spectrometry and laser induced breakdown spectroscopy

A novel calibration approach for flame emission spectrometry was reported by Lyra et al.⁸¹ for the determination of Ca and Na in milk powders. The analysis of Na by FAES can be hampered in the presence of Ca, such as with milk samples, caused by the interfering CaOH radical emission band which cannot be resolved. The group used a digital webcam as a visible light range detector and combined with chemometric methods for calibration. A set of 25 calibration standards with differing amounts of Ca and Na were measured and modelled using multiple linear regression based on the RGB (Red Green Blue) components of a 15 × 15 pixel image region. The model was tested with a prediction set of standards with good correlation observed for both Ca and Na (r values of 0.9998 and 0.9999 respectively). The model was applied to real milk powder samples and spiked samples, with recoveries between 98% and 103% found. Additionally the FAES data was compared with FAAS results with no significant difference found at the 95% confidence interval. The proposed FAES method also offered increased sample throughput over FAAS as switching the hollow cathode lamp was not required.

The use of solid sampling ICP-OES was the subject of a report by Nischkauer et al.⁶¹ who applied ETV to investigate the uptake behaviour of Pd, Pt and Rh in Brassica Napus. Hydroponically grown plants were dosed with the 3 elements and subsequently dissected into roots, stems and leaves. Solid sampling ETV-ICP-OES was employed for analysis with quantification achieved using filter papers spotted with aqueous elemental standards and dried. This approach enabled Pt to be determined without the memory effects observed with solution-based standards due to the formation of Pt-carbide. The method was compared against traditional acid digested samples with good agreement obtained. However, the ETV approach used smaller quantities therefore enabling greater spatial resolution which could facilitate better improved understanding of PGE translocation in plants.

The challenge of implementing the new United States Pharmacopeia (USP) General Chapters 〈232〉 and 〈233〉 was highlighted by Stoving et al.⁸² A method for the analysis of a suite of elements (namely As, Cd, Cu, Cr, Fe, Hg, Ir, Mn, Mo, Ni, Os, Pb, Pd, Pt, Rh, Ru, V and Zn) in pharmaceutical products was described. A microwave assisted acid digestion was applied using a reverse aqua regia mixture (3 : 1 v/v HNO₃–HCl). The LODs and LOQs obtained by ICP-OES were at least 10-fold lower than the limits set by the USP and spike recoveries were adequate for all elements except Os for which the recovery was 162% with an RSD of 13.7%. The authors attributed this to a memory effect and noted that the method required further development for Os. It was also reported that spectral interferences required visual inspection of peaks for Ir, Os, Pb, Pt and Rh. Both of these issues emphasised the difficulty of the new USP guidelines.

The use of alternative atomisation sources for OES was described in 2 works.^83,84 Matusiewicz and Ślachciński⁸³ reported a combined approach for MIP-OES employing USN and a multimode sample introduction system (MSIS) for the measurement of hydride-forming (As, Bi, Ge, Sb, Se, Sn), Hg vapour, and non-hydride-forming (Ba, Ca, Li, Mg, Sr) elements. The MSIS combines traditional pneumatic nebulisation and hydride/cold vapour generation in a specially designed cyclonic spray chamber which can be operated separately and in tandem within the same session. In this work, a USN was used prior to the MSIS to achieve high efficiency aerosol formation to enable the use of smaller sample quantities without affecting detection limits. The unique approach was assessed with 4 different biological and environmental CRMs. Zhang et al.⁸⁴ described the application of solution cathode GD-AES to determine Cd, Cr, Hg and Pb. The addition of an ionic surfactant, namely cetyltrimethylammonium chloride (CTAC), to the electrolyte solution helped to reduce the background and improved precision. Additionally, the authors compared the addition of ionic (CTAC) and non-ionic (Triton X-45 and Triton X-100) surfactants to the sample solutions. For Cr, Hg and Pb, CTAC provided the greatest enhancement whereas Triton X-100 was optimal for Cd. The optimised methodology was demonstrated using biological and environmental CRMs.

In recent times, LIBS has been applied to a number of biological applications. Grolmusová et al.⁸⁵ reported the use of LIBS as a screening tool for the detection of Wilson's disease. Liver tissues from confirmed Wilson's disease patients and a control group were analysed with LIBS equipped with a CCD camera and the data was interpreted in two ways. The first was considering the Cu/C ratio and the second was directly through the CCD images. It was demonstrated that LIBS could be used for this purpose as a quick and low-cost approach. Motto-Ros et al.⁸⁶ applied LIBS analysis to kidney tissue slices from mice exposed to Gd nanoparticles. This enabled mapping of the Gd distribution within the tissues and achieved a resolution of 100 μm. Abdel-Salam and co-workers⁸⁷ applied LIBS to evaluate the nutritional elements Ca, Fe, Mg and Na in human milk and infant formula. The work was only qualitative but it indicated that human milk contained higher levels than commercial products. Interestingly, the group also compared the CN and C₂ emission bands in order to infer protein content which was similar between the two groups of samples.

4.4 Atomic fluorescence spectrometry and vapour generation procedures

During the past year, only a limited number of works utilising AFS were published. The application of AFS for the analysis of food was reported by dos Santos et al.⁸⁸ The paper describes the analysis of rice samples for As using a slurry sample preparation procedure. The optimised method used 2 M HNO₃ as the extractant in combination with an ultrasonic bath. Analysis by HG-AFS enabled low LODs of 1.1 ng L⁻¹ to be obtained. Chen et al.⁸⁹ developed a quick and effective digestion procedure for Cd and Pb in single hair strands. The measurement was undertaken by tungsten coil ETV-AFS with an Ar–H₂ flame. The LODs were 0.05 pg and 3 pg for Cd and Pb respectively for a 10 μL sample injection and accuracy was demonstrated with a hair CRM. The method demonstrated potential for forensic applications where single hair strands could be used for profiling.

4.5 X-ray spectrometry

A comprehensive review of recent advances in X-ray spectrometry² accompanies this Update and includes applications with clinical and biological materials, foods and beverages.

Lee et al.⁹⁰ employed PIXE and Rutherford backscattering spectroscopy to enhance the quality of information to be gained from ion-beam analyses. This work included comparing spectra produced with 3 MeV proton and 36 MeV carbon ion beams applied to 7 μm thick sections of brain tissue. Signal yields were greater with PIXE but the image quality was similar with both techniques. Interestingly, certain elements showed better contrast with protons while others were superior with the carbon ion beam. The results demonstrated the value of applying more than one approach to a problem. The hard X-ray microanalysis beam line from the Canadian synchrotron was used by Gherase et al.³⁷ to determine the distribution of As in nail clippings. Calibration of the measurements, using the As K-alpha peak, was achieved by analysis of nail phantoms prepared in the same way as real samples. A 13 keV excitation was used with a 45 degree sample and 90 degree beam detection geometry. As was found in small spots of <1 mm² in the nail.

A novel way of interpreting X-ray spectra was proposed by Frankær et al.⁹¹ Strontium-containing compounds have a role to play in the treatment of osteoporosis and, in the study reported by these workers, XAS, X-ray powder diffraction and EXAFS techniques provided localisation and compositional information for Sr in bone. Results were collected from bone samples of Sr-treated dogs and from Sr-doped calcium hydroxyapatite, Sr-soaked collagen and Sr₃(PO₄)₂. The spectra from the bone samples were modelled by a linear combination of those from the in vitro prepared reference compounds. Application of this approach to this study by Frankær et al.⁹¹ is mentioned in Section 5.2.

Applications of XRF spectrometry to imaging are described in a separate Section 5.2, below.

Little new work relating to development of techniques for in vivo XRF spectrometry was seen in the last year.

5 Applications: clinical and biological materials

5.1 Metallomics and elemental speciation

A comprehensive review of recent advances in speciation and related techniques⁶ accompanies this Update and includes applications with clinical and biological materials, foods and beverages.

Speciation studies with metal-containing anti-cancer agents are seen to be important in clarifying mechanisms of action and of toxicity. A new approach to investigating Pt speciation was developed by Martincic et al.⁹² Protein G- and DAEA-monolithic convective interaction media discs were assembled together in a column for conjoint LC. This methodology has been established in biochemical and immunological research for a number of years. We believe, however, it is a first for the technique appearing in this particular ASU review. With this application, both affinity and ion exchange mechanisms were exploited for separation of Pt species in human serum. With an elution buffer at pH 7.4, immunoglobulins were retained on the Protein G disc and, at the same time, unbound Pt was separated from albumin- and transferrin-bound Pt during passage through the DAEA disc. Then, with an acidic mobile phase, Pt associated with immunoglobulin was eluted. The Pt species were detected by post-column ID-ICP-MS. The authors claimed that this novel procedure was more rapid and simpler than the more usual SEC techniques. It was found that most of the Pt was bound to albumin but with carboplatin binding to protein occurred more slowly than was seen for cisplatin and oxaliplatin. A number of Ru-complexes with potential anti-cancer activity have been developed but none are yet in clinical use. To investigate possible metabolism, Aleksenko et al.⁹³ studied the influence of cytoplasmic glutathione, ascorbic acid and citric acid on the speciation of Ru-transferrin adducts using CE-ICP-MS. Glutathione and ascorbic acid promoted release of Ru from the protein whereas the metal remained with the protein when exposed to citric acid.

For clinical investigations of As exposure and toxicity, total As concentrations may be misleading and it is necessary to separate the species typically found in urine and blood. To facilitate interpretation of results, Leese et al.²⁹ determined reference values for As^III, As^V MMA, DMA and AB in urine, corrected for creatinine concentrations. Specimens from 95 subjects who had no occupational exposure to As were analysed by anion exchange micro-column LC-ICP-MS. Analysis of the data using Bayesian statistics confirmed that consumption of shellfish and red wine had significant effects on the urinary levels of AB, DMA and MMA but that smoking had no influence on As speciation. These reference values helped in the interpretation of biological monitoring data for As exposure. Not limiting themselves to the traditional five As species, Liu et al.⁶⁸ set about determining ten species and analysed various sample types including herbs and chicken meat. These workers used CE-ICP-MS to separate AC, 3-nitro-4-hydroxyphenylarsonic acid, o-arsanilic acid, p-ureidophenylarsonic acid, and 4-nitrophenylarsonic acid in addition to those determined by Leese et al.²⁹ Conditions for the electrophoresis were optimised and a buffer of 12 mM NaH₂PO₄ and 8 mM HBO₃, pH 9.2 with an applied voltage of +30 kV was used. The LODs were 0.9–3.0 ng g⁻¹ As and the method was validated by analysis of TORT-2 and DORM-3 CRMs.

A further group of As compounds present in foods are the arsenolipids, comprising As-fatty acids and As-hydrocarbons. Amayo et al.⁹⁴ analysed Capelin Oil by RP-HPLC-ICP-MS/ES-MS. Additional analysis of unidentified compounds by acetylation and thiolation, coupled with accurate mass spectrometry pointed to an additional class of arsenolipids, cationic trimethylarsenio fatty alcohols. Also, four As-hydrocarbons that had not been previously seen were discovered and characterised.

The relevance to human health of iAs in rice and products derived from rice has recently become recognised. Thus, a number of studies have been reported concerning both levels of exposure and methods for speciation (Section 7.1.1).

A sensitive procedure to separately measure concentrations of iHg, EtHg and MeHg in whole blood down to 30 pg g⁻¹ was reported by Rahman et al.⁹⁵ Blood samples were solubilised with 2 M HNO₃ and equilibrated with enriched ¹⁹⁹Hg²⁺, Et²⁰¹Hg⁺ and Me²⁰⁰Hg⁺ using microwave heating. The spiked samples were reacted with 1% sodium tetrapropyl borate and the propylated Hg species adsorbed onto a carboxymethylsiloxane – SPME fibre. The adsorbed species were thermally desorbed and Hg determined using GC-ICP-MS. The authors reported the method to be sufficiently sensitive to determine all three species at levels of 30 pg g⁻¹. Method validation was assessed by analysing bovine blood SRM 966 Level 2 and by mass balance comparison of the sum of the measured values for individual species with total Hg determined by ID-ICP-MS using EPA protocol 3052. Meng et al.⁹⁶ also investigated Hg speciation, their interest being the species in rice and the concentrations of iHg and MeHg in hull, bran and white rice. The majority of iHg was located in hull and bran whereas the more toxic MeHg was in the edible white rice Based on XANES data, it was suggested that iHg in bran is primarily bound to cysteine in phytochelatins and is largely immobile. The MeHg in bran is also bound to cysteine in proteins. However, this MeHg–cysteine is actively transported to the endosperm during seed ripening, which has implications for human health when rice is consumed from polluted areas (especially evident throughout Asia).

