Atomic Spectrometry Update. Clinical and biological materials, foods and beverages
Andrew Taylor*a, Simon Branchb, Andrew Fisherc, David Hallsd and Mark Whitee
aSupra-Regional Assay Service Trace Element
Laboratory, Centre for Clinical Science and Measurement, School of Biomedical and Life Sciences, University
of Surrey, Guildford, Surrey, UK GU2 7XH. E-mail: A.Taylor@surrey.ac.uk
bThe Lord Rank Centre, R.
H. M. Technology, Lincoln Road, High Wycombe, Buckinghamshire, UK HP12 3QR
cDepartment of Environmental Sciences, University of Plymouth, Drake
Circus, Plymouth, Devon, UK PL4 8AA
dTrace Element Unit, Department
of Clinical Biochemistry, Glasgow Royal Infirmary University
NHS Trust, Castle Street, Glasgow, UK G4 0SF
eHealth and Safety Laboratory, Health and Safety Executive, Broad
Lane, Sheffield, UK S3 7HQ
First published on 28th February 2001
Abstract
This latest Atomic Spectrometry Update for Clinical and Biological Materials, Foods and Beverages has been prepared with a slightly revised writing team. Linda Owen, who has drafted the Foods and Beverages section for a number of years, is now responsible for FAPAS, the food analysis quality assessment scheme run by the UK Ministry of Agriculture, Fisheries and Food. She has decided that she cannot continue writing and has stepped down. Andy Fisher, an established member of the ASU organisation, has very effectively taken over this task.
Some interesting sample preparation developments, aimed at simplifying these key steps in any analysis, are reported. These look to remove interfering organic components without increasing the reagent blank. A wider range of instrumentation for ICP-MS is much more evident with time-of-flight, sector field (or high resolution) and electrospray MS being used in addition to traditional quadrupole MS. Work with capillary electrophoresis for speciation continues to impress. Reports where the movable reduction bed hydride generator has been used are starting to appear and it is likely that this trend will continue. The main areas of interest are unchanged. Selenium is of fundamental importance in both the food and clinical areas. Use of XRF, AAS and ICP-MS illustrate the different facets of studies involving Pb, while interest in As and Hg is dominated by requirements for speciation.
1 Analysis of clinical and biological materials
This Update reviews publications appearing in the year up to October 2000. These are summarised in Table 1 while the text describes the more important developments and covers themes of current interest. Our previous Update appeared in April 2000.11.1 General reviews and articles
A Handbook on Metals in Clinical and Analytical Chemistry by Seiler et al.2 covers sample collection, analytical techniques and procedures, and quality control and gives specific information on all the relevant elements.1.2 Sampling and sample preparation
Build-up of carbonaceous residues in the determination of Al in serum by ETAAS was eliminated by Almeida and Lima5 by in situ digestion with tetramethylammonium hydroxide (TMAH). With each 15 µl injection of diluted serum, 5 µl of 1 M TMAH was introduced. This not only prevented accumulation of carbon but also improved precision. TMAH has also been used by Tao et al.6 for solubilization of biological tissues for determination of Hg by CVAAS. Inorganic Hg was released by the on-line addition of L-cysteine; for total Hg, KMnO4 was used instead. Silva et al.7 demonstrated the use of a methanolic solution of TMAH for dissolution of marine tissues for determination of Cd, Cr, Cu, Mn, Ni and Pb by ETAAS, but warned that adequate ventilation was necessary to avoid the smell created in the char and atomization steps.
Acid-vapour partial digestion in a focused microwave oven was
described by Araújo et al.8
Into the microwave vessel were placed four cups containing about 30 mg
of sample and 150 µl of H2O or H2O2.
These were exposed to acid vapour coming from 15 ml of HNO3
in the base of the vessel. Attack with acid vapour at 115![[thin space (1/6-em)]](https://www.rsc.org/images/entities/char_2009.gif)
°C released
Co and Fe within 10 and 60 min, respectively. The suspension after
dilution was centrifuged and the elements in the supernatant determined by
ETAAS. As only vapour attack was used, contamination from the acid was not
a factor.
Bohrer et al.9 extended their work on deproteinisation with microwave irradiation to the determination of Cu, Mn, Ni and Zn in serum. This allowed removal of 99% of the proteins with a small dilution factor (1 + 1) and allowed interference-free determination without a chemical modifier.
In an examination of the use of enzymatic hydrolysis with pronase E for the preparation of samples for determination of a range of minor and trace elements by FAAS and ETAAS, Bermejo-Barrera et al.10 found that this was effective for mussel samples but recoveries were low for human hair (less than 70%).
°C during this step to obtain good recoveries. At room temperature,
the heavier REEs gave lower recoveries because they complexed with the organic
compounds remaining after digestion. With a concentration factor of 4, recoveries
were in the range 92–102 % and LODs were below 0.2 ng l−1.1.3 Developments in and applications of multi-element techniques
Besteman et al.14 described the direct multi-element analysis of whole blood using a capacitively coupled microwave plasma (CMP) as a source. Samples were deposited on a tungsten filament spiral electrode and then dried, ashed and atomized into the CMP. A sample size of only 2 µl was used and the elements K, Li, Mg, Mn, Na and Zn were determined in under 4 min. Concentrations found were consistent with literature values.
1.3.2.1 Reviews. Sta'astna et al.15 reviewed the application of ICP-MS to the determination of trace elements in clinical samples.
1.3.2.2 Multi-element determination by quadrupole ICP-MS (Q-ICP-MS). The potential of Q-ICP-MS for the simultaneous determination of trace elements in whole blood and serum was examined by Krachler and Irgolic.16 Of the 47 elements examined, only 7 elements (Ca, Cu, K, Mg, Rb, Sr and Zn) could be accurately determined in serum and 8 (the 7 previous + Pb) in whole blood.
Panayi et al.17 determined Cd, Cu, Hg, Li, Mn, Pb and Zn in various areas of porcine brain by ICP-MS. Standard additions coupled with internal standards were used in calibration. Cadmium, Cu and Mn were also determined by ETAAS and some samples were also analysed by instrumental NAA.
Concentrations of the toxic and essential elements in the placentas of Swedish women were determined by ID-ICP-MS by Osman et al.18 Concentrations in the umbilical cord blood and in the mother's blood at 36 weeks gestation were also measured. The results showed that Pb, but not Cd, easily crossed the placental barrier.
1.3.2.3 Developments in Q-ICP-MS. The control of interferences in ICP-MS through the use of the dynamic reaction cell, now commercially available, should result in improvements in many applications in the clinical and biological field. Sloth and Larsen19 found that methane as the reaction cell gas could reduce the potentially interfering Ar dimers at the Se atomic masses of 74, 76, 78 and 80 by approximately five orders of magnitude. With 3% v/v methanolic solutions to take advantage of carbon-enhanced ionization, the LOD was 6 ng l−1. They demonstrated that it could be used as a detector in the separation of selenoamino acids by cation-exchange HPLC based on measurement of the 80Se intensity.
1.3.2.4 Laser ablation ICP-MS. Both applications featured in this review year relate to studies on human teeth. Lochner et al.20 obtained spatial multi-element profiles on deciduous teeth by LA-ICP-MS. Calibration was made with a piece of walrus ivory, the bulk composition of which was determined by acid-dissolution and determination by ICP-AES. Their measurements of 14 elements showed differences of deposition during the development of the tooth. Antimony and Zn were consistently incorporated and occasionally Cr, Fe and Hg were included. Migration of Ag, Cu and Hg from dental amalgam was investigated by Hoffmann et al.21 Calcium was used as an internal standard and calibrants were prepared from CaSO4 to which standard solutions were added. The powder was dried, homogenized and pressed into pellets. Correction had to be made for the different fractional volatilization of Hg in teeth and calibrants. Mercury concentration was shown to be a simple exponential function of distance from the surface of the filling. The diffusion constant for Hg was higher by a factor of ten than those for Ag and Cu.
1.3.2.5 Speciation with electrophoresis and ICP-MS. Most of the focus on the combination of capillary electrophoresis (CE) and ICP-MS revolves around the design of the interface. Tu et al.22 compared two spray chamber–nebulizer combinations for determination of methylmercury and inorganic Hg separated by CE. A standard crossflow nebulizer with a Scott spray chamber gave a shorter analysis time and better resolution while a microconcentric nebulizer (MCN 100) with a cyclone spray chamber improved LODs by a factor of 11 for methylmercury and 19 for inorganic Hg. Wenzel and Hams23 also used a MCN in their interface for use in speciation of As in urine. This self-aspirated (from a reservoir) an electrolyte which passed the end of the capillary and swept the emerging analytes through into the nebulizer and hence into the plasma. Tian et al.24 coupled CE and ICP-MS through a moving reduction bed hydride generation system for speciation of As in a Chinese medicine. The outlet from the CE capillary was mixed with 0.1% KBH4 and directed onto the moving bed in a reaction chamber. The evolved hydrides were passed to the ICP. Absolute LODs for As species were in the range of 68–120 fg.
Iodine speciation in serum and urine was studied by Michalke and Schramel25 using separation by CE in 15 min and detection by ICP-MS of I as I−, IO3−, thyroxine (T4) and triiodothyronine (T3). In the serum of a healthy subject, IO3−, T4 and T3 were detected, but in a patient after a thyroid gland operation T3 was largely absent. In urine, only I− was found.
1.3.2.6 Sector field ICP-MS (ICP-SFMS). The potential of ICP-SFMS for analysis of clinical samples has been discussed by the group at the University of Oviedo, Spain26 with examples from their own published work. They foresaw one of its future applications as a multi-element detector for speciation studies. A special issue of J. Anal. At. Spectrom. (April 2000) featured ICP-SFMS and many of the papers in that issue are reviewed here. The technique is also known as high resolution ICP-MS and double-focusing magnetic sector field ICP-MS. The editors of this special issue, Jakubowski and Moens, gave a clear rationale why they favour the title sector-field ICP-MS and this we have adopted in the present review.
Many of the isobaric interferences seen in Q-ICP-MS can be resolved by using the higher resolution available with a sector field ICP mass spectrometer. Townsend27 showed that, in medium resolution mode (m/Δm = 3000), the first row transition elements, Co, Cr, Cu, Fe, Mn, Ni, Sc, V and Zn, could be accurately determined in a range of CRMs including oyster tissue and human urine. Indium was used as an internal standard. The improvement in accuracy for Zn was confirmed by Stürup28, who measured Zn isotope ratios and total Zn in human faeces, urine and serum.
This freedom from interferences and the excellent sensitivity available
with ICP-SFMS allow the multi-element determination of a wide range of
elements. Rodushkin et al.29
developed a method for 60 elements in whole blood. Samples were pressure-digested
with HNO3 using microwave heating. Three elements, As, Ge and Se,
were determined in high-resolution mode (m/Δm
about 95000); 13 elements in medium resolution (m/Δm
about 4200) and the remainder in low resolution (m/Δm
about 400). The importance of contamination-free sampling was stressed.
Begerow et al.30 examined the potential
of ICP-SFMS for monitoring environmentally and occupationally relevant metals
and compared it with ETAAS. Thirteen elements were studied in urine and serum.
Sample treatment was simply UV photolysis with HNO3–H2O2
and subsequent dilution. They concluded that the technique was valuable for
multi-element screening where the type of exposure is not known and for determination
at low concentrations for which ETAAS had insufficient sensitivity (e.g.,
Au, Pd, Pt, Th and U). The determination of 15 toxic and essential elements
in digested human milk using ICP-SFMS was explored by Prohaska et al.31 To overcome spectral interferences, medium resolution
mode (m/Δm 4000) was required for ten
of the elements but, for As, high resolution (m/Δm
8000) was necessary to resolve 75As from 40Ar35Cl.
Three internal standards, In, Re and Rh, were found necessary but, despite
internal standardization, additional mathematical correction for matrix interference
was required for As and Cd.
1.3.2.7 Applications of MIP-MS. The N2 MIP offers advantages over the Ar ICP such as fewer problems with isobaric interferences, a simpler spectrum and lower running costs. Work by Chatterjee et al.32,33 demonstrated the use of a commercial N2 MIP mass spectrometer as an element specific detector. For As,32 a 1.3 kW N2 MIP was coupled to a HPLC system using a silica-based cation-exchange column. Replacement of the supplied nebulizer with a concentric nebulizer from an ICP mass spectrometer and the use of a polyethyl ethylketone (PEEK) connecting capillary tubing gave an increase in sensitivity for As species of between 17 and 30%. The LODs for the As compounds were in the range 0.68–22 µg l−1 and the technique was successfully applied to the determination of As species in a human urine CRM. For Se,33 they coupled anion-exchange HPLC to an MIP through a HG system, using NaBH4 as the reductant, to measure selenite and selenomethionine in human urine. Selenomethionine on reduction yielded volatile (CH3)2Se and (CH3)2Se2 which were detected as Se in the MIP. Of the mobile phases, a 15 mM phosphate buffer at pH 7 suppressed the generation of volatile Se species the least and gave recoveries of selenomethionine in the range 98–104%. The LODs for selenite and selenomethionine were 0.7 and 8.7 µg Se l−1, respectively, which are better than previously obtained with MIPs and comparable to those with Ar ICP-MS.
Shinohara et al.34 compared MIP-MS and ETAAS for the determination of Ge in blood plasma, cells, urine, hair, nails and other tissues. MIP-MS offered greater sensitivity with a LOD of 0.05 µg l−1 compared with 3 µg l−1 for ETAAS. Samples were digested with HNO3–HClO4. For MIP-MS, simple dilution and addition of an internal standard was sufficient for determination, whilst, for ETAAS, solvent extraction was used to avoid interferences from the matrix and from ClO4−. Good agreement was found between results by the two methods. Hair and nail Ge concentrations were found to be useful for monitoring ingestion of Ge.
1.3.2.8 Accelerator mass spectrometry. On the basis of a study of aluminium absorption using 26Al measured by AMS, Moore et al.35 concluded that the ability of the gastrointestinal tract to exclude Al is reduced in Alzheimer's disease, leading to greater exposure to Al. Thirteen patients and 13 age-matched controls were given 26Al in a fruit drink and, from measurements on plasma samples taken before and 1 h after the drink, the fraction of 26Al absorbed was estimated. The mean fraction absorbed by the Alzheimer's disease patients was higher than the controls by a factor of 1.64.
Developments in AMS particularly for pharmaceutical research were reviewed by Turteltaub and Vogel.36 The attamole sensitivity and high precision of the technique allows studies of absorption, metabolism and elimination to be carried out in humans with low chemical and radiological doses, reducing risk to the subjects.
