Atomic Spectrometry Update: Clinical and biological materials, foods and beverages
Andrew Taylor†*a, Simon Branchb, David J. Hallsc, Linda M. W. Owend and Mark Whitee
aSupra-Regional Assay Service Trace Element Laboratory, Centre for Clinical Science and Measurement, School of Biological Sciences, University of Surrey, Guildford, Surrey, UK GU2 5XH. E-mail: A.Taylor@surrey.ac.uk
bThe Lord Rank Centre, R. H. M. Technology, Lincoln Road, High Wycombe, Buckinghamshire, UK HP12 3QR
cTrace Element Unit, Department of Clinical Biochemistry, Glasgow Royal Infirmary University NHS Trust, Castle Street, Glasgow, UK G4 0SF
dMinistry of Agriculture, Fisheries and Food, Central Science Laboratory, Sand Hutton, York, UK YO41 1LZ
eHealth and Safety Laboratory, Health and Safety Executive, Broad Lane, Sheffield, UK S3 7HQ
First published on UnassignedUnassigned24th March 2000
Abstract
This is the fifteenth ASU to review literature relevant to clinical and biological specimens, foods and beverages. Two of the original three writers are still involved in preparing this Update and the other authors have also been part of the team for several years. However, in accepting a new role within the MAFF Central Science Laboratory Linda Owen will no longer be able to write for the review and we shall miss her valuable contribution. Although there have been many changes and important innovations during the fifteen years most have been gradual developments which were discerned after a few years' consolidation. As far as this year is concerned, those items which we identified in the last review—in vivo analyses by XRF, high resolution ICP-MS and electrospray MS—are featured again. Perhaps the most exciting of the emerging techniques is capillary electrophoresis for separation/speciation coupled to a detection system such as ICP-MS. The potential of these approaches has been hinted at in the last year or so but, with the development of effective coupling technology, results are now beginning to appear.
1 Analysis of clinical and biological materials
This Update reviews the literature and relevant conference presentations appearing in the year up to October 1999. These are summarized in Table 1, while the text describes the more important publications and covers themes of current interest. Our previous Update appeared in April 1999.11.1 General reviews and articles
Speciation again features strongly in this Update. A review by Templeton2 explored the rationale for speciation in toxicology and clinical science through knowledge of the good and harmful effects on humans of different chemical species. Sanz-Medel3 reviewed progress in his research group in the speciation of Al and Si in human serum by techniques ranging from ultrafiltration with AAS determination to HPLC coupled to high resolution ICP-MS (HR-ICP-MS).A valuable review of heavy metal poisoning and its laboratory investigation by the late Dianne Baldwin and by William Marshall4 covers general aspects of metal toxicity and then deals specifically with As, Bi, Cd, Hg, Pb, Sb, Sn and Tl. Particularly interesting are the case histories quoted for most elements.
Recent work at the University of Massachusetts, USA, on high-performance flow-based, sample pretreatment and introduction procedures for atomic spectrometry was reviewed by Tyson.5 Examples in the clinical field included the determination of Se in urine by HG and ETAAS incorporating stopped flow microwave digestion and the determination of Pb in urine by HGAAS in which added Sc prevented interference from chelating agents.
1.2 Sampling and sample preparation
Details of the high temperature-high pressure digestion flow system developed by Gräber and Berndt7 have now been published. In this, liquid or slurried samples were mixed with 20% HNO3 and forced by a HPLC pump through a digestion coil heated to 260![[thin space (1/6-em)]](https://www.rsc.org/images/entities/char_2009.gif)
°C. The best kind of tubing found was stainless steel lined with PTFE, which resisted the acid attack and was safe at the pressures of >200 bar reached. The efficiency of oxidation was 90–99% and, for most elements and matrices, satisfactory recoveries of major, minor and trace elements were demonstrated. Further development was planned with Pt–Ir capillaries which would allow temperatures of 300–400°C to be reached.
In a non-pressurized flow digestion system for determination of Bi in blood and urine, Burguera et al.8 injected samples into a carrier of 0.1 M HNO3 which merged with 0.5 M HNO3 for digestion in a knotted coil irradiated with microwaves at 50 W. The Bi was collected by precipitation as the hydroxide for subsequent determination by ETAAS after re-dissolution.
1.3 Developments in and applications of multi-element techniques
Some of the problems in electrothermal vaporization seem to have been overcome in a devicedescribed by Okamato.20 A tungsten-boat furnace allowed more reasonable weights to be used (about 10 mg) and calibration with aqueous standards was possible. Samples, ground with (NH4)2HPO4 as a chemical modifier, were weighed into tungsten cuvettes and treated with TMAH for in situ digestion with heating at 130°C. After further heating at 250°C to remove excess TMAH and then 550°C to remove some (NH4)2HPO4, Cd was volatilised at 2000°C and transported into the ICP. Successful determination of Cd in a range of biological CRMs was demonstrated.
1.3.2.1 Reviews.. The coupling of size-exclusion HPLC with ICP-MS for the speciation of trace elements in biological systems was reviewed by Makarov and Szpunar.21
1.3.2.2 Multi-element determination by quadrupole ICP-MS (Q-ICP-MS).. Simultaneous speciation of selenium and arsenic in tuna fish, mussels and human urine was described by Le et al.22 A 20 µl aliquot of urine or an MeOH:H2O extract of tuna fish or mussels was injected onto a HPLC reversed-phase C18 column at 70
°C for separation followed by detection of As and Se by Q-ICP-MS at m/z 75, 77 and 78, allowing identification of potential interfering species such as ArCl.In connection with the hypothesis that sudden infant death syndrome (SIDS) is related to exposure to toxic elements, Patriarca et al.23 measured, by ICP-MS, concentrations of Ag, Cd, Co, Pb and Sb in 157 livers from infants who had died from SIDS or other known causes. No significant difference in concentration was found for any element between SIDS and non-SIDs cases but the data provide a valuable source of reference values for newborns and infants below the age of two.
1.3.2.3 Speciation with electrophoresis and ICP-MS.. Although combinations of HPLC and ICP-MS have frequently featured in previous Updates, the combination of electrophoresis with ICP-MS is relatively new. Electrophoresis is very efficient at separating proteins in biological samples and is thus useful in studying the binding of trace elements to proteins. In flat bed polyacrylamide gel electrophoresis, the problem is is how to identify and quantify the metals on the gel layer. Joyce et al.24 used laser ablation ICP-MS for a study on Au distribution in the serum of patients treated with aurothiolate drugs for rheumatoid arthritis, whereas Lustig et al.25 cut the gels into segments which were digested with aqua regia and analysed by HR-ICP-MS. They studied separation of Ga and In in serum from rabbits injected with these elements. As an alternative approach, radioisotopes of CrIII, PtII and V were incubated in vitro with human serum and, after separation, the elements were detected by autoradiography. Some problems identified were artifacts caused by the release of Pt from the electrodes affecting the distribution of Pt; the formation of 198Pt40Ar clusters, which interfered in the determination of 238U by ICP-MS, and partial cleaving of the binding of Ga, In and V to transferrin caused by the electric field and pH changes.
However, the current interest seems to be in the direct coupling of capillary electrophoresis (CE) with ICP-MS. The key to a reliable interface with good sensitivity seems to be a low consumption nebulizer, such as the microconcentric nebulizer, a low volume spray chamber and avoiding suction on the capillary by making up the flow at the nebuliser interface.26–28 Good separation of the arsenic species in urine has been shown by Michalke and Schramel29 with LODs of around 15 µg l−1 for AsIII, AsV, monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) and 65 µg l−1 for arsenobetaine (AsB) and arsenocholine. In similar work, van Holderbeke et al.27 were able to get LODs of 1–2 µg l−1 for each species.
The potential of the coupling of CE with electrospray-ionization MS (CE-ESI-MS) for trace element speciation was explored by Schramel et al.30 and, in a second paper,31 compared with CE-ICP-MS for the determination of Se species. They concluded that the elemental detection method CE-ICP-MS was up to 102–103 more sensitive than molecular detection with CE-ESI-MS.
1.3.2.4 Double focusing magnetic sector ICP-MS (HR-ICP-MS).. This technique allows the determination of many of the essential and toxic elements free of the isobaric interferences that affect Q-ICP-MS. Schramel et al.32 evaluated the potential of multi-element analysis by determining a range of trace elements (Al, As, Cd, Cr, Co, Cu, Hg, Mn, Ni, Pb, Sb, Se, Tl and Zn) in urine, whole blood and serum RMs. Whole blood was pressure-digested with HNO3 but urine and serum were diluted 10-fold (or 100-fold) with a solution containing internal standards. Results were in good agreement with accepted values. Rodushkin et al.33 also digested whole blood for the determination of 50 elements using Sc, In and Lu as internal standards. Accuracy for elements suffering from interferences was improved by applying either higher resolution or mathematical correction. Simultaneous determination of Cu, Cd, Pb and Zn in urine was shown by Townsend et al.34 to be possible with a simple 10-fold dilution with an In internal standard. Highest resolution (3000) was necessary for the determination of Cu and Zn to resolve interferences but Cd and Pb were determined at resolution 300 for increased sensitivity. The method, validated on commercial RMs, was applied to a study of workers exposed to Cd and of controls. Muniz et al.35 from the University of Oviedo, Spain, similarly found it advisable to use a high resolution scan for elements liable to interferences (Al, Ca, Co, Cr, Cu, Fe, Mn, Se and Zn) and a low resolution scan for elements not subject to interferences (Cd, Mo, Pb, Rb, Sr and U) in order to obtain higher sensitivity in their method for serum samples. These were diluted five-fold with a solution containing Ga, Sc, Tl and Y as internal standards. Good results were obtained on NIST SRM Inorganic Constituents in Bovine Serum. The method was applied to analysis of samples from healthy subjects and uraemic patients.
In a further study by the Oviedo group, Bayón et al.36 explored the potential for multi-element speciation by separating proteins in human serum by fast protein LC and detecting these elements by HR-ICP-MS. The proteins, separated on an anion-exchange column using an ammonium acetate concentration gradient at the physiological pH of 7.4, were detected on-line by spectrophotometry at 295 nm. Elements without significant isobaric interference (Bi, Cd, Hg, Pb, Se and Sn) were determined at resolution 300 for best sensitivity whereas the elements As, Ca, Cu, Cr, Fe, Mn and Zn required the highest resolution (3000). Many expected protein–metal associations were found, but significant differences were found in the distribution of Zn in the sera of healthy and uraemic subjects.
1.3.2.5 Determination of isotopes by mass spectrometry.. Isotope measurements can provide useful information about sources of exposure, even in past history. For determination of 87Sr∶86Sr ratios in prehistoric skeleton bones, Latkoczy et al.37 used measurements by HR-ICP-MS, achieving a precision better than 0.03% RSD. A microconcentric nebulizer reduced the sample volume required, important in conserving valuable historic material. Sources of Pb in prehistoric, historic and contemporary Japanese were studied by Yoshinaga et al.38 using measurements of Pb isotopes in bones and teeth by ICP-MS. In prehistoric bones, the Pb concentration was low and the isotope ratio was within the range of Japanese ores, rocks and soils, but in contemporary bones, the isotope ratio was close to that of leaded gasoline, banned in the late 1970s. However, in the teeth of children born between 1985 and 1988, the Pb isotope ratio was closer to that in airborne particulate matter and refuse incineration ash. Chaudhary et al.39 concluded that the predominant source of Pb in Mexico City in recent times was the ceramic ware used in cookery. Measurements were made of isotope ratios for Pb in ceramic cookware, leaded gasoline and whole blood samples by ETV-ICP-MS. The isotope ratios found in blood and ceramic cookware were similar.
In a comparison of electron impact-MS (EI-MS) and ICP-MS for the determination of Mg isotope ratios for tracer studies in humans, Benech et al.40 found that there was no systematic difference in results but ICP-MS gave superior precision (0.01–0.06% RSD intra-day and 0.01–0.15% RSD inter-day) to EI-MS (0.14–0.45% RSD inter-day and 0.20–1.23% RSD inter-day).
1.3.2.6 Accelerator mass spectrometry.. Applications of 26Al as a tracer and accelerator MS were reviewed by Flarend and Elmore,41 including the pharmacokinetics of an Al-containing drug. The neurotoxicity of Al and its relationship to Alzheimer's disease were studied by Yumoto et al.42 using a rat model. The 26Al entered the brains of rats after a single injection and remained almost constant from 5 to 270 d. Liver concentrations decreased from 5 to 25 d after injection and then remained constant until 75 d before increasing until day 270.
The kinetics of uptake of silicon as silicic acid and its excretion were studied by Popplewell et al.,43,44 using 32Si as a tracer and measurement by AMS. The Si was isolated as SiO2 for measurement. Uptake was practically complete within 2 h while elimination appeared to occur by two simultaneous first-order processes with half-lives of 2.7 and 11.3 h. After 48 h, elimination was essentially complete.
The goal of measuring in vivo Fe in the skin of patients with β-thalassaemia was pursued by Bradley and Farquharson.45 They aimed to measure down to 10 µg g−1 of Fe in skin with realistic monitoring periods. Preliminary results with a tungsten anode X-ray tube and K-edge filtering giving an effective 8.4 keV emission indicated that, with a counting period of 1000 s, less than 10 µg g−1 of Fe could be detected in simulated skin.
Changes in trace element concentrations in cancer were the subject of two studies. Majerska et al.46 determined Ca, Cr, Cu, Fe, K, Mn, Ni, P, Pb, Rb, S, Se, Sr and Zn concentrations in cancerous and benign breast tissue by TXRF. Most element concentrations were higher in cancerous tissue. In mice inoculated with colon and melanoma cells, Feldstein et al.47 similarly found significant differences, especially for Rb, between cancerous and normal tissues. Changes in the inner organs were much smaller. Measurements were by XRF for tissue and PIXE for blood samples.
Changes in the composition of human breast milk in Taiwanese mothers over the course of a year's lactation were reported by Lin et al.53 The elements Ca, Cu, Fe, Mg and Zn were measured in 211 samples by ICP-AES. Zinc concentrations in the colostrum were higher in older mothers (age > 30 yr) than in those younger (20–30 yr). The Zn concentration in milk fell as lactation progressed.
The use of simultaneous ETAAS for multi-element determination49 was mentioned above, but L'vov and collaborators54 have shown the possibility of using such an instrument with internal standardization to improve performance. The behaviour of Pb in urine, blood and placenta samples was compared to that of Bi and Tl introduced as internal standards. Bismuth was found to be an effective internal standard, improving precision markedly and allowing simple aqueous calibration, thus avoiding time-consuming standard additions.
In a study of concentrations of Al, Ca, Cd, Cr, Cu, Fe, Mg, Pb, Sr and Zn in bone biopsies of patients with renal failure, D'Haese et al.55 found increased concentrations of Al, Cd and Cr. Ratios to Ca of Al, Cr, Mg, Sr and Zn were also significantly higher. Whereas bone Al correlated with time of dialysis, bone Fe, Mg and Sr seemed related to the patient's age. Measurements were by AAS.
1.4 Developments in single element techniques
Applications using the tungsten-coil atomizer have been described in the past review year but there have been no major developments. Salido et al.56 used chelation with APDC and extraction into IBMK for the determination of Pb in blood using their portable bench-top Pb analyser. For marker studies of digestion in sheep, Lima et al.57 developed a method for determining Yb in faeces. After ashing, the residue was dissolved in HCl and 10 µl dispensed onto a tungsten-coil. The LOD was 0.35 µg l−1 and more than 300 firings could be obtained from one coil.The use of laser-excited AFS with electrothermal atomization (ETA-LEAFS) for the determination of Se in serum was developed by Swart and Simeonsson.58 The high sensitivity and selectivity of the method allowed a 10- or 20-fold dilution of samples and direct calibration with aqueous standards. A Pd–Mg modifier was used to reduce pre-atomization losses. Accuracy was demonstrated by determination of Se in an NIST Bovine Serum SRM. In their instrument, Aucelio et al.59 used a Katskov graphite filter furnace to enable them to use direct aqueous calibration in the determination of Pb in blood by ETA-LEAFS. The blood was diluted 20-fold with 0.01 M HNO3.
1.5 Reference materials and quality assessment
Roelandts60 has produced another of his useful updates on biological and environmental CRMs.Work on establishing values for dimethylarsinic acid (DMA) and arsenobetaine (AsB) in three candidate urine RMs was reported by Cornelis et al.61 The species were separated by cation-exchange HPLC, digested on-line with K2S2O8 and UV irradiation and then the As was measured by HGAAS. Concentrations of AsB in the three samples were similar (around 17.5 µg l−1) but concentrations of DMA differed (4.1, 55.3 and 134.1 µg l−1). Measurements of total As indicated that other As species must have been present. Further work with other laboratories was considered necessary.
1.6 Hair and nail analysis
In a study of 885 women in Rio de Janeiro, Brazil,62 17% showed anomalously high or low Ca concentrations in hair. In those with high Ca, correlated increases in Ba, Mg, P and Sr were found which were attributed to bone decalcification. Measurements were by Q-ICP-MS after digestion of the samples with HNO3–H2O2. A study by Dombovári et al.63 showed that, using measurements by micro-PIXE, Ca tends to concentrate in the outer layer of the hair and its concentration is affected by the washing procedure.Direct determination of Pb in fingernail samples by ICP-AES was possible using an injection device developed by Badiei and Karanassios.64 In this, a rhenium cup containing the sample was driven into a vaporization chamber below the injection tube in the torch. Electrical heating allowed drying, charring and vaporization. Calibration was with aqueous standards.
A micro-scale digestion procedure for hair samples in the determination of As by HGAAS was developed by Flores et al.65 About 10 mg of hair was digested with a mixture of HNO3–H2SO4–HCl in a sealed 2 ml polypropylene vial. Heating was by irradiation with microwave energy in a domestic microwave oven in a series of programmed steps of total time 38 min. Accuracy was assessed by analysis of a hair CRM using ICP-MS.
1.7 Drugs and pharmaceuticals
For studies of diiodoplatinum anticancer drugs, Patriarca et al.66 developed a method for the simultaneous determination of Pt and I by ICP-MS. Stabilization of I required a strong KOH concentration (10 M) and a long washout time (8 min with H2O).Fingerprinting of heroin samples by their trace element concentrations, as determined by ICP-MS, again features this review year. In the approach used by Myors et al.,67 samples were dissolved in 3% HNO3, spiked with In and 73 trace elements determined by quadrupole ICP-MS. Predictive models using data analysis were reasonably successful.
1.8 Marine and freshwater biology
For a study of organotin compounds in marine mussels from the Venetian Lagoon in Italy, Binato et al.68 screened samples for total Sn by ETAAS with Pd as a modifier. Sample homogenates were digested with HNO3 for analysis. To obtain quantitative data on the species, GC-MS was used after extraction with methanolic tropolone and derivatization with a Grignard reagent. Separation on a DB-5 silica column with temperature programming gave peaks for four organotin compounds which could be quantified with recoveries better than 80%.Munoz et al.69 found that many extraction methods gave poor recovery of As in fish, cockles and squid because of the strong bonding of As to thiol groups in proteins. The use of strong HCl (9 M) broke these bonds and gave good recovery. After reduction by HBr and hydrazine sulfate, the As was extracted into CHCl3, back-extracted into 1 M HCl, dry-ashed and then determined by HGAAS. Other As species, such as DMA, AsB and arsenocholine, were not extracted.
Workers at the University of Plymouth70 compared AFS and ICP-MS as detectors for the GC separation of methylmercury from marine samples. Mercury was measured as 202Hg by ICP-MS, and for AFS the gas chromatograph was coupled through a pyrolysis unit. The LOD with AFS (0.25 pg Hg) was lower than that obtained with ICP-MS (0.9 pg). The method was validated on mussel homogenate and dogfish liver CRMs and the GC-AFS version applied to the determination of Hg in livers from ringed seals and beluga whales.