Iodine status in humans is normally assessed by measurement of the thyroid hormones but there may be situations in which additional information could be of use. Han et al.⁹⁷ therefore developed a method using RP-LC-ICP-MS that separated and quantified I⁻, IO₃⁻, mono-iodotyrosine, di-iodotyrosine, triiodo- and reverse tri-iodothyronine and thyroxine in urine, within 7 minutes. Tetrabutylammonium hydroxide was used as the ion-pair reagent and the eluent was NH₄Cl with L-phenylalanine or deoxycholic acid. Recoveries of the seven species were 93–106% and the LODs were 0.046–0.094 μg L⁻¹.

As discussed in Section 7.1.4, Nori seaweed is an exceptional dietary source of I, being rich in this element. Material from Galicia in Spain was found to contain 68 μg g⁻¹ I of which 25% was water soluble I⁻. Romaris-Hortas et al.⁹⁸ investigated the non-water soluble, protein bound species by extracting with NaOH, SDS and Triton X-100. Intact proteins were separated by SDS-PAGE and five I-containing proteins were located by LA-ICP-MS.

After many years in which Se featured prominently in the reports of metallomics and speciation, there is very little novel work from this review period. Jeong et al.⁹⁹ developed an elaborate protocol for Se speciation in serum and urine. The work involved affinity column HPLC for separation of selenoproteins and RP-HPLC for speciation of iSe and selenoamino acids. Post-column ID (⁷⁸Se) was employed for quantification with octopole ICP-MS, using H as the reaction gas. This procedure identified GPx, selenoprotein P and selenoalbumin in serum at (Se) concentrations of 22.8 ± 3.4, 45.2 ± 1.7 and 16.1 ± 2.2 ng g⁻¹, respectively. Analysis of the protein by enzymatic hydrolysis showed SeCys was the main amino acid in all proteins while SeMet was found only in selenoalbumin. Urine contained Se^IV, Se^VI and SeCys.

5.2 Imaging with MS and X-rays

Recent developments with instrumentation and applications using MS imaging were summarised and discussed in a review by Becker et al.¹³ which provided a snapshot of the LA-ICP-MS field from the last 5 years. The review specifically covers the area of bio-imaging of intact tissues and describes the advances made with design, techniques, LA systems, data treatment and calibration followed by a number of applications. The challenges of quantitative imaging with MS was reviewed by Ellis et al.¹⁰⁰ which included both molecular MS and elemental MS. The discussion highlighted the issues with providing accurate and reliable quantitative data and concluded that validation of imaging approaches remains a difficulty.

This issue of calibration for LA-ICP-MS applications remains a challenge. Several workers have attempted to overcome this^101–103 with applications to biological and plant samples. Reifschneider and co-workers¹⁰¹ used a cold-curing glycol methacrylate resin to generate matrix-matched Pt calibration standards. The Pt-spiked resin was sliced and digested by microwave-assisted dissolution for total Pt determination by ICP-MS. The calibration standards were then used to quantify the distribution of Pt in tissues of mice exposed to cisplatin, achieving good LODs (8 μg kg⁻¹). Wilson's disease, a disorder affecting the metabolism of Cu, was the subject of a study by Pornwilard et al.¹⁰² using quantitative LA-ICP-MS. The group determined Cu, Fe, Mn and Zn in mouse liver slices of control and diseased animals. Quantification was achieved with characterised spiked murine brain tissue standards. Significantly increased levels of Cu, Fe and Zn were observed in Wilson's-variant samples compared with the control group. Whilst the use of quantum dots (QD) for a wide variety of diagnostic, therapeutic and optical applications is very promising, concerns about the toxicity were examined by Hsieh et al.¹⁰³ with LA-ICP-MS. Mouse lung slices (controls and exposed) were used to identify the location of CdSe QDs to specifically within the alveoli in the upper part of the lungs. Furthermore, traditional staining techniques indicated an immune response by the presence of lymphocytes and increased expression of metallothionein, which also linked to increased levels of Cu and Zn. The quantitative imaging of Cd using a standard additions approach was demonstrated, however; a number of assumptions were used and spatial resolution was lost, limiting its usefulness.

A number of groups have applied imaging techniques for food analysis. Arsenic in rice remains a hot topic (refer to Section 7.1.3) but Choi et al.¹⁰⁴ combined total As determination in white and brown rice with imaging by fs-LA-ICP-MS of single rice grains. Overall, white rice contained lower As concentrations than in brown rice and the total As content decreased with increasing degrees of milling. This was confirmed with As imaging of the rice grain cross section showing significantly higher levels on the outer surface. Another application of LA-ICP-MS for foods was described by Romaris-Hortas et al.,⁹⁸ but in combination with speciation analysis for identification of I-containing proteins in edible seaweed. The work was specifically focussed on the water insoluble components of the seaweed and utilised SDS-PAGE for protein separation with LA applied to identify the bands containing I. Five regions were detected which correlated to molecular masses of 10, 20, 27, 40 and 110 kDa. The results of an interesting study on the exposure and uptake rates of Hg in grizzly bears was presented by Noel and co-workers.¹⁰⁵ The ingestion rate of Hg was estimated using captive bears and applied to two wild populations by determining Hg along hair strands with LA-ICP-MS. This ascertained temporal effects in relation to diet, as coastal and inland regions were compared. A peak in Hg levels for coastal bears correlated to the ingestion of salmon during the migration season. The data also suggested the Hg concentrations were above the limit for neurochemical effects proposed for polar bears, which is an additional conservation concern for grizzly bears who already face challenges from habitat loss.

The use of qualitative elemental mapping for biological studies was demonstrated as a beneficial approach in two papers.^86,106 The microorganism Caenorhabditis elegans (C. elegans) was used to investigate the biological mechanisms of Mn activity.¹⁰⁶ A simple sample preparation procedure was described and the distribution of Mn was determined by LA-ICP-MS in different strains of C. elegans with mutations of the DJ1 gene which is associated with Parkinson's disease and linked to oxidative stress regulation. The results confirmed that DJ1 played a significant role in the behaviour of Mn. Laser induced breakdown spectroscopy was applied to the imaging of mouse kidney slices following intravenous injection of Gd-nanoparticles.⁸⁶ In addition to Gd, other elements were also determined, namely Ca, Fe and Si. The approach had a resolution of 100 μm which does not match that possible with LA but could still be useful in combination with classical techniques due to minimal sample preparation without the need of labels or staining.

The combination of LA-ICP-MS with other analytical techniques for imaging purposes has shown development. Herdering et al.¹⁰⁷ described the novel online combination of LA-ICP-MS and atmospheric pressure chemical ionization-MS for simultaneous spatially-resolved speciation analysis. The coupling of both MS instruments was achieved with a flow splitter and differing tubing lengths. For the atmospheric pressure chemical ionization-MS, N₂ was added to the Ar argon carrier gas from the LA system and a custom made inlet enabled the introduction of gaseous samples rather than liquids under standard conditions. The combined approach was demonstrated with imaging of eosin stained kidney slices of mice exposed to cisplatin and with human lymph nodes stained with haematoxylin and eosin (H&E). The results showed excellent correlation with traditional visualisation techniques and, for H&E in particular, it added extra resolution due to overlap of the haematoxylin (blue) and eosin (red) regions. The approach demonstrated significant potential. The use of TOF-SIMS for imaging applications was applied by Henss and co-workers⁷² in order to quantify Ca in bone cross-sections. In-house prepared collagen and mineralised hydroxyapatite standards were characterised by XRD and XPS and used for calibration with TOF-SIMS. The results demonstrated enhanced resolution for Ca and collagen with TOF-SIMS compared with XPS, which could be beneficial for bone research e.g. osteoporosis. Blaske et al.¹⁰⁸ investigated the elemental distribution of metal prostheses coated with Ag nanoparticles using both μXRF spectrometry and LA-ICP-MS. The two approaches provided complementary information, with μXRF spectrometry providing rapid and non-destructive data regarding the major elemental constituents of the implant, bone and soft tissue (Ca, P, S, Ti and V). Laser ablation ICP-MS, with its superior detection capabilities, was able to offer greater detail on the distribution of Ag, Al and Zr along with displacement of Ti and V from the prosthesis into the soft tissue.

Within the timeframe of this review period, an increase in the number of publications utilising X-ray techniques for imaging was observed in comparison to previous years. In particular, the analysis of bone was the subject of several works.^91,109,110 Pemmer and co-workers¹⁰⁹ studied cortical and trabecular bone slices after embedding in polymethylmethacrylate for Pb, Sr and Zn. Quantitative backscattered electron imaging with SEM was used to identify regions of interest followed by analysis with SR-μXRF spectrometry. Normalisation of the signals was required in order to compare between different samples and measurement sessions, which was achieved using Ca as it was determined by both techniques. The results indicated that the elements were not evenly distributed in the various bone structures and that different uptake mechanisms may apply for each of the elements investigated. The use of XAS to image the different bone components following administration of Sr malonate, a drug for the treatment of osteoporosis was described by Frankær et al.⁹¹ (see Section 5.4.15). Synchrotron rapid scanning XRF spectrometry was used to investigate differences in pathological and normal bone morphology of extant and extinct vertebrates.¹¹⁰ Images of Ca, Cu, Fe, P, REEs and Zn provided information about bone healing and remodelling which was not achievable with traditional histological analysis.

Other biological applications of X-ray techniques include the work of Ugarte et al.¹¹¹ who applied PIXE to investigate the trace element distribution in mammalian cornea and retina. The profile of elements such as Cu, Fe, and Zn, in these tissues were presented and additional information from staining indicated that Zn was not associated with metallothioneins. Gherase and co-workers³⁷ used SR-μXRF to examine As in the cross sections of finger and toe nail clippings. Nail phantoms were produced to quantify the As content in addition to imaging. It was found that regions with high As levels (>1 μg g⁻¹) were principally within the ventral and dorsal layers of the nail. In a study similar to that of Choi et al.,¹⁰⁴ who applied fs-LA-ICP-MS to the imaging of As in rice, Meng et al.⁹⁶ used SR-μXRF spectrometry and XANES to determine the speciation of Hg in rice from a contaminated region of China. The hull, bran, and white rice were measured, with the results showing that approximately 78% of iHg was removed during processing. However, around 80% of MeHg remained in the rice grain which was bound to cysteine hence increasing the mobility of Hg. The authors postulated that Hg contamination of rice is an increasing problem which requires further research and understanding.

5.3 Multielement applications

Note that discussion of individual elements follows in Section 5.4.

5.3.1 Investigations of metallic implants and biomaterials. In our 2014 Update,¹ reference was made to the number of papers concerned with analyses of specimens from patients who receive metal-on-metal hip prostheses. This interest has continued during the last 12 months. The concentrations of Co, Cr, Mo and Ni in serum from patients with total hip replacements were compared with those having hip resurfacing surgery.³³ These authors obtained results for Co and Cr that were similar to those previously reported by other workers. They also showed that serum concentrations of Mo and Ni were higher in patients than in control subjects. Evidence is accumulating to suggest that concentrations of Co in blood or serum are probably more informative than those of other elements. Beraudi et al.¹¹² analysed blood, serum and synovial fluid specimens from metal-on-metal hip replacements and from control subjects. Significant correlations were reported between Co in synovial fluid and blood or serum. A second publication from the same group was focussed on metal particulate material often present in synovial fluid.¹¹³ Using SEM-EDX and ICP-MS, concentrations of Co and Cr were measured in blood, serum and particulates. It was found that Co concentrations in whole blood correlated with the number of particles in synovial fluid. Separate to this, where there were particles consisting solely or largely of Cr, the circulating Co concentrations were considerably increased. In a further report from this group, Catalani et al.¹¹⁴ measured concentrations of V in blood, serum and urine specimens from patients whose hip prostheses included component(s) made with titanium–aluminium–vanadium alloy. The 95^th percentile values for V in patients with a well-functioning prosthesis were 0.3 μg L⁻¹ in whole blood, 0.5 μg L⁻¹ in serum and 2.8 μg L⁻¹ in urine. In 42% of the patients the serum V concentration was above the upper limit of a reference range for unexposed individuals (the reference range was taken from an unrelated publication and where details of the methods used are not known). Compared with ‘well-functioning’ values, V concentrations were increased in 42, 29 and 13% of patients' serum, urine and blood samples, respectively. Highest concentrations were seen in the samples from patients with painful, poorly functioning prostheses.