Priest et al.37 found that AMS was suitable for the determination of ultra-trace levels of plutonium in urine, down to the equivalent to about 500 nBq for 239Pu. They measured levels in London youths and in adults, some of whom were exposed occupationally. In addition, they assessed the fraction of Pu absorbed (4.5 × 10−5) when a volunteer ingested 15 g of Irish Sea sediment.
1.3.2.9 Other MS techniques. Electrospray MS is normally used for analysis of organic compounds. But, as Stewart38 points out, it has been increasingly used for elemental speciation and his review focuses on this use for detecting inorganic, organometallic and complexed metal ions. Detection is limited by background and signal suppression by the matrix so that separation is often necessary to alleviate these problems. Stewart concludes that further development of instrumentation and methods will improve the capability of this technique for elemental speciation.
It is interesting to see an application of ICP-MS with a time-of-flight mass spectrometer, now available commercially. The LODs are generally poorer than with Q-ICP-MS, so Centineo et al.39 used FI-HG to improve the sensitivity in the simultaneous determination of As, Bi, Ge, Hg, Sb, Se and Sn. The LODs they obtained in the range 0.04–5.5 µg l−1 were about two orders of magnitude poorer than those they obtained with Q-ICP-MS. Precision, however, was 2–3 times better and some isotope ratios could be determined with an RSD of 0.2–0.3%. The method was applied to the simultaneous determination of As, Hg, Sb, Se and Sn in urine using Ge as an internal standard. Recoveries of added analytes were satisfactory, but analysis of NIST SRM Human Urine gave low results for Se, presumably due to the presence in urine of Se species not generating a hydride. Results for As and Hg were in good agreement with the certified results. Direct determination of Se in this sample by conventional nebulization without HG gave a result in agreement with the certified value.
Total-reflection XRF was used by Marco et al.42 to determine Cu, Fe, Pt, Se and Zn in serum and Cu and Zn in homogenized brain tissue. The Compton scattering intensity was used for internal standardization. Results were in good agreement with those using either Co or V as internal standards and with results obtained by AAS. Selenium metabolism and excretion in humans was studied by Bellisola et al.43 using TXRF determination of Se in dried plasma and urine with Ga as an internal standard.
Japanese workers44 described a micro-PIXE camera to allow elemental analysis of a single cell. The beam of diameter 1 µm allowed mapping of individual cells for Br, K, P and S over areas of 60 × 60 µm in 9–12 h. Single brain cells of a patient with Parkinson's disease were studied by Takada et al.45 using SRXRF imaging. The beam of energy 13.5 keV had a size of 6 × 8 µm and was used for mapping over an area of 100 × 100 µm.
Teeth and bone from the chalcolithic period were analysed using SRXRF and conventional XRF respectively by Carvalo et al.46 Observations of significance were the high levels of Br and Mn in bone and the low levels of Pb in teeth. Brenn et al.47 studied Pb in human bones and teeth from an 11th century mining community. High levels of Pb on the surfaces of the teeth and bone measured by PIXE were related to long-term burial in polluted soils. A method for the determination of the elemental composition of bone in young and old people was described by Zhang et al.48 Samples of femoral head were freeze-dried, dissolved in HNO3, spiked with Y as an internal standard and the solution placed on a Mylar target for determination by PIXE with a 3.5 MeV proton beam. Huang et al.49 used SRXRF to study the trace element levels in a scan across a slice of human bone tumour with a spot size of 1 × 1 µm.
In-vivo determination of Cu, Fe and Zn in skin by XRF was explored by Bradley and Farquharson.50 Using a Mo beam hardening filter, a quasi-mono-energetic source of approximately 13.5 keV was obtained, allowing detection of Cu, Fe and Zn at the 5, 20 and 10 µg g−1 level, respectively. Improvements in the precision of in-vivo measurement of Pb in bone by XRF was achieved by applying a Monte Carlo Library Least Squares calculation.51 This used the complete spectral information and was shown to reduce the RSD by factors of between 1.4 and 20. In a second paper,52 Monte Carlo simulation was used to examine sources of error in the determination. The thickness of tissue overlying the bone, the distance of the instrument to the bone sample, the distribution of Pb in bone and the bone dimensions significantly affected the accuracy. Solutions to these problems were proposed. Bradley et al.53 found that the use of the elastic scattering peak to normalize for the quantity of bone was seriously flawed as the Pb contributed to the total elastic scattering. However, Aro et al.54 showed that the K-XRF determination of Pb in bone correlated well with determinations by ICP-MS after digestion of the bone. Measurement on the tibia and patella on eight intact human legs taken at autopsy showed correlation coefficients greater than 0.9.
1.4 Hair and nail analysis
Only one shampoo of those tested by Leblanc et al.56 was found to seriously affect the trace element composition of hair. This was based on selenium sulfide. They measured 18 elements in 15 shampoos and conditioners by ICP-MS and evaluated the effect of using them on the trace element composition of hair. Generally, although some elements were present at high concentrations in some shampoos, the effect on the hair concentrations was found to be negligible.Ultrasound-assisted acid leaching was investigated by Bermejo-Barrera et
al.4 as a dissolution procedure for the
trace elements Cd, Cr, Hg, Pb and Se in hair. Factors found to be important
were the concentrations of HCl and HNO3 and the temperature of
the ultrasonic bath (set at 90°C). Particle size was
not important and heating times beyond 10 min were found to give no
further improvement. For Cd, Pb and Se, the same HNO3∶HCl
ratio was optimal but for Cr a different ratio was found necessary. For Hg,
HCl alone was suitable but only extracted methylmercury. This simple and rapid
procedure gave results comparable to those obtained after microwave-assisted
pressure digestion.
For investigating cases of suspected As poisoning, workers at the US Federal Bureau of Investigation Laboratory used ICP-MS analysis.57 From the root of the hair to the tip, consecutive segments 1 cm long were pressure-digested with microwave heating and the As was determined with In as an internal standard to build up a time profile of As exposure. The LOD was 5 µg g−1 for a 2.5 mg sample. This sensitivity is adequate for levels associated with poisoning, but insufficient for normal levels (<0.5 µg g−1)
1.5 Marine and freshwater biology
A new arsenic-containing betaine, (carboxyethyl)trimethylarsonium, has been identified in fish muscle by LC-MS.58 Arsenosugars in algae were separated on an anion-exchange column and detected by ICP-MS in a study reported by Raber et al.59 For separation, a mobile phase of 20 mmol l−1 NH4H2PO4 at pH 5.6 and temperature 40°C was considered optimal, allowing separation of seven of the
compounds within 16 min.Thorrold and Shuttleworth60 applied LA-ICP-SFMS to the determination of trace elements and isotope ratios in fish otoliths from rivers in North Carolina, USA. Variation in ratios of Ba, Mn and Sr to Ca across the otolith were presumed to be related to variations in water chemistry over time. Examination of the Sr∶Ca ratio with high-precision analysis showed a quasi-sinusoidal profile that related to an annual cycle of change.
1.6 Progress for individual elements
Ishihara and colleagues61 used PIXE and transmission electron microscopy-EDXRF (TEM-EDX) to determine both the quantity and distribution of Al in human brain tissue. Brain tissue was freeze-dried for measurement of Al by PIXE. For measurement of Al by TEM-EDX, brain tissue was soaked in glutaraldehyde, cut to size, resoaked in sucrose solution and refrozen. Ultra-thin sections were cut from the frozen samples for microscopic analysis.
The group of Moore et al.,35 whose studies on Al metabolism using AMS have been reported in earlier ASU reviews, used the technique to study gastrointestinal (GI) absorption of Al in patients with Alzheimer’s disease (AD). Following overnight fasting, thirteen volunteer patients were given a drink containing 27 ng of 26Al. Blood samples were taken before and 1 h following administration of the tracer and 26Al in plasma, determined by AMS, to quantitatively determine the fraction of Al absorbed across the GI tract. The authors observed that absorption of Al by AD patients exceeded that of controls by a factor of 1.64. They concluded that the GI tract of AD patients was less able to exclude Al, which may result in greater systemic exposure to Al, and suggested that public health measures be considered to limit dietary Al intake.
The group of Becker-Ross et al.63 developed a high resolution continuum source atomic absorption spectrometer to identify and correct for molecular interferences affecting the determination of trace elements in complex biological matrices by Zeeman-effect ETAAS. As an example, the authors described the determination of As and Se in undiluted human urine. The molecular species NaCl and PO were responsible for the spectral interferences on As determination whilst, for Se, NO and PO were the interfering molecular species. The interferences were corrected for with an arithmetical algorithm. The concentration of As determined in a human urine CRM, 168 µg l−1, was in good agreement with the reference range (154 ± 31 µg l−1) and the absolute LODs were reported to be 25 pg for As and 35 pg for Se. Campillo et al.64 also described a method for the determination of total As in human serum, whole blood and urine, using ETAAS with Zeeman-effect background correction. Samples were diluted with 0.1% Triton X-100 (blood and serum 1 + 3 v/v, urine 1 + 1 v/v) and injected into the furnace. A second solution of 15% H2O2, 0.65% HNO3 and 0.5% nickel was injected as a chemical modifier. Calibration with aqueous standards was satisfactory for quantitative determination of As in blood and serum but standard additions calibration was necessary for quantitative determination of As in urine. Cicurczak and Peters57 described a method for the determination of total As in human hair by ICP-MS, which they used to investigate suspected cases of As poisoning. To establish a theoretical time line of excretion, hair was cut into 1 cm segments, representing about one month’s growth, and digested by microwave irradiation. An LOD of 5 µg g−1 was reported for a 2.5 mg hair mass. Samples with As levels in excess of 10 µg g−1 were considered indicative of As deposition in the hair. In all the cases examined, the results indicated that the victim had been subjected to elevated levels of As.
Finally, Concha et al.65 used HGAAS to determine the levels of As in breast milk, blood and urine of native Andean women living in a region with high As levels in the drinking water. The authors observed that the major part of the excreted As was in the form of metabolites of inorganic As indicating that the main source of ingested As was inorganic. The average milk As concentration was 2.3 µg kg−1, which the authors considered to be low in relation to the high levels of maternal exposure. Similarly, urine As levels in nursing babies were also low in relation to the mothers, which led the authors to conclude that inorganic As is not excreted in breast milk to any significant extent.
To study the pharmacokinetics of B, Yamaguchi et al.12 used ICP-AES to determine B in biological tissues and fluids from rats administered the boron neutron capture therapy compound, ‘disodium mercaptoundecahydro-closo-dodecaborate’ (BSH). They observed that B was mainly excreted in urine and noted that renal failure might occur with BSH doses of 300 mg kg−1 or above. They also observed that B did not accumulate unexpectedly in any tissue following multiple injections of the drug over a two-week period.
Huang et al.70critically evaluated the influence of matrix effects, pre-atomization losses and spectral interferences on the determination of Cr in human whole blood and urine by ETAAS. In the method they described, blood or urine was simply diluted with H2O and injected into the furnace together with NH4NO3 as a chemical modifier. They used the method to monitor blood and urine Cr concentrations in chrome electroplaters and non-exposed individuals. They noted that concentrations of Cr in both blood and urine from occupationally exposed workers were, respectively, 9.2-fold and 12.9-fold higher than in the control population. Zima et al.71 used ETAAS to determine serum Cr in patients with malignant, metabolic and renal diseases. They observed increased levels of serum Cr in haemodialysis patients (mean = 3.67 µg l−1) compared with controls (mean = 0.4 µg l−1), whilst significantly lower levels were determined in patients with diabetes (mean = 0.29 µg l−1), lymphoproliferative disease (mean = 0.24 µg l−1) and hyperlipidaemia (mean = 0.15 µg l−1). However, they found no correlation between serum Cr levels and several measured biochemical parameters, including total protein, transferrin, glucose, total cholesterol and apolipoproteins A and B. They suggested that Cr supplementation may be appropriate for some diseases and that monitoring of serum Cr may be necessary to prevent complications in some patients. Ding and colleagues72 also used AAS to determine levels of Cr in serum and urine of healthy and diabetic subjects. As with the group of Zima et al.,71 they found lower levels of Cr in both serum and urine of diabetics compared with healthy controls. However, the levels of Cr in urine reported for both controls (7.8–9.6 µg l−1) and diabetics (4.5–5.9 µg l−1) were markedly higher than have been reported in the literature, raising again the question of contamination. The reported studies re-emphasise the essential requirement that contamination risks are properly controlled for accurate determination of Cr in biological matrices.
PIXE microanalysis was the technique employed by Sergeant and colleagues74 for the quantitative determination of Fe in rat retina, in order to investigate the role of Fe in hereditary retinal degeneration. The authors described the sample preparation and post-irradiation staining techniques used to examine thin freeze-dried sections of rat retinas at different stages of the disease process.
Gwiazda and Smith78 described the application of Pb isotope measurements as a powerful tool to identify sources of Pb exposure. By determining the Pb isotope ratios both in the blood of children with elevated blood Pb levels (>15 µg dl−1) and in the potential in-house and environmental sources of Pb, the authors could provide a reliable indication of the sources of Pb exposure. Smith and colleagues79 used HR-ICP-MS to determine plasma Pb and whole blood Pb in environmentally exposed individuals to further investigate the reported variability in partitioning of Pb between plasma and blood. Over a four-week period, plasma Pb levels averaged 0.29% of whole blood Pb levels. Similarly, over a longer five-month period, plasma Pb levels averaged 0.27% of the whole blood level. The authors concluded that intra-subject variability in the whole blood–plasma Pb relationship is much lower than previously reported. They highlighted the importance of appropriate sampling procedures.
Gerhardsson et al.80 presented the interesting results of a study to determine whether bone Pb was available for chelation by 2,3-dimercaptosuccinic acid (DMSA). Following administration of a 10 mg kg−1 dose of DMSA to volunteers, the researchers determined blood and urine Pb by ETAAS, plasma Pb by ICP-MS and finger bone Pb by K-XRF. From the results they concluded that DMSA-chelatable Pb mainly reflected the blood and soft tissue Pb concentrations and that chelatable Pb was not a good index of total Pb body burden and long-term exposure. Cheng et al.81 used ETAAS to determine blood Pb levels and K-XRF to measure tibia Pb in an investigation of the relationship between low level Pb exposure and electrocardiographic (ECG) conduction disturbances. They observed that bone Pb levels were positively associated with ECG disturbances, particularly in younger men. Elevated bone Pb was associated with an increased risk of intraventricular block in men under 65 years and an increased risk of atrioventricular block in men over 65 years. The authors concluded that cumulative low-level Pb exposure may depress cardiac conduction.