1.9 Progress for individual elements
Bantan et al.71 developed a method for quantitative determination of Al–citrate species at trace levels in human serum using fast protein liquid chromatography (FPLC) coupled to ETAAS. Negatively charged Al–citrate species were separated on a strong anion exchange column with a linear elution gradient of H2O–4 M NH4NO3 at a flow rate of 1 ml min−1. Fractions (0.5 ml) were collected and analysed `off-line' by ETAAS. The authors highlighted the advantage of using NH4NO3 as the elution buffer in that it decomposed quantitatively in the furnace during pyrolysis, thereby ensuring reproducible absorbance signals for Al in the separated fractions. A method precision of 2% RSD and an LOD of 2 ng ml−1 were reported. The authors used the method to quantitatively determine Al–citrate species in human serum samples spiked with 50–100 ng ml−1 of Al3+. Low molecular weight (MW) Al species were separated from high MW Al complexes by micro-ultrafiltration. The ultrafiltrate, which contained 15–19% of the Al, was applied to the FPLC column. They determined that most of the ultrafiltered Al corresponded to Al–citrate species. The same group72 also coupled FPLC to ES-MS-MS to investigate the speciation of low molecular weight Al species in human serum. They identified Al–citrate, Al–phosphate and a ternary Al–citrate–phosphate complex as the main Al complexes in serum ultrafiltrate and noted that the relative proportions of these species varied from individual to individual.
The group of Holderbeke et al.27 used capillary electrophoresis (CE) to separate As species in a variety of biological matrices for quantitative determination by ICP-MS. Because of the low sample capacity of CE and the relatively inefficiency of pneumatic nebulization, a more efficient sample introduction system was considered necessary. Moreover, the conventional cross-flow nebulizer also introduced laminar flow in the capillary which led to dispersion of the sample and reduced sensitivity. In order to improve the sensitivity, a novel interface was developed to directly couple the capillary to a microconcentric nebulizer. The interface was described as being simple to install and remove and could be used with a variety of different ICP-mass spectrometers. With this coupled technique, the group could separate four anionic As species (AsIII, AsV, MMA and DMA) and two cationic As species (AsB and arsenocholine) in a single run. The LOD for each species was reported to be 1–2 µg l−1.
Lintschinger et al.73 coupled HPLC with ICP-MS to determine As species in urine. The five As species AsIII, AsV, MMA, DMA and AsB were separated on an `Ion-pac' column using gradient elution with 2 mM TMAH followed by 10 mM (NH4)2CO3 and again with 2 mM TMAH. The eluate was directly introduced into the nebulizer of the ICP for determination of As. Calibrations were linear from 0.5–10 µg l−1 for all five species and LODs were 0.5 µg l−1.
Finally, Ebdon et al.74 used the same combination of HPLC and ICP-MS to study As speciation in blood plasma from renal dialysis patients. For an injection volume of 175 µl, an absolute LOD of 0.25 ng of As was obtained. In the absence of any reference materials, the method was validated with spike recovery experiments. The authors found that AsB was the only detectable As species in all samples analysed. They observed that prior to dialysis AsB levels were similar to those determined in healthy individuals and in all but a few patients were significantly reduced following the dialysis treatment.
Moyano et al.18,75 developed an FI-ICP-AES method with `on-line' preconcentration and ultrasonic nebulization in order to achieve the necessary sensitivity for accurate quantification of Bi in biological fluids. Bismuth was preconcentrated by complexation with quinolin-8-ol on an Amberlite XAD resin and eluted with HNO3 directly into the ultrasonic nebulizer. An LOD of 0.03 µg l−1 was reported for a preconcentration of 100 ml of aqueous solution. The method was evaluated by analysis of human urine samples which were previously digested with HNO3–H2O2.
Factors influencing the determination of low concentrations of B in biological matrices were also reviewed by Downing et al.77 They considered that the ubiquitous nature of B and the volatility of boric acid, which could lead to contamination or analyte losses, were key contributory factors to the analytical discrepancies that had arisen from the analysis of B by different methods. They provided examples to aid the analyst in avoiding such problems in the determination of B in biological samples by ICP-MS.
Moreton and Delves75 described a method to determine both total B and 10B∶11B isotope ratios in a range of biological samples and culture media using quadrupole ICP-MS. Blood, plasma, brain tissue and media were wet digested in open vessels with HNO3 or HNO3–H2SO4, whilst cultured cells were solubilized with 1 M NaOH. The authors identified analytical problems with variable blank values, matrix suppression and 12C overlap on the measurement of 11B. Reported detection limits were <1 µg l−1 for total B and <0.1 µg l−1 for 10B. A novel calibration method based on measurement of 10B∶11B ratios in standards and samples was used to calculate elevated 10B levels, as 10B could not be quantitatively determined directly despite the low LOD for the method.
Watson-Clark et al.16 used ICP-AES to determine tissue levels of B in rats following administration of 10B containing drugs. They used the method to investigate a liposome model for delivery of boron neutron capture therapy drugs to sinovial tissue in rats with collagen induced arthritis. They observed increased synovium–blood B ratios which led them to suggest that delivery systems may be of potential value in the treatment of rheumatoid arthritis with B based drugs.
°C) to be used, thereby reducing background absorption from the salt matrix. With aqueous calibration, the authors reported an LOD of 0.16 µg l−1 and a precision of 3.2–4.3% RSD at 2–4.56 µg l−1. Fuyi and Zucheng11 described a method for the direct determination of Cd in solid biological matrices by slurry sampling ETAAS. The slurry was prepared by suspending the powdered material in a solution containing 1 ml of 60% PTFE slurry, 0.4 ml of HNO3 and 0.2 ml of 0.5% plant glue solution. The method was validated by analysis of biological CRMs. Okamoto20 described a solid sampling method for the direct determination of Cd in biological samples. The sample was mixed with (NH4)2HPO4, as a fusion flux agent, and introduced into a tungsten cuvette. The cuvette was then placed in a tungsten boat furnace and TMAH added. The cuvette was initially heated to a sufficient temperature to wet digest the sample and then further heated to atomize the digested sample.Mota and colleagues79 investigated two alternative sample introduction methods for the determination of Cd in biological samples by ID-ICP-MS. In the first, the sample solution was spiked on-line with the enriched isotope solution immediately before the nebulizer, using a peristaltic pump. In the second, the sample solution was reacted with NaBH4, using merging zones FI, to generate volatile Cd species which were transported to the plasma. Both approaches gave good results for ultra-trace levels of Cd in a wide range of biological RMs. The authors considered, however, the on-line spiking method to be more convenient as it was fast and required minimal sample preparation. Goenaga Infante and colleagues,80 from the same research department, adopted a similar approach, using vesicular HG-ICP-MS, to determine Cd species in rabbit liver metallothionein and human urine. Cadmium species in purified metallothionein samples were satisfactorily resolved on an anion-exchange column using a gradient elution with 2–200 mM Tris–HCl at pH 7.4. Three Cd species were determined in metallothionein isoform 1 (MT1) and two Cd species identified from isoform 2 (MT2). With the same chromatographic conditions, two Cd species were detected in human urine and these had similar retention times to the first two Cd species resolved from MT1. The authors confirmed that hydride species of Cd were generated from liver MT with the same efficiency as inorganic Cd2+ ions. They reported a 2-5 fold improvement in analytical sensitivity compared with pneumatic nebulization.
An important and comprehensive study of Cd concentrations in human kidney from the UK population was described by Lyon and colleagues.81 They presented results for analysis of over 2500 samples of human renal cortex, collected and analysed over the period 1978–1993. Samples were oven dried and digested with HNO3 on a heating block. Digests were diluted with H2O for determination of Cd by FAAS using an air–C2H2 flame. The accuracy of the method was validated by comparison with a flame fluorescence method and analysis of CRM NBS 1577 bovine liver. Quality control is a critical factor in longitudinal studies such as this. Quality control was monitored with a freeze dried horse kidney RM, having an assigned value of 184–193 µg g−1. No temporal trend in the QC value was observed throughout the 16 year period of analysis. The authors reported a mean kidney Cd concentration of 19 µg g−1 and a median value of 16 µg g−1. Kidney Cd levels were about 5 µg g−1 higher in smokers compared with non-smokers. The kidney Cd concentration was also influenced by age, rising gradually to a mean maximum of 23 µg g−1 in middle age and declining again in old age. No significant geographical variations across the UK were observed.
`Abnormally' low hair Ca was identified in twenty cases of senile osteoporosis. They considered the evidence supported the argument of the usefulness of hair analysis as a complimentary diagnostic tool for endocrine disorders and disturbances in bone metabolism.
Mohamedshah et al.84 used GC-MS and ETAAS to determine 53Cr and total Cr in biological fluids in order to investigate the distribution of Cr in lactating women following oral administration of a stable 53Cr tracer. The authors detected 53Cr in blood within 2 h of administration. They noted, however, that blood Cr changes in response to oral administration were variable and they considered that blood Cr was not tightly regulated. They did not detect 53Cr in breast milk nor did they determine any change in the natural Cr concentrations in milk. They also noted that absorption and urinary excretion of Cr were similar for both lactating women and non-pregnant, non-lactating women. All these observations led the authors to hypothesize that losses of Cr in breast milk during lactation were not compensated for by increased absorption or decreased elimination.
Wardley et al.86 also described a method for the determination of I in urine using ICP-MS. Samples were simply diluted 1 + 19 v/v with H2O and matrix matched calibration was used for quantitative analysis across the concentration range 5–100 µg l−1. The authors used the method to study excretion of I during normal pregnancy. They observed that excretion of I increased significantly from 28–40 weeks of pregnancy, returning to non-pregnant control levels by ten weeks post-partum.
Patriarca et al.66,87 developed an ICP-MS method for the simultaneous determination of I and Pt in human serum in order to investigate the reaction mechanisms of diiodoplatinum anti-cancer drugs. To eliminate both the memory effects of I and instability, arising from formation of volatile I species at low pH values, both standards and samples were diluted in 10 mM KOH. Detection limits for I and Pt in 10 mM KOH were 2.2 µg l−1 and 23 ng l−1, respectively, and the method was validated by analysis of BCR SRM 063R (skimmed milk powder) and NIST SRM 2670 (toxic metals in urine). The authors used the method to determine I∶Pt ratios in the low molecular weight fraction of reaction mixtures between diiodoplatinum complexes and human serum. They observed different reaction kinetics for diiodo-PtIV and diiodo-PtII ligands and found evidence for release of I in the reaction process.
Accurate quantitation of Pb in serum or plasma is important for studies of the `biologically-active' fraction of lead in the transport of lead between body compartments. Smith et al.89 presented results of a detailed investigation of sampling factors that influenced the determination of serum and plasma Pb levels by ICP-MS. They observed that serum collected by an ultraclean method contained approximately 0.4% of the whole blood Pb, but this proportion increased to 1.2% when clotted blood was allowed to stand for up to 1 h before centrifugation. Plasma separated from blood collected into low-Pb heparin anticoagulant also contained about 0.4% of the total blood Pb but was not influenced by standing time prior to separation. In contrast, plasma from blood collected in EDTA contained increased levels of Pb, around 2% of the total Pb, due to redistribution by chelation with the EDTA. Haemolysis also clearly led to elevated plasma or serum Pb levels. In the light of these observations, the authors stressed the importance of a consistent methodological approach to sampling. Going one step further, in the study of the distribution of Pb in biological fluids, Hall et al.90 described a method for the determination of Pb binding ligands in amniotic fluid using high-performance size-exclusion chromatography (HPSEC) coupled with ICP-MS. Proteins, peptides and amino acids were separated on a silica based size exclusion column, which had a mass fractionation range of 1000–800000 Da, using an isobaric mobile phase of 0.1 M Tris-HCl–1% propan-2-ol. Chromatographed species were identified in the eluent by UV detection. The eluent was combined with a stream of Tl as internal standard and pumped into the ultrasonic nebulizer of the ICP-mass spectrometer for determination of Pb and Cu. To correct for signal suppression from the Tris buffer, the spectrometer was tuned with 205Tl in the mobile phase. Copper was always measured to identify the caeruloplasmin peak which was used to normalize the retention times of element binding ligands in all samples. Good separation of Pb binding ligands was obtained within 20 min and Pb was identified with peaks corresponding to caeruloplasmin, pre-albumin and a Zn binding peptide. No Pb binding to albumin or transferrin was observed in the analysed amniotic fluid samples.
Zong et al.91 examined in further detail the contributory factors to background correction errors observed in the determination of Pb in bone matrices by Zeeman-effect ETAAS. They observed that overcorrection was due to the high concentration of phosphate in the bone matrix and noted that the overcorrection was unaffected by atomization temperature but was influenced by the strength of the magnetic field at atomization. This led them to hypothesize that the overcorrection was caused by Zeeman-effect splitting of the absorption bands of molecular phosphate species generated by the furnace programme. The overcorrection error was minimized by reducing the phosphate levels in the sample or replacing the normal graphite tube with an end-capped tube. Lima et al.92 described an interesting method for the determination of Pb in digests of biological matrices by ETAAS in which tungsten–rhodium coating of the graphite tube acted as a permanent chemical modifier. A tube coating of 250 µg of W and 200 µg of Rh was as effective as a conventional Pd–Mg(NO3)2 chemical modifier for the determination of Pb in a range of biological materials but offered a number of advantages in that the coating improved both the lifetime of the tube by up to 115% and significantly reduced the degradation in signal sensitivity over the tube lifetime. The coating could withstand acid concentrations up to 5% HNO3. The reported detection limit was 15.5 ng g−1 in biological matrices and an RSD of 3.6% was obtained for over 1000 consecutive firings of 10 µl of a digested plankton CRM. An interesting combination of in-torch vaporization with ICP-AES was described by Badiei and Karanassios64 for the quantitative determination of Pb in finger nails. Microsamples of washed nail clippings were placed directly in a rhenium cup which was mechanically raised into a vaporization chamber attached to a conventional ICP torch. The sample was vaporized by electrical heating of the rhenium cup and the atomized sample transferred into the plasma in a stream of Ar–H2. This approach overcame the requirement for large sample amounts to be digested for quantitative determination by pneumatic nebulization ICP-AES.
Two groups described methods employing on-line FI and micro-column pre-concentration to separate Pb from matrix interferences for the determination of Pb in biological samples by ETAAS. Yan et al.14 used a macrocyclic immobilized silica gel adsorbent (Pb–O2) packed into a 50 µl capacity conical microcolumn to selectively extract Pb from a range of biological RMs. The adsorbed Pb was quantitatively eluted from the column with 40–50 µl of 0.03 M EDTA directly into a pre-heated graphite furnace for determination. Potential interferences from Ba, Sr and K, which competed with Pb for the cavities in the macrocyclic adsorbent, were minimized by adjusting the concentration of EDTA and volume of eluent used. With optimized conditions, a pre-concentration factor of 23 was achieved, giving an LOD of 2 ng l−1 and a precision of 2.9% RSD for 500 ng l−1 Pb. The sampling frequency was 23 samples per hour. Measured values in good agreement with certified values were obtained using aqueous calibration standards for a range of biological CRMs. In the method described by Ivanova et al.93 Pb and Cd were pre-concentrated from HNO3 digested blood by chelation and adsorption onto a PTFE knotted reactor coil for determination by ETAAS. Using an FI system, the digested sample was reacted with a solution of ammonium diethyldithiophosphate and the chelate adsorbed onto the walls of a 100 cm knotted reactor. The complexes were eluted from the column with 35 µl of CH3OH directly into a graphite furnace pre-treated with iridium. A pre-concentration factor of 99 and an LOD of 1.6 ng l−1 was obtained for Pb with a sampling cycle of 109 s. By setting the furnace temperature programme to the same timescale as the FI cycle, preconcentration was performed in parallel with ETAAS determination of the previously preconcentrated sample. Results of analysis of blood RMs were in good agreement with certified values for Pb. The method was also applied to the determination of Cd in biological matrices.
A comprehensive review of biological monitoring for occupational lead exposure was presented by Skerfving et al.94 In addition to discussing sources of exposure and toxicokinetics of Pb, the authors discussed the relative merits of different indicators of Pb exposure. They considered that determination of plasma Pb might be a more suitable indicator of Pb exposure because of the non-linearity of the blood Pb-exposure relationship. The authors also focused on in-vivo XRF methods for biomonitoring of long term exposure and discussed recent data95 which described a model for estimating retrospective blood lead levels from finger bone Pb measurements and records of past exposure. A group from the Mexican National Institute for Public Health96 studied the influence of bone Pb on blood and plasma Pb levels. Blood and plasma Pb were determined by HR-ICP-MS. Patella and tibia bone Pb was determined, in-vivo, using a spot-source 109Cd XRF instrument. Both blood Pb and bone Pb were highly correlated with plasma Pb and multivariate regression analysis indicated that traebecular bone Pb influenced plasma Pb independently of blood Pb. The same group97 studied the influence of bone Pb on blood Pb levels in teenagers from urban areas of Mexico. They observed that after adjusting for covariates, bone Pb remained a significant predictor of blood Pb levels and concluded that accumulated bone Pb contributed a moderate but significant source of circulating lead during adolescence in addition to that from current environmental exposure. Whilst the determination of blood Pb is still likely to remain the most widely used indicator of Pb exposure for some time, it will be ineresting to follow developments in the measurement of alternative indicators and to observe whether they move from the research field into more widespread routine monitoring applications.
Kibble et al.99 described a sensitive method using ETAAS with Zeeman effect background correction for the quantitative determination of picomolar concentrations of Mg in rat renal tubular fluid. They observed that an NH4NO3 chemical modifier satisfactorily overcame the severe chloride interference and noted that absorbance signals were markedly reduced with furnace ashing temperatures above 1200°C. The method had a reported LOD of 0.04 pmol. Using the method to study renal handling of Mg, the authors observed that there was both an increasing concentration gradient and net reabsorption of Mg along the proximal tubule.
The determination of Hg by pneumatic nebulization ICP-MS can suffer from memory effects. Nixon et al.103 evaluated gold and dichromate in HCl as wash agents to overcome memory effects in the spray chamber in the determination of Hg in blood and urine. They observed that dichromate was more effective than gold and noted that rapid sample introduction and rapid introduction of wash solution also reduced memory effects. The method was validated by analysis of blood and urine quality assurance samples, and good agreement with target values were found for both blood (r = 0.98) and urine (r = 0.99) matrices. Knight et al.104 coupled CVAAS with ICP-MS to quantitatively determine total Hg and measure stable isotope ratios in small masses of hair. Hair samples were microwave digested in 7 ml capacity microvessels. The resulting digest was reduced with 10% SnCl2–10% HCl for quantitative determination of total Hg by CVAAS, using magnesium persulfate as a drying agent for the optical cell. Recoveries of spiked samples were around 100% and values determined for Hg in hair CRMs were in good agreement with the certified values. Coupling of the AA spectrometer to the ICP-mass spectrometer enabled isotope ratio measurements to be obtained in the same analytical run.
To determine total Hg or inorganic Hg species in whole blood, Chen et al.105 described an FI method with on-line digestion and CVAAS using a mercury specific detector system. For total Hg determinations, whole blood samples were mixed 1∶10 v/v with a KBr–KBrO3 oxidation reagent, containing Triton X-100, for microwave digestion. Determination of inorganic Hg did not require microwave digestion and blood samples were simply allowed to react with KMnO4 to release Hg from blood proteins. Calibration was performed with bovine blood spiked with HgCl2. Good agreement with target values was obtained for both total Hg and inorganic Hg in NIST SRM 966-2 and reported LODs were 0.14 µg l−1 and 0.45 µg l−1 for total and inorganic Hg, respectively. A similar approach using on-line microwave digestion FI-CVAAS was described by two groups for the determination of total and inorganic Hg in urine. In the first method described by Gallignani et al.,106 inorganic Hg was determined following sample reduction with SnCl2, whilst total Hg was determined following on-line oxidation with persulfate and subsequent reduction with SnCl2. Standard additions calibration was used for quantitative analysis by using an Hg solution as the carrier with time based flow-injection. An LOD of 0.1 µg l−1 was reported with a precision of 1% RSD and 1.5% RSD for inorganic and total Hg, respectively. In the second method described by No et al.107 total Hg in urine was determined by FI-CVAAS following reaction with KBr–KBrO3–HCl and microwave digestion in a totally closed system. Calibration was linear from 0.05 µg l−1 to 20 µg l−1 and precision was 2% at 5 µg l−1.