Most of the work relating to metal-on-metal hip prostheses has concerned the concentrations of Co and Cr in biological specimens. However, in patients with failed total hip replacement, concentrations in blood or serum are not as high as in those with failed resurfacing. Examination of removed devices suggests that there are problems associated with the titanium alloy stem that goes into the femoral bone. For this reason methods are developed to measure Ti concentrations in blood and serum. Determination of Ti by Q-ICP-MS is complicated by isobaric interferences from the relatively huge concentrations of Ca isotopes. To determine concentrations in specimens from normal subjects as well as from patients, Balcaen et al.³⁴ used ICP-MS/MS. The effectiveness of O₂ and NH₃/He as collision cell reaction gases, to overcome spectral interferences on Ti, was investigated. It was observed that O₂ was ineffective as a reaction gas but that conversion of Ti⁺ ions into Ti(NH₃)₆ cluster ions provided an interference-free method with an instrumental LOD of 3 ng L⁻¹. Serum concentrations were less than 1 and 2–6 μg L⁻¹ in normal subjects and patients with implants, respectively. Silver-coated prostheses reduce rates of infection compared with uncoated metal devices. Blaske et al.¹⁰⁸ were interested in the impact of nanosilver-coating on the surrounding tissues following implantation. Using LA-ICP-MS, the distribution of Ag, Ti and V from an implant was compared with μXRF visualisation for Ca and P (in hard tissues) and with S (in soft tissues). Metal displacement from the implant into surrounding bone tissue occured for Ag, Al, Ti, V and Zr. The high concentrations of Al and Zr present at the surface of the implant were suggested to be as residues from the pre-operative treatment of the device.

5.3.2 Biological fluids. Two reports of isotopic measurements in blood provided interesting results. Observations of animal samples indicate body accumulation of light Cu and heavy Zn throughout life. Although not investigated in humans this work led Jaouen et al.¹¹⁵ to suggest a possible approach to age assessment. Recognising that isotopic composition is influenced by diet, they selected a study population from an isolated area of Russia were there was limited variation in the diet. Blood samples were collected from 39 subjects aged 18 to 74 years and ⁶⁵Cu : ⁶³Cu and ⁶⁶Zn : ⁶⁴Zn ratios measured, obtaining results that were consistent with the animal findings. It was also noted that the Cu and Zn isotopic ratios were significantly lighter and heavier, respectively, than in European and Japanese populations. The Russian subjects are known to have high basal metabolic rates associated with living in a polar climate and the authors suggest that there may be acceleration of Cu and Zn stores. Van Heghe et al.¹¹⁶ suggested that loss of Cu and Zn associated with menstrual blood loss may be responsible for the significant difference in the isotopic composition of Cu and Fe in whole blood between men and women. To assess this hypothesis, the whole blood Cu, Fe and Zn isotopic composition was determined for (i) reference groups of healthy men and menstruating women, (ii) women in their menopause and (iii) women who were not menstruating because of an intra-uterine device (IUD). It was found that.

• non-menstruating women had heavier and lighter isotopic compositions for Cu and Fe, respectively, than menstruating women.

• menstruation had no effect on the Zn isotopic composition.

• non-menstruating women showed an isotopic signature for Cu and Fe that was identical to that of the male reference population and there was no difference between results for the two groups.

• the menopausal women had a lighter Zn isotopic composition compared with those using the IUD, an observation that may be due to a hormonal effect.

As part of this study, the effect of age on the isotopic composition of Cu, Fe and Zn in whole blood was also investigated. However, contrary to the results from Jaouen et al.,¹¹⁵ no age effect for these three elements was found. In neither of these papers do the authors suggest mechanisms that would explain the dichotomy of accumulation of light elements on the one hand and heavy ones on the other.

Well validated ICP-MS methodologies for the measurement of trace elements were presented for blood and urine samples for biomonitoring purposes,¹¹⁷ and for urine.^27,64 These reports also include valuable data on reference values. Yu et al.²⁰ from the NIST proposed an ID-SF-ICP-MS method as an alternative to the established ID-TIMS reference procedure for measuring concentrations of Ca, K, Mg and Na in serum. Results for the analysis of SRM 956c matched the certified concentration for both concentrations and uncertainties.

Whilst not exactly a fluid, a sample type that is of growing interest, particularly for occupational biomonitoring and respiratory research, is exhaled breath. The breath can be cooled to give a liquid sample, a condensate, which contains dissolved materials and particulates. Barreiros et al.¹¹⁸ compared ICP-MS and TXRF for the analysis of exhaled breath condensate samples, determining precision, trueness and measurement uncertainty for Cd, Cu, K, Mn, Pb and Sr. Specimens were collected from lead processing workers exposed to different levels of contaminants and the results obtained by ICP-MS allowed good discrimination among the groups. The specific situation of welders exposed to Cd and Mn was investigated by Bredberg et al.¹¹⁹ whose approach was to isolate and analyse particulate material from the exhaled breath. Samples were collected from a group of volunteers before, five minutes and 24 h after a 2 h period of exposure to welding fumes. Little or no Cd and Mn was determined in the pre-test specimens. Of the nine subjects only four produced particulates with measurable amounts of these metals and the concentrations were very varied increasing from <LOD to 82–84 pg L⁻¹ for Mn and from 20–86 to 2600 pg L⁻¹ for Fe. The authors considered this approach had potential as a non-invasive method for monitoring occupational exposures to a range of toxic elements but the enormous range of concentrations would suggest that this sample type is not particularly useful.

In a study of lung physiology in patients with cystic fibrosis and non-cystic fibrosis bronchiectasis, Smith et al.¹²⁰ measured metal ion concentrations in sputum. Compared with samples from apparently healthy controls, increased concentrations of Ca, Fe, Mg and Zn were found with significant correlation between markers of inflammation and results for Mg, Fe and Zn. Patients with severe lung disease also had high concentrations of Mo and it was proposed that this metal may serve as a biomarker for severe cystic fibrosis airways disease.

5.3.3 Tissues. To determine whether concentrations of trace elements may be associated with the risk of neural tube defects, placental samples from cases of newborns with these defects and from healthy infants were analysed by Liu et al.¹²¹ Concentrations of Cu, Fe, Mn, Se and Zn were determined and Mn concentrations of 99.25–166.76 in the case samples were significantly higher than those of 80.14–119.79 ng g⁻¹ in the healthy infants.

A situation that parallels occupational or environmental exposure to atmospheric pollution is pulmonary delivery of drugs carried by CdSe quantum dots (QDs). Using a mouse inhalation model, Hsieh et al.¹⁰³ used LA-ICP-MS to look at lung slice samples. It was found that Cd and Se were co-localised in the bronchiolar region along with high concentrations of Cu. Tissue staining demonstrated accumulation of lymphocytes at the same location. The results suggested that there was no degradation of the QDs and that their inhalation triggers an inflammatory response.

Concentrations of metals within the eye are rarely determined but in a preliminary investigation of 14 patients with cataracts the lens, removed during surgery, together with some aqueous humour, were taken for analysis by XRF spectrometry.¹²² Chromium and Ni were found in both sample types, Ba only in lens with Ni only in aqueous humour. Whether these results have any clinical significance remains to be seen. The distribution of Ca, Cu, Fe and Zn in cornea and retina of rats was investigated by Ugarte et al.¹¹¹ in a second study. Concentrations in different components of these structures were reported. Interestingly, distributions of Zn and metallothionein were not co-incident.

5.3.4 Bone. An interesting application of XRF spectrometry was reported by Gonzalez-Rodriguez and Fowler¹²³ who addressed the problem of identifying the bones of the same skeleton when a number of bodies were interred in mass graves. Measured concentrations of a number of elements and their ratios were used for PCA. It was found that Zn : Fe and K : Fe ratios were particularly valuable and good identification was possible when the bones of up to four skeletons were located together.

Pemmer et al.¹⁰⁹ examined samples of femoral neck and head bone from healthy subjects and patients with osteoporosis. The techniques of SR-μXRF and quantitative backscattered electron imaging were used to determine the concentrations and location of trace elements. The variations in spatial distribution of Ca, Pb, Sr and Zn were inferred to indicate different mechanisms of accumulation.

5.4 Progress for individual elements

5.4.1 Aluminium. House et al.¹²⁴ reported a method for the determination of total Al in breast tissue. Breast tissue biopsy samples were digested using microwave heating and Al quantitatively determined using ETAAS. A method LOD of 0.48 μg L⁻¹ was reported and the authors reported a mean tissue Al concentration of 0.39 μg g⁻¹ dry weight. They considered the method to be sufficiently sensitive and robust to be used in future studies on the distribution of Al in breast tissue but observed no statistically significant differences in Al levels across different regions of the breast in this study.

Ichou and colleagues³⁵ used AAS to quantitatively determine Al in an investigation of Al concentrations in 26 commercial parenteral nutrition compounds and 56 hospital-prepared parenteral mixtures. They observed that 50% of the commercial preparations and all of the hospital-prepared mixtures had Al concentrations in excess of the US FDA maximum allowable concentration of 25 μg L⁻¹. They estimated that two thirds of patients administered parenteral nutrition in the hospitals studied had a daily Al intake significantly above the recommended level (2 μg per kg per day). They considered further guidance was necessary on acceptable levels of Al in parenteral nutritional products. Work by Cabrera-Vique and Mesias¹²⁵ who investigated the dietary intake of Al in two distinct populations (families and university students), and of Chuchu et al.¹²⁶ who determined the Al content of 30 infant formula feeds (ready-to-drink milk and milk-powder products) is discussed in Sections 7.1.1 and 7.1.2, respectively.

5.4.2 Antimony. Filella et al.¹⁶ presented a comprehensive review of published data on Sb concentrations in human whole blood, plasma and serum. The review was the last in a series of papers on human biomonitoring, published in Critical Reviews in Environmental Science and Technology. The review discussed the main problems in measuring Sb in the complex blood matrix. The authors concluded that establishing a reliable reference range for Sb in blood was impossible due to the problems of sample contamination, instrument sensitivity and lack of CRMs. Nevertheless, they considered that most recently published data suggested a concentration ceiling of 1 μg L⁻¹. Quiroz and colleagues¹²⁷ developed a method for the determination of Sb species in human erythrocytes using a combination of HPLC coupled with HG-AFS. Sample treatment involved protein precipitation followed by SPE of the analyte on a C₁₈ column, elution with EDTA and chromatographic separation of species using PRP-X anion exchange resin and 20 mmol L⁻¹ EDTA mobile phase. Although the authors reported that optimised experimental conditions had been identified, the fact that recoveries were only 90% for Sb^V and only 55–75% for Sb^III suggests there is still scope for further work to develop the method to achieve truly quantitative results. They also noted that both species were able to penetrate the erythrocyte membrane and that this membrane transfer was temperature dependent. Heparin was identified as the most suitable anticoagulant to retain the original distribution of Sb in blood.

5.4.3 Arsenic. Speciation studies again dominate the published work on As in biological systems. Chen and colleagues¹⁴ presented a summary review of methods for As speciation in biological matrices developed over the past five years. The reviewers compared different sample pre-treatments, including SPE, liquid–liquid extraction, LC and CE, and considered that all of them offered effective separation, selectivity and sensitivity for quantitative determination. They considered HPLC coupled with ICP-MS to be the most powerful hyphenated technique for As speciation in biological matrices. Leese and colleagues,²⁹ at the UK Health and Safety Laboratory, used that technique to establish background concentrations for the UK population. This work, and that of Liu et al.⁶⁸ who coupled CE with ICP-MS to separate and determine 10 As species in biological CRMs, are discussed in Section 5.1.

The environmental As crisis in Bangladesh and other regions of India, highlighted in our previous reviews, continues to be investigated and reported on. Kalman et al.¹²⁸ determined As species in urine samples collected from children chronically exposed to As in drinking water from an As contaminated region of Bangladesh. The trivalent species of MMA is particularly toxic compared to the pentavalent form. Therefore, care was taken to use sample collection, storage and preparation methods that conserved As species, in particular MMA^III. They reported that efforts to preserve MMA^III and MMA^V using complexing agents were not entirely successful. Of the 643 samples stored for more than three months before analysis, MMA was only detected in 41 samples and in only two of these was the level in excess of 1 μg L⁻¹. They concluded that MMA was not suitable as a biomarker of As exposure in epidemiological studies.

Leffers et al.^129,130 noted that risks to human health from exposure to arsenosugars is still unclear. To help address this, they examined the intestinal availability and transfer of different arsenosugar metabolites using LC-Q-ICP-MS. They reported that thio-DMA was readily transported across the intestinal barrier and was metabolised to its oxygen analogue DMA. It also caused barrier leakage in a similar manner to inorganic As^III. They concluded that arsenosugar intake needs to be considered when assessing risks to health arising from dietary As exposure.