In addition to the two studies described in the previous paragraph, a considerable number of studies have been reported on the ‘in-vivo’ determination of bone Pb by XRF, suggesting that the technique is at last becoming more widely used as a routine tool for epidemiological studies of Pb exposure. Rosen82 described the use of XRF techniques to study chelation therapy in children poisoned by Pb and to evaluate Pb exposures in both children and adults in urban communities. Ao and colleagues51,52 developed a Monte-Carlo simulation method to identify and estimate sources of error in the in-vivo determination of bone Pb by K-XRF and L-XRF. The simulation results indicated that the thickness of soft tissue overlying the bone, the distribution of Pb in the bone, the bone dimensions and distance of the XRF instrument from the bone had a significant impact on the accuracy of the methods. Aro et al.54 described a series of rather gruesome experiments to validate in-vivo K-XRF measurements of bone Pb. Bone Pb levels were determined in eight amputated intact cadaver legs by K-XRF. The legs were dissected to remove skin and soft tissue, and XRF measurements were repeated on the exposed bone tissue. Samples of bone tissue were then removed, digested and Pb determined by ICP-MS. The authors reported good correlation (>0.9) between values determined by K-XRF and ICP-MS for both tibia and patella, providing strong evidence for the validity of in-vivo K-XRF measurements.
Potula et al.83 reported the findings of an investigation on the impact of Pb in drinking water on body burdens of Pb in middle aged and elderly men from Boston, USA. They examined the relationship between levels of Pb determined in tap water in the 1970s by ETAAS and both blood Pb and bone Pb levels determined in the 1990s using ETAAS and K-XRF. Progressively higher bone Pb levels were observed in individuals who reported moderate to high levels of tap water ingestion and who had lived in houses with first morning tap water Pb levels >50 µg l−1. The authors concluded that ingestion of Pb from contaminated tap water was an important predictor of elevated bone Pb levels in later life.
Fleming and colleagues84 described the evaluation of a physiologically based computer model of Pb disposition in humans (the O’Flaherty model). A group of lead smelter workers with well-characterized exposure histories were selected to evaluate the model outputs. Simulated blood Pb and bone Pb data were compared with the experimentally measured values and refinements made to the model parameters. Previously observed trends for both accumulation of Pb in cortical bone and release of bone Pb were satisfactorily predicted by the model. The authors suggested that further refinements of the model may help in explaining the underlying relationship between Pb exposure and Pb distribution in the body.
Bohrer et al.9 used dilute TCA and microwave irradiation to deproteinize human serum samples for quantitative determination of Mn and Ni by ETAAS. The treatment removed around 99% of the protein matrix with a minimal 1 + 1 dilution factor and eliminated the need for chemical modification. The new method was compared with other acid digestion procedures and the authors reported satisfactory recoveries from spiked serum samples.
Different derivatization methods for the determination of Hg species by GC-ICP-MS were investigated by Fernandez et al.89. The group compared butylation with Grignard reagent, aqueous ethylation with NaEt4B and propylation with NaPr4B. Aqueous calibration with ethylmercury as internal standard was used for quantitative determination of the butylation and propylation derivatives, whilst methylpropylmercury was used as the internal standard for determination of ethylation derivatives. The methods were evaluated by analysing DOLT2 CRM which has a certified value for methylmercury. Mester et al.90 directly coupled solid phase microextraction (SPME) with ICP-MS to determine methylmercury in biological materials. To achieve rapid desorption and efficient sample introduction into the plasma, a thermal desorption interface comprised of a splitless-type GC injector was sited directly at the base of the torch. The group examined both direct liquid immersion SPME and headspace extraction and noted severe matrix effects when direct immersion extraction was used with standard additions calibration for biological tissue samples. No matrix effects were observed with headspace extraction. The method was validated by analysing marine biological CRMs.
Brunetto and colleagues91 used headspace injection to determine inorganic Hg and organomercury species in whole blood by AAS. For determination of inorganic Hg, a 2 ml volume of whole blood was reacted with H2SO4–SnCl2 in a closed headspace vial and the released Hg0 carried in a N2 stream to a heated quartz cell for quantitative determination by AAS. For determination of methylmercury, whole blood (2 ml) was treated with iodoacetic acid and H2SO4 and the released methylmercury was separated on a semi-capillary GC column and carried in a He stream to the heated quartz cell. Reported LODs were 0.6 µg l−1 and 0.2 µg l−1 for inorganic Hg and methylmercury, respectively. The authors evaluated the method by determining Hg species in blood CRMs and obtained results in good agreement with the certified values for total Hg.
Svenes and Andersen93 used ETAAS to determine Ni levels in lung tissue samples from former nickel refinery workers, who had been exposed to a variety of soluble and insoluble Ni compounds. Lung tissue samples were taken from non-occupationally exposed individuals to obtain reference values. Samples were taken from various locations in both the right and left lung. The mean lung Ni concentration for the reference group was 0.74 µg g−1 compared with an arithmetic mean value of 50 µg g−1 for the refinery workers. Statistical analysis of the data indicated that there was no significant difference in the Ni levels of samples taken from the right or left lung and that levels in the bronchus were significantly lower than in the remaining lung tissue. The authors concluded that a single biopsy sample did not satisfactorily reflect the lung Ni burden.
°C.Cho et al.95 also used ETAAS to determine plasma and perfusate Pt levels in studies on the pharmacokinetics of cisplatin administered to cancer patients by continuous hyperthermic peritoneal perfusion. Blood and perfusate samples were taken during the 90 min perfusion and 30 min after completion of perfusion. The authors determined the maximum perfusate cisplatin concentration to be ten times higher than the plasma Pt concentration and the area under the concentration–time curve (AUC) of the perfusate to be thirteen times higher than the AUC of plasma. They concluded that this method of drug administration offered a pharmacological advantage over other methods in achieving higher direct drug exposure to the tumour with limited systemic absorption.
Ruiz et al.96 developed a method for the determination of Pt bound to DNA by TXRF. They quantitatively determined Pt concentrations from 3 to 30 ng ml−1, with a precision between 2 and 8%, in cultured HeLa cells incubated with three Pt containing drugs (cis-diamminedichloroplatinum, Pt-Benecil and K2PtCl4).
Inagaki and Haraguchi11 also used ICP-MS
to quantitatively determine REEs in human serum after acid digestion with
HNO3–HClO4 and preconcentration of the REEs onto
Chelex-100 chelating resin. They observed that recovery of higher mass REEs
was poor at room temperature, due to formation of stable complexes with residual
organic compounds in the digested samples. This was overcome by preconcentrating
the digested solution at higher temperatures. Optimum conditions for efficient
preconcentration of all REEs were a solution temperature of 80°C
and pH of 6. Under these conditions, recovery of all REEs varied between 92
and 102% and LODs were less than 0.2 × 10−12 g ml−1.
The authors used the method to determine concentrations of REEs in blood samples
from five healthy volunteers. They reported extremely low concentrations ranging
from 1 × 10−12 g ml−1
for Eu to 230 × 10−12 g ml−1
for Ce.
°C
and 1900°C, respectively. For determination of Se using FI-ETAAS,
Se hydride was generated by the FIA system and adsorbed onto an iridium-coated
graphite tube for quantitative measurement by ETAAS. The reported LODs for
the different techniques were 0.7, 0.5 and 0.05 ng ml−1
for ETAAS, HG-ICP-AES and FI-ETAAS, respectively. Sabe et al.100 also investigated the effectiveness of different
chemical modifiers for the determination of Se in human serum using Zeeman-effect
ETAAS. They considered Pd to be the most satisfactory modifier on the basis
of analytical sensitivity. Serum samples were diluted 1 + 4 v/v
with 0.05% Triton-X100 and 20 µl volumes were injected
into the graphite furnace together with 5 µl of 0.5 g l−1
Pd and 10 µl of 0.05% Triton-X100. The LOD for the method
was 2.6 µg l−1 and a precision of 2%
RSD was reported for a serum Se concentration of 81.5 µg l−1.Turner et al.101 described a sensitive method for the determination of total Se in water and serum by ETV-ICP-MS with isotope dilution. Samples were spiked with a solution enriched with 77Se and the 77Se/82Se ratio measured. The researchers optimized the ETV temperature programme to eliminate polyatomic interferences on the 82Se and 77Se masses. The method was evaluated by analysing water and bovine serum CRMs and the results obtained by the ID method were in good agreement with the certified values. Precision was much improved compared with results obtained by conventional ETV-ICP-MS (0.06–0.8% compared with 0.9–5.5%). Using ISO guidelines, the authors calculated that the overall method uncertainty for the ID-ICP-MS method was 2.26% compared with an uncertainty of 7.7% for the conventional ICP-MS method. In an alternative approach to eliminate polyatomic interferences on the determination of Se by ICP-MS, Sloth and Larsen19 used an ICP-mass spectrometer equipped with a dynamic reaction cell to quantitatively determine the six naturally occurring Se isotopes. By using CH4 as the collision gas in the reaction cell, the signal intensity of the interfering Ar species on Se masses 74, 76, 78 and 80 was reduced by five orders of magnitude. Furthermore, the use of 3% methanol for carbon-enhanced ionization significantly improved the sensitivity for Se, giving an LOD of 6 pg ml−1.
Moor et al.102 described a novel, robust sample introduction system for the determination of total Se in biological materials by HG-ICP-MS. Rapid hydride generation was achieved (within 60 ms) by mixing the acidified sample and NaBH4 reductant at the tip of the cross flow nebulizer, whilst a modified Scott spray chamber acted as the gas–liquid separator. An LOD below 10 ng l−1 and a precision of 2% RSD was reported. The method was evaluated by analysing a series of marine biological CRMs. Nakaguchi et al.103 evaluated different acid digestion methods for the determination of Se in hair samples. Satisfactory results for the determination of total Se in NIES Hair CRM were obtained with HNO3–H2O2 and HNO3–HClO4 mixtures.
To investigate the effect of the Finnish Se fertilization programme on Se status of the Finnish population, Wang et al.104 used ETAAS to determine serum Se levels in nearly 1600 healthy children and young adults. Over the period 1985–1990, when Se was added to fertilizer, the mean serum Se levels in young adults increased from 1.04 µM to 1.59 µM, whilst levels in children rose from 0.87 µM to 1.31 µM. The authors concluded that the Se supplementation programme had succeeded in improving the Se status of the Finnish population.
Several research groups have described methods for the quantitative determination of biologically relevant Se species. The group of Gammelgaard et al.105 successfully separated the Se species selenite, selenate, selenomethionine (SeMet) and trimethylselenonium ion (TMSe+) in aqueous solutions on a cation-exchange column using 10 mM oxalic acid and 20 mM K2SO4 elution buffer with detection of Se by ICP-MS. However the same conditions were not suitable for separation of the species in diluted urine, due to a marked shift in retention times, and only TMSe+ was satisfactorily separated from the other species. Quantitative determination of Se was based on measurement of the 82Se isotope and a large interference on the 78Se mass was observed using this chromatographic system. An LOD of 0.8 µg l−1 was reported. The authors determined Se species in urine samples from 9 volunteers. The TMSe+ species was only quantitatively determined in two of the samples where it represented less than 10% of the total Se content. The same researchers successfully separated selenite and selenate species in human urine on an anion-exchange column with an eluant of 25 mM NaOH in 2% CH3OH for quantitative determination by ICP-MS106. Using the 82Se isotope for quantitative measurement, detection limits for the two species were 0.4 µg l−1 and 0.8 µg l−1 for selenite and selenate, respectively. They determined the two Se species in 23 urine samples. Selenite concentrations ranged from <0.4 µg l−1 to 7.1 µg l−1, whereas no selenate was detected in any of the urine samples.
Chatterjee et al.33 coupled HPLC with HG-MIP-MS to determine selenite and SeMet species in human urine. The two species were satisfactorily separated in spiked urine using an anion exchange column with phosphate buffer eluant. Stable coupling of the HPLC-HG system to the N2-MIP allowed quantitative determination of Se using the major 80Se isotope. In a further alternative approach, Feldman et al.107 coupled HPLC to HR-ICP-MS for separation and quantitative determination of selenocysteine, selenomethionine and selenoethionine. Satisfactory separation was achieved on a reversed-phase column with CH3OH eluant. A mass resolution factor of 1400 enabled the Se isotopes to be measured free from overlapping interferences with an improved detection limit of 0.002 ng ml−1 for selenocysteine. Johansson et al.108 described a method for the speciation of Se in biological samples using IC-HG-AAS with on-line microwave-assisted species conversion. Selenium species were converted to selenite by reaction with HBr/BrO3− and reacted with NaBH4 for determination of the hydride by AAS. The researchers observed that the HBr/BrO3− ratio had to be carefully controlled to achieve a high conversion efficiency and minimum interference from residual Br on the determination of Se. The authors used the method to determine Se species in a biological CRM. Finally, Suzuki and colleagues109 used HPLC coupled with ICP-MS to investigate the interaction of Se with Hg in the body. Following the administration of 82Se enriched selenite and HgCl2 to rats, plasma samples were analysed and a ternary complex of Hg–Se–selenoprotein P identified.
°C, followed by wet
ashing with HNO3–H2O2 and dilution
with 1 M HNO3. The reported method required minimal
urine U concentrations of 14 ng l−1 to achieve
a sufficient 235U signal intensity in order to determine a valid
U isotope ratio. The method was used to identify potential exposure to depleted
U by quantitatively determining the 235U and 238U isotopes.
The authors reported that exposure to depleted U results in the percentage
contribution of 235U in urine to fall below the value of 0.72%
for natural U. Total U levels in urine from a group exposed to non-depleted
U were below 50 ng l−1 and the 235U
percentage contribution was consistent with natural U (0.7–1%).
By contrast, concentrations of total U in urine from the group suspected to
have been exposed to depleted U were greater than 150 ng l−1
and 235U percentages varied between 0.2 and 0.33%, confirming
exposure to depleted U.The group of Baglan et al.113
also used ICP-MS to determine U isotopes in human urine spiked with natural
U and in rat urine containing metabolized depleted U. The results obtained
by ICP-MS were in good agreement with values determined by alpha spectrometry
and certified by an inter-comparison network for radio-toxicological analysis.
They considered that ICP-MS offered significant advantages over other analytical
techniques for monitoring urine U in exposed workers, due to the combination
of high sensitivity, accuracy and speed with which U in urine could be determined.