Cao and colleagues108 examined the efficacy of different organic compounds as chemical modifiers for the determination of Hg in biological matrices by ICP-MS. As Hg has a low ionization efficiency in the plasma it has a relatively poor analytical sensitivity with pneumatic nebulization ICP-MS. The ionization efficiency may be improved by the addition of organic compounds to the plasma. The authors observed that enhanced signals were obtained with diluents containing NH3 and either ethylenediamine or triethanolamine, as the organic matrix improved the transport efficiency of Hg. Signal enhancement was strongly influenced by nebulizer flow rate and RF power. With optimized conditions, a ten-fold improvement in sensitivity was obtained with either ethylenediamine or triethanolamine and final concentrations of less than 10%. The optimized method gave measured values in good agreement with certified values for a range of biological CRMs.
Interest continues in the release of Hg from mercury amalgam fillings as the health risks remain a subject of controversy. The groups of Drexler et al.109 and Drasch et al.110 described similar interesting studies on the relationship between levels of Hg in human breast milk, dental amalgam fillings and dietary factors. In the first study, Hg levels were determined by CVAAS in blood, urine and breast milk taken from over 100 women in the first week after giving birth. The mean level of Hg in breast milk collected shortly after birth was 0.9 µg l−1 and showed a significant positive correlation with the number of amalgam fillings. Urine Hg levels were also positively correlated with both the number of amalgam fillings and surfaces. Two months after birth, breast milk Hg levels were significantly lower (<0.25 µg l−1). Furthermore, they were no longer correlated with amalgam fillings but were positively correlated with fish consumption. This led the authors to argue that, for breast fed infants, Hg exposure from maternal fish consumption was more important than from amalgam fillings. The second group also used CVAAS to determine Hg in breast milk samples taken from 44 women within the first week of giving birth. They too found that fish consumption was the main contributory factor to breast milk Hg levels and also noted that, after several days, breast milk Hg fell to levels that were equal or lower to those in formula milk feeds. They considered that the low Hg burden in breast milk strongly argued against any limitation on breast feeding for women with large numbers of amalgam fillings.
In order to investigate the peripheral neurotoxic effects of Pt based drugs, Screnci et al.113 developed a method for the determination of Pt in milligram samples of peripheral nerve tissue by ICP-MS. Tissue samples of 5–10 mg were digested with HNO3 in closed vessels and diluted to a final volume of 10 ml with H2O. Calibration standards were prepared in the same way as samples to correct for the observed 25% suppression in Pt signal caused by the acid matrix. Recoveries of Pt from spiked sciatic nerve samples were 112 ± 7.2%, between assay precision was 13.9% RSD and the LOD was 5 pg mg−1. The authors noticed alterations in the Pt levels of nerve tissues perfused with paraformaldehyde which they hypothesized may be due to washout of Pt during the fixation process.
In the second paper in this review relating to salivary trace element measurements, Holding and colleagues92 described a method for the determination of Pt in saliva using ETAAS. The method was developed to investigate the potential of salivary Pt measurements as a non-invasive method for monitoring unbound plasma concentrations of active Pt species after treatment with cisplatin. Saliva samples (0.5 ml) were mixed with an equal volume of methylbenzenethionium hydroxide in methanol and incubated overnight at 40°C to solubilize salivary proteins. The solubilized samples were diluted to a final volume of 5 ml with HCl. Calibration with matrix matched standards was necessary for quantitative determination and an LOD of 0.025 µg ml−1 was reported. The authors monitored salivary Pt levels in two groups given cisplatin by two different infusion regimes. The mean concentrations of Pt in saliva rapidly rose to 0.27 µg ml−1 following a 30 min infusion and declined to undetectable levels after 24 h. The mean saliva Pt concentration taken after an 8 h infusion was 0.12 µg ml−1. Plasma levels of Pt determined following the two infusion regimes were not significantly different (2.98 against 2.54 µg ml−1 for 30 min and 8 h infusions, respectively). The authors concluded that levels of free Pt in plasma were higher after a 30 min infusion compared with an 8 h infusion.
Fujimori et al.115 described a novel sample pre-treatment for the determination of La and other REEs in a bovine blood SRM. The blood sample was digested with HNO3–HClO4 and the pH of the digest adjusted to pH 12 with NaOH. This treatment caused co-precipitation of REEs with Fe derived mainly from haem-iron. The excess Fe was removed by solvent extraction with IBMK and the residual aqueous solution introduced into the nebulizer of the ICP-MS for quantitative determination of REEs. Levels of lanthanides determined in the blood SRM ranged from 0.9 pg g−1 for Tm to 1880 pg g−1 for Ce.
The rare earths Dy and Eu are often used as tracers in animal nutrition studies. Unfortunately, the sensitivity of ETAAS for quantitative determination of REEs is severely affected by the formation of thermally stable carbides. In order to overcome this problem and develop more sensitive methods for the determination of Dy and Eu in faecal samples, Nobrega et al.116 examined the use of a tungsten coil atomizer. In dilute HNO3, Dy and Eu were thermally stable at 1500 and 1300°C, respectively, and both elements were atomized at 2195°C. Addition of 10% H2 to the argon purge gas also improved atomization efficiency. In the digested samples, interference from alkaline earths could not be overcome with chemical modifiers and matrix matched calibration was necessary.
Sample introduction by ETV was used by Turner et al.122 to determine Se in serum by ICP-MS. With a simple 1 + 19 v/v dilution in 1% HNO3 and optimization of the ETV temperature programme, most of the interferences normally associated with the determination of Se by nebulization ICP-MS were eliminated. An LOD of 0.1 ng g−1 was reported for Se measured at masses 77 and 82. The method was validated by analysis of quality control samples and NIST SRM 1598, Bovine serum. Good results, in agreement with target and certified values, were achieved with measurements at 74Se, 77Se, and 82Se whilst values were less accurate for measurements at 78Se due to interference from argon adduct ions. Preliminary work by the group indicated that this interference was reduced by adding N2 to the Ar gas. Mei et al.123 examined the efficacy of different chemical modifiers for the determination of Se in phosphorus-rich biological matrices by ETAAS with Zeeman effect background correction. They reported that a suppression of the Se signal was observed when the phosphate content of the digested sample was greater than 1 mg ml−1. For samples digested with HNO3–H2O2, an (NH4)3RhCl6 and citric acid chemical modifier was found to be more effective than a Pd chemical modifier in overcoming the interference. A sensitive method for the determination of total Se in serum by ETA-LEAFS was described by Swart and Simeonsson.58 The excitation source for Se at 196.026 nm was generated from the output of a dye laser operating a 234 nm. Due to the high sensitivity of the method, serum samples could be diluted 10–20 fold in H2O. A Pd–Mg(NO3)2 chemical modifier was added to the diluted samples to prevent pre-atomization losses of Se. The method was validated by analysis of NIST SRM 1598 and a value of 42 ng g−1 determined, compared with a certified value of 42.4 ng g−1. The authors used the method to determine pre- and post-operative serum Se levels from bone marrow transplant patients.
Two groups described FI-HG methods for the determination of Se biological fluids. Ohta and colleagues124 coupled FI-HG with MIP-MS to accurately determine Se in serum by ID measurement. Serum samples were spiked with a known amount of enriched 78Se and digested with HNO3–H2O2–HCl. The digested sample was mixed with a stream of HCl and NaBH4 in an FI system and the generated hydride transported to the MIP in a stream of N2 for measurement of the 78Se∶82Se ratio. Mass bias was corrected by analysis of a standard Se solution. The method gave comparable results to those obtained by argon ICP-MS using standard additions for calibration. Li and colleagues125 examined optimum microwave digestion conditions for the quantitative determination of Se in urine by FI-HG-AAS. Samples were digested in closed vessels within a high pressure, high temperature microwave system. Decomposition of organoselenium compounds was achieved with an optimized microwave programme reaching a maximum temperature and pressure of 200°C and 8 bar, respectively. The addition of 50–100 µl of a urea solution to the digestion mixture eliminated the interference on hydride generation caused by absorption of NOx fumes into the digest solution during microwave heating. Digested samples were analysed off-line using an automated FI system. The method had a reported a LOD of 3 µg l−1 and was validated by analysis of urine SRMs.
Studies on Se species were also prominent in this review period. Shiobara et al.126 developed a HPLC-ICP-MS method to determine Se species in the blood, liver and urine of rats administered selenite or selenate, in order to investigate the metabolic pathway for Se. Plasma, liver or urine samples were applied to a size exclusion column and eluted with Tris-HCl buffer. The eluent was monitored by UV spectrophotometry for peak identification and introduced directly into the nebulizer of the ICP-mass spectrometer. Total plasma and blood Se were determined by nebulization ICP-MS following digestion with HNO3–H2O2. The authors noted that selenite was mainly taken up by erythrocytes and reduced to selenate before being transported to the liver. Selenate was not taken up by erythrocytes but was transported directly to the liver, with a small proportion being excreted directly in the urine as selenate.
Michalke and Schramel127 investigated Se speciation in human milk using SEC and ETV-ICP-MS. Pooled milk samples, collected during the first week following delivery, were chromatographed on a size exclusion column. Selenium in the collected fractions was quantitatively determined by ETV-ICP-MS and the organic ligands were identified by capillary electrophoresis. Final confirmatory identification was obtained by a combination of CE (isotachophoresis) and ETV-ICP-MS. The authors reported no evidence of species transformation during the analytical procedure and they identified GSeH, Se-cystamine, Se-cystine and Se-methionine as the main native Se species in human milk. Finally, Nichol and colleagues128 reported observations on changes in plasma Se status and selenoproteins following minor surgery. Selenoproteins were separated by affinity chromatography and the Se content of the separated fractions determined by ETAAS. Hair and nail Se was determined by ETAAS following digestion with HNO3–H2O2. The authors noted a negative acute phase response in plasma selenoprotein levels following surgery and recommended that measurement of an acute phase protein marker of inflammatory response, such as C-reactive protein, should also be made in order that changes in plasma Se can be properly interpreted in such cases.
°C over an 8 h digestion period. Titanium and Zr in the digest were determined by ICP-AES at the 336.122 nm and 343.823 nm emission lines, respectively. Linear correlation was obtained over the concentration range 25–1000 ng ml−1 for Ti and 50–2000 ng ml−1 for Zr and the reported detection limits were 34 ng ml−1 and 26.9 ng ml−1 for Ti and Zr, respectively.In the second method, Ti and Zr were determined in the digested samples by ICP-MS, using an ultrasonic nebulizer and membrane desolvation for sample introduction. The authors noted that 20-fold sample dilution and introduction of a dry aerosol into the plasma reduced isobaric interferences from polyatomic species. Detection limits of 1.4 ng ml−1 and 9.9 ng ml−1 were reported for Ti and Zr, respectively. The authors compared the results obtained by ICP-MS for digested serum samples with results obtained using ETAAS and no sample pre-treatment. They determined significantly lower Ti levels using the ETAAS method and they considered this to be due to the absence of a digestion step which was necessary to fully dissolve Ti from wear particles in the serum.
To study the relationship between Zn nutritional status during pregnancy and Zn levels in human milk, Ortega et al.133 used AAS to determine Zn concentrations in maternal blood and transitional and mature milk from Spanish women. They found that, during pregnancy, subjects with a dietary Zn intake less than 50% of the recommended level had both lower serum and milk Zn levels than subjects with higher dietary Zn intakes and noted that although dietary Zn intakes were clearly below the recommended levels in all cases studied, abnormally low levels of serum and milk Zn were rarely observed. They considered that the normal reference limits for serum Zn and milk Zn levels in Spanish women may need to be re-defined.
1.10 Conclusions
Evident in this Update is the development that has occurred in speciation. Combinations of HPLC with ICP-MS have featured in previous Updates and their ability to separate, for example, the species of As has been the subject of many studies in this Update.73,74 It is, however, the association of trace elements with proteins in serum that is proving more difficult to study. The thorough study of Bayón et al.36 using fast protein LC and ICP-MS shows the problem. The technology is now there to identify the trace elements, generally with sufficient sensitivity, but the difficulty is in achieving good separation and identification of the proteins. This is where techniques based on electrophoresis show promise as good separation of the proteins can be achieved. However, as the work of Lustig et al.25 on flat plate electrophoresis showed, this also creates other problems. The electric field causes movement of some trace elements independently of the associated protein especially when the bond is weak. Solutions to the difficulties in coupling CE to ICP-MS have been found and this technique is likely to achieve prominence because of the ability to produce a direct display of the separated species rather like a chromatogram. Good separation of As species27,29 and Se species31,127 have been shown and it will be interesting to see how this technique develops.More experience has been gained in the use of HR-ICP-MS for multielement determination of trace elements. There seems to be a general consensus that elements need to be sorted into two categories. Those subject to isobaric interferences are measured at a high resolution (3000) whereas for other elements, the lowest resolution (300) is chosen to give the highest sensitivity. The wide range of elements that can be determined in this way is impressive.
Recent studies118–121 have shown that Se can be reliably determined in serum and urine by Q-ICP-MS when an organic solvent is included in the diluent. Comparison with Zeeman ETAAS120,121 has indicated that ICP-MS is more reliable as the instrument response is essentially independent of the Se species, whereas differences occur in ETAAS.
A significant step forward has been reached in assessment of the risk of exposure to mercury from dental amalgam. Two studies on lactating mothers109,110 have both concluded that fish consumption is a more significant source of exposure to Hg than release from dental fillings.
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, 1999. It highlights papers which describe novel work and significant advances in both instrumental and analytical techniques, and the 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.2.1 Sampling and sample preconcentration
Two teams described the preparation of slurries for direct determination of trace elements in milk and associated products by ETAAS. A rapid method was described for the determination of Cu and Pb in dairy products.135 Samples were slurried in a solution of H2O2–HNO3–KH2PO4–C2H5OH and 20 µl aliquots of the resulting digests were injected directly into the atomizer of an AA spectrometer and subjected to a furnace heating programme for drying, calcination, atomization and cleaning. Copper was measured at 324.8 nm and Pb at 283.3 nm, with corresponding LODs of 0.11 and 0.7 ng ml−1. Campillo and co-workers136 suspended infant formula and powdered milk samples in a medium containing 20% EtOH, 0.65% HNO3, 6% H2O2 and 0.1% NH4H2PO4, which was directly introduced into the electrothermal atomizer. Liquid milk samples (cow and human) were diluted with this solution. The H2O2 and HNO3 components prevented the build-up of carbonaceous residues inside the atomizer. Aqueous standards were used for calibration and the LODs were 70 and 15 pg, respectively, for Cu and Zn. Results agreed well with those obtained following conventional dissolution of the samples, and method reliability was confirmed by analysing three CRMs. The team also measured the free and protein bound fractions by ultrafiltration membrane permeability of the milk samples. Murillo et al.137 described a technique for the determination of Cu, Fe and Ni in edible oils by ICP-AES following emulsion sample preparation. Response surface methodology was applied in order to find the optimum emulsion and surfactant concentrations. The optimum amount of oil in the emulsion was found to be in the range 2–35% in most of the surfactants used, but greater than 35% for Triton X-100. Surfactant concentration was between 0.5 and 9%. Good agreement was reported between calibration curves for emulsified aqueous standards and oil-in-water emulsions, with best results when Tween 80 was used. Recoveries ranged from 90 to 100% for most of the elements studied.
The review year has seen a revival of interest in the use of high pressure ashing, which was considered to be leading-edge technology during the 1980s, as an alternative to microwave digestion. White et al.140 reported their work with a new, more user-friendly, design of high pressure asher (HPA) with larger reaction vessels, and compared the results to those obtained by microwave-assisted digestion. A range of samples, including food SRMs (Cd, Pb), sewage sludge (Co, Cr, Cu, Hg, Pb, Zn) and soil (Cu, Hg, Ni, Zn), were pre-treated under a variety of conditions and the elements detected by ICP-MS, CVAAS, HGAAS and voltammetry. Benefits of the HPA were reported to be minimum acid requirements, minimum organic residue, complete sample mineralization, no loss of elements, minimal contamination, automated sample preparation and maximum operator safety. However, no numerical values were presented for microwave-assisted digestion of the SRMs, and no percentage efficiency comparison was made between HPA and microwave-assisted digestion. Zbinden and Andrey141 prepared food matrices by wet ashing in an HPA for measurement of trace element contaminants (Al, As, Cd, Hg, Pb and Se) by ICP-MS. They placed 0.4–0.5 g of sample with 2 ml of sub-boiling HNO3 in a 15 ml quartz vessel, which was then sealed with PTFE strips and a quartz cap. Particular attention was paid to eliminating carbon-related interferences which can occur with rapid wet ashing methods, causing an enhanced signal for As and Se and a suppressed signal for Pb. This was apparently achieved by adding 2% propan-2-ol to the digested samples and to the external calibration standards. However, the carbon content of the solutions did not affect the determination of Al and Cd, and no comparison was reported between the proposed method and aqueous solutions for Hg. Blake and Bourqui142 compared high pressure ashing with microwave digestion for the determination of Cd and Pb in food CRMs and raw materials by ETAAS. They reported similar accuracy and precision for the methods used, and stated a preference for the HPA due to higher sample throughput. Limits of detection in solution were 3 µg l−1 for Cd and 5 µg l−1 for Pb, which were stated as being close to the requirements currently proposed by the European working group for heavy metals methodology.
Gräber and Berndt7 have now published their work on the development of a new high temperature/pressure flow system for continuous digestion of biological samples and subsequent determination of Cu, Fe, Mn and Zn by ICP-AES. Preliminary work on this technique was in a conference abstract reported in last year's review,1 and the full details of this system, now applied to three CRMs, is a welcome addition to the literature.