5.4.4 Cadmium. Studies involving nanomaterials continue to become more evident in ASU Reviews. In our 2013 Review, we reported on the use of CdTe quantum dots for the indirect determination of urine protein concentrations. In this review period, the research group of Hsieh et al.¹⁰³ investigated the potential of CdSe quantum dots for lung imaging and pulmonary drug delivery by studying the spatial distribution of quantum dots in mouse lung tissue following inhalation of the nanoparticles. Distribution of Cd was quantitatively determined in slices of mouse lung tissue using LA-ICP-MS. The researchers observed an accumulation of Cd and Se in the bronchiolar region and noted a high correlation between Cd and Se spatial distribution, suggesting that degradation of the quantum dots was negligible over the 17 day study period. Comparison of the laser ablation data with haematoxylin-eosin staining of the tissue slices revealed a close relationship between quantum dot deposition and lymphocyte accumulation. The group concluded that the inhalation of quantum dots triggered an inflammatory response, an hypothesis that was further supported by the determination of increased Cu concentrations in the same tissue samples.

Baghban et al.⁵⁷ used TiO₂ nanoparticles modified with alizarin red S for the solid-phase extraction of Cd²⁺ and Pb²⁺ from biological solutions followed by quantitative determination using FAAS. The researchers established optimised values for extraction pH, eluent concentration and both sample and eluent flow rates. They reported an enrichment factor of 100 for a 200 mL initial sample volume, giving LODs of 0.11 ng L⁻¹ and 0.3 ng L⁻¹ for Cd and Pb respectively. Their method was validated by analysing water SRM 1643e and was used to determine both Cd and Pb in a range of water and biological samples.

Christopher and Thompson¹⁸ quantitatively determined Cd in SRM 3280 Multivitamin/Multi-element tablets using both collision cell Q-ICP-MS and SF-ICP-MS instrumentation with ID. Cadmium was separated from the interfering elements Mo and Sn, both present at mg kg⁻¹ levels in the tablet matrix, by a combination of precipitation and solid-phase extraction procedures, which allowed quantitative determination of ¹¹¹Cd : ¹¹³Cd and ¹¹¹Cd : ¹¹⁴Cd isotope ratios.

5.4.5 Chromium. Quarles and colleagues,⁶⁴ at the US Centers for Disease Control, developed a method for the determination of Cr and Ni in urine using ICP-DRC-QMS as a simpler, more robust and cost effective replacement for their current method using SF-ICP-MS. Using the instrument in kinetic energy discrimination mode and with He as the cell gas, polyatomic interferences were satisfactorily eliminated for the quantitative determination of ⁵²Cr and ⁶⁰Ni. Reported LODs were 0.162 μg L⁻¹ for Cr and 0.248 μg L⁻¹ for Ni and the method was validated by analysing NIST SRM urine samples. The authors noted that, whilst LODs were similar for both analytical methods, the quadrupole instrument offered better precision.

5.4.6 Cobalt. Work of interest in this review period, relates to the release of Co and other metal ions following metal hip replacement surgery and this was described in detail in Section 5.3.1.

5.4.7 Copper. In our last ASU Review,¹ we highlighted papers on the determination of Cu isotopes for early diagnosis of Wilson's disease. In this review period, a Slovakian research team⁸⁵ used LIBS to quantitatively determine elevated levels of Cu in liver samples from patients with Wilson's disease. The team used a Nd : YAG laser and echelle-type spectrometer with an intensified CCD camera to give coverage of a spectral range of 200–950 nm. Seven liver samples from individuals with suspected Wilson's disease and five reference samples were examined. The authors considered the method to be a quick and low cost approach for monitoring the pathological accumulation of Cu in patients with the disease. Pornwilard and colleagues¹⁰² used LA-ICP-MS for the bio-imaging of Cu in liver samples from mice with a genetic mutation identical to that producing Wilson's disease in humans. Quantitative determination of Cu and other trace elements was achieved by ‘quasi matrix-matched’ calibration with in-house standards of trace element-spiked murine brain tissue having well characterised element concentrations. Levels of Cu, Fe and Zn in diseased tissue samples (143 μg g⁻¹ for Cu, 80 μg g⁻¹ for Fe and 32 μg g⁻¹ for Zn) were all elevated compared with the controls (4 μg g⁻¹ for Cu, 41 μg g⁻¹ for Fe and 18 μg g⁻¹ for Zn).

5.4.8 Iodine. Iodine deficiency is becoming recognised as a global public health problem and recent I status in humans is usually monitored by measuring urinary I excretion. However, it is less suitable as an indicator of long-term I status. Prejac and colleagues¹³¹ described a method for the determination of total I in human hair in order to evaluate its potential as an indicator of long-term I status. Hair samples were collected from 871 healthy Croatians and I quantitatively determined using ICP-MS. A median hair I concentration of 0.499 μg g⁻¹ was reported with no observable difference between hair I concentrations in men and women. By applying a logistic sigmoidal distribution curve to the data the authors suggested a hair I concentration below 0.15 μg g⁻¹ represented overt I deficiency and a value above 2 μg g⁻¹ representing excessive I exposure. They considered hair I measurement to be a robust indicator for long-term I status.

Two groups, one in Brazil and one in Korea, reported studies on I status in infants by monitoring urinary I excretion. The Brazilian group¹³² investigated urinary I excretion and the relationship with maternal milk I concentration in a group of 33 infants aged less than 6 months. Iodine in urine and maternal milk was quantitatively determined using ICP-MS. Levels of I in kitchen salt from the participating households were also determined by titration. The median value for urine I was 253 μg L⁻¹ and the mean concentration of I in maternal milk was 206 μg L⁻¹. A positive correlation between urinary I excretion and maternal milk I concentration was reported. The authors concluded that the elevated urinary I excretion was due to high I concentrations in maternal milk which, in turn, were due to high I levels in the salt. They recommended that salt I be reduced.

The Korean group investigated I status in a group of pre-school children by measuring urinary I excretion. Samples were collected from 611 healthy children aged between two and seven years. Urine I was quantitatively determined using ICP-MS. A median urine I concentration of 438.5 μg L⁻¹ was reported. The authors estimated that two thirds of the children had excessive I intake compared with less than 55 having insufficient intake. They argued for preventive measures for excessive intake to be introduced.

5.4.9 Iron. This review period has seen the publication of further work investigating the putative role of Fe in neurodegenerative diseases. Ramos et al.¹³³ presented findings from a very detailed study of Fe distribution in 14 different regions of the human brain. Post mortem samples were obtained from 42 adults with a median age of 71 years and no known history or evidence of neurodegenerative or neurological diseases. After microwave-assisted acid digestion, total Fe in the samples was determined using ETAAS. The authors reported that Fe distribution was heterogeneous with highest levels found in the putamen (304–1628 μg g⁻¹) and globus pallidus (225–1870 μg g⁻¹) and lowest levels in the pons (11–253 μg g⁻¹) and medulla (13–115 μg g⁻¹). Brain Fe concentrations were also age-related and this was most pronounced in the regions with highest Fe concentrations. The researchers examined Fe levels in brain samples from two individuals who had Alzheimer's disease and one with Parkinsonism. The Parkinson's disease samples showed higher concentrations of Fe in the basal ganglia compared with controls, whilst the Alzheimer's samples had elevated Fe concentrations in the hippocampus. Feng and Wang¹³⁴ investigated the use of ID-LA-ICP-MS for the spatial discrimination and quantitative determination of Fe in thin tissue slices. They developed a calibration method using spiked homogenised sheep brain and bovine liver CRM, both immobilised in gelatin to simulate tissue slices. The results obtained with the laser ablation approach were in good agreement with those using ID-ICP-MS following microwave digestion. The authors proposed to use the method to study brain Fe distribution in mice.

The determination of carbohydrate-deficient transferrin (CDT) is an important biomarker for a number of clinical conditions and for forensic diagnoses. Ordonez et al.¹³⁵ highlighted the fact that CDT is not a singular molecular entity but a group of transferrin species and that the various immunological methods for CDT determination requires a CRM as a universal calibrator for method harmonisation. To address this, the researchers developed a sensitive method for the separation and quantitative determination of transferrin sialoproteins in human serum using IC-ID-ICP-MS. The method was used to determine concentrations of individual transferrin sialoforms in NIST CRM 909c human serum.

5.4.10 Lanthanides. Recent reviews in this series¹ have noted ever increasing interest in nanomaterials, both in relation to health risks associated with exposure to nanomaterials and their role as potential therapeutic agents. Abid et al.¹³⁶ studied the deposition and translocation of Europium-doped Gd₂O₃ nanoparticles following intra-tracheal instillation in mice. The nanoparticles were produced by spray-flame pyrolysis and their size, crystallography and surface properties fully characterised. In vitro dissolution in surrogate bio-fluids indicated very little solubility of the particles. Twenty-four hours after instillation, the target organs were harvested, acid digested and nanoparticle concentrations determined using ICP-MS. Nanoparticles were detected at low ppb concentrations in all organs examined. A significant proportion was detected in faeces and only 59% remained in the lungs, suggesting rapid clearance. The authors considered this model to be valuable in understanding the clearance of nanoparticulates from the lung.

Motto-Ros et al.⁸⁶ investigated the use of LIBS for mapping the intracellular localisation of Gd in mouse kidney slices, following IV injection of a suspension of Gd nanoparticles. Satisfactory mapping with a resolution of 100 μm was achieved. An approach for quantitative determination of Gd was also reported which gave results in good agreement with those obtained using ICP-OES.

5.4.11 Lead. Occupational exposure to Pb has been recognised since antiquity, yet it is only in the past 40 years that attention has focused on the sub-clinical effects of environmental exposure to the element. Nieboer and colleagues at McMaster University¹³⁷ reviewed recent developments in the quantitative determination and characterisation of Pb in body fluids, Pb toxicokinetics and modelling. They concluded that these developments have helped identify relationships between Pb in blood and other tissues and adverse health outcomes, thereby helping develop strategies to reduce environmental Pb exposure particularly in young children. Oulhote et al.¹³⁸ undertook a detailed study to identify the contribution of different environmental sources of Pb to children's contemporary blood Pb levels. The study involved 484 French children aged from 6 months to 6 years. Blood Pb and Pb in water, residential soils and dusts were quantitatively determined using ICP-MS. A multivariate additive statistical method was used to analyse the data and the authors reported that very low levels of environmental exposure were significant predictors of children's blood Pb levels. They noted that blood Pb levels (geometric mean: 14 μg L⁻¹) increased by 65% when Pb levels in residential dusts increased from the 25^th percentile to the 95^th percentile and that the sharpest rise in blood Pb occurred at the lowest levels of environmental Pb contamination.

The Amazon is often romantically thought of as one of the world's last wildernesses. It was interesting, therefore, to see the results of a study to establish a reference value for blood Pb in a population of blood donors from Rio Branco, the capital city of Acre in the Western Brazilian Amazon. Blood samples were collected from 1196 donors during 2010–2011 and the concentration of Pb determined using ICP-MS. Upper reference limits, 95^th percentile values, were reported to be 109 μg L⁻¹ for men and 70.7 μg L⁻¹ for women. The authors noted that these were higher than those reported for other adult populations and argued that exposure of this population to local sources of Pb needs to be addressed.

5.4.12 Manganese. The toxic effects of excess Mn on the CNS are well recognised. Liu and colleagues¹²¹ investigated the relationship between placental Mn levels and the risk of foetal neural tube defects (NTDs). A case-control study was undertaken on 80 foetuses or newborns with NTDs and 50 healthy newborns. Placental Mn concentrations were determined using ICP-MS. Median placental Mn was significantly higher in NTD cases (131.6 ng g⁻¹) compared with controls (101.5 ng g⁻¹). After correcting for confounding factors, the authors established a clear dose–response relationship between placental Mn and risk of NTD and that Mn concentrations above the median were associated with a four-fold increase risk of NTD.

Richardson et al.⁶⁷ developed a simple and robust method for the quantitative determination of Mn in whole blood and plasma using ICP-MS without the use of collision-cell technology. Blood and plasma samples were diluted with a solution containing 0.005% Triton X-100, 0.2% butan-1-ol, 0.2% propan-2-ol, 1% HNO₃, containing Ga as an internal standard and centrifuged to remove cell debris. Manganese was measured at mass 55 using aqueous calibration standards. Polyatomic interference from FeH was overcome by modifying the geometry of the skimmer cones. The method was validated by analysing a series of external quality assessment scheme samples.