Muramatsu et al.114 used ICP-MS
to quantitatively determine Th in autopsy tissues from subjects who had previously
been administered Thorotrast medium. They determined Th concentrations in
27 organs and found highest levels in the spleen (mean 16000 µg g−1),
liver (2100 µg g−1) and bone
marrow (600 µg g−1). The lowest
levels ( below 2–7 µg g−1)
were determined in heart and brain tissue. The levels determined in all tissues
were several thousand times higher than values reported for healthy unexposed
individuals.
Priest and colleagues37 used the highly sensitive technique of AMS to achieve the necessary detection limits to quantitatively determine Pu in human bioassay samples. The authors reported an LOD of about 500 nBq for 239Pu and noted that AMS did not suffer the disadvantage of isobaric mass interferences or poor recoveries observed with other spectrometric techniques. The group used the method to determine 239Pu in urine from non-exposed youths and occupationally exposed adults. Mean urinary excretion was 3.5 µBq d−1 in the youths and ranged from 2–260 µBq d−1 in the adults. They also measured the absorbed fraction of Pu following voluntary ingestion of a 15 g quantity of Irish sea sediment and calculated this to be 4.5 × 10−5.
Sturup28 described a method for the simultaneous determination of the four Zn isotopes and total Zn in human serum, urine and faeces by HR-ICP-MS. An RSD of 0.7% was determined for 67Zn/66Zn, 68Zn/66Zn and 70Zn/66Zn ratios and an RSD of 1.2% determined for the 64Zn/66Zn ratio. Using a mass resolution factor of 6000, all Zn isotopes were accurately determined, free from overlapping interferences, with the exception of 64Ni on 64Zn, which had to be corrected for mathematically.
Inagaki et al.116 developed a simple method for speciation of Cu- and Zn-binding proteins, which employed selective extraction of albumin–Cu and albumin–Zn species with Chelex-100 chelating resin and quantitative determination of Cu and Zn by ICP-MS. The method was used to determine loosely bound Cu and Zn (albumin species) and firmly bound species (caeruloplasmin–Cu and α-2 macroglobulin–Zn) in sera from healthy volunteers. Observed concentrations of α-2 macroglobulin–Zn and caeruloplasmin–Cu were in the ranges 109–202 ng ml−1 (12.4–31.3% total Zn) and 513–880 ng ml−1 (90.6–99.7% total Cu), respectively. The authors considered that the method might be valuable for medical diagnosis.
Sturniolo et al.117 used AAS to determine trace elements including Cu, Fe and Zn in duodenal mucosa tissue from Wilson’s disease patients undergoing treatment with ZnSO4 or penacillamine. They found a significant correlation between duodenal Zn concentration and metallothionein. They concluded that Zn treatment increased intestinal metallothionein levels, which, they hypothesized, may prevent oxidative damage caused by metal toxicity.
1.7 Conclusions
Two important objectives of trace element studies in clinical chemistry seem closer to realization.One is to be able to study individual cells. Japanese workers44,45 demonstrated that, with micro-PIXE and SRXRF, major elements can be mapped in single cells. We await the day when techniques will be sensitive enough to study more of the trace elements.
Another has to be an analytical method of high sensitivity capable of determining simultaneously a wide range of elements without interference and with a good linear calibration range. Sample preparation should be minimal. The recent work with ICP-SFMS seems remarkably close to that objective. Methods have been developed for blood,29 serum,30 urine27,30 and human milk.31 In all cases, the accuracy with which a wide range of elements can be determined is impressive. The limitations seem to be that not all elements can be determined with a single resolution and that, with ICP-MS, samples need to be completely digested.
For techniques, like ETAAS, which are less fussy about the degree of digestion, ultrasound-assisted extraction offers a rapid and simple approach for dealing with solid samples, as demonstrated by Lima et al.3 and Bermejo-Barrera et al.4
Initial impressions of some recent commercial developments in MS can be obtained from recent publications. The dynamic reaction cell in Q-ICP-MS allows gas-phase chemistry to solve some of the isobaric interferences in that technique. Methane introduced into the cell largely removed the problem of Ar dimers in the determination of Se.19 The time-of-flight mass spectrometer appears to be better than the quadrupole mass spectrometer in true simultaneous operation and gives better precision, but the sensitivity is poor by comparison.39 The high-power N2 MIP offers reasonable sensitivity, fewer problems with isobaric interferences and lower running costs than an Ar ICP. It seems particularly suited as an element-specific detector for As32 and Se.33
2 Analysis of foods and beverages
This review covers the analysis of foods and beverages by atomic spectrometric techniques published during the year ended October 2000. It highlights papers that describe novel work and significant advances in both instrumental and analytical techniques, and studies to which these have been applied. Table 1 complements the text with summaries of these and other publications. Conference abstracts have been included where it was considered that the work described might contribute to the literature when published in greater detail.It is noted that there has been a marked decrease in the number of relevant papers in this review period when compared with previous years.
2.1 Sampling and sample preconcentration
°C and evaporated to a volume
of approximately 1 ml. The residue was dissolved in 10 M
HCl (20 ml) and these acid digests were then placed in a
separating funnel. Potassium iodide (5 ml, 5 M)
and benzene were added and the funnel was shaken for 5 min. The benzene
layer was then poured into a beaker and IBMK (3 ml) and cobalt(III)
oxide powder (30 mg) were added. The mixture was sonicated
and stirred for 10 min to allow the Se to become adsorbed to the cobalt
oxide powder. After vacuum filtration using a PTFE membrane, the entire membrane
was transferred to a test tube and 1 ml of water added. Shaking of
the test tube enabled a uniform dispersion, or slurry, of the cobalt oxide
containing the Se to be formed. Aliquots of this were introduced directly
to the atomizer using manual pipetting. Recoveries were reported to be 100%,
precision at the 0.2 mg l−1 level was 3.4%
(n = 6),
the linear range extended to 0.5 mg l−1 and
the LOD was 16 µg l−1. The method was
validated by the analysis of several CRMs, including NIST SRM 1548a Typical
Diet. A solvent extraction method has been described for the determination
of Cr in foodstuffs.120 After an initial
dry ash sample pre-treatment, any CrIII was oxidized by KMnO4,
and the CrVI was pre-concentrated in IBMK as chromium oxychloride.
This was then introduced directly to a flame atomic absorption instrument.
An LOD of 4 µg kg−1 was obtained, and
a number of food samples were analysed with method reliability assured by
the analysis of two CRMs.°C
for 20 min to ensure reduction of the Se. For the determination of
As, an aliquot of the ash solution (5 ml) was mixed with
hydroxylamine hydrochloride solution (2 ml, 50%) and
0.4 ml of KI–ascorbic acid and diluted to 10 ml. Detection
limits were 0.05 and 0.09 ng ml−1 for As and
Se, respectively. Recoveries were 96–105% for As and 88–107%
for Se. A simple and rapid digestion procedure for the determination of As
in food by ICP-MS has been reported by Fernando et al.122
Food samples (2–4 g) were digested using 5 ml
of HNO3 in a two stage, open vessel, atmospheric pressure, controlled
temperature microwave digestor. After dilution, the samples were analysed
directly by ICP-MS. A number of different food types containing differing
amounts of fat, protein, fibre and carbohydrate, and CRMs were analysed to
validate the method. An investigation into the effects of Cd, Pb, Ni and V
concentrations on the uptake and transport processes in cucumber plants has
been reported123. The analytes of interest
were Ca, Fe, K, Mn and Zn. During the study, the root samples were digested
using HNO3 in a microwave device using a three-step procedure.
The sample was heated at 250, 300 and 500 W for 3, 10 and 20 min
at a pressure of 20, 80 and 120 psi, respectively. The digests were then diluted
to 25 ml, spiked with an internal standard and then an aliquot deposited
on a quartz glass carrier and dried. The dried samples were then analysed
by TXRF using a Si(Li) detector. Results of the studies were presented
and discussed.A microwave digestion procedure has been compared with a UV irradiation process in the presence of hydrogen peroxide as a sample pre-treatment procedure for the determination of Pb isotope ratios in port wine by ICP-MS.124 Sample (1.5 ml) was mixed with HNO3 (0.15 ml) and H2O2 (1.5 ml) followed by high-pressure microwave digestion. The resulting digest was diluted to 15 ml prior to analysis. Alternatively, the UV irradiation method involved mixing sample (20 ml) with 0.12 ml of 30% hydrogen peroxide and exposure to a 1000 W mercury high-pressure vapour lamp for 1.5 h. After filtration, the sample was diluted 10-fold using 0.5% HNO3. Although both methods proved to be adequate for determining Pb isotope ratios, the UV irradiation method was chosen to analyse the samples because it required the addition of lower amounts of chemicals and provided larger volumes of solution. Precision for the 207Pb/206Pb and 208Pb 206Pb was 0.3% and for 204Pb/206Pb it was 0.8%. Three different digestion procedures (high pressure microwave digestion, conventional wet digestion and dry ashing) were compared for the analysis of an assortment of vegetables (tomatoes, peas, corn, tomato concentrate, canned peas and canned sweetcorn) by ICP-AES.125 The results obtained from the microwave and conventional wet digestions were similar, but losses were observed for the dry ashing procedure. A total of 16 analytes were determined, inter-element effects were discussed and the method was validated by the analysis of the CRMs 1570a Spinach Leaves and CL-1 Cabbage Leaves using matrix matched standards.
°C. The LODs were
0.5, 0.7 and 0.6 µg l−1 for cows' milk,
human milk and infant formula, respectively. The method was used to determine
V in 17 infant formula samples, 13 human milk samples and 10 cows’ milk
samples.2.2 Speciation
The methods of speciation for As, Hg and Se are discussed under the relevant analyte sections later in the review. There are still several new speciation applications that have been reported, indicating the ongoing interest in determining the overall toxicity of a sample rather than merely the total element concentration.Size exclusion chromatography (SEC) has been used in two papers to determine Fe speciation in foodstuffs. In one, Harrington et al.128 coupled SEC with ICP-SFMS to determine Fe speciation in meat. The use of the sector field instrument enabled the main Fe isotope at m/z 56 to be monitored on-line. The SEC column used was TSK gel G2000SW and the mobile phase used to separate the Fe metalloproteins was tris(hydroxymethyl)aminomethane hydrochloride (pH 7.2, 0.1 M). On cooking, the steak showed a decrease in myoglobin content compared with the raw steak, but it also contained two unidentified Fe-containing species of mass 8.3 kDa and 4.8 kDa. Unfortunately, the sum of the Fe species present did not agree with the total Fe content in the extracts determined using ICP-AES. Despite this, useful information concerning the Fe speciation was obtained. In the second paper,129 Fe speciation in breast milk and infant formula whey was achieved by Bermejo et al. using a TSK G2000 column, fraction collection and off-line determination by ETAAS. Water was used as mobile phase to simplify the determination of Fe. The procedure was described as being sensitive and precise, with the LOD being 1.4 µg l−1, the LOQ 4.7 µg l−1 and with RSD typically <10%. The same authors have used a very similar technique to fractionate Cu species in milk whey samples.130 Although the same column was used, the mobile phase was ammonium nitrate (0.2 M) and ammonia (pH 6.7). Again, the method was described as being sensitive (LOQ = 1.5 µg l−1) and precise (RSD, 10%). It was found that Cu was associated with molecules of mass 76 and 16 kDa in breast milk, but in cows’ milk based infant formulas it was present in molecules of molecular mass 14 and 36 kDa.
Other methods of chromatography coupled with ICP-MS detection have also been reported. These include the determination of tributyltin (TBT) in oyster tissue using HPLC-ID-ICP-MS using an enriched 117Sn standard of TBT.131 Extraction of the TBT was achieved using 0.5 M sodium acetate–1.0 M acetic acid in methanol using a temperature programmed microwave digestion system. Spike extraction efficiencies ranged from 103 to 104.5% for oyster samples and the method precision (n = 6) was 1.51%. The extraction efficiency on BCR 477 was found to be only 84 ± 2.3%. It was also noted that exposure to microwave radiation did not alter the tin speciation. Ground and drinking waters have been analysed for Cr speciation.132 Stability of CrIII and CrVI in the water proved to be troublesome, but the authors presented the optimum conditions for sample storage. The two species could be determined by IC-ICP-MS in less than 3 min and, using Rh as an internal standard, the precision was improved. Limits of detection were 0.1 µg l−1 for both species without any preconcentration.
2.3 Developments in methodology for flame atomic absorption spectrometry
This has been a relatively quiet area of research in this review period. Despite this, the use of emulsions in sample preparation procedures during the determination of different analytes in milk has been presented by different authors. Milk fat has been analysed for Zn by emulsifying the sample with sodium dodecylbenzosulfonate (NaDBS) and aspirating this directly into the instrument.133 Calibration was by standard additions and the LOD achieved was 2.3 µg l−1 for cows’ milk and 2.9 µg l−1 for infant formula. Recovery was found to be close to 100%. Other surfactants were tested and, although Triton X-100 was successful, saponin, viscalex and glycerol did not form homogeneous emulsions. Other workers134 have used emulsification to determine Ca in milk tea powder. This paper is in Chinese and details are scarce, although it appears that the emulsifying agent used was emulsifier OP, that standard additions was used to calibrate and that the work was performed using an air–acetylene flame. The method apparently yielded results that agreed well with those obtained using a dry ashing procedure and was described as being simple and accurate.Zhang et al. determined Cd in flour by atom trapping FAAS using derivative signal processing.135 It was reported that the LOD and sensitivity were improved by two- and three orders of magnitude over those of conventional FAAS with 1–3 min collection time, respectively. The proposed method gave a recovery range of 94.7–119%. Again, details were scarce.
2.4 Developments in methodology for electrothermal atomic absorption spectrometry
Nothing terribly novel has been published in this review period, although the use of multi-element ETAAS instruments has increased the speed of analysis markedly. Correia et al.136 determined Cd and Pb simultaneously in foodstuffs. Sample (0.5 g) was digested using HNO3 (5 ml) in a closed-vessel microwave oven. The best matrix modifier was a mixture of NH4H2PO4 (0.5% w/v) and Mg(NO3)2 (0.03% w/v) and the optimal compromise furnace conditions were an ash temperature of 750°C and an atomize temperature of 1600°C. Limits
of detection were 0.38 pg for Cd and 9.3 pg for Pb. The reliability
of the procedure was demonstrated by the analysis of certified spinach and
bovine liver samples. Precision was better than 6%. In another paper,
Cd, Cr, Cu, Ni and Pb were determined in potable and surface waters.137 Direct calibration was achieved using a mixed
Pd–Mg modifier giving an analytical performance in terms of LOD (<1 µg l−1
for Cr, Cu, Ni and Pb and <0.1 µg l−1
for Cd) that exceeded the requirements of the strictest international
regulation. The paper was validated by spike/recovery experiments for
a large number of samples, yielding recoveries of 85–115%. It
is noted however, that a CRM was not analysed. Similarly, there was no indication
of how the temperature programme used was optimized.Matrix modification is a topic that still receives attention.