°C (40 s), 1000°C (20 s) and 2650°C (3 s), respectively. The LOD was 10 ng l−1 with an RSD (n = 11) for 0.4 µg l−1 Pt of 2.5%, and recoveries of 0.2–0.4 µg g−1 Pt from spiked tap water, cod muscle and animal blood were >90%. Sample throughput was 21 h−1. Yan et al.14 developed a fully automated procedure for the determination of ultra-trace Pb in biological materials by on-line coupling FI microcolumn separation and preconcentration with ETAAS, using a macrocycle immobilized silica gel sorbent (Pb–O2). Lead was selectively collected on a conically shaped column packed with Pb–O2 over a wide range of sample acidity. The retained analyte was eluted quantitatively from the column with 46 µl of 0.03 mol l−1 EDTA solution at pH 10.5. The eluate was driven by an air flow into a graphite tube pre-heated to 110°C. Potential interferences from BaII, SrII and KI were eliminated or minimized by an appropriate increase in eluent volume and/or EDTA concentration. Sample loading rate was 3 ml min−1, with 20 s preconcentration time, giving an enhancement factor of 23 and a sampling frequency of 23 h−1 with a collection efficiency of 70%. The LOD was 2 ng l−1 with an RSD (n = 9) of 2.9% at the 500 ng l−1 Pb level. A number of SRMs (rice flour, blood and urine) were used to validate the method. In a conference presentation, Bruhn et al.144 described their work on a preconcentration procedure for the determination of Cr and Mn in biological and food samples by FI-FAAS. A time-based FI on-line preconcentration procedure using a minicolumn packed with controlled pore glass–quinolin-8-ol chelating resin was optimized and applied to the analysis of acid digests of mussels and non-fat powdered milk. It was reported that optimization of the FI system concentrated on four parameters, which were, for Cr, the eluent concentration, the sample flow rate, the eluent flow rate and the amount of minicolumn packing, and for Mn the loading time, the sample flow rate, the eluent concentration and eluent flow rate. Under optimized conditions, using a minicolumn packed with 60 mg of chelating resin, the sample loading times were 40 s for Cr and 50 s for Mn, with a 6 s elution sequence. Retention efficiencies were 97.6% for Cr and 99.3% for Mn, with mean reproducibilities (CV%) of 2.9% and 1.7%, respectively. Enrichment factors were 27 and 47, concentration efficiencies 32 and 47, and LODs were 1.5 and 0.5 µg l−1. Interferences from concomitant cations and anions were assessed and methods for their minimization were considered. Accuracy and precision of the method were checked by analysis of CRMs.2.2 Speciation
Three applications of size-exclusion HPLC-ICP-MS were described by Szpunar et al. in a paper and two conference abstracts. Speciation of metal–carbohydrate complexes in fruit and vegetable samples showed kinetically inert and thermodynamically stable metal complexes of B, Ba, Ce, Pb and Sr with polysaccharides at Mr > 50 kDa.145 A pectinolytic enzyme extraction method was used to release the solid water-insoluble fraction of the analysed samples into the aqueous phase. The metal-binding carbohydrate was identified as the dimer of rhamnogalacturonan-II, a pectic polysaccharide present in plant cell walls. Other metals such as Cu, Mg and Zn eluted as complexes with low molecular mass non-carbohydrate compounds. Two conference presentations146,147 reiterated this work, concentrating on speciation of Pb in foodstuffs of plant origin and wine, with particular attention to sample preparation procedures such as enzymatic lysis to selectively extract the species of interest. Abollino et al.148 used solid-phase extraction with ICP-AES to speciate Cu and Mn in milk. Milk samples were diluted 9-fold with acetic acid–sodium acetate to give a pH of 4.83, precipitating casein and other macromolecular compounds, which were separated by filtration. Precipitates and whole milk samples were analysed for Cu and Mn by ETAAS. The filtrate was loaded onto an FI manifold and passed through an anion exchange column (AG-1 X-8) and a cation exchange column (Chelex-100). The loaded columns were flushed in turn with 2 M HCl, and Cu and Mn in the eluates were measured directly by ICP-AES. The method separated cationic, anionic and casein-bound Cu and Mn species. A German team separated CrVI and CrIII species in tap water by HPLC with measurement by diode-laser FAAS.149 Tetrabutylammonium acetate and acetic acid were added to water to give solutions of 5 and 8 mM, respectively. Aliquots (1 ml) were injected onto a reversed-phase C18 column with a mobile phase of 0.3 mM tetrabutylammonium acetate–0.04 M acetic acid in aqueous 40% MeOH (pH 3–3.2) with hydraulic high pressure nebulization into an air–C2H2 flame for diode-laser AAS detection. The laser wavelength was modulated at 17 kHz and the detection wavelength of 425.44 nm was obtained by frequency-doubling in a KNbO3 crystal. The beam was then split, with one half passing through the flame for detection by a low-noise Si PIN photodiode, and the other half detected by a similar photodiode direct. The pre-amplified outputs were normalized and their ratio was amplified logarithmically and passed to a lock-in amplifier. The frequency of the reference signal was twice that of the laser modulation frequency. This arrangement compensated for the laser residual amplitude modulation noise and for the frequency-doubling off-set signal and its fluctuations. This resulted in a much cleaner chromatogram. CrVI and CrIII species were separated in less than 90 s and the LOD for CrVI in tap water was approximately 30 pg ml−1.In a conference presentation, Baker and Miller-Ihli150 discussed the application of capillary electrophoresis (CE)-ICP-MS to the chemical speciation of metals in foods. They described an interface which utilizes a coaxial flow of make-up buffer to provide electrical connection to the CE capillary and to minimize suction on the capillary from the nebulizer. The interface was used with three nebulizer and spray chamber combinations (cross-flow nebulizer with double-pass spray chamber, microconcentric nebulizer [MCN] with double pass spray chamber, and a different MCN with a cyclonic spray chamber). Results indicated that each nebulizer could be used successfully for CE-ICP-MS measurements, but that the MCNs provided the best LODs. Calibration strategies were also discussed for quantitative analyses, including calibration against aqueous standards, matrix-matched calibration and standard additions. Full publication of this work will be a useful addition to the literature on this powerful technique.
Le et al.22 developed a method for the simultaneous speciation of both As and Se species using HPLC-ICP-MS with elevated column temperatures. Thirteen As and Se species were studied, including AsIII, AsV, MMA, DMA, arsenobetaine (AsB), arsenocholine, tetramethylarsonium (TETRA), two arsenosugars, selenate, selenite, selenocystine and selenomethionine. Nearly baseline resolution of these species was reported using a reversed-phase C18 column with hexanesulfonate as an ion pair reagent and a constant column temperature of 70°C. Arsenic, Se and potential interfering species were monitored by ICP-MS at m/z 75, 77 and 78. The method was applied to canned tuna fish, in which AsB and selenocystine were identified as the major As and Se species. Speciation of six arsenosugar metabolites in human urine was completed in 19 min, compared with 37 min at room temperature.
2.3 Developments in methodology for flame atomic absorption spectrometry
A curious method was described for the determination of trace sulfide in beer by indirect AAS.151 Beer was chilled to 5°C and the pH of a 500 ml sample was adjusted to 4 with CO2. The solution was warmed, 1 M sodium dodecylsulfate and 1 M Cd(NO3)2 were added and N2 was bubbled through the solution. The foam was collected, de-foamed with EtOH and evaporated to dryness with 1 ml of 2 M HNO3. The precipitate was washed twice with 0.1 M acetic acid and the residue dissolved in 1 M HNO3 and diluted for measurement by air–C2H2 FAAS. Cadmium in the foam-concentrated CdS was determined at 228.8 nm, providing an indirect determination of sulfide. The LOD for sulfide was 5 µg l−1, and recovery by the standard additions method was between 94 and 96% with RSDs of 4.9 to 6.3%. Liu et al.152 described the direct determination of Ca in soya-bean flour by suspension sample introduction FAAS. Samples were ground to 100 mesh and shaken with some 0.1% agar to give a suspension, then diluted to 25 ml. A 2 ml portion of the suspension was further treated with 8 ml of the agar solution and 1 ml LaIII solution. Calcium absorbance was measured at 422.7 nm, and the air and C2H2 flows were 0.35 and 0.09 m3 h−1, respectively. The LOD using a standard additions method was 0.14 µg ml−1, with an RSD of 2.8% for 1.15 mg g−1 of Ca in flour. The addition of LaIII masked interferences from P and Al. A procedure was described for the rapid determination of Ca, Mg and Zn in honey by FAAS with no previous mineralization stage.153 The samples were dissolved in a solution containing dilute HCl and a La salt, and introduced directly into the FAA spectrometer by means of a simple continuous-flow manifold. The computer controlled system performed an automatic on-line dilution of the solutions, thus decreasing matrix effects due to the organic matter content and allowing analytical signals within the linear response range to be obtained. Concentrations of Ca, Mg and Zn measured were compared with reference values obtained by a mineralization-based procedure. The authors reported that the main advantages of this direct method were automation, time-saving and a decrease in the contamination risk.2.4 Developments in methodology for electrothermal atomic absorption spectrometry
Several teams have reported the development of rapid methods for the determination of trace elements in foodstuffs by ETAAS. Lima et al.154 described a simplified method for direct measurement of Pb in sweet fruit-flavoured powder drinks, syrups and honeys. Samples were dissolved in H2O and acidified to 0.2% v/v HNO3. An aliquot (20 µl) of the sample solution was directly injected with 10 µl of 0.05% m/v Pd–0.03% m/v Mg(NO3)2 into an end-capped THGA. Build-up of carbonaceous residue inside the atomizer was eliminated for sugar solutions not exceeding 8.0% m/v when a heating programme with two pyrolysis steps (600 and 1000°C) was performed without air ashing. Under these conditions one atomizer could support around 250 firings. Several chemical modifiers were tested, and best recovery and repeatability were obtained with a mixture of 5 µg Pd–3 µg Mg(NO3)2. An LOD of 7.0 ng g−1 Pb was achieved, which was appropriate for the Codex recommendation for the maximum allowed Pb content in the sugar samples. A Japanese group155 proposed a similar method for the measurement of Cu, Fe and Pb in raw sugar, refined sugar, liquid sugar and molasses. Samples were adjusted to 0.1–5% with 6% HNO3, and Cu, Fe and Pb were measured at 324.8, 248.3 and 283.3 nm, respectively. Heating programmes were optimized for each element, and LODs in the samples were 0.47 µg l−1 for Cu, 1.36 µg l−1 for Fe and 4.38 µg l−1 for Pb for a 5% sugar solution. Recoveries ranged between 100.7 and 105.7% with CVs between 3.97 and 9.08%. A French group156 described the optimization and experimental design methodology for rapid measurement of Cu in a butter dispersion. The optimum ashing ramp and atomization temperature for Cu determination at 324.8 nm were calculated using a centred composite plane. Calibration graphs were linear for 0–50 ppb and the LOD was 7 ppb of Cu in butter. The method was also applied to an anhydrous butter oil–water emulsion. Lendinez et al.157 described the determination of Cr in wine without sample pre-treatment and in other alcoholic beverages after mineralization. Sub-samples (5 ml) of beer, cider, brandy, rum, whisky, gin, vodka, anisette and liqueurs were digested with 1 ml of 65% HNO3 and 35 mg of V2O5 for 90 min at 120°C, then diluted to 10 ml with H2O. The prepared solutions were analysed by ETAAS using drying, ashing and atomization temperatures of 120, 1000 and 2600°C, respectively, for wine, and 150, 1650 and 2500°C, respectively, for other alcoholic beverages. For wine, 10 µl was injected with 10 µl 0.5% HNO3 onto the tube wall. For the other beverages, 10 µl sample aliquots were injected onto a L'vov platform with 10 µl 0.5% Mg(NO3)2. Chromium was measured at 357.9 nm and the LOD was 1 pg. One hundred and twenty-four samples of ten alcoholic drinks were analysed, giving mean Cr values ranging from 7.85 µg l−1 for cider to 24.45 µg l−1 for anisette.Bruhn et al.158 described a study of chemical modifiers for the determination of Cd and Pb by tungsten coil ETAAS with the aim of overcoming the problems of matrix interferences specific to this technique. Optimum conditions (chemical modifier type and concentration, pyrolysis and atomization voltages) were investigated for the determination of Cd and Pb in mussels and non-fat powdered milk. Best results for Cd were obtained using Pd (35 mg l−1) and Pd (50 mg l−1)–Mg (150 mg l−1), and for Pb, the combinations Pd (50 mg l−1)–ascorbic acid (100 mg l−1) and Pd (50 mg l−1)–Mg (50 mg l−1) for acid digested solutions of mussels and non-fat powdered milk, respectively. Results were validated by comparison with results obtained by ETAAS, by spike recoveries and analysis of CRMs.
2.5 Developments in methodology for inductively coupled plasma mass spectrometry
Multi-element and isotope ratio determinations in food and clinical samples were described by Crews et al.159 Three examples of the use of ICP-MS were described. Firstly, thirty-six elements were determined in food samples and the quality criteria used to judge the data were discussed. Size exclusion chromatography was coupled with ICP-MS for the speciation of Cu in blood samples, and, finally, Se isotope ratios were measured for Se standards separated by ion exchange chromatography-ICP-MS. Barnes160 reviewed the status of research and commercially available ICP-MS instruments and their applications and limitations for stable isotopic studies. He considered the requirements for reliable isotope measurements in biological samples, and possibilities for stable isotope analysis in chemically separated compounds using on-line coupling of chromatography and electrophoresis with ICP-MS. Cantone et al.161 investigated the possibility of labelling a solid meal with an aqueous solution of Mo. Cress seeds were grown for 10 d on blotting paper soaked in a solution labelled with 95Mo. The concentration of 95Mo in the edible part of the cress was measured by ICP-MS and was found to be 48.5 ± 0.4 µg g−1. Kawasaki et al.162 investigated the distribution of B isotope ratios in brown rice and soil extracts by ICP-MS. Samples were prepared by dry ashing or by microwave digestion, and B was separated from matrix elements on an ion exchange resin (IRA743). Boron isotope ratios were measured with a precision of 0.24% (RSD for n = 6), with a sample throughput of four samples h−1, each sample being measured six times. The ratio of 11B∶10B in Japanese rice samples ranged from 3.97 to 4.13, with about 75% of these samples being in the range from 4.01 to 4.06. Two samples harvested near the coast had an isotope ratio of 4.13, presumably due to the influence of sea-water. Australian rice had the highest isotope ratio (4.19) of all the samples examined, whilst Californian rice was characterized by a ratio of 4.10. The isotope ratio for Chinese rice (4.04) was in the same range as those measured in Japanese samples. The authors suggested that these results indicate that B isotope ratios in rice could be used to determine the production region. A Portugese group163 developed a method for the determination of Pb isotope ratios in Port wine by ICP-MS. Samples were pre-treated by UV irradiation (mercury high pressure vapour lamp, 1000 W) for 1.5 h, then filtered to 0.45 µm pore size, and diluted ten-fold with 0.5% HNO3. Two different types of mass bias correction were compared, these being external correction with a Pb isotope standard solution, and secondly, internal correction with Tl as an internal standard. No significant difference was found between the results obtained by the two methods. The RSDs associated with the mean values of the Pb isotope ratios were approximately 0.3% for 207Pb∶206Pb and 208Pb∶206Pb, and about 0.8 % for 204Pb∶206Pb. These precisions were considered good enough to differentiate natural variations in abundances in these samples. The method was applied to 24 Port wine samples, and significant correlations (p < 0.05) were found between both the 207Pb∶206Pb ratio and the 204Pb∶206Pb ratio and the age of the dated Port wines. Total Pb concentrations were measured by ETAAS, and varied from 47 to 804 µg l−1. A significant (p < 0.05) decrease of Pb concentration with the age of the wine was noted, as well as a significant correlation (p < 0.05) between the total Pb concentration and the 208Pb∶206Pb ratio.High resolution (HR)-ICP-MS is a technique which is attracting considerable interest, and a novel application was reported by Park et al.164 They measured the relatively short-lived radionuclide, 226Ra, in mineral waters, and compared the result with that obtained by liquid scintillation counting. Conventional methods of measuring 226Ra in drinking water involve co-precipitation of matrix elements with barium sulfate followed by dissolution in alkaline EDTA, which requires an equilibration period of at least 4 weeks. The advent of HR-ICP-MS and improved sample introduction techniques offered the opportunity for a rapid method giving detection limits of low pg l−1. A cation exchange technique was used for separation of 226Ra from matrix elements in the water samples. Matrix separation efficiency was higher than 99% for Ca, the major matrix element, and analyte recovery efficiency was better than 97%. A method LOD of 0.01 pg l−1 was achieved, which was much lower than the LOD of 1 pg l−1 required by United States Environmental Protection Agency. Yamasaki et al.165 used a conference presentation to describe the use of HR-ICP-MS for the multi-element analysis of a single grain of rice in order to determine its authenticity as a `high quality' rice. A charge decoupler was installed on an HR-ICP-mass spectrometer to obtain maximum sensitivity (1 GHz ppm−1 for In). A single grain of rice was digested with 1 ml HNO3 by microwave heating, and, after cooling, internal standard solution (In) and H2O were added to give a final weight of 10 g. The digest solution was introduced to the ICP via an MCN or a Babington-type nebulizer in order to reduce the consumption of sample solutions. The authors reported that the levels of around 50 elements, with concentrations greater than 0.1 ppm in brown rice, were measured satisfactorily with acceptable speed and precision. Klaue and Blum166 used magnetic sector ICP-MS to determine As in potable water using standard liquid sample introduction in the high resolution mode (M/ΔM = 7800) and compared the results with those obtained using HG-ICP-MS in the low resolution mode (M/ΔM = 300). Spectral separation of interfering ArCl from the As signal was possible in the high resolution mode, but the sensitivity was compromised to give detection and determination limits of 0.3 and 0.7 µg l−1, respectively. A gas–liquid separator was used for hydride generation sample introduction, and detection limits in the region of 0.2 ng l−1 were achieved with complete ArCl removal, even for high Cl matrices. It was reported that the results for both methods agreed at As concentrations >1 µg l−1, but only HG-ICP-MS provided accurate results for concentrations of 0.01–1 µg l−1. The authors also evaluated membrane desolvation, mixed-gas plasmas and addition of organic solvents.
2.6 Developments in individual elements
Various methods were reported for the speciation of As in a range of matrices. Ackley et al.168 used microwave-assisted extraction of As species from fish tissue. A variety of extraction solvents were investigated, including H2O, two different MeOH–H2O mixtures, and a 5% TMAH solution. Quantitative extraction of As from a dogfish muscle CRM (DORM-2) was achieved using MeOH–H2O (80 + 20, v/v) with microwave heating at 65 °C in a closed-vessel microwave digestion system. Extracted As species were separated by both ion-exchange and ion-pair chromatography with detection by ICP-MS. Analysis of DORM-2 and three different varieties of fish showed that the majority of As was present as AsB, a non-toxic species. Moldovan et al.169 reported the successful separation of AsIII, AsV, MMA, DMA, AsB and arsenocholine in one chromatographic run. The sample was separated on a mixed mode column (Spherisorb ODS/NH2), using 5.0 mM phosphate buffer at pH 5.0 as the mobile phase. Final detection was by ICP-MS or microwave-assisted oven (MO) coupled with HGAAS. The detection limits obtained with the HPLC-ICP-MS system (0.04–0.28 ng) were approximately twenty times lower than those achieved by HPLC-MO-HGAAS. Chloride present in the samples was chromatographically separated from the As species, and interference from 40Ar35Cl was insignificant. The methods were successfully applied to the determination of six As species in H2O and urine (after sample clean-up). Van Holderbeke and colleagues27 used CE to separate four anionic (AsIII, AsV, MMA and DMA) and two cationic As species (AsB and arsenocholine) in a single run. Low concentrations of these species (<10 µg l−1) were determined by coupling CE on-line with ICP-MS, using an MCN. Higher concentrations could be determined by UV detection. The team reported on the modifications necessary to make a conventional CE system compatible with ICP-MS, the optimization of operating parameters and sample stacking conditions, together with the effect of the sheath liquid and an induced laminar flow. The LOD (based on the height of a peak for which the S/N was 10∶1) was 1–2 µg l−1 As for each species. The CE-ICP-MS system was used to analyse samples of mineral water, soil leachate and urine. Munoz et al.170 reported a precise, simple and rapid method for the determination of inorganic As (AsIII + AsV) in seafood products. The inorganic species were isolated from the matrix by microwave-assisted distillation and determined by HGAAS. Under optimized conditions, AsB, arsenocholine and TETRA ion added to seafood samples were not distilled. However, minor species were distilled and were recovered with varying percentages: 109% MMA, 11% DMA and 0.2% trimethylarsine oxide. The concentrations expressed as As contributed by these species imply an overestimate of inorganic As of approximately 24 ng g−1 (dry mass), whereas the concentrations of inorganic As found in natural seafood samples were between 0.053 and 1.145 µg g−1 dry mass. No significant difference was found between results obtained by this method and those from acid digestion-solvent extraction-HGAAS.