5.4.13 Mercury. Whilst attention has again primarily focused on methods for sample preparation and on the speciation of Hg in biological matrices (described in Sections 3.2 and 5.1), other groups continue to describe methods for the determination of total Hg. Peng et al.⁷⁹ described a novel method for the determination of total Hg in biological matrices using atom-trapping CV-AAS. The atom-trap consisted of a quartz tube atomiser the inner surface of which had been coated with a thin film of gold nanoparticles. Mercury vapour was generated from samples by reduction of Hg²⁺ with HCl and tetrahydroborate and efficiently trapped onto the gold surface of the atomiser. Desorption of the Hg, for quantitative determination, was achieved by simply heating the atomiser by increasing the applied voltage to 30 V. With optimised parameters for atom trapping and desorption, an LOD of 0.01 μg L⁻¹ was reported for an initial sample volume of 5 mL. The method was validated by analysing two biological CRMs, DORM-4 dogfish muscle and GBW07601a human hair powder. Liu et al.³⁸ quantitatively determined total Hg in biological samples using ID-ICP-MS following photochemical VG. Samples were solubilised in HCOOH and Hg vapour generated by UV photochemical reduction. An LOD of 0.5 pg g⁻¹ was reported, which the authors considered to be a 350-fold enhancement compared with more conventional pneumatic nebulisation sample introduction. The validity of the method was assessed by analysing several CRMs and good agreement with the certified values was obtained.

Ten years ago we noted the ‘bravery’ of researchers who determined levels of Hg in tissues from aligators captured in the Florida everglades. In this review, we must draw attention to similar ‘bravery’ shown by the Canadian research group who determined the concentrations of Hg in hair from wild grizzly bears.¹⁰⁵ Joking aside, the researchers used LA-ICP-MS to detect temporal changes of Hg in samples collected from both captive and wild bears. By feeding the captive bears a controlled diet containing known Hg levels, the group generated data that helped predict Hg ingestion rates in the wild animal population. They reported that 70% of the bears studied had Hg levels exceeding that identified as being the neurochemical effect level in polar bears.

5.4.14 Platinum. Interesting work on the spatial distribution of trace elements in biological tissues continue to be published. These bio-imaging studies provide valuable insight into the localisation and mode of action of metal-based therapeutic agents. Reifschneider and colleagues¹⁰¹ described a novel approach for the imaging of tissue Pt using LA-ICP-MS on tissue samples embedded in cold-curing resins. Quantitative measurements were achieved using calibration standards prepared by spiking resin blanks with platinum acetylacetonate prior to curing. High spatial resolution and an LOD of 8 μg kg⁻¹ were reported. The authors used the method to investigate the distribution of Pt in mouse, cochlea, testes and kidney at different time points following administration of cisplatin.

The technique of conjoint LC, was applied by Martincic et al.⁹² to achieve 2D separation of Pt species in human serum. Details of the methodology are given in Section 5.1 and the method was used to investigate the interaction kinetics of Pt-based therapeutic agents with serum proteins. Platinum was preferentially bound to albumin with less than 13% being associated with IgG and transferrin.

Much of the developmental work on XRF-CT for biomedical imaging has focused on K-shell X-rays, but little has been reported on the potential of L-shell XRF imaging. Bazalova et al.¹³⁹ reported studies on Monte-Carlo simulations of L-shell XRF-CT imaging of cisplatin in small-animal imaging phantoms. The phantoms contained a series of ‘objects’ of 0.6 to 2.7 mm diameter having Pt concentrations between 10 and 250 μg mL⁻¹ and placed at different depths within the phantoms. By including excitation and fluorescence beam attenuation correction, the authors reported that L-shell XRF-CT was capable of providing accurate information on cisplatin distribution in biological tissues.

5.4.15 Strontium. We have previously noted renewed interest in Sr following its introduction as a pharmacological agent for the treatment of osteoporosis. Frankær et al.⁹¹ investigated the localisation of Sr in bone samples from dogs administered Sr malonate using XRF spectrometry. They reported a novel approach for analysing X-ray spectra which produced a compositional model to estimate the distribution of Sr in different bone components. The researchers postulated and visualised seven possible locations for Sr ions in the bone matrix. The X-ray data revealed that 35–45% of bone Sr was incorporated in the highly structured apatite matrix by substitution of Ca in the crystalline structure. A further 30% was located in sites with a highly disordered structure similar to Sr²⁺ surrounded by oxygen atoms, in solution, whilst the remainder was associated with the surface of the apatite structure or adsorbed to bone collagen. The researchers noted that this incorporation model was independent of dose level and period of drug administration. They suggested that the data provide evidence towards an understanding of the mechanism(s) involved in Sr-induced calcification.

Tipple et al.³⁶ investigated the merit of hair Sr isotope ratio measurements for monitoring dietary and environmental sources of exposure. They highlighted once again the problem of differentiating surface bound element, representing external contamination, from that incorporated into the hair structure following ingestion. They applied a series of increasingly aggressive washing procedures to hair samples and at each stage quantitatively determined the Sr isotope ratios in the hair and leachate using MC-ICP-MS. They observed that Sr isotope ratios varied as a function of the aggressiveness of the washing treatment and considered that the ratios obtained for hair and leachate from the most aggressive treatment reflected the isotope ratios for the internal and external Sr signatures respectively. They considered this approach was valid for using hair specimens for geospatial studies.

5.4.16 Thallium. Staff and colleagues³¹ investigated urinary Tl levels in occupationally exposed workers. Urine samples were collected from 447 exposed workers and 113 non exposed individuals, and Tl determined using ICP-MS. An upper background reference limit, defined as the 95^th percentile value of the non-exposed group, was determined to be 0.27 μmol mmol⁻¹ creatinine. Thirty nine percent of samples from the occupationally exposed group exceeded this reference level. Creatinine correction was also reported to be appropriate for reporting urinary Tl values.

5.4.17 Tin. Feizbakhsh et al.¹⁴⁰ prepared a surface-modified ion-exchange resin for the pre-concentration of Sn from biological matrices. Amberlite XAD-2 resin was modified by covalent immobilisation of brilliant green using an azo-spacer. The modified resin was characterised using SEM and FTIR and binding sites were determined to be homogeneous throughout the resin. Sorption capacity was 40 mg g⁻¹ and the resin could be re-used for up to 10 cycles without any significant loss of binding capacity. The authors used the resin to pre-concentrate Sn from human plasma for quantitative determination using ICP-AES.

5.4.18 Titanium. Nanosized TiO₂ is one of the most widely used nanomaterials in a wide range of industrial applications including construction, health care and consumer goods and, for this reason, there is considerable interest in the toxicokinetics of this material. Several years ago one of the writers of this Update participated in a project to assess possible toxicity of Ti-nanoparticles and then recognised the interference from Ca on measurements of Ti by ICP-MS. The work of Krystek et al.¹⁴¹ is therefore, of personal interest. In a similar experiment, tissues were taken from rats exposed to TiO₂ nanoparticles, digested using HNO₃ and HF for measurement of Ti by ICP-MS. To validate the results, some specimens were also analysed by three other laboratories. The isobaric and polyatomic interferences were resolved by using HR-ICP-MS (⁴⁷Ti) or Q-ICP-MS (⁴⁶Ti, ⁴⁷Ti) in collision cell mode. Determination of the low abundant isotopes was possible because of the high Ti concentrations in the specimens analysed. An inter-laboratory comparison was also undertaken between four laboratories all analysing the same samples using ICP-MS. Good agreement between laboratories was reported for tissue samples where Ti concentrations were above 4 μg g⁻¹.

5.4.19 Zinc. Lamer et al.¹⁴² used the high precision of MC-ICP-MS to discriminate and determine Zn derived from ZnO nanoparticles in complex biological media with a high background Zn content. In earlier work, they had identified a slightly increased uptake of Zn in blood of women following a dermal application of sunscreen containing nanoparticulate Zn when compared with application of a similar formulation containing larger ZnO particles. In this paper, they compared the results of that previous study with results obtained from independent analysis of the same samples and additional samples by another laboratory using the same instrumental technique of MC-ICP-MS. The two data sets showed good correlation (r = 0.98) and additional data from previously unanalysed samples gave further evidence of the increased uptake of Zn from nanoparticles after dermal application of sunscreen.

6 Applications: drugs and pharmaceuticals, traditional medicines and supplements

Geophagia, or the deliberate ingestion of clay was shown many years ago to be responsible for gross Zn deficiency. Despite the recognition of this problem, clay-based products are consumed by pregnant women and others in many parts of the world. As some are available in the Dutch market, Reeuwijk et al.¹⁴³ analysed 10 African and 26 Surinam ‘traditional clays’ and 27 so-called ‘health clays’ measuring concentrations of As, Cd, Hg and Pb at up to 45.1, 0.75, 2.2 and 99.7 mg kg⁻¹, respectively. Calculations of potential exposure were made on the basis of estimates of daily consumption and bioavailabilty and compared with health based guidance values. Of the 36 traditional clays, 34 provided intakes greater than toxicological limits by as much as 20-fold, while two of the health clays were of similar concern.

Other work reported in the last year generally referred to methods of analysis rather than presenting new data. Christopher et al.¹⁸ used ID-ICP-MS to determine the concentration of Cd in the SRM 3280 Multivitamin/Multielement Tablets. The method required precipitation and SPE steps to eliminate polyatomic interferences from MoO⁺ and MoOH⁺. In order to separately measure concentrations of Cr^III and Cr^VI avoiding any inter-species conversion, Martone et al.¹⁴⁴ used the EPA method 3060A to extract Cr^VI followed by EPA method 3052 to separate Cr^III from the residue. Ion-exchange chromatography-ID-ICP-MS was then used to measure the Cr concentrations. The method was applied to analysis of commercial supplements and the Cr^VI contents were from below the LOD to 16% of the total Cr concentrations. As reported in previous Updates, the US Pharmacopeia proposes to introduce limit values for elemental impurities in pharmaceuticals. Associated with this are the analytical requirements for ICP-AES and ICP-MS methods used for measurements. An ICP-AES method for the analysis of tablets was reported by Stoving et al.⁸² which provided the necessary LODs, repeatability, and recovery results.