A paper has been presented by Thomaidis and Methenitu that compared W and
Zr as permanent modifiers for the determination of Cd in foods of animal origin.138 The tungsten modifier (240 µg
of W plus 200 µg Rh) stabilized the Cd to a temperature
of 550°C in aqueous standards but to only 500°C for
acid digests of meat, fish and milk. The Zr modifier (120 µg
Zr plus 4 µg Ir) stabilized the Cd to 450 and 400°C
for standards and acid digests, respectively. The performances with respect
to characteristic mass and LOD for the two systems were comparable (1.4 pg
and approximately 0.03–0.04 µg l−1,
respectively). The performance of both permanent modifiers remained stable
for 1200 firings. Calibration was performed using aqueous standards and the
method was validated by the successful analysis of numerous CRMs including
meat, liver, kidney, tuna, mussel and milk.
The topic of slurry sampling has been addressed by Bermejo-Barrera et
al.139 An assortment of seafood samples
including tuna, mussels, clams and cockles as well as a large number of relevant
CRMs (DORM-1, DOLT-1 and CRM 278) were analysed for Cd using slurry
sampling with Triton X-100 as dispersant. Using NH4H2PO4
at a concentration of 50 mg l−1 as matrix modifier,
a pyrolysis temperature of 600°C could be used without analyte
loss. Atomization was at 1200°C. Surprisingly, the use of air
or oxygen in the pyrolysis stage was found to be unnecessary. The authors
demonstrated that calibration using aqueous standards was sufficient for all
sample types except for mussels, where the standard additions method was necessary.
Slurry introduction of baby foods for the determination of Cd, Pb and Se has
also been reported.140 Suspensions were prepared
in a medium containing 0.1% Triton X-100, H2O2,
HNO3
(1%) and a matrix modifier, the components
of which differed for the three analytes. For Cd the modifier was 1%
NH4(H2)PO4 and 0.2% Ni;
for Pb it was 1% NH4(H2)PO4;
and for Se it was 0.5% Ni. The furnace temperature programme was optimized
for each analyte and the optimal conditions gave LODs (3σ)
of 0.4, 3.4 and 5.2 ng g−1 for Cd, Pb and Se,
respectively. The reliability of the procedures was established by the analysis
of six biological CRMs and by comparison with a microwave digestion procedure.
The other relevant papers are very much applications based. These
include the determination of Fe in wine, grape juice and other alcoholic beverages141 and the determination of Al in the edible parts
of fish.142 This latter paper, by Ranau et
al., deserves some comment because it involved a microwave activated
oxygen plasma to pre-treat the sample. Freeze dried, homogenized fish samples (1 g)
were ashed at a pressure of 60–90 Pa and an oxygen pressure of 2–2.5 × 10−5
Pa. The residue was dissolved in 0.2% HNO3 and aliquots (20 µl)
were analysed by ETAAS using a mixed palladium and magnesium matrix modifier.
Calibration was by standard additions and the LOD was 1 µg l−1.
In a paper by Soares et al., CrVI was determined in infant
milk formulas.143 The analyte was separated
chromatographically using a Chromabond NH2 ion-exchange column
and then determined using ETAAS. The LOD was 1.8 µg l−1,
the calibration was linear between 1.8 and 50 µg l−1
and spiking/recovery experiments were used as method validation, with
a recovery of >93% being obtained. Infant cereals have also been
analysed.144 Sample (10 g)
was ashed up to 450°C in a temperature programmable muffle furnace,
the residue taken up in HNO3, diluted to 10 ml and then
analysed directly for the analytes Cd and Pb using the 228.8 nm and
283.3 nm resonance lines. Recoveries were close to 100%.
2.5 Developments in methodology for inductively coupled plasma mass spectrometry
Lead isotope ratios in 20 wines from five different continents were measured using an axial ICP-TOF-MS.145 The wine was microwave digested in the presence of HNO3 and then the Pb extracted by diethyldithiophosphate into hexane. After evaporation of the hexane, the Pb was re-dissolved into 0.5% HNO3. The concentration of Pb in the wines ranged from 5 to 150 ng ml−1. The ratios obtained by ICP-TOF-MS were compared with those from multi-collector (MC)-ICP-MS and Q-ICP-MS. In general, the ICP-TOF-MS agreed well with the MC-ICP-MS, although a correction had to be made for the isobaric interference of 204Hg on 204Pb. The results from the Q-ICP-MS were not in agreement with the other two instruments.Sector field ICP-MS has been used to determine trace elements in both water146 and human milk.31 In the second of these papers, Prohaska et al. determined a suite of elements (Ag, Al, As, Au, Co, Cr, Cu, Fe, Mn, Ni, Pb, Pt, Sc, Ti and V) using the high resolution ICP-MS. The performance with respect to sensitivity, spectral and non-spectral interferences, blank levels, relative stability and accuracy, was evaluated. In addition, a microconcentric nebulizer used in conjunction with a membrane desolvation device was used in an attempt to enhance the signal and to decrease the interferences. This proved to be partially successful, with a 5-fold enhancement being obtained. However, not all interferences were removed completely. The introduction of nitrogen led to no signal enhancement and also had the added detrimental effect of forming other nitrogen-based interferences. The same research group published a similar paper in which several analytes were determined in human milk and milk formulas.147 Of the analytes determined, Ag, Au, Pt, Sc, Ti and V were claimed to be reported for the first time in this sample type. An assortment of alcoholic beverages has been analysed using a double focusing sector field ICP-MS instrument.148 Apart from acidification, no sample pre-treatment was required and a variety of analytes was determined in addition to Pb isotope ratios. Standards had to be matrix matched to avoid severe matrix interferences. Results were compared with those obtained previously using TIMS. Rivero-Martino et al. used a double focusing instrument to determine a suite of elements in milk whey.149 The analysis was split into two sections. The first used a resolution (m/Δm) of 300 (Cd, Hg, Pb and Sr) and the second used a resolution of 3000 (Al, Ca, Cr, Cu, Fe, Mg, Mn, Na, Ni, Se and Zn). The lower background and greater sensitivity of the instrument yielded better LODs when compared with a quadrupole instrument. The method was validated by the successful analysis of BCR 063R skimmed milk powder. As an application, cow, human and formula milk whey were analysed and considerable differences were observed. In a similar paper by the same research group, a number of analytes were determined in biological materials, including clinical samples.26 The prospect of using this instrument as a speciation detector as well as the possibility of using it to confirm/establish “reference values” was also discussed.
The other papers published in this area are concerned with the analysis of different foodtypes and beverages. These include the determination of U in tap water, where Rh was used as an internal standard;150 the determination of 50 major and trace elements in Danish potatoes after microwave digestion of the samples;151 the determination of Cd and Pb in cereals and pulses from North-Eastern China;152 and the changes in concentration of several analytes in human milk during lactation.55 This last paper, by Krachler et al., discovered that, as lactation continued, the concentration of the essential trace elements Cu, Mn, Mo, Se and Zn decreased, whereas the concentration of Co increased. The accuracy of the method was assured by the analysis of the certified materials BCR 063 and 150.
2.6 Developments in individual elements
Several papers concerning As speciation have been published. Slekovec et al.154 compared the use of several different atomic spectrometric detectors after separation of the As species using a Hamilton PRP-X 100 anion-exchange column. The coupling of HPLC-FAAS proved to be too insensitive for most applications; HPLC-ETAAS also required substantially more As to be present but HPLC-ICP-MS allowed As down to 1 ng to be detected. As an application, the aqueous extracts of several varieties of Slovenian mushrooms were analysed, yielding very different inter-species distribution of As compounds. Laccaria amethystina contained ∼26 mg kg−1 of which 97% was DMA and 3% was arsenite; Laccaria laccata contained 26–32 mg kg−1 of which 80% was arsenate, 14% was arsenite and 3% was DMA; Boletus cavipes contained ∼12 mg kg−1 of which 50% was arsenate, 40% arsenite and 10% DMA, and Thelephora terrestris contained ∼38 mg kg−1 of which 70% was arsenate and 30% arsenite. Another paper that used chromatography to separate the As species prior to ICP-MS detection has been published by Wangkarn and Pergantis.155 A narrow-bore column containing an octadecyldimethylsilyl based reversed-phase packing material used in conjunction with a mobile phase containing 5 mM tetrabutylammonium hydroxide at pH 6 as an ion-pair reagent, separated arsenite, DMA, arsenate and MMA in less than 2 min. If 4-hydroxyphenylarsonic acid was used as an internal standard, the run time was lengthened by 30 s. Several wines and a kelp powder were analysed, with the latter sample being analysed for four additional arsenosugars. Cationic As species have been determined in seafood products after extraction with methanol–water followed by HPLC-thermal oxidation-HG-AFS.156 The analytical figures of merit (recovery, precision, LOD and linear range) were reported for each of the As species under investigation (arsenobetaine, arsenocholine, trimethylarsine oxide, and tetramethylarsonium ion). Limits of detection ranged from 0.9–6.3 µg kg−1, precision varied between 0.7 and 8.4% and the recovery was reportedly >97% for all species. The procedure was applied to the RMs DORM-2, NFA-shrimp and NFA-plaice and the results were compared with those obtained by other workers.
Several papers addressing Hg speciation in seafood have been presented. This includes one by Rio-Segade and Bendicho that used a selective reduction method for the separate determination of inorganic and total Hg in mussel tissue using an FI-CVAAS technique.163 The mussels were microwave digested using HNO3–H2O2 and a sub-sample of the digest reacted with sodium borohydride to reduce the Hg ready for detection as “total” Hg. A separate sub-sample was ultrasonically extracted using HCl and the HgII was selectively reduced using stannous chloride. The accuracy of the method was tested by analysis of BCR 278 Mussel Tissue, with the results showing no significant deviation from certified values. Recovery tests indicated that all the Hg present in mussels was present as methylmercury. Speciation of Hg in the CRM DOLT-2 has been achieved by Logar et al.164 Sample was homogenized with 10 mM Tris hydrochloride and then ultra-centrifuged. The soluble part of the sample was then passed through a Sephadex G-75 column for the separation of various protein fractions. Both HgII and methyl-Hg (MeHg) were then determined in the different fractions and in the solid phase. This paper also compared alkaline dissolution and acid leaching extraction techniques for the remaining solid phase. Detection was by ethylation derivatization, gas chromatography (GC), pyrolysis and CVAFS. The sum of the HgII and MeHg species was compared with the total Hg concentration obtained using acid dissolution of the solid sample and CVAAS detection. It was found that the alkaline dissolution was the most appropriate method for the simultaneous determination of MeHg and HgII. The development of a routine method for the determination of total and organometallic mercury in food has been described in a conference presentation.165 Total Hg was determined using a HNO3–H2O2 microwave assisted dissolution, whereas, for speciation purposes, aqueous acid leach (HCl), alkaline extraction (both KOH–methanol and TMAH–methanol), enzymolysis using trypsin and oxidation (KBr, sulfuric acid and copper sulfate) were compared. Detection was by a variety of techniques including ICP-MS, CVAAS and CVAFS. Each step of the procedure was validated by the use of CRM DORM-2, TORT-1 or DOLT-1, as well as mass balance procedures and spiking/recovery experiments. Unfortunately, the abstract did not specify which was the best method to use.
There have been several papers published on Se speciation. These have been split into two main areas of interest. Chiral speciation of selenomethionine enantiomers in selenized yeast by HPLC-ICP-MS has been reported by Perez-Mendez et al.167 The HPLC column consisted of a glycopeptide antibiotic teicoplanin based chiral stationary phase used in conjunction with a mobile phase comprising 2% methanol–water used at a flow rate of 1 ml min−1. The system was capable of separating selenomethionine and selenoethionine enantiomers within 8 min. The LOD for each selenomethionine enantiomer was 0.8 µg l−1 (as Se). Chiral speciation of other seleno-aminoacids has also been reported by Ponce de Leon et al.168,169 In the first of these two papers DL-selenocystine, DL-selenomethionine and DL-selenoethionine were separated on a Daicel Crownpak CR(+) crown ether column using a 0.1 M perchloric acid mobile phase. Limits of detection using UV spectrometry were 34.5–47.1 ng, but these were improved 40–400-fold by using ICP-MS. The method was applied to the analysis of dietary selenium supplements. In the second paper,169 the same authors used a similar technique for determining nine seleno-aminoacids. Samples analysed included Se-enriched onion, garlic and yeast. Two different extraction methods were compared, i.e, water extraction and an enzymolysis procedure using pepsin. It was found that the water was less efficient at extracting the analytes, but that the same species were present in both extraction methods. A chromatogram of a water extract of selenized yeast was given and showed 8 identified Se aminoacids (including enantiomers) and one unidentified peak.
The other main area of Se speciation has been size exclusion chromatography (SEC).
This has been used by Onning and Bergdahl with on-line coupling with ICP-MS
to fractionate soluble Se compounds in fish.170
The column used was Superdex 200 HR 10/30. The LOD was 0.2 µg l−1
and the concentration range investigated was 0–20 µg l−1.
It was found that 47% of selenium was extractable from plaice, but
that figure dropped to only 23% for cod. It was noted that the recovery
of the chromatographic step alone was 70%, indicating that there was
some interaction of the sample with the column. The results of ultrafiltration
using a membrane with a cut off at Mr 10000 and
TCA precipitation were compared with the SEC. In general, good agreement was
found between the methods. It was also found that the size distribution of
Se in plaice differed markedly from that in cod, with 69% of Se in
plaice being <Mr 10000, whereas in cod this
figure was 20%. A conference presentation by Bermejo-Barrera et
al.171 described SEC coupled with a
HG-ETAAS technique for Se speciation in infant formulas and milk whey. The
sample was ultracentrifuged to dispose of milk fat and casein and then the
whey was ultrafiltered using a device with a membrane cut-off of 10000
Da. The sample was then injected onto a TSK gel 2000 SW column and protein
fractions collected, microwave digested using HNO3–H2O2–HCl
and analysed by HG-AAS using a trapping temperature of 800°C.