°C and 1000°C, respectively, for Hg determination by ETAAS. The accuracy of the method was tested by the recovery of iodide from water samples (98.1%) and by using a skimmed milk powder CRM. Repeatability of the measurements at different concentration levels gave an RSD lower than 10% for water and the CRM, and 1.33% for infant formulae. The LODs and LOQs were 2.5 µg l−1 and 8.5 µg l−1, respectively, for drinking water and 1.1 µg g−1 and 3.8 µg g−1, respectively, for infant formulas. As part of a conference presentation, Bratter et al.174 described their work to determine the total I concentration in urine, serum and milk by ICP-MS. Approximately 0.2 ml of sample was diluted in 10 ml of ultrapure NH3 solution (1% v/v) and130Te added as an internal standard. The LOD for I in milk was 4 µg l−1 and the method was validated by an independent analytical method (RNAA) and three SRMs, which confirmed good agreement of the results. Iodine concentrations in breast milk (40–80 µg l−1) were found to correlate with maternal intake levels in different geographical regions, and were generally lower than in commercial formulas based on cows milk. By coupling a chromatographic column on-line with ICP-MS, the team were able to investigate the binding pattern of I in breast milk whey, and found that approximately 80% of I in breast milk is present as iodide associated with `about six binding components'. Cows milk and soy-based formulas were found to contain only inorganic I. Sanchez and Szpunar175 also described a method for speciation of I in milk. They linked SEC with ICP-MS to study I species in milk samples from cows, goats and humans, and in a range of infant formulas. They reported that the whey fraction contained 95% of the total I in the milk samples, compared with 15–50% for the infant formulas. Iodine was present mainly as iodide in all samples except the infant formulas, which contained more than half the total I as a complex of Mr > 1000 kDa (not identified). Total I in the samples was measured by ICP-MS following microwave-assisted digestion in NH4OH, validated using a skimmed milk powder CRM.°C (held for 1 min) to 140°C (held for 3 min), then to 200°C (held for 3 min) at 30°C min−1, with He as carrier gas and AFS detection using Ar as sheath gas. The absolute detection limit was 0.2 pg for both methyl- and ethylmercury as Hg. Madson and Thompson180 used GC with AES to determine methylmercury in food homogenates following extraction by a referenced method. The resulting solutions were analysed by GC on a fused silica column coated with DB-Wax operated with temperature programming from 120°C (1 min) to 220°C (2 min) at 40°C per min with He as carrier gas and AES detection of Hg at 253.652 nm. The limits of detection and determination of methylmercury were 0.11 and 0.3 ng g−1 of sample, respectively. Ethylmercury did not interfere. The method was applied to 32 samples of cereal products, grains, fruits and vegetables, and the concentration of methylmercury was below the LOD for most fruits and vegetables, rising to 0.85 ng g−1 of Hg in four basmati rice samples. Recovery of 0.9 ng g−1 Hg added as methylmercury chloride was 70–114%, and the RSD was 3.2% (n = 5).Studies of Se speciation using a variety of techniques were reported. Puskel et al.183 applied their experience of using a hydraulic high pressure nebulizer as an interface between ion-pair HPLC and AFS to analyse selenoamino acids. They separated selenomethionine (SeMet), selenoethionine (SeEt) and selenocystine (SeCys) on a C18 column, using trifluoroacetic acid (TFA) and MeOH in H2O as the eluent. The effects on retention times of MeOH and TFA concentrations were investigated, and the Ar and H2 gas flow rates on the AFS signal intensity optimized. The LODs and retention times for SeCys, SeMet and SeEt were 50, 42 and 71 ng l−1 and 2.1, 3.9 and 6.9 min, respectively. The advantages of this relatively novel method were reported to be low cost, the simple composition of the eluent and the insensitivity of the method to the matrix, although this technique is not suitable for the simultaneous separation of organic and inorganic Se compounds. The identification of unknown signals in Se species in yeast extracts by reversed phase chromatography (RPC)-ICP-MS was investigated by Casiot et al.184 Their strategy involved collection of the Se-containing fraction in the RPC eluate, its lyophilization, followed by pneumatically assisted ES-MS and ES tandem MS of the lyophilizate. Confirmation of the fragmentation pattern was obtained using the S analogue of the anticipated seleno-compound. Using this approach, Se adenosylhomocysteine was identified as the major Se species in an extract of a selenized yeast sample. The same group evaluated eight solid–liquid extraction procedures for the recovery of Se species from yeast.185 Speciation of Se in the extracts was characterized by a range of HPLC methods, including SEC, anion-exchange and RPC with ICP-MS detection. Leaching with H2O and MeOH gave only 10–20% Se recovery, split into eight compounds, among which SeIV and SeMet were identified. An additional 20% of SeMet was recovered by leaching with pectinolytic enzymes. A selenoprotein comprising approximately 30% of the total Se present was solubilized by sodium dodecylsulfate. Proteolytic enzymes gave recoveries of Se above 85%, with the majority as SeMet. The yeast sample was completely solubilized by TMAH, although the Se species present were entirely degraded to SeMet and inorganic Se. Based on this work the authors have proposed a sequential leaching procedure for evaluation of Se speciation in yeast without using a coupled technique. Kotrebai et al.186 analysed Se-enriched garlic and yeast extracts and digests using ion-pair HPLC with on-line detection by ICP-MS and ESI-MS. The principal Se compounds in these samples were identified as SeMet and Se-adenosylselenohomocysteine in yeast, and γ-glutamyl-Se-methyl-SeCys and possibly γ-glutamyl-SeMet in garlic. These compounds accounted for 85 and 90% of the total Se content of the yeast and garlic samples, respectively. It was reported that comparison of the chromatograms of the garlic enzymatic digest with a H2O extract showed no major difference in peak height of γ-glutamyl-Se-methyl-SeCys, indicating that this compound is not incorporated into proteins. This supports the suggestion that potentially dangerous accumulation of Se in body proteins does not occur from Se-enriched garlic ingestion, which may prove to be important when choosing appropriate forms of Se supplement.
2.7 Single and multi-element analysis of foods
This section has been restricted to reviews of work carried out on single and multi-element analysis of foods by a variety of techniques. Crews187 published a review with 77 references which discussed flame emission and AAS, AES, NAA and MS for trace element analysis and its application in food authenticity studies. Ashurst et al.188 presented a review with 141 references which described the mass spectrometric analysis of stable isotopes and its application to the determination of food authenticity. Zahlbruckner et al.189 described experiences with a TXRF system in routine food control, which discussed the suitability of the technique for food analysis and presented representative data for the determination of Ag, Cd, Cu, Fe, Ni, Pb, Sr and Zn in water. Rendle and Taylor190 developed methods for the determination of heavy elements by XRF spectrometry in toxicological samples, and presented results for elements detected in foodstuffs and urine samples.Knowledge gaps in analytical quality control were assessed by Dabeka191 with respect to a typical food analysis procedure (determination of Pb by ICP-MS). It was reported that a sample weight test was the most sensitive of the quality control methods to analytical errors, since it evaluates the accuracy of each sample run in the batch as opposed to generalizing about the batch as a whole and is most sensitive at low concentrations where errors due to contamination or poor sensitivity are most likely. It has the added advantage of not requiring any additional work or reagents if more than one sample replicate is normally run. Recovery studies were the least reliable indicator of accuracy.
2.8 Dietary intake studies
Once again this year, there have been many investigations of the dietary intake of various elements in a range of foods. Duplicate portion studies were reported by six groups. Van Cauwenbergh et al.192 used AAS in an inter-laboratory study to measure Li in duplicate meals collected from four research institutes. Duplicated meals were collected for a 24 h period, then passed through a simulated eating procedure. Each sample was homogenized, freeze-dried and a 400 mg portion was mixed with 1 ml of H2O, H2O2 (250 µl) and HNO3 (2 ml) for microwave digestion. The detection limit was 0.13 ppb of Li on a wet weight basis and the average recovery of 1–4 ppb Li added to foods was 105%, with an RSD of 3% for 10 ppb Li. The mean dietary intake of Li for adults was reported as 8.6 (±4.6) µg day−1. In a Swedish study,193 duplicate portions of all foods and beverages consumed by 15 women during seven consecutive 24 h periods were collected and analysed by AAS after dry ashing. Seventeen elements were measured (Al, As, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Se and Zn). For the purpose of analytical quality assurance, a set of six different simulated diet RMs was prepared which consisted of a number of foods mixed in different proportions, and a procedure for performance evaluation using these RMs was developed. The study showed that the dietary intake of essential mineral elements is generally adequate, and the intake of non-essential elements is low. A Polish group194 collected samples of 24 daily food rations from a company canteen and three daily rations from a welfare house canteen. Food rations typical of those consumed by blue-collar workers and families with average incomes living in major Polish cities were determined from census data and were used as a reference. The samples were ashed at 450°C in a muffle furnace and dissolved in 15% HCl. Cadmium and Pb were determined by FAAS using APDC as a complexing agent and IBMK as the organic phase. Mercury was measured by CVAAS after wet digestion with HNO3 and H2SO4. The average intake of the tested metals did not exceed the FAO/WHO provisional tolerable weekly intake. Deelstra195 developed and validated an analytical procedure for the determination of Si by ETAAS in 24 h duplicate portion diets. Daily dietary Si intake was evaluated in Belgium at two locations on seven consecutive days, and the estimated daily dietary intake of Si was between 10.1 and 42.8 mg, with a mean of 18.6 mg d−1. Total Cr was measured by ETAAS in basic foodstuffs from the typical Austrian food basket by Schonsleben and Wilplinger.196 Various basic foodstuffs, such as cereals, potatoes, vegetables, fruits, meat and sugar, were digested in HNO3 by pressurized microwave decomposition in quartz vessels, prior to measurement by ETAAS using PdCl2 modifier. The daily total Cr intake was established as approximately 47.9 µg. Wilplinger197 also studied the average daily intake of Mn in a selected diet at 12 different locations all over Austria. All the diets were cooked to the same recipe and calculated for a normal person of 70 kg. Pooled diets were homogenized and lyophilized, and 150 mg portions were digested with 2 ml sub-boiled 65% HNO3 at 200–300°C and 80 bar pressure by microwave power (760 W). Manganese absorbance was measured by ETAAS at 279.5 nm (20 µl injection with 7 µl 1% ascorbic acid). The LOD was 10.2 pg and the results for two SRMs were in good agreement with the certified values. It was reported that the mean dietary intake was 4.39 mg Mn, in line with the Deutsche Gesellschaft für Ernahrung recommended daily intake of 2–5 mg Mn, and differences between the 12 locations were insignificant.Dietary intakes of trace elements from wines and grapes were reported in two papers. Teissedre et al.198 measured V levels by ETAAS in French and Californian wines. Wine was injected into a graphite furnace at 75°C, dried at 90°C, then ashed using a temperature programme from 110°C to 300°C and finally taken to 1000°C (held for 90 s with gas flow of 3 ml min−1 and zero gas flow for 30 s). Atomization was at 2750°C with measurement by AAS at 318.5 nm, using 4% HNO3 as the matrix modifier. The LOD was 42 pg with a recovery of 100.3% and RSD in the range 1.3–3.5%. Red wine was reported to contain vanadium at between 7 and 90 µg l−1 whilst white wine had V levels of 6.6 to 43.9 µg l−1. The method was adapted for the determination of V in grapes after acid digestion, giving concentrations of 2–27 µg kg−1 for white and 5–11 µg kg−1 for red varieties. The contribution of wine consumption to daily V dietary intake in France was estimated to be 11 µg day−1. The same group reported the measurement of Ni in French wines and grapes by ETAAS199 and traced possible sources of contamination in wine. The accuracy of the method was validated using standard additions and precision and accuracy were tested to confirm reliability. Concentrations of Ni ranged from 5.4 to 87.9 µg l−1 in red wine, from 7.5 to 74.5 µg l−1 in white wine, from 19.5 to 24.6 µg l−1 in rose wine, and from 8.9 to 26.9 µg l−1 in Champagne. Nickel levels in grapes ranged from 4.2 to 94.0 µg kg−1. For a given vineyard and winery, Ni concentrations in wine increased with storage time, suggesting Ni contamination from stainless steel storage tanks and from Ni-containing pigments in bottles. The total daily dietary intake of Ni from wine consumption in France was calculated to be 4.37 µg d−1 person−1, and the daily contribution of Ni from wine to dietary intake may be as high as 7%.
2.9 Reference materials and collaborative trials
In the wake of the Seventh International Symposium on Biological and Environmental Reference Materials (BERM-7), Roelandts published a paper60 which presented additional biological and environmental reference samples. Three tables were included which provide an easy-to-use survey, together with information on the name of the material, the sample code, the producer, the reference to certification, the names and addresses of the suppliers of each material and specific remarks.Two collaborative studies were described. Fecher and Ruhnke200 reported the results from an inter-laboratory study, with 25 participating laboratories, on the determination of As and Se in foodstuffs, which compared various digestion methods. Homogenates of mussel tissue, egg powder and Brazil nuts were digested by five methods. High temperature digestion with HNO3 in a HPA system was investigated at different temperatures up to 320°C. Nitric acid digestion was also carried out by microwave heating in Teflon, PFA and quartz vessels, by open digestion under reflux conditions, and under pressure in a Tölg bomb with temperatures up to 200°C. Dry ashing was carried out using a temperature gradient with magnesium oxide–magnesium nitrate as the ashing agent. Arsenic and Se were subsequently measured by ETAAS, HGAAS, ICP-MS, HG-ICP-MS, ICP-AES and voltammetry. The results from the inter-laboratory study were compared with reference values determined by an independent laboratory (no information given on how these values were obtained). It was reported that accurate results can only be expected if the digestion and measurement procedures are attuned to each other. For example, the authors mention that foodstuffs of marine origin require a digestion temperature of 320°C to allow full As determination by HGAAS. In addition, owing to the very low concentrations, HGAAS was preferred to ETAAS for the measurement of both As and Se in vegetables, although As was measured only in mussel tissue since concentrations were below the LODs (not given) for the other materials. The study concluded that neither HClO4 nor H2SO4 are needed for digestion if sufficient HNO3 is used at a high temperature. Julshamn et al.201 reported that eleven laboratories took part in a collaborative study of a method for the determination of Ca and Mg in foods by AAS. Samples were digested with HNO3 and H2O2 by microwave heating, following a specified digestion procedure (details given). Repeatability ranged from 2.2 to 8.1% for Ca and 1.9 to 4.9% for Mg. Reproducibility was from 5.9 to 23% for Ca and 4 to 13% for Mg. It was reported that the method was suitable for the determination of Ca in foods containing more than 4000 mg of Ca per kg of dry matter and for Mg in the range 250–2000 mg kg−1 of dry matter. The method was approved for inclusion in the Nordic Committee on Food Analysis (NMKL) analytical methods.
| Element | Matrix | Technique; atomization; presentation* | Sample treatment/comments | Ref. |
|---|---|---|---|---|
| * Hy indicates hydride and S, L, G and Sl signify solid, liquid, gaseous or slurry sample introduction, respectively. Other abbreviations are listed elsewhere. | ||||
| Al | Serum | AA;ETA;L | Al species were separated using fast protein LC with NH4NO3 as eluent. Al citrate was collected, taken for measurement and found to be 15–19% of the total serum Al | 71 |
| Al | Blood, urine | AA;ETA;L | Absorption of Al and citrate were measured following a single oral dose. Peak serum concentrations occurred at different times after ingestion | 202 |
| Al | Serum | AA;ETA;L | Low molecular weight complexes were isolated by ultrafiltration and were then separated by FPLC. Complexes with citrate and phosphate were identified | 72 |
| Al | Urine | AA;ETA;L | Samples were mixed with H2O2, HNO3 and Triton X-100. The LOD was 1.1 ng ml−1 | 203 |
| Al | Dialysis concentrates | AA;ETA;L | The pH was adjusted to 4.0 and the sample passed five times through a column of Chelex-100. The Al was eluted with 0.5 M HNO3, diluted with H2O and measured | 204 |
| Al | Baby food | AA;ETA;L | A study of baby foods, using microwave sample digestion and ETAAS for analysis found the highest levels of Al in formulas based on hydrolysed vegetable protein or soya | 205 |
| Al | Coffee, tea | AA;ETA;Sl | Using aqueous standards an LOD of 2 µg l−1 was achieved. Using a 0.1% m/v slurry the RSD was 8.2% | 206 |
| Al | Beer | AE;ICP;L | Beer, 25 ml, was mixed with 5 ml HNO3–10 ml HCl and heated at 90–95°C for 30 min. More HCl was added, the sample covered, refluxed for 15 min, cooled and diluted to 25 ml using H2O. Using analysis of variance it was shown that storage conditions affected the Al content of the beer | 207 |
| Al | Tissues | AMS;-;- | 26Al was measured to determine distribution of the metal following chronic feeding experiments. Accumulation of Al and signs of dementia were examined | 208 |
| Al | Blood, brain, liver | AMS;-;- | The distribution of 26Al was monitored for several months after a single injection. Binding to brain cell nuclei was observed | 42 |
| Al | Biological specimens | AMS;-;- | The technique of AMS and the use of 26Al as a tracer for studies of metabolism, were reviewed | 41 |
| As | Egg powder, mussel tissue, nuts | MS;ICP;L AA;ETA;L AE;ICP;L AA;Hy;L | The named techniques were used to determine As and Se as part of a comparison of digestion procedures involving 25 laboratories | 200 |
| As | Urine | AA;Hy;HPLC | As species in candidate RM samples were separated using a system which included on-line digestion with UV radiation and alkaline persulfate solution, prior to HG | 61 |
| As | Urine | AA;Hy;L | Analysis of untreated urine failed to measure dimethyarsinic acid. Treatment with 2 M HCl at 80°C for 5 h was necessary | 209 |