7 Applications: foods and beverages

Table 2 Foods and beverages

Element	Matrix	Technique	Sample treatment/comments	Reference
Al	Cola, fruit juices and water	HR-CS-AAS	Samples were prepared using SPE by chelating the analyte with ({4-^51 amino}-1H-pyrazol-4-yl) diazenyl benzoic acid in aqueous solution followed by absorption onto polystyrene-graft-ethyl methacrylate copolymer resin and elution with HCl. The LOD for Al was 0.32 μg L^−1	51
Al	Infant formulas	ETAAS	Samples (30 ready to drink milk and milk powders) were treated with HNO3 and H2O2 and subjected to microwave digestion. It was reported that Al was found in all milk products tested in the range 100 to 430 μg L^−1. Certain soya based milk samples contained as much as 700 μg L^−1 Al	126
Al	Rice (Brazil)	ETAAS	Determination of Al, Cd and Pb in rice using a solid sampling method. Samples (17) were treated with Pd/Mg chemical modifier under optimised heating programme conditions. Calibration was achieved using aqueous standards. The LOD value for Al was reported as 114.0 μg kg^−1	75
Al	Total diets (Spain)	ETAAS	The dietary intakes of Al in two population groups in southern Spain was estimated over a 7 day period. Samples were prepared using acid digestion prior to analysis. The mean Al intake for each group was 2.93 and 1.01 mg per day with a range of 0.12 to 10.00 mg per day	125
As	Baby formulas	FI-HG-AAS, ETAAS	Five different extraction procedures (acetic acid, EDTA, NaOH, MeOH/H2O, acetonitrile) were evaluated. The extracts were subjected to microwave assisted digestion with HNO3, prior to determination as total As. The highest recovery (88%) was achieved for the 5 M NaOH extract	175
As	Codfish and oyster candidate CRM	ID-LC-MS-MS	Quantification of AB using a tandem mass spectrometer with an electrospray interface. A certified As value of 6.60 mg kg^−1 ± 0.31 mg kg^−1 (n = 12) for the CRM was reported	73
As	Chicken meat and herbal plants; lobster hepatopancreas (NRCC TORT-2) and fish protein (NRCC DORM 3) CRMs	ICP-MS	On-line CE with a novel interface was used for separation of a range of inorganic (2) and organic As species (8) prior to detection. The LODs for As obtained were in the range 0.9 to 3.0 ng g^−1. The method was tested using the CRMs listed opposite	68
As	Drinking water	ETAAS	An SPE method using an Empore SDB-XD disc (top), an activated carbon disc and a Cation-SR disc loaded with Zr and Ca in a three layer stack was developed for the separation of DPAA, phenylarsonic acid, and iAs using specific elution conditions. An LOD of 0.13 μg As L^−1 was reported using a 200 mL sample	35, 58
As	Mushrooms (Xerocomus badius)	HG-AAS	Two HPLC based separation systems were evaluated for the speciation and coupled detection of As^III, As^V and DMA. High levels of all three species (up to 27.1, 40.5 and 88.3 mg kg^−1 for As^III, As^V and DMA respectively) were found in samples from certain forest locations in Poland while elsewhere levels contained <0.5 mg kg^−1	156
As	Rice	HG-AFS	Samples were slurried in HNO3 and subjected to ultrasound for 30 min then treated with HCl, KI and ascorbic acid prior to HG. The LOD for As was given as 1.1 ng g^−1. Results were reported in the range 0.12 to 0.47 μg g^−1 for supermarket rice samples	88
As	Rice (Australia)	HPLC-ICP-MS	Samples were extracted using HNO3 and iAs, DMA and MMA separated and determined in common rice. The results obtained for total As were in the range 0.006 to 0.45 μg g^−1 (n = 47). Most As was present in the inorganic form with some DMA found in all samples. Results were verified using XANES	155
As	Rice (Denmark)	HG-AAS	All iAs was oxidised to As^V by treatment with HNO3 and H2O2. A strong anion exchange SPE cartridge was used to separate iAs selectively prior to detection. The LOD for the method was 0.02 mg kg^−1 and recoveries were given in the range 101–106% for spiked rice samples. The As content of 36 retail rice samples were reported to be between 0.03 and 0.60 mg kg^−1	151
As	Rice; rice flours (NIST SRM 1568a and ERM BC211)	HG-AFS	The As was extracted from rice using microwave assisted digestion in HNO3/H2O2 then oxidised to As^V which was then separated from organic forms via silica-based strong anion SPE. Validation was performed using SRMs	152
As	Total diet (Hong Kong)	HG-ICP-MS	Total diet samples (600) were subdivided into 15 food groups and total As and iAs contents determined. The LOD reported was 3 μg As kg^−1. The highest ratio of iAs to total As was found in vegetable produce	146
As	Total diet (Japan)	HG-ICP-MS	A study of iAs content in 19 food composites representative of the Japanese diet. Samples were extracted using synthetic gastric juice prior to LC separation and high efficiency photo oxidation HG	145
Br	Drinking waters	HPLC-ICP-MS	Comparison of ICP-MS instrument systems for the low pressure LC separation and determination of BrO3^− (as Br). The time for the LC separation was 13 min. The LOQ reported was 0.2 μg BrO3^− L^−1. The median BrO3^− content of tap water (80 samples) found was 5 μg L^−1	176
Cd	Drinking water and alcoholic beverages	FAAS	Homogeneous liquid–liquid extraction of Cd^II as DDC complex, using with a perfluorooctanoate anion by digestion of the complex with HNO3. A preconcentration factor of between 10- and 50-fold was reported	49
Cd	Fish, oyster and shrimp samples; lake superior fish tissue (NIST SRM 1946); mussel tissue (NIES-6 CRM, Japan) and oyster tissue (NIST SRM 1566)	FAAS	Use of dipyridyl-functionalized graphene nano-sheets as novel SPE sorbent for separation and preconcentration of Cd ions. The LOD for the method was 0.19 ng Cd mL^−1, the RSD was 1.6%, and a 99.1% recovery of Cd was achieved. The method was verified using SRMs	52
Cd	Honey	ETAAS	Samples were slurried in HNO3 and H2O2 and introduced to pyrolytic graphite atomiser tubes. A Pd/Mg matrix modifier was added prior to the determination of Cd only. Aqueous standards were used for calibration with fructose added for Cd measurements. The LOQ for Cd was reported as 2.0 ng g^−1	62
Cd	Multivitamin tablets (NIST SRM 3280)	ICP-MS	The Cd was separated from interfering sample matrix elements (Mo and Sn) using precipitation and SPE protocols. This permitted an ID approach to the measurement of ^111Cd : ^113Cd and ^111Cd : ^114Cd isotope ratios using collision cell quadrupole and sector field instruments	18
Cd	Rice (Brazil)	ETAAS	See Al, ref. 75. The LOD value for Cd was reported as 3.0 μg kg^−1	75
Cd	Rice grain (Japanese reference materials)	XRF	RMs were prepared by treating base rice grain with methanol containing a quantity of Cd, which was heated and then cooled. The Cd-containing rice was then packed into a polyethylene cup covered with a thin (6 μm) polypropylene film, prior to analysis. The LOD of the method was 0.13 mg kg^−1 and XRF response was linear in the range 0.50–9.8 mg kg^−1. The Cd content of the materials was verified using AAS	22
Cr	Dietary supplements	ID-MS	Investigation of Cr speciation using EPA methods and protocols for extraction (3060A), digestion (3052) and measurement (6800), with ion exchange chromatographic separation. Hexavalent Cr was found in off-the-shelf dietary supplements at levels up to 122.4 μg g^−1	144
Cr	Foodstuffs; Korean CRMs rice (08-01-001), oyster (108-04-001) and water dropwart (108-05-001)	ICP-MS	The determination of Cr in 30 food items from supermarkets was carried out using an instrument fitted with a collision reaction cell to remove spectral interference on Cr. The method was assessed using Korea Research Institute of Standards and Science (KRISS) CRMs	66
Cr	Honey	ETAAS	See Cd, ref. 62. The LOQ for Cr was reported as 9.4 ng g^−1	62
Cu	Bottled water	FAAS	A DLLME method was described for the 70-fold preconcentration of Cu^II using ethanol and chloroform as disperser and extraction solvents. The LOD for Cu^II was given as 0.95 μg L^−1 and the RSD was 1.9%. The method was verified using NRCC-SLRS-4 CRM (river water)	48
Cu	Chocolate	ICP-OES	Samples (22) were prepared using a hot ashing procedure. The Cu content was reported to be in the range 1.85 to 16.50 μg g^−1. A linear correlation was found between Cu level and cocoa content	160
Hg	Bass, mullet, shrimp and mussels	CV-AAS	A method based on SPE using an Amberlite XAD-4 sorbent functionalised with 2-(2′-benzothiazolylazo)-p-cresol for preconcentration of Hg. The LOD in the solid sample was 0.011 μg g^−1	78
Hg	Dietary supplements (ayurvedic); Ephedra sinica (NIST 3240) tomato leaves (NIST 1573a) and dogfish liver (NRCC DOLT3) SRMs	CV-AAS, ICP-MS	Comparison of a direct sampling Hg trap and vapour generation method and a digestion method with detection using ICP-MS. The Hg content of dietary supplements was given in the range 0.002 to 56 μg g^−1 with a LOQ of 5 ng. Average mercury recoveries were close to 100%. The method was validated using the SRMs listed opposite	177
Hg	Fish muscle (Brazilian Amazon)	ETAAS	Cu(NO3)2 was added to acid digested samples as a chemical modifier. Solutions were analysed using sodium tungstate as a permanent modifier. The method allowed the stabilisation of Hg to 1600 °C. An LOD of 0.014 mg kg^−1 and LOQ of 0.047 mg kg^−1 were reported	76
Hg	Fish protein (NRCC CRM DORM 4)	FI-HG-AAS	A gold nanoparticle coating was applied to the inner walls of an electrically heated quartz tube atomiser to trap Hg vapour. The analyte was desorbed by increasing the atomiser operating temperature. An LOD of 0.01 μg L^−1 was achieved using a 5.0 mL sample. The RSD of the method was typically 4%	79
Hg	Fish RM (Brazil)	FIA-CV-AAS, ID-ICP-MS	The preparation and certification of a RM for total Hg and MeHg in fish were described. The material was reported to contain total Hg of 0.271 ± 0.059 μg g^−1 and MeHg of 0.245 ± 0.053 μg g^−1	19
Hg	Waters, tea, vegetables, table salt	CV-AAS	Use of Fe3O4 magnetic nanoparticles as solid phase sorbent for extraction and preconcentration of Hg. The eluent used was HCl–thiourea. The method LOD was given as 0.05 ng mL^−1 and a preconcentration factor of up to 250 was achieved	54
I	Milk powder (BCR-151 CRM)	ICP-MS	Samples (500 mg) were prepared by high pressure digestion in HNO3/H2O2 followed by cold oxidation with Na2S2O8 and further heating for 30 min. The total I content was determined on the resulting solution. Good agreement was obtained with the certified CRM value	149
I	Infant formula and nutritional products	ICP-MS	Proposed AOAC method (first action 2012.14). Samples were treated with HNO3 in a closed microwave digestion oven prior to detection of total I using Te as an internal standard. The LOQ was reported as 1.5 μg per 100 g of sample. Recoveries of I spikes in nutritional products were in the range 90–105%	150
Mn	Tea waste	FAAS	Investigation of the use of tea waste as an adsorbent for the removal of Mn from food samples using acetic acid. The LOD was 0.6 ng g^−1. An artificial neural network was used to model Mn extraction efficiency	178
Mo	Foodstuffs (8) and rice flour (NIST SRM 1568a)	FAAS	Preconcentration of Mo by CPE after formation of a complex with Victoria pure blue in the presence of excess thiocyanate and cetylpyridinium chloride. The method was applied to the analysis of cucumber, apple, banana, peas, soya beans, tomato, and tea. An LOD of 2.18 μg L^−1 was reported for Mo	45
Ni	Slovenian foodstuffs; mussel tissue (NIST SRM 2976) and typical diet (NIST SRM 1548a)	ICP-MS	Samples, including soya products (yoghurt and tofu), cacao and cacao products (dark and milk chocolates) teas and hazel nuts were subjected to microwave assisted acid digestion prior to measurement. The method was verified using SRMs	147
Ni	Sugar cane spirit and whisky	FAAS	The determination of Ni in alcoholic beverages was carried out using an online SPE method prior to detection. The Ni was adsorbed onto mandarin orange (Citrus reticulate) orange peel and desorbed with 1 mol L^−1 HCl as eluent. The LOD was given as 30.0 μg L^−1, (n = 7). Throughput was reported as 15 samples h^−1	59
Ni	Water and food	ETAAS	Extraction and preconcentration of Ni using SPE with carbon nanotubes functionalised with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol. The analyte was eluted in 1 M HNO3 with an enrichment factor of 180. The LOD was reported as 4.9 ng L^−1	53
Pb	Cola, fruit juices and water	HR-CS FAAS	See Al, ref. 51. The LOD was 0.32 μg Pb L^−1	51
Pb	Drinking water and alcoholic beverages	FAAS	See Cd, ref. 49. Results obtained for the determination of Pb^II in drinking water, distilled spirits and fruit wine were given in the ranges 9.2–23 ng mL^−1, 23–50 ng mL^−1 and 24–53 ng mL^−1, respectively	49
Pb	Honey	ETAAS	See Cd, ref. 62. The LOQ for Pb was reported as 5.4 ng g^−1	62
Pb	Rice (Brazil)	ETAAS	See Al, ref. 75. The LOD value for Pb was reported as 16.0 μg kg^−1	75
Pd	Brassica Napus	ETV-ICP-OES	Solid sampling method (5 mg) for determination of precious metals using aqueous standards dried on paper filter strips for calibration of instrument response. The reported LOD for Pt was 0.38 μg g^−1 obtained using a 5 mg sample weight. Good agreement was achieved with results obtained with a sample digestion method	61
Pt	Brassica Napus	ETV-ICP-OES	See Pd, ref. 61. The reported LOD for Pt was 0.38 μg g^−1	61
Rh	Brassica Napus	ETV-ICP-OES	See Pd, ref. 61. The reported LOD for Rh was 0.13 μg Rh g^−1	61
Sb	Water and foods	FAAS	A FI alumina micro-column SPE system was used to separate Sb^III (as DDC complexes) and Sb^V (retained in solution) prior to determination by FAAS using a STAT to increase sensitivity. The LODs were 6.0 ng L^−1 for Sb^III and 8.2 ng L^−1 for Sb^V with RSDs (n = 11) of 2.8% and 3.5% respectively	56
Se	Rice (Se enriched)	ETAAS	CPE, (sequentially with water and cyclohexane) was used to separate inorganic and organic Se fractions achieving 82-fold enrichment. The method provided an LOD of 0.08 μg L^−1, and an RSD of 2.1% (n = 11). Recoveries for Se in enriched samples were in the range 90.3–106.0%	74
U	Bottled waters (France)	ICP-MS	Use of AQUALIX (calix[6]arene derivatives) columns for the separation and preconcentration of U from still mineral water, sparkling mineral water, and spring waters	35, 50
Various (9)	“Baby leaf” vegetables	FAAS, ETAAS	Use of a HR-CS-AAS instrument for the determination of Ca, Cu, Fe, K, Mg, Mn, P, Na and Zn. Samples were prepared by microwave-assisted digestion. Recoveries were reported in the range 91% to 110% for these elements	80
Various (14)	Cabernet Sauvignon wine	ICP-MS	Study of the effect of storage temperature and packaging on trace element content (0.1 to 500 μg L^−1) of commercial wines	179
Various (7)	Dog foods	ICP-MS, ICP-AES	Forty-five samples of over-the-counter dry dog foods and 5 therapeutic dry foods formulated for dogs with hepatic or renal disease were analysed for Ca, Cu, Fe, Mn, P, Se and Zn. The Ca and P concentrations were outside the recommended ranges for some food samples	180
Various (7)	Edible salt and water CRMs (CWW-TMG waste water and SEM-2011 water sample in high-salt matrix, 0.5% (w/v))	ICP-MS	An aerosol dilution protocol was described for the direct analysis of salt. The LODs reported for Co, Cr, Cu, Fe, Mn, Ni and Zn were 12, 6, 18, 2, 34, 68, and 87 ng L^−1, respectively. Recovery of analyte spikes were in the range 96–101%. Verification of the method was achieved via the analysis of two CRMs	65
Various (14)	Eggs (Brazil)	ICP-MS	Samples (34 conventional and 21 home produced) eggs were analysed for As, Ba, Cd, Co, Cu, Fe, Mg, Mn, Mo, Pb, Se, Sr, V, and Zn content. Statistical differences were found in Ba, Cd, Co, Fe, Mo, Pb, Se and Zn levels in the two egg sample groups	181
Various (4)	Foodstuffs	ICP-MS	Proposed AOAC method (first action 2013.06). Samples were digested using HNO3 under pressure in a closed vessel using microwave assisted heating. Elemental concentrations were reported in the following ranges: 0.06–21.4 mg kg^−1 for As; 0.03–28.3 mg kg^−1 for Cd; 0.04–0.6 mg kg^−1 for Hg and 0.01–2.4 mg kg^−1 for Pb as dry matter. The repeatability RSDs reported varied from 2.6 to 27% depending on the element and level	182
Various (4)	Marine biological samples and fish protein (NRCC CRM DORM-3)	ICP-OES	A fast, green sample preparation method involving microwave assisted dissolution using choline chloride-oxalic acid deep eutectic solvent followed by HCl addition, centrifugation and filtration was applied to fish muscle and liver tissues, and macro-algae samples. Good agreement was obtained with certified CRM values for Cu, Fe, Ni and Zn with recoveries of >96% reported	44
Various (26)	Multivitamin/multielement tablets (NIST SRM 3280)	Various	Characterisation by NIST of SRM 3280 using multiple techniques for 26 elements, 13 multivitamins and 2 carotenoids	17
Various (13)	Slim instant coffee	ICP-OES	Sample preparation procedures (acid digestion, extraction, partial decomposition, solubilisation and dissolution) were compared for the determination of Ba, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, P, Pb, Sr and Zn in coffees. It was reported that extraction with aqua regia gave the best results with LODs between 0.11 and 108 ng mL^−1, and RSDs between 0.6 and 5%	183
Various (8)	Tap and bottled water	ICP-OES	An SPE method employing Dowex 50W-x8 and Chelex-100 resins was used for the preconcentration of Cd, Co, Cr, Cu, Fe, Ni, Pb and Zn. The LODs were reported in the range 0.01–0.39 μg L^−1 with RSDs of <3% achieved using the Dowex resin	184
Various (11)	Total diet (Italian study 2012–2014)	Various	A description of the protocols, methods and techniques used for the sampling, treatment and determination of Al, iAs, Cd, ^134Cs, ^137Cs, ^40K, MeHg, iHg, Pb, ^90Sr and U in total diets	185
Various (4)	Vegetable oils	ETV-ICP-MS	Samples were prepared as emulsions with 1.5% v/v Triton X-100 and 50 μg mL^−1 ascorbic acid. Nano particulate Pd was used as a modifier. Using a standard additions approach, the following LODs were obtained: 0.5 ng g^−1 for As; 0.4 ng g^−1 for Cu; 1.1 ng g^−1 for Hg and 0.4 ng g^−1 for Pb	70
Various (11)	Whole milk powder (NIST 1549) and bovine liver (NIST 1577) SRMs	ICP-OES ICP-MS	Optimisation of a minimal consumption HNO3/H2O2 sample digestion procedure allowing a 10-fold reduction in amount of acid used. The determination of Ca, Cu, Fe, K, Mg, Mn, Mo, Na, and Zn was carried out by ICP-OES. The Cd, Co, and Pb were measured using ICP-MS. Good agreement was obtained with SRM certified values	43