The protein fractions between 100 and 10000 Da showed the highest
Se content.
2.7 Single and multi-element analysis of foods
Joseph et al. used energy dispersive XRF (EDXRF) to determine eight analytes (Ca, Cu, Fe, K, Mn, Rb, Sr and Zn) in five Indian spices (pepper, clove, cardamom, cinnamon and cumin).172 The dried, powdered spices were mixed with an equal quantity of cellulose binder to obtain self-supporting pellets of 2.5 cm diameter, which were then analysed using EDXRF. A pepperbush CRM was prepared and analysed in the same way and the results agreed well with certificate values. Total reflection XRF (TXRF) has been used by Capote et al. to determine Cu, Fe and Zn in alcoholic beverages.173 Sample (10 µl) was mixed with 10 µl of internal standard (10 mg l−1 V) on a siliconized quartz carrier and then dried. The residue was analysed using a TXRF instrument equipped with a Mo anode X-ray tube and a Si(Li) detector. LODs were 0.02, 0.022 and 0.019 mg l−1 for Cu, Fe and Zn, respectively. The procedure was used to analyse five commercial and four illicit alcoholic beverages. Accuracy was checked by comparing the results with those obtained using FAAS. Most of the other papers in this area are applications, although an interesting one by Salido and Jones involving the simultaneous determination of Cd, Cu and Pb in drinking water using tungsten coil AAS has been published.174 The tungsten coil was crafted from a commercially available slide projector bulb and the detector was a charge coupled device spectrometer. Using a current of 6.7 A (which produced an atomization temperature of 2200°C),
limits of detection were 0.2, 0.8 and 3.0 µg l−1
for Cd, Cu and Pb, respectively, when a 20 µl sample volume was
injected. Other papers reported the analysis of: mushrooms in an attempt to
elucidate the mechanisms of bio-accumulation;175
infant formulas;176 honey;177
and wines.1782.8 Dietary intake studies
This area of research has had the biggest drop in interest in this review period with only two papers being published. In one (in Japanese) foods were analysed for B in an attempt to estimate daily intake.179 Sample (10 g) was dry ashed at 80°C for 6 h,
at 250°C for 4 h and then at 550°C for 8 h.
The residue was taken up in 0.5 M HNO3 and then
diluted to 20 ml prior to analysis by ICP-AES at the 249.77 nm
line. It was reported that most co-existing ions did not interfere and that
B daily intake ranged typically from 1.23–2.15 mg. Analytical
precision for the analysis of polished rice was found to be 1.78% and
the results from this method compared well with those obtained using the curcumin
method. In the second paper,180 Lopez et
al. determined Al levels in wine, beer and other alcoholic beverages.
The influence of packaging and containers on the Al contamination of the beverages
and their contribution to dietary intake was investigated. Samples were digested
using HNO3 and V2O5 and then analysed by
ETAAS. The LOD was 4 pg, mean recovery was 98.2% and precision
was typically 5.2%. Results were compared with those obtained using
a microwave digestion procedure.2.9 Reference materials and collaborative trials
The results of an inter-laboratory trial for the determination of Si in food and biological samples (serum, urine, water, beer and spinach) have been reported.110 The trial was set up in accordance with ISO 5725-2. The relative overall repeatability standard deviation varied between 4% for spinach powder (with a mean content of 176 mg kg−1) to 11% for serum (mean content: 5.33 mg l−1). However, the inter-laboratory relative standard deviation ranged from 15% for spinach after sample digestion (mean content 3.32 mg l−1) to 107% for the spinach powder. This indicated that laboratories could come to reasonable agreement if pre-digested samples were presented to them, but that solid samples requiring digestion led to severe problems.| Element | Matrix | Technique; atomization; presentationa | Sample treatment/comments | Ref. |
|---|---|---|---|---|
| a Hy indicates hydride and S, L, G and Sl signify solid, liquid, gaseous or slurry sample introduction, respectively. CCMP is capacitively coupled microwave plasma. Other abbreviations are listed elsewhere. | ||||
| Ag | Teeth | MS;ICP;LA | Teeth in hot H2O were cleaned by ultrasonic energy. The spatial distribution of metal in a tooth was determined | 21 |
| Al | Plasma | MS;-;S | AMS was used to show that the intestinal absorption of 26Al was increased in patients with Alzheimer’s disease compared with control subjects | 35 |
| Al | Serum | AA;ETA;L | Accumulation of carbonaceous residues was reduced by injection of TMAH onto the sample. K2Cr2O7, Triton X-100 and HNO3 were included in the modifier solution | 5 |
| Al | Brain | XRF;-;S | Frozen tissue in liquid N2 was dried under vacuum for PIXE analysis. Additional frozen material was fixed in glutaraldehyde and sucrose, cut into sections and examined by EDXRF | 61 |
| Al | Fish | AA;ETA;L | Freeze dried homogenates were ashed at a pressure of 60–90 Pa and an O2 pressure of 2–2.5 × 10−5 Pa. The ash was dissolved in 0.2% HNO3 and a 20 µl aliquot taken for ETAAS. A Zeeman-effect instrument was used in conjunction with Pd(NO3)2 and Mg(NO3)2 as chemical modifiers. The LOD was 1 µg l−1 | 142 |
| Al | Alcoholic beverages | AA;ETA;L | 70 samples of Spanish alcoholic beverages were digested using HNO3 and V2O5 and analysed using ETAAS. The influence of packaging on contamination was discussed | 180 |
| As | Urine (CRM) | MS;MIP;L | An ICP-MS nebulizer and polyether ether ketone sample tubing replaced the original fittings of an N2-MIP. Sensitivity and separation of 7 species were improved. Results for a candidate CRM were reported. See also Se, ref. 33 | 32 |
| As | Urine | MS;ICP;CE | An interface between the electrophoretic output and the microconcentric nebulizer was described | 23 |
| As | Urine | MS;ICP;HPLC | Six As species were separately determined. No ArCl interference was evident | 62 |
| As | Urine | AA;ETA;L | The optical system consisted of a continuum light source, a double echelle monochromator and a linear array charge coupled device detector. Spectral interferences were detected and mathematical corrections applied. Accurate results were obtained with RMs | 63 |
| As | Breast milk, water | AA;Hy;L | Arsenic exposure in very young children was evaluated by determining As in the breast milk of Andean women. The women lived in an Argentine region with high As concentrations in the drinking water (ca. 200 µg l−1). The authors concluded from their studies that inorganic As is not excreted in breast milk to any significant extent | 65 |
| As | Drinking water | AA;ETA;L | Inorganic As species were determined in water samples using 2,3-dimercaptopropane-1-sulfonate as a complexing agent and C18 cartridges to preconcentrate the complex. Total As and AsIII were determined analytically and AsV by difference. LODs were 0.11 and 0.15 µg l−1 for AsIII and AsV, respectively | 181 |
| As | Chinese medicines | MS;ICP;CE-HG | A tablet was extracted with warm H2O and the As species separated by CE. The electrophoresis outlet went via a movable reduction bed hydride generation system to the ICP torch. Recoveries of AsIII, DMA, MMA and AsV were 105, 85, 108 and 88%, respectively | 24 |
| As | Foods | AA;Hy;FI | Samples were microwave digested, diluted to 20–50 ml,
evaporated to dryness then ashed in a muffle furnace. The resulting ash was
dissolved in 6 M HCl, heated at 90°C for 20 min
to reduce the Se and diluted to 10 ml. A 5 ml portion was removed
and 2 ml 50% hydroxylamine hydrochloride and 0.4 ml KI–ascorbic
acid added. Se was determined after 60 min. The LODs for As and Se
were 0.05 and 0.09 ng ml−1, respectively | 151 |
| As | Foodstuffs | MS;ICP;L | A 2-stage open vessel atmospheric pressure microwave digestion procedure was used for sample dissolution. Cl interference on the As signal was found to be minimal | 122 |
| As | Seafood | AF;Hy;HPLC | Arsenobetaine, arsenocholine trimethylarsine oxide and tetramethylarsonium ion were determined by coupled HPLC–ICP-MS. The optimisation of the experimental variables was described | 156 |
| As | Seafood | AA;ETA;L,Sl | Two methods based on ultrasound—ultrasonic slurry sampling and ultrasound-assisted extraction—were compared with a H2O2–HNO3 microwave digestion procedure. A longitudinal Zeeman-effect ETAA spectrometer was used for final measurements in each case. Significantly lower As recoveries were obtained with the slurry method for several of the sample matrices | 153 |
| As | Mushrooms | MS;ICP;HPLC AA;ETA;HPLC AA;F;HPLC | DMA, MMA, AsIII and AsV were separated by HPLC and then determined using one of the named detectors. Only ICP-MS had the sensitivity to detect minor species in the samples which all originated from Slovenia | 154 |
| As | Wine, kelp powder | MS;ICP;HPLC | A narrow-bore column was used in conjunction with tetrabutylammonium hydroxide as ion-pairing agent to determine DMA, MMA, AsIII and AsV in wine samples. Separation could be achieved in less than 2 min. The method was also used to identify 4 arsenosugars and DMA in kelp powder | 155 |
| B | Blood, urine, tissues | AE;ICP;L | The pharmacokinetics of a compound used for boron neutron capture therapy were studied | 12 |
| B | Serum, plasma, urine | MS;ICP;L | Specimens were diluted 20–100 fold. Various diluents were investigated and 0.25% m/v mannitol + 0.1 M NH3 gave best precision, minimal memory effect and lowest background. Be was used as internal standard and the LOD was 0.015 ng ml−1 | 67 |
| B | Foods | AE;ICP;L | Sample, 10 g, was ashed at 80°C for
6 h, 250°C for 4 h and finally 550°C
for 8 h. The residue was dissolved in 0.5 M HNO3
and diluted to 20 ml. B was measured in the test portion at 249.77 nm.
Daily B intakes were estimated (in Japanese) | 179 |
| Be | Liver, kidney | AA;ETA;L | The effects of two chelating agents on the toxicity and distribution of Be were investigated. Tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid) reduced the tissue concentrations and the toxicity of Be | 66 |
| Ca | Eye tissue | XRF;-;S | Thin sections of retina were taken from the eye of rats with hereditary retinal degeneration, lyophilised and the distribution of Ca, Fe and K mapped by PIXE | 74 |
| Cd | Biological samples (CRMs) | AA;ETA;Sl, L | Ultrasonication was used to assist extraction of metals into HNO3. This approach was compared with slurry sampling and with digestion and it provided superior LODs and precision. The furnace was pre-treated with a W–Rh modifier | 3 |
| Cd | Liver | MS;ICP;HPLC MS;ES-HPLC | Cytosol from liver homogenate was purified by SEC. Cd-macromolecules were then separated by HPLC with parallel ICP-MS and ES-MS detection | 68 |
| Cd | Tissues | XRF;-;S | In vivo measurements of Cd, Hg and Pb were reviewed | 41 |
| Cd | Potable water, biological SRMs | AA;F, air–C2H2;L | Samples were acidified, then merged with 0.1% ammonium diethyldithiophosphate and the complexes adsorbed on a C18 conical column. The complexes were back flushed with ethanol for introduction into the FAA spectrometer. Factors for Cd, Cu and Pb were between 25–86 and LODs in the range 2–7 ng l−1 | 126 |
| Cd | Drinking water | AA;ETA;tungsten coil | Cd, Cu and Pb were simultaneously determined at LODs of 0.2, 0.8 and 3.0 g l−1, respectively, using a tungsten coil atomiser. The instrument, which used a charge coupled device spectrometer as detector, performed well when compared with conventional ETAAS | 174 |
| Cd | Baby foods | AA;ETA;Sl | Slurries were prepared in 0.1% Triton X-100–30% H2O2–1% HNO3 with matrix modifiers of Ni, Ni + NH4H2PO4 and NH4H2PO4 alone for Se, Pb and Cd, respectively. Standard additions calibration was required for the Cd determination | 140 |
| Cd | Flour | AA;F, air–C2H2;L | Using an atom trap and derivative signal processing an LOD of 0.019 µg l−1 was achieved, a 2–3 order of magnitude improvement over conventional FAAS | 182 |
| Cd | Seafood products | AA;ETA;Sl | Samples were slurried in Triton X-100 and the use of NH4H2PO4
as matrix modifier allowed ash temperatures of up to 600°C to
be used. The performance of the method was verified by use of CRMs | 139 |
| Cd | Foodstuffs, CRMs | AA;ETA;L | Cd and Pb were determined simultaneously using a transversely
heated atomizer with Zeeman-effect background correction. Samples, 0.5 g,
were microwave digested in 5 ml concentrated HNO3. Pyrolysis
and atomization temperatures were 750 and 1600°C, respectively,
for the simultaneous determination | 136 |
| Cd | Animal derived foodstuffs | AA;ETA;L | W–Rh and Zr–Ir modifiers were compared with PO4–Mg modifier systems. The performance of all the systems employed was similar, although the W–Rh allowed slightly higher pyrolysis temperatures | 138 |
| Cd | Cereals, pulses | MS;ICP;L | The Cd and Pb levels were determined in a range of cereals and pulses purchased in North Eastern Chinese markets. The highest levels found were 54.3 ng g−1 Pb in foxtail millet and 73.5 ng g−1 Cd in soybean | 152 |
| Cd | Brassicas | PIXE;-;- | PIXE and STIM were used to investigate Cd uptake and elemental distribution in Cd-stressed plants | 183 |
| Ce | Hair, wheat flour (CRMs) | MS;ICP;L | Concentrations of Ce, Nd and Sm in 2 CRMs were measured using an ID approach | 98 |
| Co | Biological specimens (CRMs) | AA;ETA;L | A laboratory-made PTFE vessel with 4 cups was made to fit into an open microwave digestion flask. 30 mg sample and 150 µl H2O or H2O2 were placed into each cup with HNO3 at the base of the flask. Partial digestion and extraction was achieved by the vapour phase during heating and the supernatant taken for analysis | 8 |
| Cr | Plasma | AA;ETA;L | CrIII was separated from CrVI by extraction using a two-phase aqueous system—isopropyl alcohol–(NH4)2SO4 + NH4SCN | 69 |
| Cr | Infant formula, dietetic milk | AA;ETA;LC | CrVI was found in the range <10–75 ng g−1 in commercial brands of infant formula and dietetic milk. The CrVI was isolated using an NH2 ion exchange column and ETAAS for final measurement. The LOD was 1.8 µg l−1 | 143 |
| Cr | Foods | AA;F, air–C2H2;L | CrIII was determined following oxidation using KMnO4 | 120 |
| Cr | Drinking water | MS;ICP;LC | Coupled IC-ICP-MS, using Rh as internal standard, allowed the determination of both CrIII and CrVI at an LOD of 0.1 µg l−1. The separation took 3 min. The optimum conditions required to maintain species stability were discussed | 132 |
| Cu | Serum | MS;ICP;SEC | Total concentrations were measured after dilution 1 + 19 with 0.1 M HNO3. Species with firmly-bound and loosely-bound metal were separated using Chelex-100 and SEC with Superose 12HR | 116 |
| Cu | Teeth | MS;ICP;LA | See Ag, ref. 21 | 21 |
| Cu | Biological samples (CRMs) | AA;ETA;Sl, L | See Cd, ref. 3 | 3 |
| Cu | Skin | XRF;-;S | Instrumental conditions were described for measuring Cu, Fe and Zn with LODs of 5, 20 and 10 µg g−1, respectively | 50 |
| Cu | Milk, infant formula | AA;ETA;L AA;F, air–C2H2;L | Concentrations in the bioavailable fractions of the named samples were determined using ETAAS for Cu and FAAS for Fe and Zn. Two different gastric pHs were studied | 184 |
| Cu | Breast milk, infant formula | AA;ETA;HPLC | Cu was speciated in the low molecular weight fraction of milk whey using SEC-HPLC-ETAAS. In breast milk Cu was found in the 15 and 76 kDa fractions and in cow milk-based infant formula in the 14 and 38 kDa fractions | 130 |
| Cu | Potable water, biological SRMs | AA;F, air–C2H2;L | See Cd, ref. 126 | 126 |
| Cu | Drinking water | AA;ETA;tungsten coil | See Cd, ref. 174 | 174 |
| Fe | Biological samples (CRMs) | AA;ETA;L | See Co, ref. 8 | 8 |
| Fe | Eye tissue | XRF;-;S | See Ca, ref. 74 | 74 |
| Fe | Skin | XRF;-;S | Conditions to detect Fe in skin phantoms were investigated and an LOD of 15 ppm was obtained. This is suitable to detect increased Fe in skin of patients with thalassaemia | 73 |
| Fe | Skin | XRF;-;S | See Cu, ref. 50 | 50 |
| Fe | Breast milk, infant formula | AA;ETA;L | Speciation of Fe in milk was performed using SEC-HPLC with H2O as the mobile phase. Fe was found to be principally associated with the 3 and 76 kDa fraction in the milk and more irregularly distributed in the formulae. The authors suggested new formulas should be developed to more closely match the Fe distribution in human milk. See also ref. 130 | 129 |
| Fe | Milk, infant formula | AA;ETA;L AA;F, air–C2H2;L | See Cu, ref. 184 | 184 |
| Fe | Grape juice, wines, other alcoholic beverages | AA;ETA;L | A method was developed for routine quality control of samples produced in Spain. HNO3–H2SO4 was found to be the best digestion medium | 141 |
| Fe | Meat | MS;ICP;HPLC | SEC-high resolution ICP-MS was used to determine metalloproteins in beef and to deduce the effect of cooking on the speciation. In uncooked meat the Fe was found in myoglobin. On cooking Fe was still associated with myoglobin, but also 2 additional unidentified proteins | 128 |
| Ge | Clinical specimens | AA;ETA;L MS;MIP;L | Samples were digested with HNO3–HClO4. The two methods provided comparable results but a lower LOD was given by MIP-MS | 34 |
| Hg | Blood | AA;CV;GC | Inorganic Hg in the sample, within a headspace vial, was
reduced and the atomic vapour carried by a flow of N2 to the quartz
flow-through cell. A separate sample in a head space vial was treated with
iodoacetic acid and H2SO4 and the methylmercury injected
onto the GC column. After elution with He the gas passed into the quartz tube
at 1000°C for measurement of the Hg | 91 |
| Hg | Biological specimens (CRMs) | AA;CV;FI | Samples were solubilized with TMAH and the inorganic Hg determined using an FI system | 6 |
| Hg | Biological samples (CRMs) | AA;-;S | Samples were pyrolyzed at 750°C in an O2
atmosphere and the Hg collected on a gold-amalgamator. Following thermal desorption,
measurements were made with a silicon UV diode detector | 185 |
| Hg | Urine | AA;CV;L | Samples diluted 1 + 9 with HNO3.