| As | Seafood | AA;Hy;L | Methods for preparation prior to measurement of AsIII and AsV were tested. An improved HG method was presented involving solubilization in HCl, HBr–hydrazine sulfate reduction, extraction into CHCl3 and then into HCl, and dry ashing | 69 |
| As | Seafood | AA;Hy;L | Inorganic species were isolated by microwave-assisted distillation. Some of the more volatile species were also distilled-over, contributing to a positive bias in the results | 170 |
| As | Tissues | AA;ETA;L | Samples were collected after a fatal poisoning. Tissues were dried and analysed directly for total As measurements, or after extraction with CH3OH and separation of As compounds by HPLC | 210 |
| As | Baby foods | AA;ETA;Sl | Samples were suspended in a medium containing 0.1% m/v Triton X-100–1% v/v HNO3–0.3% Ni(NO3)2 and introduced into the furnace. The LOD was 22 ng g−1. Results were validated against a procedure based on microwave digestion | 211 |
| As | Urine | AF;Hy;HPLC | Concentrations of HCl and NaBH4 and gas flow rates were optimised. As species were separated using 20 µl sample | 212 |
| As | Beer, wine | AF;Hy;FI | As was determined in beer and wine at LODs of 0.3 and 0.5 g l−1, respectively, using FI–HG–AFS. Optimum conditions were 6 M HCl, and 0.5% m/v NaBH4 and 6 M HCl and 1% NaBH4 for beer and wine, respectively. No mineralization step was necessary | 213 |
| As | Serum | AF;ETA;L | Preliminary results showing that ETA–LEAFS may be used for the analysis of diluted serum | 214 |
| As | Cereals | AF;Hy;L | Sample, 2 g, was soaked overnight in 20 ml HNO3–HClO4, 4 + 1, heated until fumes appeared, then cooled. H2O was added, the digest heated to reduce the volume to 2 ml and then diluted to 50 ml with H2O. A 10 ml portion was taken, treated with 6 ml of a reductant containing thiourea–ascorbic acid and 3 ml 50% HCl and the solution diluted to 25 ml with H2O. A further portion was removed, treated with KBH4 and the hydride transferred to the AF spectrometer. The LOD was 0.3 µg l−1 (in Chinese) | 215 |
| As | Plasma | MS;ICP;HPLC | Arsenobetaine was the only As species found in samples from patients undergoing haemodialysis | 74 |
| As | Liver | MS;ICP;HPLC | As compounds were extracted with CH3OH–H2O, separated by ion exchange chromatography coupled to ICP-MS. Samples from marine mammals were examined | 216 |
| As | Nails | MS;ICP;L | Preparation steps—washing, decomposition—were evaluated. As was determined using an Ar–N plasma with Te as internal standard | 217 |
| As | Biological specimens | MS;ICP;HPLC | Eight As species were separated by anion exchange chromatography using an Ion Pac AS 7 column. A HNO3 gradient was applied and 1,2-benzenedisulfonic acid was added as ion pairing modifier. LODs were 0.16–0.60 µg As l−1 | 218 |
| As | Urine, water | MS;ICP;HPLC AA;Hy;L | HPLC was used to remove chloride interference and to separate 6 of the most common As species. Eluate was either introduced directly into the ICP-MS or into a microwave oven coupled to HGAAS. A cleanup step was necessary in the analysis of the urine samples. The performance of the 2 methods was compared | 169 |
| As | Mineral water, urine | MS;ICP;CE | Necessary modifications, such as use of a microconcentric nebulizer, to allow successful coupling of CE to ICP-MS were described. LODs of 1–2 µg l−1 were achieved for 6 species. It was possible to separate both anionic and cationic forms in one run | 27 |
| As | Urine | MS;ICP;HPLC | 6 arsenosugars in 20 µl urine were rapidly separated on an ODS-2, 250 × 4.6 mm column at 70°C. Samples were analysed following consumption of mussels | 22 |
| As | Urine | MS;ICP;HPLC AA;Hy;HPLC | As species separated on a Spherisorb ODS–NH2 column were detected by ICP-MS or by HGAAS. Detection limits were much lower using ICP-MS and Cl− was retained on the column | 169 |
| As | Urine | MS;ICP;CE | Six As species were separated. Details of the on-line coupling were presented. The LOD was 1–2 µg l−1 | 27 |
| As | Urine | MS;ICP;HPLC | The sample was injected onto a Dionex IonPac column. As species were eluted with 2 mM TMAH for 0.5 min, 10 mM (NH4)2CO3 for 7.5 min and 2 mM TMAH for 7 min | 73 |
| As | Water | MS;ICP;L;HG | High-resolution- and HG-ICP-MS were compared. The loss of sensitivity in the high resolution mode made HG the method of choice for samples containing less than 1 µg l−1. Both techniques overcame isobaric interference from ArCl. Membrane desolvation, mixed-gas plasmas and organic solvent addition were also discussed | 166 |
| As | Wine | MS;ICP;FI | A microscale FI system utilizing a microconcentric nebulizer was used to reduce enhancement caused by C-containing substances. Sample volumes were between 0.2–1.0 µl and yielded absolute LODs in the range 25–59 fg | 167 |
| As | Fish | MS;ICP;HPLC | 13 As and Se species were separated using HPLC-ICP-MS. The column temperature was raised to 70°C to increase speed of separation. ArCl+ interference was controlled by simultaneous monitoring of 75, 77 and 78 m/z | 22 |
| As | Cereals, meat, vegetables | MS;ICP;HPLC | Preliminary results from a study to evaluate dietary intake of As species were presented | 219 |
| As | Fish | MS;ICP;HPLC | Using CH3OH–H2O, 80 + 20 v/v, and microwave heating at 65°C quantitative extraction of As was achieved. The extracted As was then speciated using ion-exchange and ion-pair LC-ICP-MS | 168 |
| As | Coffee | AE;ICP;Hy | Following microwave digestion using HNO3–H2O2, As and Se were determined by HG-ICP-AES, at LODs of 2 and 1 µg l−1, respectively. Using standard additions all samples of Brazilian coffee had levels below the LODs | 220 |
| Au | Serum | MS;ICP;LA | Distribution of Au among plasma proteins was investigated using gel electrophoresis prior to LA | 24 |
| B | Blood, synovial tissue | AE;ICP;L | Uptake of B into tissue of rheumatoid animals was investigated. The B was administered in liposomes | 16 |
| B | Biological specimens | MS;ICP;L | Techniques for measuring isotopes of B were reviewed. Features such as sample preparation and interferences were also discussed | 221 |
| B | Biological specimens | MS;ICP;L | A wide range of analytical techniques were reviewed. Further discussion of ICP-MS was given with emphasis on sources of contamination, sample digestion and instrumental parameters | 77 |
| B | Biological samples | MS;ICP;L | Total B and 10B were measured following HNO3 digestion. Variable blanks and matrix effects were overcome using Be as internal standard | 75 |
| B | Brown rice | MS;ICP;L | Samples were digested by dry ashing or microwave methods. B was separated from matrix elements using an ion-exchange resin. The 11B∶10B ratio may be of use in determining geographical origin | 162 |
| Bi | Urine | AE;ICP;FI | The FI manifold allowed for retention and preconcentration of Bi on quinolin-8-ol and Amberlite XAD-7 at pH 5.0. Extraction was with HNO3 and the LOD was 0.03 ng ml−1 | 18,19 |
| Bi | Blood, urine | AA;ETA;FI | 500 µl sample was mixed with HNO3 and passed through a digestion coil with microwave heating. The flow was merged with an Sn2+ reagent and taken through a precipitation coil. A portion was removed from the outflow for ETAAS | 8 |
| Ca | Foods | AA;-;L | Results were described of an inter-laboratory trial of a method based on HNO3–H2O2 digestion in a microwave oven, followed by AAS determination of Ca and Mg | 201 |
| Ca | Honey | AA;F;FI | Sample was dissolved in dilute HCl containing La and then introduced to the flame using continuous FI. Results for Ca, Mg and Zn compared well with those obtained using a lengthier mineralization procedure | 153 |
| Ca | Milk, milk powder | AA;-;FI | Ca and Zn were determined by high performance flow injection hydraulic high pressure nebulization and a motorized injection insert valve with a 100 µl sample loop. Samples were diluted 1 + 1 with H2O, following reconstitution if necessary. Using this procedure it was possible to perform 200 measurements h−1 | 10 |
| Cd | Urine | AA;F;L | The chelate with cupferron was collected onto activated C, eluted and aspirated into a slotted quartz tube. The LOD was 0.03 µg l−1 | 15 |
| Cd | Kidney | AA;F;L | Weighed samples were dried and heated at 110°C for 60 min with HNO3. The mean Cd concentration in 2700 samples of renal cortex was 19 µg g−1. Influences of smoking and age were demonstrated | 222 |
| Cd | Blood | AA;ETA;FI | Samples were digested with HNO3 and HClO4. Excess acid was removed under vacuum and the residue taken into dilute HNO3. The Cd and Pb in this solution were concentrated as the ammonium diethyldithiophosphate (ADDP) complexes onto the wall of a PTFE knotted reactor. The FI manifold included a device for purification of the ADDP by passage through C18 bonded silica gel. The trapped metals were eluted with 35% CH3OH into a graphite tube which had been pretreated with Ir. Enhancement factors of 26 and 99 and LODs of 0.2 and 1.6 ng l−1 were obtained for Cd and Pb, respectively | 93 |
| Cd | Urine | AA;ETA;L | 1 ml urine, 250 µl Pd (8 g l−1), 500 µl NaN3 (4 g l−1) and 250 µl 1% HCl were mixed. 10 µl were injected into the furnace. The modifier permitted a high ash temperature to be used | 78 |
| Cd | Urine, serum, blood | AA;ETA;L | Samples were diluted with 0.015% Triton X-100–0.1% NH4H2PO4. 10 µl were pipetted into the furnace with a wash solution (0.015% Triton X-100–0.65% HNO3) and an oxidizing solution (15% H2O2–0.65% HNO3). A fast heating programme was employed | 223 |
| Cd | Powdered RMs | AA;ETA;Sl | 10–35 mg sample were mixed with 1 ml 60% PTFE slurry, 0.4 ml HNO3 and 0.2 ml plant glue. The LOD was 0.12 pg | 11 |
| Cd | Powdered RMs | AA;ETA;L | See Cu, ref. 224 | 225 |
| Cd | Placenta | AA;ETA;L | Microwave digestion with HNO3 and HClO4 was used to study prenatal exposure in four regions. The LOD was 0.16 µg kg−1 | 226 |
| Cd | Fingernails | AA;ETA;Sl | Nails were prepared as slurries for direct analysis | 227 |
| Cd | Horse muscle | AA;ETA;S | With the small mass of sample taken, large variations in results were obtained from the same sample. This was reduced by analysis of at least six samples | 228 |
| Cd | Infant formula, milk | AA;ETA;L | Samples, 3 ml or 0.39 g of powder, were mixed with 10 ml of HNO3–HClO4, 9 + 1, left overnight and then slowly heated to 160–170°C. When fumes of HClO4 appeared the solution was cooled, diluted to 10 ml with H2O and a portion taken for analysis using Zeeman-effect ETAAS. NH4H2PO4 was used as chemical modifier and the LODS for Cd and Pb were 0.75 and 7.5 µg l−1, respectively | 229 |
| Cd | Mussels | AA;ETA;L | Cd and Pb were extracted from tissue using dilute HNO3 and ultrasound. The extraction was performed in the autosampler cups. A two-level full factorial design was used to optimize extraction time, ultrasound amplitude, acid concentration and particle size; the latter two variables were found to be the most significant | 10 |
| Cd | Food CRMs | AA;ETA;L | A thorough comparison of high pressure ashing and microwave digestion was described. The high pressure asher was felt to offer an advantage in sample throughput, but both methods offered similar technical performance. LODs were enhanced using an EDL and end-capped graphite tubes | 142 |
| Cd | Mussels, non-fat powdered milk | AA;ETA;L | In a study of tungsten coil ETA the use of Pd, Mg or ascorbic acid chemical modifiers in overcoming matrix interferences was described. For Cd the most satisfactory modifiers were Pd (35 mg l−1) or Pd–Mg (50 + 150 mg l−1) and for Pb the choice was Pd–ascorbic acid (50 + 100 mg l−1) or Pd–Mg (50 + 50 mg l−1) | 158 |
| Cd | Biological specimens | AE;ICP;S | Powdered sample mixed with (NH4)2HPO4 was placed in a tungsten sample cuvette which was located on a tungsten boat furnace. TMAH was added and the temperature of the furnace was increased by resistance heating to effect sample digestion. With a further increase of the furnace temperature, analyte vaporization and transfer to the ICP occurred | 20 |
| Cd | Food SRMs | MS;ICP;L AA;Hy;L AA;CV;L | High pressure ashing was proposed as an alternative to microwave assisted digestion. A number of virtues were apparent for the former, including minimal acid requirements, limited residual matrix, no loss of analyte and the potential for automated sample preparation | 140 |
| Cd | Urine, tissues | MS;ICP;FI | ID measurements were employed. Samples were either mixed on-line with the spike solution and pumped into the nebulizer or used for generation of volatile species using sodium tetraethylborate | 79 |
| Cd | Metallothionein | MS;ICP;HPLC | Details of the linking between the HPLC and the ICP-MS were described | 230 |
| Cd | Liver, urine | MS;ICP;HPLC–HG | Cd speciation in biological specimens using vesicle assisted HG measurements was discussed | 80,231 |
| Co | Wheat flour | AA;ETA;Sl | Sample, 150 mg, was mixed with 5 ml 15% HNO3–10% H2O2, agitated ultrasonically for 15 min and a 20 µl aliquot taken for measurement of Co, Cr and Ni at 240.7, 357.9 and 232 nm, respectively | 232 |
| Co | Cobalamin | MS;ICP;HPLC | See Cd, ref. 230 | 230 |
| Co | Pharmaceuticals | AE;-;L | Drugs or ointments were mixed with sodium cobaltinitrite. Complexes of the drug with the anion were precipitated and removed by filtration. Excess Co in solution was measured in an indirect method for the determination of naphazoline, tolazoline or xylometazoline | 233 |
| Cr | Serum | AA;ETA;L | Samples from patients with bone cancer were analysed after dilution with NH4NO3 and Triton X-100 in 1% HNO3. Portions were placed into an La-coated furnace (in Chinese) | 234 |
| Cr | Urine | AA;ETA;L | Chemical modifiers, background correction and furnace heating were studied and the optimized conditions were reported | 83 |
| Cr | Urine | AA;ETA;L | Various factors—heating temperatures, background correction, chemical modifiers—were investigated | 235 |
| Cr | Urine | AA;ETA;L | See Al, ref. 203. The LOD was 0.42 ng ml−1 | 203 |
| Cr | Milk powder, mussels | AA;ETA;L | Various chemical modifiers were evaluated for the determination of Cr using tungsten coil ETA spectrometry. Ascorbic acid–Mg mixtures gave the best results | 236 |
| Cr | Alcoholic beverages | AA;ETA;L | Cr in wine was wall atomized, following dilution of a 10 µl portion with 10 µl HNO3. Other beverages, 5 ml, were digested by heating with 1 ml HNO3–35 mg V2O5 at 120°C for 90 min. The resulting digest, 10 µl, was mixed with 10 µl 0.5% Mg(NO3)2 and atomized from a L'vov platform. The absolute LOD was 1 pg | 157 |
| Cr | Foods | AA;ETA;L | The results of a survey of Cr in Austrian foods was detailed | 196 |
| Cr | Wheat flour | AA;ETA;Sl | See Co, ref. 232 | 232 |
| Cr | Food CRMs | AA;F;FI | FI-preconcentration-FAAS was used to determine Cr and Mn in CRMs. A multifactorial method was used to optimize operating parameters | 144 |
| Cr | Water | AA;F;HPLC | CrIII and CrVI were separated on a C18 column. The eluate passed via a high pressure nebulizer to the flame for detection using a diode laser. The wavelength of 425.44 nm was obtained by frequency doubling. Full details of the instrumental arrangement were described. The LOD for CrVI was 30 pg ml−1 | 149 |
| Cr | Food, food utensils | AA;-;L | The leaching of Cr and Ni from cooking utensils used to prepare 11 different menus was measured. There were differences depending on menu, but they were insignificant in relation to the levels of the elements in the foods themselves | 237 |
| Cu | Water, wine | -;-;- | A wide range of analytical techniques, including those using atomic spectroscopy, were compared for the determination of Cu. The paper also provided information on the binding of Cu in the samples (in German) | 238 |
| Cu | Brain | AA;F;FI XRF;-;Sl | Brain homogenate was diluted with H2O and HNO3 to give a slurry which was taken for FI or used for TXRF | 9 |
| Cu | Biological specimens | AA;ETA;L | Metals were vaporized and passed by a flow of Ar through an open molybdenum column at 1900°C. Cu and Mn were separated from other metals and measured by AAS | 224 |
| Cu | Plasma, blood cells | AA;ETA;L | Cells were isolated by density gradient centrifugation. Specimens were from renal failure patients | 239 |
| Cu | Cow and human milk, infant formula | AA;ETA;L | Samples were suspended in 20% C2H5OH–0.65% HNO3–6% H2O2–0.1% NH4H2PO4 and injected directly into the furnace. LODs for Cu and Zn were 70 and 15 pg, respectively. Metal–protein binding was investigated | 240 |
| Cu | Butter | AA;ETA;L | Method optimization was conducted using a centred composite plane for experimental design. The LOD was 7 ng g−1 in butter (in French) | 241 |
| Cu | Dairy products | AA;ETA;Sl | Samples were slurried in 10 ml H2O2–HNO3–NH4H2PO4–C2H5OH, 100 + 2 + 1 + 40, then injected directly. LODs for Cu and Pb were 0.11 and 0.7 ng ml−1 | 135 |
| Cu | Sugars | AA;ETA;L | Sugars were diluted to 0.1–5% in 6% HNO3 and analysed by ETAAS. At wavelengths of 328.4, 248.3 and 283.3 nm the LODs for Cu, Fe and Pb were 0.47, 1.36 and 4.38 µg l−1, respectively (in Japanese) | 155 |
| Cu | Olive oil | AA;-;L | Cu and Fe were measured in 47 samples of virgin olive oil. Oxidation of the oils was investigated (in Italian) | 242 |
| Cu | Milk | AE;ICP;FI AA;ETA;L | Proteins were precipitated, separated and Cu and Mn determined in both fractions using ETAAS. The filtrate was loaded into an FI manifold and passed through an anion exchange column. The column was back flushed with 2 M HCl, the eluate passing into an ICP-AE spectrometer. This allowed cationic, anionic and casein-bound Cu and Mn to be determined | 148 |
| Cu | Edible oils | AE;ICP;L | Emulsified samples were prepared to allow sample introduction without the use of organic solvents. Various surfactants were used to prepare the emulsions and recoveries for Cu, Fe and Ni were in the range 90–110% | 137 |
| Cu | Serum | MS;ICP;L | Cu, Fe and Zn were determined using ID and a double focusing mass spectrometer | 243 |
| Cu | Metallothionein | MS;ICP;HPLC | See Cd, ref. 230 | 230 |
| Dy | Faeces | AA;ETA;L | A tungsten-coil atomizer was employed to eliminate carbide formation. 10% H2 was included in the Ar purge gas to improve atomization efficiency | 116 |
| Eu | Faeces | AA;ETA;L | See Dy, ref. 116 | 116 |
| Fe | Liver | -;-;- | Large variation in the concentration of Fe within a single organ was observed | 244 |
| Fe | Liver | AA;ETA;L | Paired specimens of fresh and paraffin-embedded tissue were examined. Wax was removed from the embedded samples by washing with xylene and the tissues were digested with HNO3 and H2O2. A small positive bias was noted for the embedded specimens when they contained high concentrations of Fe. At less than 100 mmol kg−1 no differences were seen | 245 |
| Fe | Sugars | AA;ETA;L | See Cu, ref. 155 | 155 |
| Fe | Pharmaceuticals | AA;-;L | See Co, ref. 233, but potassium ferricyanide was used to form the drug–anion complex | 233 |
| Fe | Olive oil | AA;-;L | See Cu, ref. 246 | 246 |
| Fe | Edible oils | AE;ICP;L | See Cu, ref. 137 | 137 |
| Fe | Red blood cells | MS;ICP;L | Young erythroid cells, with greater uptake of Fe, were separated so that a smaller dose of stable isotope could be used to investigate Fe absorption | 88 |
| Fe | Serum | MS;ICP;L | See Cu, ref. 243 | 243 |
| Fe | Skin | XRF;-;S | Parameters for the in vivo measurement of Fe were developed. The LOD was <10µg g−1 | 45 |
| Ga | Cabbage leaves | AE;ICP;L | ICP-AES was used in the validation of a spectrophotometric method for the determination of Ga, Sc and V in potentially polluted cabbage samples from the Upper Silesia region of Poland. Method agreement was good (in Polish) | 247 |
| Hg | Blood | AA;CV;FI | KBr–KBrO3 mixed with Triton X-100 was added to blood and heated. The digested solution was taken for measurement of total Hg. Inorganic mercury was determined by omission of the heating step | 105 |