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7.1 Single and multielement applications in food and beverages

7.1.1 Dietary intake studies. Studies in several countries have focused on one particular element. Release of Al from utensils has long been known to contribute to the Al content of foods during cooking and processing. Cabrera-Vique and Mesias¹²⁵ investigated the dietary intake of Al in two distinct populations (families and university students) from southern Spain, using a duplicate diet sampling strategy. Diets were sampled on seven consecutive days and, following acid digestion, total Al was quantitatively determined using ETAAS. Mean dietary Al intake was 2.93 mg per day in families and 1.01 mg per day in students, which was estimated to represent 17% and 6% respectively of the WHO tolerable weekly intake. The highest Al intakes were observed in those subjects with a low adherence to the traditional Mediterranean diet and who consumed a high proportion of canned and processed food. On the face of it, this work appears to counter the popular view that students have an unhealthy diet but, on the other hand, it may simply indicate that they eat less than the general population of Spain. The contribution of As species found in different foodstuffs to the Japanese diet was assessed by Oguri et al.¹⁴⁵ using photo-oxidation HPLC-HG-ICP-MS. Composite food samples (n = 19) prepared from 159 food items were subjected to digestion by synthetic gastric juice (0.07 M HCl and 0.01% pepsin). Of the 19 composite samples, iAs was detected in nine in a range from 0.423 to 450 ng g⁻¹ fresh weight. The daily intake of iAs was calculated at 24 μg per person per day or 21 μg per person per day on a bioavailable fraction basis. The two food groups contributing highest iAs were cereals and algae (13 and 5.7 μg per person per day, respectively) and these were wholly represented by rice and hijiki, a brown edible seaweed (Sargassum fusiforme). The authors summarised by suggesting there was a significant risk to the Japanese population by consuming these staple foods. The bioaccessible DMA level, assessed at 5.9 μg per person per day and total DMA (6.8 μg per person per day) were lower than previous studies while MMA and TMAO (0.30 and 4.6 μg per person per day) were similar. Total AB intake was estimated at 73 μg per person per day, mainly arising from seafood consumption. Total As and iAs were studied in the first Hong Kong Total Diet Study using HR-ICP-MS and HG-ICP-MS.¹⁴⁶ The groups with the highest As content, from 600 samples across 15 different food groups, were unsurprisingly in fish and seafood, and vegetable products. Total Ni was determined using ICP-MS in a range of selected food products in Slovenia by Scancar et al.¹⁴⁷ Their results show that soy products, cocoa-derived confectionery and hazelnuts were all a good source of dietary Ni whereas different teas and infusions did not contribute.

The heavy metal status of gluten-free foods for coeliac people was studied for the first time, using ICP-MS.¹⁴⁸ Samples (n = 17) were obtained commercially in Palermo, Italy from locally and internationally-sourced gluten-free foodstuffs and analysed for As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn. While all samples had heavy metal concentrations below locally acceptable levels, one sample of rice noodles from China had the highest As and Mo concentrations (0.088 and 0.47 mg kg⁻¹, respectively) and local bread and breadstick samples showed the highest concentrations in Ba, Cd, Cu, Hg, Pb, Sr and V. Generally there was a low health risk associated with consumption of these products although Cd, Pb and Ni did present a potential risk. However, from some of the trace metal concentrations, the authors determined that a diet based largely on highly-refined cereal gluten-free products would not provide adequate elemental nutrition compared to wheat-derived products.

7.1.2 Human milk and infant formula. Interest continues around the intake of I, because of its importance in thyroid development and function, and follows a recent trend highlighted in the last few years' reviews. The link between iodized salt and high I levels in infants was explored by de Lima et al.¹³² Samples of infant (<6 m old) urine, maternal milk and kitchen salt were collected from 33 households in Brazil. Analysis by ICP-MS gave mean I concentrations of 293, 206 μg L⁻¹ and 39.9 mg kg⁻¹, respectively. They demonstrated a positive correlation between I in maternal milk and infant urine which were causally linked to the consumption of iodized salt. Several methodologies have been proposed for the determination of I in human milk or infant formula including one proposed by Leppänen et al.¹⁴⁹ which involves an efficient two-stage high-pressure wet digestion procedure prior to ICP-MS. The samples (500 mg) were heated in pressure vessels with concentrated HNO₃ and H₂O₂ for 2 h at 300 °C. Upon cooling, Na₂S₂O₈ was added and further heated at 100 °C for 30 min resulting in a clear liquid. The accuracy was verified against a CRM (BCR-151) and was found within the certified range. Another wet digestion method was accepted by the AOAC for first action.¹⁵⁰ Sample preparation involved microwave-assisted HNO₃-mediated digestion and used ICP-MS determination with Te as internal standard. The method had an LOQ for total I of 1.5 μg 100 g⁻¹, an analytical range of 5–100 μg 100 g⁻¹ and demonstrated recoveries from 90 to 105%.

It was recently claimed that the Al content of infant formula is still too high.¹²⁶ Analysis of 30 of the most widely-available and popular infant formulae in the UK were analysed by transversally-heated ETAAS following digestion with concentrated HNO₃ and H₂O₂ (30% v/v). The Al concentrations ranged from 106–422 μg L⁻¹ (based on a reconstituted volume) for non-soya milks; the two soya milks presented Al concentrations of 656 and 756 μg L⁻¹ confirming the long-known fact that soya milk has much high Al levels. The authors detailed the impact of the packaging which in many cases contains Al foil. They concluded emotively that all samples of infant formula were contaminated with Al – by comparison with EU-recommended levels for drinking water (50 μg L⁻¹) – and called for regulatory involvement.

7.1.3 Cereals, flour and rice. Spatial location of contaminants in staple foodstuffs, particularly rice, is becoming as important as element speciation, so that processing techniques can minimise contamination, as reported in last year's review.¹ The localisation of Hg in rice collected from a contaminated region was studied by Meng et al.⁹⁶ Also reported for other heavy metals, the majority of the iHg is located in the outer hull and the bran and 78% is removed during winnowing. Using SR-μXRF spectrometry, the Hg was shown to be localised on the surface of the brown rice (bran). From further XANES analysis, the authors proposed that iHg was bound to cysteine and associated with phytochelatins which prevent mobility explaining why iHg is localised on the outer layers. In contrast, the more toxic MeHg in the bran is bound primarily to cysteine and associated with proteins, conferring mobility. During ripening, the bound MeHg is transported into the endosperm or white rice such that after processing 80% of the MeHg remains. Similar results were obtained by Choi et al.¹⁰⁴ using ICP-MS for total As determination in white and brown rice with imaging by fs-LA-ICP-MS of single rice grains. Further details of this work is presented in Section 5.2.