A portion was taken into an FI system for reduction and measurement. Organomercury
compounds were pre-oxidized by heating with H2SO4 and
KMnO4 for 30 min at 80–100°C. An analysis
rate of 30–40 samples h−1 was reported | 87,186 |
| Hg | Urine | MS;ICP;CV | A laboratory-built vapour generator was described with ID calibration. The LOD was 0.07 ng ml−1 | 88 |
| Hg | Biological specimens | AE;GD;LC | Organomercury and organolead species were separated by LC, detected and quantified by particle beam-hollow cathode GD-AES | 187 |
| Hg | Biological tissues (CRMs) | MS;ICP;S | Powdered sample was leached into 3 M HCl. The vial was sealed and the headspace sampled by solid-phase microextraction using a fibre support coated with polydimethylsiloxane/divinylbenzene. Hg was released by thermal desorption into the ICP | 90 |
| Hg | Biological tissues | MS;ICP;GC | Conditions were investigated for Grignard butylation, Na(C2H5)4B ethylation and propylation with Na(C3H7)4B as derivatization methods prior to the GC separation of Hg species. A novel interface to link the gas chromatograph to the ICP was described | 89 |
| Hg | Teeth | MS;ICP;LA | See Ag, ref. 21 | 21 |
| Hg | Tissues | XRF;-;S | See Cd, ref. 41 | 41 |
| Hg | Wine | AA;CV;FI | Using a continuous flow system, LODs of <5 ng l−1 were achieved (in German) | 162 |
| Hg | Fish | -;-;- | A review of the application of atomic spectrometry procedures for the determination of Hg in fish | 188 |
| Hg | Fish | AA;CV;L | CVAAS was used to confirm the applicability of a non-instrumental method of Hg determination, which involved digesting the sample, and subsequent collection on paper of the vapour released following treatment with SnCl2. The paper was impregnated with an emulsion of Cu2I2–3 % carboxymethylcellulose–MgCl2. A coloured complex of Cu2(HgI4) was formed, the intensity of the colour being proportional to the Hg concentration | 161 |
| Hg | Dogfish CRM | AF;CV;GC AA;CV;L | The study reported the role of Hg speciation in protective methods of Se. The sample was homogenised with 10 mM Tris hydrochloride buffer and centrifuged. The soluble portion was analysed by SEC to identify the protein fractions. Total Hg, methylmercury and Se were determined in the whole sample and the pellet and supernatant | 164 |
| Hg | Mussel CRM | AA;CV;FI | Total Hg was determined following HNO3–H2O2 digestion, NaBH4 reduction and FI–CVAAS measurement. A separate sub-sample was ultrasonicated in an HCl medium and inorganic Hg determined following selective reduction using SnCl2 | 163 |
| Hg | Foods | MS;ICP;L AA;CV;L AF;CV;GC AE;CV;L | Total Hg was determined on microwave HNO3–H2O2 digests. Hg species were measured following either solvent or trypsin-mediated extraction. Either GC-pyrolysis-AFS or selective solvent extraction achieved separation | 165 |
| I | Serum, urine | MS;ICP;CE | Iodide, iodate, T4 and T3 were separated and detected using this hyphenated technique | 25 |
| I | Milk | AA;ETA;L | Iodide was oxidised to I2 and the I2 was then distilled using microwave heating. The distillation was performed using the iodide-catalysed Sandell–Kolthoff reaction between CeIV and AsIII. The distilled I2 was then reduced using hydroxylamine hydrochloride and determined using ETAAS. The measurement of I2 was performed indirectly via the Hg in the complex formed between iodide, HgII and 2,2′-dipyridyl, which was selectively extracted into IBMK. The LOD was 0.3 µg l−1 and distillation efficiencies better than 87% | 158,159 |
| K | Serum | AE;F;L | Performance of reference methods was assessed. Imprecision was <1.5% and bias was <0.65% | 97 |
| K | Eye tissue | XRF;-;S | See Ca, ref. 74 | 74 |
| Mg | Biological fluids | AA;F;L AA;ETA;L AE;ICP;L | Analytical developments and the biological role of Mg were reviewed | 85 |
| Nd | Hair, wheat flour (CRMs) | MS;ICP;L | Concentrations of Ce, Nd and Sm in 2 CRMs were measured using an ID approach | 98 |
| Ni | Lung | AA;ETA;L | Concentrations were measured in tissue from different regions of lung from former Ni refinery workers | 93 |
| Ni | Urine | AA;ETA;L | Samples collected from individuals living in communities around a Ni refinery were analysed | 92 |
| Pb | Biological samples (CRMs) | AA;ETA;Sl, L | See Cd, ref. 3 | 3 |
| Pb | Urine | AA;ETA;L | Normal concentrations were measured in diluted urine. PdCl2 was used as chemical modifier | 76 |
| Pb | Urine, blood, plasma, bone | AA;ETA;L MS;ICP;L XRF;-;S | Samples were collected after treatment with a chelating agent | 80 |
| Pb | Blood, bone | AA;ETA;L XRF;-;S | Pb in blood, tibia and patella was determined and associations with the conduction of impulses in heart muscle investigated. Accumulated Pb may influence cardiac conduction | 81 |
| Pb | Biological specimens | AE;GD;LC | See Hg, ref. 187 | 187 |
| Pb | Bone, teeth | XRF;-;S | Samples from 11th century skeletons buried in a lead-mining region were analysed by PIXE. Concentrations at the surface and the core of specimens were 1000 and 5–10 ppm, respectively | 47 |
| Pb | Bone | XRF;-;S | Application of the technique to the investigation of hypertension, osteoporosis and foetal exposure to Pb was discussed | 82 |
| Pb | Bone | XRF;-;- | Computer modelling was used to investigate the effect of Pb concentration on elastic scattering intensities. The results showed that corrections for quantity of bone were affected when Pb was <1% | 53 |
| Pb | Bone | XRF;-;S | See Cd, ref. 41 | 41 |
| Pb | Bone | XRF;-;S | Applications of Monte Carlo simulation to improve in vivo measurements were described | 51,52 |
| Pb | Tissues | XRF;-;S | Good correlation was obtained between measurements in exposed bone and in bone surrounded by muscle and skin | 54 |
| Pb | Biological tissues | MS;ICP;ETV | Sample, mixed with (NH4)2HPO4, was placed into a tungsten boat furnace. TMAH was added for preliminary solubilization and the Pb was then vaporized into the ICP | 75 |
| Pb | Potable water, biological SRMs | AA;F, air–C2H2;L | See Cd, ref. 126 | 126 |
| Pb | Drinking water | AA;ETA;tungsten coil | See Cd, ref. 174 | 174 |
| Pb | Baby foods | AA;ETA;Sl | See Cd, ref. 140 | 140 |
| Pb | Foodstuffs, CRMs | AA;ETA;L | See Cd, ref. 136 | 136 |
| Pb | Cereals, pulses | MS;ICP;L | See Cd, ref. 152 | 152 |
| Pb | Port wine | MS;ICP;L | Port wine, 120 ml, and 30% H2O2, 120 µl, were UV-irradiated for 1.5 h. The sample was then filtered, diluted 10-fold with 0.5% HNO3 and Pb isotope ratios determined. Precision was sufficient to differentiate natural variations in isotope abundance. Other preparation methods involving UV treatment and microwave digestion were also considered | 124 |
| Pb | Alcoholic beverages | MS;ICP;L | Using double-focusing sector ICP-MS no pre-treatment other than acidification and dilution was required. LODs were in the fg ml−1 region. Excellent precision was found for Pb isotope ratios, outperforming quadrupole instruments | 148 |
| Pb | Wines | MS;ICP;L | TOF-ICP-MS was used to determine Pb concentration and isotope ratios in 20 wines from 5 continents. The wines were microwave digested in HNO3, the Pb extracted into hexane using diethyl dithiophosphate, the hexane evaporated and the residue re-dissolved in 0.5% HNO3. The Pb isotope ratios obtained by a quadrupole ICP-MS were not in agreement with those obtained using either a TOF or a multicollector ICP-MS | 145 |
| Pt | DNA | XRF;-;L | TXRF was shown to be suitable for measuring Pt incorporation into DNA | 96 |
| Pu | Urine | AMS;-;- | Samples from youths and from adults with occupational exposure were analysed. Absorption, by a volunteer, of Pu from ingested Irish Sea sediment was also measured | 37 |
| REEs | Serum | MS;ICP;L | Samples were digested with HNO3 and HClO4. REEs were concentrated with Chelex 100 at pH 6. The reaction temperature and the ratio of resin to sample were optimized to ensure quantitative recoveries of all the elements. LODs were <0.2 × 10−12 g ml−1 | 11 |
| Se | Plasma, liver, kidney | MS;ICP;HPLC | Endogenously labelled selenoproteins were separated by SEC. The kinetics of incorporation of Se into proteins and release into the circulation were described | 189 |
| Se | Serum, water (CRMs) | MS;ICP;ETV | Polyatomic interferences associated with Cl− and other ions were removed when the sample was vaporized into the ICP by ETV. The methodological uncertainties were also presented | 101 |
| Se | Plasma selenoprotein P | MS;ICP;L | Selenoprotein P was separated by immobilised metal–ion affinity chromatography from other plasma proteins. 82Se was then measured and the LOD was 2 µg l−1 | 190 |
| Se | Serum | AA;ETA;L | Concentrations in samples from children were increased following a programme for supplementation of fertiliser | 104 |
| Se | Blood | AA;ETA;L AE;ICP;HG | Se in blood and blood fractions was measured with Pd and Mg(NO3)2 as the chemical modifier | 99 |
| Se | Urine | MS;ICP;IC | Four Se species were separated. Particular interest was focused on the trimethylselonium ion | 191 |
| Se | Urine | MS;ICP;IC | Trimethylselonium ion was separated from other Se species on an Ionpac CS5 column. Measurements were made using the 82Se isotope | 105 |
| Se | Urine | MS;ICP;IC | Selenite, selenate and selenomethionine were separated on an IonPac AG11 in series with an AS anion-exchange column. The 80Se isotope was used for quantitation | 106 (see also 105) |
| Se | Urine | MS;MIP;HPLC-HG | Using a high power N2-MIP selenite and selenomethionine were determined, using 80Se, following separation by HPLC on a PRP-X100 column | 33 |
| Se | Urine | AA;ETA;L | See As, ref. 63 | 63 |
| Se | Biological samples | MS;ICP;LC | Improved separation of selenoamino acids was accomplished by increased trifluoroacetate concentration in the mobile phase and a smaller ES chamber size | 192 |
| Se | Biological samples | AA;Hy;IC | In a complex system Se species were separated by IC then treated with HBr/BrO3− to effect conversion to selenate for reduction to the hydride and measurement. Interferences were problematic and the extraction of exogenous and endogenous Se were not the same | 108 |
| Se | Hair | AA;Hy;L | Digestion of samples with HNO3–H2O2 or HNO3–HClO4 gave satisfactory results whereas HNO3–H2SO4 and HNO3–H3PO4 were unreliable | 103 |
| Se | Amino acids | MS;ICP;HPLC | ICP-MS with a dynamic reaction cell, using CH4 as sheath gas and 3% v/v CH3OH diluent, removed isotopic interferences and afforded enhanced sensitivity compared with conventional instrumentation. The LOD was 6 pg ml−1 | 19 |
| Se | Tissues | MS;ICP;HPLC | Se species were extracted from samples by an enzymic hydrolysis using subtilisin. Trimethylselonium, selenocysteine, selenomethionein and selenoethionein were separated and measured. Compared with determination of total Se only 30% was recovered by this procedure | 193 |
| Se | Foods | AA;Hy;FI | See As, ref. 151 | 151 |
| Se | Nutritional supplements | AF;Hy;FI | Samples were HNO3–H2O2 digested within 10 min using focused microwave digestion and Se reduced and measured using a continuous FI–HGAAS system. The LOD was 0.4 ng ml−1 | 166 |
| Se | Food, biological samples | AA;ETA;Sl | Se was extracted into benzene using HCl containing KI. Co2O3 was added to the benzene to collect the Se. The Co2O3 was then extracted from the benzene by vacuum filtration and suspended in 1 ml of H2O. An aliquot of this slurry was then introduced onto a tungsten coil furnace. Recoveries were 100% for SeIV and SeVI and the LOD 16 µg l−1 | 119 |
| Se | Infant formulas, milk whey | AA;ETA;HPLC | Se species were determined in whey protein fractions using SEC-HG-ETAAS. Iridium-coated tubes were used | 171 |