| Hg | Serum | AA;CV;L | Total and inorganic Hg were determined and the results examined in relation to fish consumption and amalgam fillings. Concentrations were higher in samples collected in 1968–9 compared with 1980–1 | 248 |
| Hg | Urine | AA;CV;FI | An automated on-line system with microwave digestion, addition of Br reagent and CV-AAS was described. Linearity at 0.05–20 µg l−1 was reported | 107 |
| Hg | Urine | AA;CV;FI | The FI manifold provided for measurement of HgII with SnCl2 reduction, for microwave assisted oxidation with persulfate to measure total Hg and for on-line standards addition calibration | 106 |
| Hg | Breast milk | AA;CV;L | Hg in milk was related to the mother's amalgam fillings and to fish consumption | 110 |
| Hg | Breast milk, blood, urine | AA;CV;L | Maternal samples were collected a few days and 2 months after giving birth. Results were examined relative to amalgam fillings and dietary intake of fish | 109 |
| Hg | Biological tissue | AA;CV;L | A single flask was used for digestion and then for vapour generation | 249 |
| Hg | Biological specimens | AA;CV;FI | The FI manifold added potassium peroxodisulfate and H2SO4 to the sample. With heating, organomercury compounds were destroyed prior to vapour generation. With no heating only inorganic Hg was measured | 250 |
| Hg | Foods | AA;CV;L | Hg was determined in food digests using a technique described as circulating enrichment-CVAAS. The LOD was not given (in Chinese) | 251 |
| Hg | Potable water | AA;ETA;L | Following adjustment of pH to 5–8, 20 ml of sample was mixed with 2,3-dimercaptopropane-1-sulfonate and 1 mM sodium acetate buffer. The solution was diluted to 25 ml with H2O, left to stand for 1 h and the resulting Hg-containing complex concentrated on 2 C18 cartridges. The complex was then eluted, the volume adjusted to 2 ml and 50 µl taken for ETAAS. At 253.7 nm the LOD was 0.053 µg l−1 | 178 |
| Hg | Fish | AE;GC;L | 3 different extraction procedures were evaluated for the determination of methyl- and ethylmercury in fish, soil and sediments, with LODs of 0.2 pg for both species. For fish the best method was based on acidic KBr–CuSO4 isolation, CH2Cl2 extraction and alkaline digestion | 179 |
| Hg | Food | AE;GC;L | Methylmercury was measured in a range of foods including cereals, fruits and vegetables, the highest levels, 0.85 ng g−1, being found in Basmati rice. The method had an LOD of 0.11 ng g−1 | 180 |
| Hg | Serum, urine | AE;GD;L | The method was reported to be more selective and sensitive than ICP-AES (in Korean) | 252 |
| Hg | Urine | MS;-;GC | Hg and methylmercury were ethylated with NaBEt4, extracted on polydimethylsiloxane fibres and separated by GC | 253 |
| Hg | Hair | MS;ICP;CV | Following digestion in small PTFE vessels the CV system was used for sample introduction. Measurements of Hg isotopes were made | 104 |
| Hg | Biological materials | MS;ICP;GC | Multicapillary GC provided very effective separation of Hg species while ICP-MS allowed for sensitive measurements. Samples were prepared by microwave assisted solubilization with TMAH and formation of volatile complexes with NaBEt4 | 102 |
| Hg | Biological specimens | MS;ICP;L | Transport efficiency, and hence signal intensity, was improved by addition of NH3 with either ethylenediamine or triethanolamine to the diluent | 108 |
| Hg | Blood, urine | MS;ICP;L | Dichromate in HCl was superior to Au in HCl in reducing spray chamber memory effects. The LOD was 0.15 µg l−1 and accurate results were obtained for RMs | 103 |
| Hg | Potable water | MS;ICP;L AF;CV;L | Two papers from the same research group described the use of Au as a stabilizing agent, following amalgamation with Hg. Au was added off-line to both samples and standards and, to prevent memory effects, to the ICP-mass spectrometer wash solution. The use of Au as a preservative allowed the long-term storage of solutions containing up to 1 µg l−1 Hg. The use of CVAAS was compromised by Au suppressing the standard signals | 176, 177 |
| Hg | Urine | MS;-;GC | HgII and alkylated species of Hg, Pb and Sn were treated with NaBEt4 and separated by capillary GC. Tandem MS for detection provided much improved LODs | 254 |
| Hg | Skin creams | XRF;-;S | Skin cream was warmed to melt and poured into a mould to prepare a solid pellet. The LOD was 3.3 µg g−1. Concentrations up to 29000 µg g−1 were found | 255 |
| I | Infant formula, tap water | AA;ETA;L | The ion pair 1,10-phenanthroline–HgII–I− was extracted into IBMK, allowing the determination of I in infant formulae and water at LODs of 1.1 and 2.5 µg l−1, respectively | 173 |
| I | Milk, infant formula | MS;ICP;SEC | I was speciated in milk from different animals—cow, goat, human—different geographical origins and in infant formulas from different manufacturers. Iodine was present as iodide in all of the samples except the formulas, where it was bound to a high MW species | 175 |
| I | Breast milk, infant formula, serum, urine | MS;ICP;ID | 127I was determined in milk, serum and urine samples following dilution in 10 ml of NH3. 130Te was the internal standard and, assuming a 50-fold dilution, the LOD in the sample was 4 µg l−1. HPLC-ICP-MS was used to elucidate I–protein binding patterns | 174 |
| I | Dairy products | MS;ICP;FI | I was determined directly in milk by FI-ICP-MS and in cheese and cream by bomb ashing followed by ICP-MS. The LOD of the 2 approaches were 9 and 60 ng g−1, respectively. Explanations for differing concentrations in different parts of Denmark were offered | 172 |
| I | Dietetic foods | MS;ICP;L | I was determined following extraction with TMAH. The method was validated by a ring trial involving 15 laboratories (in German) | 172 |
| I | Urine | MS;ICP;L | Excretion increased during pregnancy and then returned to normal | 86 |
| I | Plasma proteins | MS;ICP;L | Measurement of complexes of diiodo–Pt anticancer drugs was described | 66, 87 |
| I | Thyroid, urine | XRF;-;S | The size of the thyroid gland and the I content were determined in vivo | 256 |
| Li | Red cells, plasma | AA;ETA;L | Normal concentrations were determined, the medians were 0.23 and 0.13 µM for red cells and plasma, respectively | 98 |
| Mg | Foods | AA;-;L | See Ca, ref. 201 | 201 |
| Mg | Honey | AA;F;FI | See Ca, ref. 153 | 153 |
| Mg | Renal tubular fluid | AA;ETA;L | Cl− caused a suppression of the signal, NH4NO3 as a chemical modifier overcame this effect. Picomole quantities were measured in nanolitre sample volumes | 99 |
| Mg | Plasma, urine | MS;ICP;L | Mg isotopes were measured by EI-MS and by ICP-MS. Results were similar but superior precision was evident for the latter technique | 40 |
| Mn | Blood, urine | AA;ETA;L | Mg(NO3)2 modifier was applied inside the graphite tube and heated to achieve in situ decontamination. The diluted sample was then pipetted on top and the Mn atomized | 100 |
| Mn | Blood, urine | AA;ETA;L | Samples were diluted: urine 1 + 1 with 0.2% HNO3, blood 1 + 9 with 0.1% Triton X-100. A series of chemical modifiers were investigated and 15 mg of Pd [as Pd(NO3)2] was found to be most effective. Aqueous standards were used and the LOD was 0.6 µg l−1 | 101 |
| Mn | Urine | AA;ETA;L | See Cu, ref. 224 | 257 |
| Mn | Milk | AE;ICP;FI AA;ETA;L | See Cu, ref. 148 | 148 |
| Mo | Tissues | AA;ETA;L | Tissue samples were ashed at 450°C. Residues were dissolved in HNO3 and 20 µl injected into a tantalum-lined graphite tube (in Chinese) | 258 |
| Mo | Urine | AA;ETA;L | See Al, ref. 203. The LOD was 0.81 ng ml−1 | 203 |
| Mo | Foods | MS;ICP;L | Extrinsic labelling of solid foods, using aqueous solutions of 95Mo, was shown to be a useful method of determining Mo biokinetics in humans | 161 |
| Ni | Saliva | AA;ETA;L | Matrix effects were reduced with a Pd–Lu modifier. The LOD was 0.11 µg l−1 | 111 |
| Ni | Wine | AA;ETA;L | Ni was determined in a wide range of French wines. The Ni arose from stainless steel storage vessels or from pigments in the bottle glass. It was calculated that wine may contribute as much as 7% to the French dietary intake of Ni | 199 |
| Ni | Wheat flour | AA;ETA;Sl | See Co, ref. 232 | 232 |
| Ni | Food, food utensils | AA;-;L | See Cr, ref. 237 | 237 |
| Ni | Edible oils | AE;ICP;L | See Cu, ref. 137 | 137 |
| Pb | Blood | AA;ETA;FI | See Cd, ref. 93 | 93 |
| Pb | Blood | AA;ETA;L | Pb was extracted as the APDC chelate into IBMK. 20 µl organic phase were deposited onto a tungsten-coil atomizer and the LOD was 24 pg | 56 |
| Pb | Urine, blood, placenta | AA;ETA;L | Samples were spiked with Bi as internal standard and measurements were made with a simultaneous multi-element system. Assay imprecision improved considerably when internal standardization was used; standard additions calibration was unnecessary. | 54 |
| Pb | Urine, serum, blood | AA;ETA;L | See Cd, ref. 223 | 223 |
| Pb | Urine | AA;ETA;L | Results from an inter-laboratory comparison programme were reported | 259 |
| Pb | Urine | AA;F;L | See Cd, ref. 15. The LOD was 0.27 µg l−1 | 15 |
| Pb | Sweat, urine | AA;ETA;L | Samples were passed through a column of `Kryptofix-222B' and the retained Pb eluted with 0.1 M HNO3. Thus, the Pb was separated from up to 0.3% NaCl-rich matrices | 260 |
| Pb | Biological samples | AA;ETA;L | Aliquots from acid digests were pipetted onto a graphite platform which had a tungsten carbide–rhodium coating. The permanent modifier extended tube lifetime, was tolerant to 5% v/v HNO3 and was as effective as a Pd + Mg(NO3)2 modifier | 261 |
| Pb | Fingernails | AA;ETA;Sl | See Cd, ref. 227 | 227 |
| Pb | Placenta | AA;ETA;L | See Cd, ref. 226. The LOD was 3.9 µg kg−1 | 226 |
| Pb | Teeth | AA;ETA;L | Teeth were dissolved in HNO3–H2O2 and the solution analysed with NH4H2PO4 as chemical modifier. Concentrations depended on tooth type in children but not in adults | 262 |
| Pb | Bone | AA;ETA;L | Overcorrection observed with Zeeman-effect systems was shown to be caused by molecular absorption in the presence of phosphate, which is split in the magnetic field. The error was reduced by reducing the phosphate in the modifier or by using an end-capped transversely heated tube | 91 |
| Pb | Blood, urine and rice SRMs | AA;ETA;FI | A fully automated system allowed sample to be passed, via FI, to a conical micro-column, of 50 µl volume, packed with silica gel sorbent. The sample was eluted using 46 µl of 0.03 M EDTA, pH 10.5, and blown into the furnace pre-heated to 110°C. For a 20 s preconcentration the LOD was 2 ng l−1 | 14 |
| Pb | Milk | AA;ETA;L | Milk was injected directly into a platform tube, with Pd present as chemical modifier (in Japanese) | 263 |
| Pb | Milk | AA;ETA;L | Milk, 300 µl, was diluted with 200 µl of Triton X-100. 100 µl Pd Mg(NO3)2 and 200 µl of Pb standard were added. At 283.3 nm the LOD was 5 ng ml−1 in milk | 264 |
| Pb | Infant formula, milk | AA;ETA;L | See Cd, ref. 229 | 229 |
| Pb | Sugars | AA;ETA;L | See Cu, ref. 155 | 155 |
| Pb | Powdered drinks | AA;ETA;L | Samples of sugar-based drinks were dissolved in H2O, acidified by addition of 0.2% v/v HNO3, and 20 µl of sample and 10 µl of 0.05% m/v Pd–0.03% m/v Mg(NO3)2 injected into an end capped cuvette. The LOD was 11 pg. The method was also suitable for sugar and honey analysis | 154 |
| Pb | Edible oils and fats | AA;ETA;L | It was found that matrix effects in fat analysis were directly related to the degree of unsaturation | 265 |
| Pb | Food CRMs | AA;ETA;L | See Cd, ref. 142 | 142 |
| Pb | Mussels | AA;ETA;L | See Cd, ref. 10 | 10 |
| Pb | Mussels, non-fat powdered milk | AA;ETA;L | See Cd, ref. 158 | 158 |
| Pb | Dairy products | AA;ETA;Sl | See Cu, ref. 135 | 135 |
| Pb | Urine | AA;Hy;FI | Ferricyanide was added to the sample to give PbIV. The FI manifold mixed this sample with an acid stream and with NaBH4 to generate the hydride. An LOD of 80 ppt was reported. Interference from EDTA was eliminated by addition of Sc | 266 |
| Pb | Tap water | AE;ICP;FI | Pb was pre-concentrated as a Pb–DDC complex using FI-ICP-AES with a knotted reactor and ultrasonic nebulization. The LOD was 0.2 ng ml−1 for a 10 ml sample | 267 |
| Pb | Fingernail | AE;ICP;S | The sample was placed into a rhenium cup which was inserted into a vaporization chamber located within the plasma. The analysis was rapid, with no sample treatment, and accurate results were reported | 64 |
| Pb | Serum, urine | AE;GD;L | See Hg, ref. 252 (in Korean) | 252 |
| Pb | Food SRMs | MS;ICP;L AA;Hy;L AA;CV;L | See Cd, ref. 140 | 140 |
| Pb | Plasma, serum | MS;ICP;L | Conditions of sample collection—tubes, anticoagulant, haemolysis and storage time—were investigated. Concentrations were less than 2% of the whole blood levels | 89 |
| Pb | Bone, teeth | MS;ICP;L | Pb isotope ratios in contemporary samples matched that of leaded petrol, whereas ratios in ancient samples were typical of rocks and soils | 38 |
| Pb | Biological specimens | MS;ICP;L | Quadrupole and double focusing instruments were evaluated, with examination of mass bias and detector dead time on the measurement of Pb isotopes | 268 |
| Pb | Amniotic fluid | MS;ICP;SEC | Binding ligands were separated by high performance SEC. Caeruloplasmin, pre-albumin and a Zn–peptide were among the ligands identified | 90 |
| Pb | Blood | MS;-;S | Mobilization of Pb from bone at various stages of pregnancy in monkeys was monitored by TIMS | 269 |
| Pb | Wine | MS;ICP;LC | Pb species were determined using SEC-ICP-MS. Quantification was carried out against peaks obtained using FI-ICP-MS. The results showed the majority of Pb to be bound to rhamnogalacturon II and indicated that toxicity may need to be re-assessed, since it is based on the presence of mineral Pb | 146, 147 |
| Pb | Port wine | MS;ICP;L | Pb isotope ratios were used to date the age of port samples. The samples had been pre-treated by UV-irradiation | 163 |
| Pb | Urine | MS;-;GC | See Hg, ref. 254 | 254 |
| Pb | Urine | MS;-;GC | Butylated derivatives of alkyllead compounds were prepared by a Grignard reaction and extracted into hexane for injection onto a GC column | 270 |
| Pb | Bone | XRF;-;S | Subjects with occupational exposure were investigated and Pb was measured in vivo. Associations with cumulative exposure were noted | 271 |
| Pb | Bone | XRF;-;S | A review of the physiology and toxicity of Pb with reference to recent work involving in vivo measurements in bone | 94 |
| Pb | Blood, plasma, bone | MS;ICP;L XRF;-;S | The relationships between Pb in blood, plasma and bone were investigated in situations of bone mineral loss | 96 |
| Pb | Bone, blood | AA;ETA;L XRF;-;S | Bone and blood Pb concentrations were investigated in subjects living in areas of high environmental exposure | 272 |
| Pt | Saliva | AA;ETA;L | Saliva, from patients treated with cisplatin, was solubilized with hyamine hydroxide. The LOD was 0.025 µg ml−1 | 92 |
| Pt | Muscle, blood | AA;ETA;L | Samples were prepared in 0.7 µM HNO3 and mixed with 1% APDC. Pt in the solution was adsorbed onto the walls of a PTFE knotted reactor and eluted with a small volume of CH3OH. This solution was pumped to the graphite atomizer and the LOD was 10 ng l−1 | 143 |
| Pt | Peripheral nerves | MS;ICP;L | 5–10 mg of tissue was digested with HNO3. Counts were suppressed as a consequence of the digestion procedure so calibration solutions were treated in exactly the same way | 113 |
| Pt | Plasma proteins | MS;ICP;L | See I, ref. 87 | 66, 87 |
| Pt | Blood, cod, tap water | AA;ETA;FI | 1 ml 1% APDC was added to sample solution, 100 ml, containing 0.1–1 µg l−1 Pt in 0.7 M HNO3. The complex was adsorbed onto the wall of a knotted reactor, washed using 0.02% APDC, eluted using CH3OH and transferred to an ETA-AA spectrometer. At 265.9 nm the LOD was 10 ng ml−1 | 143 |
| Pt | Plasma | MS;ICP;HPLC | Pt complexes formed after treatment with JM216 were well separated on a C8 column. The MS response was suppressed by CH3OH from the mobile phase but the reported results were still very good | 112 |
| Ra | Mineral waters | MS;ICP;L | 226Ra was determined in Korean mineral water by HR-ICP-MS. A laboratory prepared cation exchange column was used to separate the analyte from matrix elements. The LOD was 0.01 pg l−1. Results were compared with those obtained using liquid scintillation counting | 164 |
| REEs | Human hair and wheat CRMs | MS;ICP;L | Samples were prepared by dry ashing and microwave digestion. The results were compared with those obtained by open vessel digestion procedures. The LODs for 14 REEs were in the range 0.01–0.16 ng g−1 in the sample | 139 |
| REEs | Blood | MS;ICP;L | Sample digested with HNO3–HClO4 was adjusted to pH 12 to precipitate REEs with Fe (derived from haem). Excess Fe was removed by IBMK extraction | 115 |
| REEs | Hair | MS;ICP;L | Good agreement was found for results obtained after preparation by dry ashing, microwave acid digestion or conventional acid digestion | 139 |
| REEs | Urine stones | MS;ICP;L | The sample was heated with HNO3. After reduction of the volume HClO4 was added with reheating | 114 |
| REEs | Fossilized bone | XRF;-;S | Analytical parameters for SR-XRF were determined. REEs were heterogeneously distributed in prehistoric bone | 273 |
| Sc | Cabbage leaves | AE;ICP;L | See Ga, ref. 247 | 247 |
| Se | Clinical specimens | -;-;- | A comprehensive review of techniques used to measure Se in blood, plasma, urine, etc. | 117 |
| Se | Egg powder, mussel tissue, nuts | MS;ICP;L AA;ETA;L AE;ICP;L AA;Hy;L | See As, ref. 200 | 200 |
| Se | Plasma, hair, nails | AA;ETA;L | Se was measured to determine if there were concentration changes associated with the acute phase response | 128 |
| Se | Plasma | AA;ETA;L MS;ICP;L | Using ETAAS, sensitivities varied for different Se species and for aqueous compared with plasma specimens. This variation was not found with ICP-MS | 121 |
| Se | Wine | AA;ETA;L | Using Pd, 500 µg l−1 in 2% hydroxyammonium chloride, as chemical modifier, and Zeeman-effect background correction, Se was determined in table wine at an LOD of 9 µg l−1 | 181 |
| Se | Tissues | AA;ETA;L | A modifier with (NH4)3RhCl6–citric acid was more effective than Pd in overcoming phosphate interference | 123 |
| Se | Serum, hair | AA;Hy;L AA;ETA;L | AAS and fluorimetric methods were compared by evaluating data from an Italian quality assessment scheme | 274 |
| Se | Urine | AA;Hy;L | Urine was first passed through a Sep-Pak Vac C18 column and then through a PRP-X100 anion exchange column. Using an FI system the eluent was mixed with K2S2O8–NaOH, microwave heated, merged with HCl, re-heated and the hydrides formed by reaction with NaBH4. Five Se compounds were detected | 240 |
| Se | Urine | AA;Hy;FI | Decomposition of Se compounds to selenate using high pressure microwave heating was studied. High blank values associated with NOx absorbed into the digest were eliminated by addition of urea. Good recoveries were obtained when a temperature of 200°C and a pressure of 8 bar were used | 125 |
| Se | Chinese teas | AA;Hy;L XRF;-;L | Following addition of Ga as internal standard, 5 µl were removed, dried onto a carrier and analysed by TXRF. Either infusions or HNO3 digests were analysed. Samples with a low Se content were analysed using HGAAS. Levels of Se up to 7530 ng g−1 were determined in the teas. Also see Various, ref. 182 (in German) | 182 |
| Se | Grains | AA;Hy;L | Se was determined in 20 samples of grain from the Zhangjiakou region of China as part of a study of the role of Se deficiency in Keshans disease | 275 |
| Se | Meat | AA;Hy;L | Meat, 1 g, was digested overnight in HNO3–HClO3–H2SO4, 12 + 3 + 1.5. The resulting digest was heated via a temperature programme to 240°C, cooled, diluted to 20 ml with H2O, a 10 ml portion mixed with 10 ml HCl and the resulting solution held at 75°C for 25 min prior to measurement | 276 |
| Se | Serum | AF;ETA;L | See As, ref. 214 | 214 |