Reliable techniques for iAs determination still need to be improved, as demonstrated by Rasmussen et al.¹⁵¹ using HG-AAS. The iAs was solubilised and oxidised to As^V using dilute HNO₃ and H₂O₂ heated to 90 °C for 60 min in a water bath and eluted from strong anion exchange resin. Mean recoveries were 101–106% for spiked rice samples and CRMs. The LOD was 0.02 mg kg⁻¹, repeatability 6% RSD and intra-laboratory reproducibility was 9%; the method compared favourably with HPLC-ICP-MS. Of 36 rice samples obtained commercially in Finland and analysed using the method, the lowest and highest median iAs concentrations were 0.09 (range: 0.03–0.16, n = 11) and 0.36 (0.13–0.60, n = 2) mg kg⁻¹ for white and red rice, respectively, while black and brown rice presented median concentrations of 0.14 mg kg⁻¹ (black rice: 0.08–0.31, n = 5; brown rice: 0.14–0.40, n = 10). Chen and Chen¹⁵² proposed an inexpensive and simple technique using a Si-based strong anion exchange cartridge to separate As^V from organic forms, following a microwave-assisted digestion of rice, for determination by HG-AFS. The LOD was 1.3 ng g⁻¹ and the recovery was 94 ± 3%. The official AOAC method uses HPLC-ICP-MS for speciation of As (As^III, As^V, MMA, DMA) in husked and polished (white) rice.¹⁵³ Interlaboratory validation involved 13 reporting laboratories analysing 20 portions of ten rice samples of both types. The repeatability (RSD_r) and reproducibility (RSD_R) were in the ranges 3.8–7.7% and 10–36%, respectively and the performance characteristics deemed the method suitable for determination of iAs at concentrations ≥0.03 mg kg⁻¹. Baba et al.¹⁵⁴ proposed a pentafluorophenylpropyl RP-HPLC stationary phase with isocratic elution (HCOOH in MeOH) for an effective separation of As^III, As^V, MMA and DMA in rice following an extraction with HNO₃ (0.15 M). Given there is uncertainty in the extent of oxidation of As^III caused by the digestion of rice with HNO₃ (2% or 0.45 M for comparison), for subsequent determination by HPLC-ICP-MS, Maher et al.¹⁵⁵ compared this method with XANES which does not require prior sample treatment. They confirmed similar proportions of As^III, As^V, MMA and DMA were obtained with either technique and the latter indicated the presence of As^III–GSH. Subsequent analysis by HPLC-ICP-MS of rice samples, available in Australia from local and imported sources, indicated total As ranged from 0.06 to 0.45 μg g⁻¹. All iAs concentrations were below 0.2 μg g⁻¹ and represented from 17 to 100% of As present. Negligible amounts of MMA were found although DMA was present in nearly all samples at concentrations <0.05 μg g⁻¹, potentially arising from the use of As-containing phytochemicals, now banned in Australia.

7.1.4 Vegetables, fruits and nuts. Speciation of I in seaweed (Nori) indicated that only 25% of the total I (67.1 ± 1.3 μg g⁻¹) was water soluble.⁹⁸ Proteins were extracted from the water insoluble fraction with urea, precipitated with acetone and separated on SDS-PAGE and bands subjected to LA-ICP-MS. Protein bands containing I were found with M_r of 10, 20, 27, 40 and 110 kDa. Digestion of the protein extracts using protease XIV and trypsin and analysed by SEC-ICP-MS confirmed the presence of mono-iodotyrosine and di-iodotyrosine. This work highlights the presence of these iodoamino acids and paves the way for further understanding on the nutritional value of seaweed. The edible mushroom Xercomus badius (aka Boletus badius), a relative of the European cep, is known to bioaccumulate heavy metals and their toxicology statuses can be influenced by anthropomorphic activity. Species of As, As^III, As^V and DMA were determined using HPLC-HG-AAS in samples from Polish forests reflecting different levels of human activity.¹⁵⁶ Fruiting bodies collected from high activity areas showed elevated concentrations: 27.1, 40.5 and 88.3 mg kg⁻¹, respectively. Those collected from low anthropomorphic-impact areas presented concentrations lower than 0.5 mg kg⁻¹ for all species determined, including two samples from commercial sources. Ready-to-eat “baby leaf” vegetables were analysed for their mineral content (Ca, Cu, Fe, K, Mg, Mn, Na, P, Zn) using HR-CS-AAS following microwave digestion.⁸⁰ The samples showed high levels of Fe as well as Ca and K. The reason why the authors analysed the data by linear discriminant analysis is not clear, but concentration differences in these elements were sufficient to classify them into their relative species.

7.1.5 Fish and seafood. Arsenolipids are seen as key to understanding As cycling in the environment but only a few have been identified to date. Working on capelin oil extracted from Mallotus villosus, a forage fish of the Arctic waters and key food for Atlantic cod, Amayo et al.⁹⁴ detected 12 arsenolipids by HPLC-ICP-MS/ESMS. They identified four new arsenohydrocarbons and, following acetylation and thiolation of the extracts, the M_r were 305, 331, 347 and 359. The molecular formulae were C₂₀H₄₄AsO⁺ and C₂₀H₄₄AsO⁺ and were established as cationic trimethylarsino fatty alcohols.

7.1.6 Drinking water and non-alcoholic beverages. An easily-implemented ICP-MS method for determination of organic and inorganic Br concentrations in drinking water, which can replace HPLC with low pressure LC, was proposed by Tirez et al.¹⁵⁷ The system comprised a peristaltic pump operating at 170 μL min⁻¹ as part of the FI system which included the spectrometer's autosampler and a 50 mL baffled cyclonic spray chamber. An anion exchange column was used with NH₄NO₃ as mobile phase; the BrO₃⁻ ion eluted in 13 min and an LOD of 0.2 μg L⁻¹ was achieved. Known interferents, bromoacetic acid, dibromoacetic were assessed and found to have little influence. Eighty samples of tap water covering different waters supplies from the Flemish region of Belgium were collected over three years and analysed with the new system. The median BrO₃⁻ concentration was determined as 0.5 μg L⁻¹, below European Commission limits.

7.1.7 Alcoholic beverages. The geographical classification of wines from different countries or regions using an elemental fingerprint has been reported in this review over many years. There are some key elements that come up time again as demonstrating a discriminant power in such studies. This is again confirmed in a thorough study by Coetzee et al.¹⁵⁸ looking at 23 wine estates in the Stellenbosch region. Five of the most common geo-pedologically discriminating elements in wine (B, Ba, Mg, Rb, Sr) were among 10 elements (B, Ba, Cs, Cu, Mg, Ni, Rb, Sr, Tl and Zn), determined by ICP-MS after simple dilution, found to have the most variance in the dataset by PCA. Cluster analysis divided the red wine samples into three groups representing different soil types. Further discriminant analysis of each cluster separately allowed the authors to demonstrate discrimination of each wine estate. How this impressive result could be used for socioeconomic benefit is not addressed. “Terroir” is a term widely used in the wine industry to explain organoleptic differences in wine within a same region; Cugnetto et al.¹⁵⁹ used the elemental composition from leaves, grapes and wine to explain this using trace element analysis by ICP-AES. Differences, calculated by PCA, in the leaf elemental composition alone allow the greatest separation of the studied sub-regions of North West Italy (Lombardy; Piedmont, south; Piedmont, north; Val d'Aosta) based on Ba, Si, Sr, V. When the elemental composition of the grape and resulting wine was used, only those wine samples from the northern region were differentiated from the southern Piedmont, based on Ba, Mg, Mn, Si, Sr, V and Ti concentrations. However, the effect of rootstock (two rootstock species on a Nebbiolo scion studied) and variety (Nebbiolo vs. Barbera) on how elements are transported from the soil and accumulated in the berry highlights how many variables need to taken into consideration when trace elements are used to carry out geographical classification of wines.

7.1.8 Other foods. Few can resist the temptation of chocolate, now even more so given that Weber and Solioz¹⁶⁰ have suggested it can be a dietary source of Cu. Samples of 22 commercially-available chocolate were hot ashed in silica crucibles at 400 °C for 3 h, then at 600 °C for 14 h, redissolved in concentrated HNO₃ then H₂O₂ added, with subsequent determination by ICP-AES. The Cu concentration ranged from 1.85 ± 0.10 μg g⁻¹ to 16.5 ± 1.29 μg g⁻¹. The authors also demonstrated a significant correlation between Cu and cocoa content (R² = 0.8929) and suggested that 100 g of high cocoa solids chocolate was sufficient to meet 100% the Daily Recommended Intake.

Abbreviations

AAS	Atomic absorption spectrometry
AB	Arsenobetaine
AC	Arsenocholine
AES	Atomic emission spectrometry
AFS	Atomic fluorescence spectrometry
AMS	Accelerator mass spectrometry
AOAC	Association of official analytical chemists
ARS	Alizarin red S
ASU	Atomic spectrometry update
CCD	Charge coupled detector
CDT	Carbohydrate-deficient transferrin
CE	Capillary electrophoresis
CF	Cystic fibrosis
CF-CVAAS	Continuous flow cold vapour atomic absorption spectrometry
CNS	Central nervous system
CPE	Cloud point extraction
CRM	Certified reference material
CT	Computer tomography
CTAC	Cetyltrimethylammonium chloride
CV-AAS	Cold vapour atomic absorption spectrometry
DEAE	Diethylaminoethyl
DDC	Diethyldithiocarbamate
DES	Deep eutectic solvents
DLLME	Dispersive liquid–liquid microextraction
DMA	Dimethylarsenic
DPAA	Diphenylarsinic acid
DRC	Dynamic reaction cell
DT	Dithizone
SEM-EDS	Scanning electron microscopy-energy dispersion X-rays analysis)
EDTA	Ethylenediaminetetraacetic acid
EDXRF	Energy dispersive X-ray fluorescence
EPA	Environmental protection agency
ES	Electrospray
ESI	Electrospray ionisation
ETA	Electrothermal atomization
ETAAS	Electrothermal atomic absorption spectrometry
ETV-ICP-AES	Electrothermal vaporization inductively coupled plasma atomic emission spectrometry
EU	European union
EXAFS	Extended X-ray absorption fine structure
FAAS	Flame atomic absorption spectrometry
FAES	Flame atomic emission spectrometry
FAO	Food and agriculture organisation
FDA	Food and drug agency
FI	Flow injection
FTIR	Fourier transform infrared
GC	Gas chromatography
GD	Glow discharge
GF	Graphite furnace
GPx	Glutathione peroxidase
GSH	Glutathione
H&E	Haematoxylin and eosin
HG	Hydride generation
HLLE	Homogeneous liquid–liquid extraction
HPLC	High performance liquid chromatography
HR-CS-FAAS	High resolution continuum source FAAS
HR-ICP-MS	High resolution inductively coupled plasma mass spectrometry
IC	Ion chromatography
ICP-MS	Inductively coupled plasma mass spectrometry
ID	Isotope dilution
IL	Ionic liquid
INAA	Instrumental neutron actovation analysis
IUD	Intra-uterine device
LA	Laser ablation
LC	Liquid chromatography
LDA	Linear discriminant analysis
LIBS	Laser induced breakdown spectroscopy
LOD	Limit of detection
LOQ	Limit of quantification
MALDI	Matrix-assisted laser desorption ionization
MC-ICP-MS	Multicollector inductively coupled plasma mass spectrometry
MIP	Microwave induced plasma
MMA	Monomethylarsenic
MS	Mass spectrometry
MSIS	Multimode sample introduction system
NDT	Neural tube defects
NIST	National institute of standards and technology
OES	Optical emission spectrometry
PAGE	Polyacrylamide gel electrophoresis
PGE	Platinum group elements
PCA	Principal component analysis
PIXE	Particle-induced X-ray emission
PT	Proficiency testing
PTFE	Poly(tetrafluoroethylene)
QD	Quantum dot
Q-ICP-MS	Quadrupole inductively coupled plasma mass spectrometry
RA	Residual acid
RBS	Rutherford back scattering
RCC	Residual carbon content
REE	Rare earth elements
RNAA	Radiochemical neutron activation analysis
RP	Reversed phase
RSD	Relative standard deviation
SD	Standard deviation
SDS	Sodium dodecylsulfate
SEC	Size exclusion chromatography
SeCys	Selenocysteine
SEM	Scanning electron microscopy
SEM-EDX	Scanning electron microscopy-energy dispersion X-rays analysis
SF-ICP-MS	Sector field inductively coupled plasma mass spectrometry
SIMS	Secondary ion mass spectrometry
SPE	Solid phase extraction
SPME	Solid phase microextraction
SRM	Standard reference material
SR-XRF	Synchrotron radiation X-ray fluorescence
STAT	Slotted tube atom trap
TIMS	Thermal ionization mass spectrometry
TMAH	Tetramethylammonium hydroxide
TMAO	Trimethylarsine oxide
TOF	Time-of-flight
TXRF	Total reflection X-ray fluorescence
USN	Ultrasonic nebuliser
USP	United states pharmacopeia
UV	Ultraviolet
VG	Vapour generation
WHO	World health organisation
XANES	X-ray absorption near-edge structure
XAS	X-ray absorption spectroscopy
XPS	X-ray photoelectron spectroscopy
XRD	X-ray diffraction
XRF	X-ray fluorescence
XRF-CT	X-ray fluorescence computer tomography
M r	Relative molecular mass
2D	Two dimensional
3D	Three dimensional

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