| Se | Baby foods | AA;ETA;Sl | See Cd, ref. 140 | 140 |
| Se | Dogfish CRM | AF;CV;GC AA;CV;L | See Hg, ref. 164 | 164 |
| Se | Fish | MS;ICP;L | Different approaches to fractionation of soluble Se species in fish were described. When SEC was used to separate the species there was evidence of interaction between the fish extracts and the column, with recoveries equating to only 70% | 170 |
| Se | Yeast | MS;ICP;HPLC | Selenoaminoacid enantiomers were separated on a glycopeptide antibiotic teicopanin-based chiral column. Resolution could be achieved in 8 min using a 2% H2O–CH3OH mobile phase. The LOD for selenomethionine enantiomers was 0.8 µg l−1 as Se. The method was applied to selenized yeast | 167 |
| Se | Garlic, onion, yeast | MS;ICP;HPLC | A crown ether HPLC column was used for the chiral separation of 9 selenoamino acids. Elevated temperatures improved resolution. Aqueous and enzymatic extraction procedures were compared | 169 |
| Se | Nutritional supplements | MS;ICP;HPLC | The procedures described in ref. 168 were used to determine D,L-selenocystine, D,L-selenomethionine and D,L-selenoethionine in 10 commercial Se supplements. Anion exchange chromatography was also used for species unretained on the chiral column. Results were found not to support label claims. | 168 |
| Si | Serum, urine, spinach, water, beer | AE;ICP;L AA;ETA;L XRF;-;- MS;ICP;L | Several methods were compared in an interlaboratory trial. The trial showed that spectrometric techniques were suitable for Si measurement, but that progress in sample pre-treatment was still required | 110 |
| Sm | Hair, wheat flour (CRMs) | MS;ICP;L | Concentrations of Ce, Nd and Sm in 2 CRMs were measured using an ID approach | 98 |
| Sn | Oyster tissue CRM | MS;ICP;HPLC | TBT was extracted using 0.5 M sodium acetate–1.0 M CH3COOH in CH3OH and a temperature programmed microwave oven. TBT was measured using HPLC-ICP-IDMS and a 117Sn-enriched TBT standard | 131 |
| Th | Tissues | MS;ICP;L | Tissues taken from thorotrast patients at autopsy were analysed to determine concentrations following treatment | 114 |
| Ti | Plasma | AA;-;- | Pharmacokinetics of Ti, following administration of titanocene dichloride to patients with solid tumours, were characterized | 111 |
| U | Urine | MS;ICP;L | Accurate, sensitive measurements were made without any sample preparation | 113 |
| U | Urine | MS;ICP;L | U isotopes were measured in a study to identify individuals with exposure to depleted uranium | 112 |
| U | Waters | MS;ICP;L | U was determined directly without sample pre-treatment using Rh as internal standard. The LOD was 2 ng l−1. The method was applied to mineral and tap water from different parts of Spain and Morocco | 150 |
| V | Milk, infant formula | AA;ETA;L | 30 µl portions of milk were injected into
a heated furnace, with a drying and ashing stage occurring between each injection.
BaF2 was added as chemical modifier, stabilizing the V up to 2000°C.
The LODS were 0.5, 0.7 and 0.6 µg l−1
for cows’ milk, human milk and infant formulae, respectively | 127 |
| W | Plasma | AE;ICP;L | Concentrations from 100 ng ml−1 to 90 µg ml−1 were measured with a method used for a pharmacokinetic study | 13 |
| Zn | Serum | MS;ICP;SEC | See Cu, ref. 116 | 116 |
| Zn | Serum, urine, faeces | MS;ICP;L | Zn isotopes were determined using HR-ICP-MS | 28 |
| Zn | Skin | XRF;-;S | See Cu, ref. 50 | 50 |
| Zn | Milk fat | AA;F, air–C2H2;L | Milk samples were ultracentrifuged for 1 h, the upper fat layer removed and treated with the surfactant sodium dodecylbenzosulfonate. 10 zirconia beads were added, the samples stirred in a tube stirrer for 1 min and the emulsion analysed by FAAS. The LOD was 2.3 µg l−1 for cows’ milk and 2.9 µg l−1 for infant formula. Other surfactants were also considered | 133 |
| Zn | Milk, infant formula | AA;ETA;L AA;F, air–C2H2;L | See Cu, ref. 184 | 184 |
| Various | Clinical and biological samples, foods | -;-;- | New analytical developments in and applications of atomic spectrometry to the analysis of biological materials were reviewed | 1 |
| Various | Clinical and biological samples | XRF;-;- | Analytical developments and new applications of XRF to the analysis of biological materials were presented | 40 |
| Various | Clinical samples, foods | MS;ICP;L | A review of the analytical potential of double-focusing ICP-MS, with particular reference to speciation studies and ID analysis | 26 |
| Various | Hair | -;-;- | This is an extensive handbook detailing the clinical importance of metals together with sample collection, analysis and quality assurance | 2 |
| Various (13) | Serum, urine | MS;ICP;L AA;ETA;L | Samples were subject to UV photolysis followed by dilution in 0.5% HNO3. Standard additions calibration was employed. Using ICP-SFMS at medium and low resolution, accurate measurements for occupational monitoring were achieved | 30 |
| Various (9) | Placenta, blood | MS;ICP;L | Homogenized samples were digested with HNO3 (Ca, Cd, Co, Cu, Mn, Mo, Pb, Se, Zn) | 18 |
| Various (57) | Blood | MS;ICP;L | Microwave heating was used to digest the samples and the matrix matched standards. Factors affecting LODs were discussed | 29 |
| Various (6) | Blood | AE;CCMP;L | Blood, 2 µl, was placed on a tungsten electrode, dried, ashed and atomized into the plasma (K, Li, Mg, Mn, Na) | 14 |
| Various (7) | Urine | MS;ICP;Hy | An FI system was described for the simultaneous determination of As, Bi, Ge, Hg, Sb, Se and Sn | 39 |
| Various (9) | Infant formulae | AE;ICP;L | Samples and standards were prepared in an aqueous solution, 10% v/v, of mixed tertiary amines containing EDTA (Ca, Cu, Fe, K, Mg, Mn, Na, P, Zn) | 176 |
| Various (18) | Human milk | MS;ICP;L AA;Hy;L | ICP-MS and HGAAS (for Se) were used to measure changes in 55 milk samples from 46 healthy mothers during lactating periods lasting up to 293 days after birth. The authors concluded that apart from Se the daily intakes of essential trace elements in fully breast fed infants were below dietary recommendations. The levels of Be, Bi, Cs, La, Rb and Tl were the first to be reported for human milk, it was claimed | 55 |
| Various (15) | Human milk | MS;ICP;L | A range of essential and toxic elements were determined using sector field ICP-MS in 27 transitory and mature human milk samples and 4 selected infant formulas. The authors claimed their results for Ag, Au, Pt, Sc, Ti and V were the first to be reported for human milk and infant formula | 147 |
| Various (15) | Human milk | MS;ICP;L | A further paper from the research group who published ref. 148, this time concentrating on signal enhancement and spectral interference reduction. To this end, microconcentric nebulizers, membrane desolvation and torch shielding were applied to their studies | 31 |
| Various (15) | Milk whey | MS;ICP;L | Whey samples were diluted 1 + 4 for minor elements and 1 + 1999 for major elements with ultra-pure water and Ga, Y, Rh, In and Tl added as internal standards. Lower backgrounds and greater sensitivity were found using double focusing rather than quadrupole instruments | 149 |
| Various (8) | Brain | MS;ICP;L AA;ETA;L | Different brain regions were analysed (Cd, Cu, Hg, Li, Mn, Pb, Mn, Zn) | 17 |
| Various (14) | Teeth | MS;ICP;S | Profiles of deposition of elements throughout teeth were examined using LA-ICP-MS | 20 |
| Various | Single cells | MS;ICP;LA | The sample was digested with peptidase and 150 nl applied to a capillary electrophoresis inlet. Fractions from the outlet were collected as spots on a support medium. The dried spots were used for laser ablation and ionization into a TOF mass spectrometer | 194 |
| Various (18) | Hair, shampoos | MS;ICP;L | Shampoos and hair conditioners were diluted 1∶100
in dilute HNO3. Hair was digested with HNO3 at 120°C
in a PTFE container. Except for Se, elements in shampoos did not contaminate
the hair | 56 |
| Various (5) | Hair | AA;ETA;L AA;CV;L | Acids, reagent volumes, time and temperature were investigated using a multivariate strategy to determine optimal leaching conditions. Accurate results were obtained for CRMs (Cd, Cr, Hg, Pb, Se) | 4 |
| Various (8) | Hair, mussel | AA;F;L AA, ETA;L | Conditions to optimize the use of Pronase E for enzymatic sample pre-treatment were investigated. Results were compared with those given by acid digestion and were satisfactory for mussel but not for hair (Ag, As, Cd, Cu, Fe, Mg, Pb, Zn) | 10 |
| Various (6) | Biological specimens (CRMs) | AA;ETA;L | TMAH solubilization was described. Results were in good agreement with certified values (Cd, Cr, Cu, Mn, Ni, Pb) | 7 |
| Various (9) | Biological specimens | MS;ICP;L | Tissues were prepared by digestion under pressure and fluids were diluted. In was added for internal standardization. Polyatomic interferences were eliminated with magnetic sector ICP-MS (Co, Cr, Cu, Fe, Mn, Ni, Sc, V, Zn) | 27 |
| Various (9) | Biological samples (CRMs) | MS;ICP;FI | The described arrangement consisted of an FI manifold with a knotted reactor to effect APDC extraction with CH3OH and elution into an axial ICP. The detector was a TOF mass spectrometer (Ag, Cd, Co, Cu, In, Mo, Ni, Pb, Sb) | 195 |
| Various (13) | Biological samples | MS;ICP;Hy | A moving bed reactor for generation of volatile species was described. The nebulizer design resulted in the elimination of transition metal interferences | 102 |
| Various (5) | Chinese medicine | AE;ICP;Sl | Powdered sample was mixed with a 60% PTFE emulsion, diluted with H2O and sonicated. Standard additions calibration was used for the measurements (Cd, Cr, Cu, Mn, Ti) | 196 |
| Various (5) | Potable water | AA;ETA;L | 20 µl of sample and 5 µl of mixed Pd–Mg modifier were injected into the furnace and Cd, Cr, Cu, Ni and Pb determined simultaneously at LODs of 0.01, 0.02, 0.09, 0.18 and 0.11 ppb, respectively | 137 |
| Various | Water | MS;ICP;L | Application of sector field ICP-MS to ultra-trace element analysis was discussed | 146 |
| Various (REE) | Alcoholic beverages | MS;ICP;L | Using the method described in Pb, ref. 148, REE and actinides were determined | 148 |
| Various (REE) | Wines | MS;ICP;L | A diluent containing 4.88 ml H2O + 0.1 ml HNO3 + 0.02 ml In was added to 5 ml of sample and the solution nebulized. LODS were <0.1 µg l−1 and <2 ng l−1 for 14 REEs determined by quadrupole and sector field instruments, respectively. Microwave digestion of the sample in HNO3 was found to improve accuracy | 178 |
| Various (17) | Vegetables | AE;ICP;L | High pressure microwave digestion, conventional wet digestion and dry ashing were used for sample preparation. Dry ashing was found to lead to losses of some elements and the microwave procedure was declared to be the most appropriate method | 125 |
| Various (12) | Honey | AE;ICP;L MS;ICP;L | Elements As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Pt, Sn, V and Zn were determined in several types of honey. Differences in elemental levels in freshly collected, extracted, ripened and sealed honey were discussed | 177 |
| Various (5) | Serum, brain | XRF;-;- | Tissue samples were homogenized and dispersed in 5% HNO3. Compton scattering intensity was used for internal standardization (Cu, Fe, Pt, Se and Zn) | 42 |
| Various | Brain cells | XRF;-;S | Using SR-XRF, metals in a single cell from patients with Parkinson’s disease were determined | 45 |
| Various (9) | Cucumber plants | TXRF;-;- | The effect of Cd, Ni, Pb and V on the uptake of Ca, Fe, K, Mn and Zn was investigated. Ga or Ni was used as internal standards | 123 |
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