| Se | Garlic | AF;F, H2–Ar;HPLC | Selenoamino acids were determined by HPLC separation, on a C18 column with trifluoroacetic acid–CH3OH as mobile phase, interfaced to AFS. The interface incorporated hydraulic high pressure nebulization and desolvation to prevent water reaching the relatively cool flame. LODs for the 3 amino acids studied were 42–71 ng ml−1 | 183 |
| Se | Serum | AF;ETA;L | After dilution in H2O the sample was placed into a graphite furnace with a Pd–Mg modifier. Se was atomized, UV excited and measured by LEAFS | 58 |
| Se | Coffee | AE;ICP;L | See As, ref. 220 | 220 |
| Se | Serum | MS;MIP; Hy | A lyophilized sample was digested with HNO3 and H2O2. After heating with 35% HCl the solution was taken to an FI system for addition of NaBH4. The formed hydride was passed to an N2 MIP and the 78Se∶80Se ratio determined | 124 |
| Se | Plasma | MS;MIP;L | Samples were digested with HNO3 and H2O2 or simply diluted with 0.1% Triton X-100. Other elements could be measured simultaneously | 277 |
| Se | Serum, blood, red cells | MS;ICP;L | Dilution of samples 1 + 14 in 1% v/v butan-1-ol eliminated interferences from Ar adduct ions on 78Se. Good accuracy and precision were demonstrated | 119 |
| Se | Serum | MS;ICP;ETV | A 1 + 19 dilution in 1% HNO3 was prepared and the Se vaporized into the plasma. Many common interferences were thus eliminated | 122 |
| Se | Serum, urine | MS;ICP;L AA;ETA;L | Samples were diluted in C2H5OH–Triton X-100–HNO3 and the 78Se isotope was used for the measurement. Performance was superior when compared with ETAAS with a Ni chemical modifier | 120 |
| Se | Urine | MS;ICP;L | Factors such as instrument parameters, internal standards, salt content of urine, Se species, and C-containing sensitivity enhancers were systematically examined. The LOD was 2.2 µg l−1 when the optimized conditions were used | 118 |
| Se | Blood, liver, urine | MS;ICP;HPLC | Samples were collected after administration of selenate. Following acid digestion, material was subjected to SEC with measurement by ICP-MS in order to determine biotransformation in vivo | 126 |
| Se | Urine | MS;ICP;HPLC | Species were separated on a Spherisorb 5 ODS/AMINO column | 278 |
| Se | Urine | MS;ICP;HPLC-HG | Performance of Q-ICP-MS was compared with HR-ICP-MS for the separation of Se species | 279 |
| Se | Fish | MS;ICP;L | See As, ref. 22 | 22 |
| Se | Yeast | MS;ICP;HPLC | 8 solid–liquid extraction procedures for Se in yeast were evaluated. A sequential leaching procedure was found to be necessary to prevent incomplete recovery and species degradation | 185 |
| Se | Garlic, yeast | MS;ICP;HPLC, MS;ES;HPLC | MS techniques characterized the principal Se species in garlic as γ-glutamyl-Se-methylselenocysteine and possibly γ-glutamyl-selenomethionine and in yeast as selenomethionine and Se-adenosyl-selenohomocysteine | 186 |
| Se | Yeast | MS;ES;HPLC, MS;ICP;HPLC | Se–adenosylhomocysteine was identified as the major Se species in an Se-enriched yeast using tandem ES-MS to characterize peaks separated using ICP-MS. The ES-MS determination required preconcentation of eluate to reduce the effect of salt suppression on the signal | 184 |
| Si | Foods | AA;ETA;L | Daily Si intake in Belgium was calculated in 2 locations over 7 consecutive days. The mean intake was 18.6 mg d−1 | 195 |
| Si | Urine | MS;-;S | Gastrointestinal uptake and excretion of 32Si was assessed. SiO2 was isolated from urine samples and measured by AMS | 44 |
| Si | Urine | AMS;-;- | Gastrointestinal uptake and urinary excretion of silicic acid was followed using 32Si tracer | 43 |
| Sn | Urine | MS;-;GC | See Hg, ref. 254 | 254 |
| Sr | Bone | MS;ICP;L | Sr isotope ratios were calculated in prehistoric human bones as a marker of population migration | 37 |
| Sr | Blood, urine, bone | AA;ETA;L | Modifiers, background correction and furnace heating were investigated. Similar results were obtained with the conditions (i) La modifier, wall atomization, no background correction and (ii) Zeeman-effect background correction, no modifier. The LODs were 0.13 and 0.30 µg l−1, respectively | 129 |
| Ti | Serum | AE;ICP;L | Samples were from patients with joint replacements. Serum, HNO3 and HF were heated in a closed vessel and the solution taken for analysis. The LOD was 34.1 ng ml−1 | 17 |
| Ti | Serum | MS;ICP;L | Following HNO3–HF digestion, the samples were introduced via an ultrasonic nebulizer and desolvating membrane | 130 |
| U | Serum, urine | MS;ICP;FI | Concentrations of U in human specimens, mainly derived from drinking water and beverages, were determined | 280 |
| V | Hair | AA;ETA;L | Atomization signals were improved when a very rapid temperature increase was used | 281 |
| V | Serum | AA;ETA;L | After digestion the pH was adjusted to 2 for extraction of VV into IBMK with cupferron. The organic phase was evaporated to dryness and the residue dissolved in HCOOH for measurement of V | 131 |
| V | Human hair, vegetables, water | AA;ETA;L | A combination of fast ramp rates and pyrolytically coated graphite tubes were found to overcome common problems in ETAAS determination of V, such as peak tailing and memory effects | 281 |
| V | Cabbage leaves | AE;ICP;L | See Ga, ref. 247 | 247 |
| Yb | Faeces | AA;ETA;L | This marker of intestinal transit time was determined using a tungsten-coil atomizer after samples were ashed in a muffle furnace | 57 |
| Zn | Biological specimens | AA;F;FI, | In a complicated system a Zn–thiocyanate complex was formed, collected onto a polyurethane minicolumn, eluted with 30% acetone in 2% HNO3 and introduced into the nebulizer. With a 1 min collection time the LOD was 3 µg l−1 | 132 |
| Zn | Brain | AA;F;FI, XRF;-;Sl | See Cu, ref. 282 | 282 |
| Zn | Honey | AA;F;FI, | See Ca, ref. 153 | 153 |
| Zn | Milk, milk powder | AA;-;L | See Ca, ref. 10 | 10 |
| Zn | Cow and human milk, infant formula | AA;ETA;L | See Cu, ref. 240 | 240 |
| Zn | Powdered RMs | AA;ETA;L | See Cd, ref.225 and Cu ref. 224 | 225 |
| Zn | Plasma, blood cells | AA;ETA;L | See Cu, ref. 239 | 239 |
| Zn | Serum | MS;ICP;L | See Cu, ref. 243 | 243 |
| Zn | Plasma | MS;ICP;L | Polyatomic interferences were discussed and approaches to the measurement of Zn by ICP-MS were presented | 283 |
| Zn | Plasma | -;-;- | Zn protein binding was investigated in a subject with high plasma Zn concentration. The Zn was associated with calprotectin, present at an exceptionally high concentration | 284 |
| Zr | Serum | AE;ICP;L | See Ti, ref. 17. The LOD was 26.9 ng ml−1 | 17 |
| Zr | Serum | MS;ICP;L | See Ti, ref. 130 | 130 |
| Various | Clinical specimens | -;-;- | A review of metal toxicology and its laboratory investigation | 4 |
| Various | Foods | -;-;- | The use of trace element analysis in food authenticity studies was described in a review containing 77 references | 187 |
| Various | Clinical and biological materials, foods, beverages | -;-;- | Review, 593 references | 1 |
| Various | Biological RMs | -;-;- | An addition to a valuable regular compilation of available RMs | 60 |
| Various (4) | Water | AA;F, air–C2H2;L | Sample, 25–500 ml, was acidified with 5 ml l−1 HNO3 and pre-concentrated on a column containing NaDDC. Ions were then eluted using propan-2-ol and Cd, Cu, Pb and Zn determined at LODs of <20 µg l−1 | 285 |
| Various (10) | Bone | AA;F;L AA;ETA;L | Bone biopsies from 100 patients with chronic renal failure were analysed for Al, Ca, Cd, Cr, Cu, Fe, Mg, Pb, Sr, Zn | 55 |
| Various (17) | Beverages, foods | AA;-;L | A duplicate portion study, conducted over 24 h on 7 consecutive days, was described. The subjects were 15 Swedish women. The results did not indicate any potential nutritional problems | 193 |
| Various (6) | Fruit | AA;F, air–C2H2;Sl AE;F;Sl | Lyophilized sample, 50 mg, was mixed with 0.72 M HNO3, ultrasonicated for 5 min and diluted to 50 ml with H2O. Recoveries, validated using CRMs, lay in the range 95–105% (Ca, Fe, K, Mg, Na, Zn) | 286 |
| Various (4) | Urine | AA;Hy;FI | Elegant use of FI technology for sample preparation and atomization, as applied to a range of analytical tasks, was described (As, Cd, Pb, Se) | 5 |
| Various (15) | Chinese teas | AA;Hy;L XRF;-;L | Following addition of Ga as internal standard, 5 µl was removed, dried onto a carrier and analysed by TXRF. Either infusions or HNO3 digests were analysed. The results were dependent on the region in China in which the samples were grown. Also see Se entries (in German) | 182 |
| Various (5) | Hair | AA;ETA;L | Digested samples were analysed with a mixed Mg–Rh chemical modifier (Cr, Cu, Fe, Mn, Pb) | 287 |
| Various (13) | Urine | AA;ETA;L MS;ICP;L | Specimens from 496 subjects were analysed to establish reference ranges for 13 elements | 51 |
| Various (13) | Blood, urine | AA;ETA;L MS;ICP;L | Reference values were determined using specimens from more than 200 individuals in the UK | 48 |
| Various (5) | Blood, urine | AA;ETA;L MS;ICP;L | Techniques were compared as part of a project to determine reference conentrations in the UK population (Al, Cd, Co, Ni, Pb) | 50 |
| Various (4) | Plasma, blood cells, platelets | AA;ETA;L | Components of blood were separated by density centrifugation and solubilized by enzymatic digestion. Concentrations were determined in several clinical disorders (Cr, Cu, Se, Zn) | 288 |
| Various (4) | Serum, blood, urine | AA;ETA;L | Serum and urine were diluted with HNO3–Triton X-100, blood with NH3–NaEDTA–NH4H2PO4. Simultaneous measurements were made in studies of reference ranges for European populations (Cd, Cr, Ni, Pb) | 49 |
| Various (5) | Serum | AA;-;L | Cu, Fe, Mn, Ni and Zn were determined throughout the menstrual cycle. Differences were seen between controls and women with infertility (in Chinese) | 289 |
| Various (4) | Dialysis concentrates | AA;ETA;L | NaCl was removed using a polyethylene column conditioned with 1-(2-pyridylazo)-2-naphthol. Metals were eluted with 0.1% HClO4 or ethanolic HNO3 (Cd, Cu, Pb and Zn) | 12, 13 |
| Various (4) | Biological materials | AA;ETA;L AA;F;L | Samples were digested using HNO3–H2O2 in non-pressurized containers within a domestic microwave oven (Cd, Cu, Pb and Zn) | 290 |
| Various (4) | Penguin liver, kidney | AA;ETA;L | Dried samples were digested with HNO3 for the measurement of Cd, Cr, Mn and Pb. Results were used as biological indicators of pollution in Antarctica | 291 |
| Various (4) | Ham | AA;ETA;L AA;F, air–C2H2;L | Cu, Fe and Mn were determined by ETAAS and Zn by FAAS. During the curing of Iberian ham only the Cu levels changed, being significantly decreased in the final product (in Spanish) | 292 |
| Various (8) | Cerebrospinal fluid | AE;F;L AA;F;L AA;ETA;L | Reference values were reported for Ca, Cu, Fe, K, Mg, Na, Se and Zn | 52 |
| Various (4) | Plasma, red cells | AE;ICP;SEC | Metalloproteins were separated on an EMD BioSEC 650 (S) column (Cu, Fe, Mn and Zn) | 293 |
| Various | Biological samples | AE;ICP;L MS;ICP;L | An extensive review of multi-element analytical atomic spectrometry including speciation techniques | 294 |
| Various | Bovine liver, juice, milk | AE;ICP;L | A high temperature/high pressure system, operating at 260°C and up to 300 bar, was described. By incorporating resistively heated capillaries continuous digestion of liquid samples was possible. The system was claimed to leave a smaller residual C content than other continuous flow systems | 7 |
| Various (8) | Drinking water | AE;GD;L | The development of a low power plasma source for on-line monitoring of heavy metals was described. Fundamental studies of various operating parameters were conducted (Al, Cd, Cr, Cu, Fe, Mn, Pb and Zn) | 295 |
| Various (14) | Blood, serum, urine | MS;ICP;L | A double focusing magnetic sector instrument was evaluated using RMs. Urine and serum were prepared by dilution with internal standard, blood was heated with HNO3 and diluted. LODs were determined and accurate results were obtained | 32 |
| Various (15) | Serum | MS;ICP;L | Samples were diluted 1 + 4 with water. Ga, Sc, Tl and Y were added at 10 µg l−1 as internal standards and the samples analysed in a double-focusing mass spectrometer at low, and then medium, resolution scans | 35 |
| Various (4) | Blood | MS;ICP;L | Equivalent results were obtained when samples were either digested or diluted with NH3–Triton X-100–EDTA (Co, Cr, Ni and Pb) | 296 |
| Various | Biological fluids | MS;ICP;L | It was reported that a hexapole collision cell in ICP-MS reduced spectral interferences and other problems associated with many elements | 297 |
| Various (7) | Biological specimens | MS;ICP;L | Several applications were described to illustrate the effectiveness of a direct injection high efficiency nebulizer (As, B, Cr, Hg, Pb, REEs and Se) | 298 |
| Various (5) | Follicular fluid | MS;ICP;L | Cd, Cu, Fe, Se and Zn were measured in specimens collected at an in vitro fertilization clinic | 299 |
| Various | Blood, urine | MS;ICP;L | Further work on the use of Virkon, to destroy viruses in clinical samples, was reported | 6 |
| Various | Breast milk | MS;ICP;L | Interferences associated with the milk matrix were evaluated and the effectiveness of a double focusing instrument to eliminate these was demonstrated | 300 |
| Various (4) | Urine | MS;ICP;L | Samples were diluted 1 + 9 and In was used as internal standard for measurements with a high resolution mass spectrometer (Cd, Cu, Pb and Zn) | 34 |
| Various (50) | Blood | MS;ICP;L | After microwave digestion with HNO3 samples were diluted with H2O. In, Lu and Sc were added as internal standards for measurement by double focusing ICP-MS | 33 |
| Various (8) | Serum | MS;ICP;L | RMs were measured to demonstrate accuracy. The Se concentrations of 150 specimens were also determined by ETAAS and results were compared (Al, Cd, Co, Cu, Mn, Ni, Se and Zn) | 301 |
| Various (5) | Liver | MS;ICP;L | Liver samples from infants who had died were digested and analysed to determine reference concentrations (Ag, Cd, Co, Pb and Sb) | 23 |
| Various (73) | Heroin | MS;ICP;L | Drug, dissolved in 3% HNO3, was spiked with internal standard and analysed. 188 samples were taken to develop models for prediction of origin | 67 |
| Various | Serum proteins, DNA fragments | MS;ICP;L | SEC was used for rapid and simple separation of macromolecules. Metals were detected by ICP-MS with a magnetic sector mass spectrometer | 302 |
| Various (10) | Serum, proteins | MS;ICP;HPLC AA;-;HPLC | Techniques for speciation were reviewed (Ca, Cu, Fe, Hg, Mg, P, S, Se, Sr and Zn) | 303 |
| Various | Biological specimens | MS;ICP;HPLC | A review of SEC for investigating metal speciation in biological systems | 21 |
| Various (11) | Serum | MS;ICP;LC | Serum proteins were separated by fast protein LC and trace elements measured by double focusing ICP-MS at both low and medium resolution. Polyatomic interferences were avoided with this approach (Al, Ca, Cr, Cu, Fe, Mn, Pb, Se, Sn, Sr and Zn) | 36 |
| Various | Foods | MS;-;- | A review, with 141 references, discussing the application of MS analysis of stable isotopes and its application to food authentication | 188 |
| Various (18) | Milk, infant formula | MS;ICP;L | 18 elements were determined in formulas based on cow and soya milk, powdered cows milk and in the water used to suspend the powders. In the cow milk the concentration of all the elements were lower than formula milk and did not meet the dietary requirements of infants | 304 |
| Various (13) | Cereals, pulses | MS;ICP;L AE;F;L | 56 samples of Mexican cereal, pulse or cereal-based products were analysed as part of a study to generate Mexican food composition tables | 305 |
| Various (8) | Apple, carrot | MS;ICP;HPLC | Aqueous extraction and enzymatic digestion in conjunction with SEC-ICP-MS were used to speciate metals in fruit and vegetables. B, Ba, Ce, Pb and Sr were found to exist as complexes of the carbohydrate rhamnogalacturon-II, whilst Cu, Mg and Zn eluted as complexes with low molar mass non-carbohydrate compounds | 145 |
| Various (6) | Foods | MS;ICP;L | A high pressure asher was used for sample decomposition. The addition of 2% isopropyl alcohol to samples and standards overcame interferences from residual C, which can cause signal enhancement for As and Se and suppression for Pb (Al, As, Cd, Hg, Pb and Se) | 141 |
| Various (12) | Foods | MS;ICP;L | A pressurized microwave oven, for sample decomposition, was used in conjunction with an ICP-mass spectrometer equipped with an ultrasonic nebulizer and a membrane desolvator. Recoveries were good for most elements, but for As and Se they varied between 100 and 200% | 138 |
| Various | Foods | MS;ICP;L | Analytical quality control procedures were discussed, mainly with reference to the determination of Pb | 191 |
| Various | Foods | MS;ICP;L | A review of the status of research and commercial ICP-MS instruments and their applications and limitations for stable isotopic studies. Stable isotope speciation analysis was also considered | 160 |
| Various | Rice | MS;ICP;L | A study to authenticate the Koshihikari rice cultivar grown in the Niigata region of Japan was described. One grain, 20–25 mg, was placed into a PTFE bottle and 1 ml HNO3 added. The sample was then microwave digested at 600 W for 90 min. 1 g of 10 ppb In was added along with enough ultra-pure H2O to bring the bottle weight to 10 g. The digest was then measured using HR-ICP-MS. 50 elements were used to characterize the rice origin | 165 |
| Various | Foods | MS;ICP;CE | The role of CE-ICP-MS in speciation was discussed and the authors detailed experimental strategies required to interface the techniques. In particular, they described how to prevent excess suction on the capillary from the nebulizer. The merit of the coupling was illustrated by the determination of vitamin B12 | 150 |
| Various | Metalloproteins | MS;ICP;CE | Development of an interface to connect the electrophoretic output to the ICP-MS, without loss of resolution or sensitivity, was reported | 26 |
| Various (5) | Serum | MS;ICP;GE | Gel electrophoresis (GE) was carried out in duplicate. One was stained to show the positions of separated proteins, the second was cut into segments and metals extracted into aqua regia for measurement (Cr, Ga, In, Pt and V) | 25 |
| Various (5) | Cultured cells | XRF;-;S | Cells were collected by centrifugation, HNO3 added and left at room temperature for 48 h. 5 µl was dried onto a quartz reflector to make the TXRF measurements (Ca, Cu, Fe, S and Zn) | 306 |
| Various (6) | Blood, tissues | XRF;-;S | Samples were taken from animals inoculated with cancer cells. Differences were observed between control and cancerous tissue with a marked increase in Rb (Br, Cu, Fe, Rb, Se and Zn) | 47 |
| Various (9) | Bone, liver, kidney, hair | XRF;-;S | Samples collected post mortem from 61 subjects were examined. Tissues were lyophilized, powdered and pressed into pellets. The influences of age, gender, etc., were determined (As, Cu, Fe, Mn, Pb, Rb, Se, Sr and Zn) | 307 |
| Various (16) | Water | XRF;-;L AA;F;L | Element concentrations in Nigerian ground water from 3 different locations were measured. Levels of Hg were found to exceed WHO limits in tap water supplies | 308 |
| Various (4) | Water | XRF;-;- AA;ETA;L | Cr, Cu and Pb were determined simultaneously using a tungsten coil atomizer, whilst Cd, Cr, Cu and Pb were determined using both XRF following solid phase filter-disk extraction and a novel ETAA spectrometer, employing a Rowland Circle with 4 HCLs placed around it. All 3 techniques gave results in the low µg l−1 range | 309 |
| Various (4) | Oils | XRF;-;L | Samples were treated with NaOH and starch, heated and cooled to give a saponified material which was analysed using XRF (As, Hg, K, Na) (in Japanese) | 310 |
| Various | Hair | PIXE;-;S | Total concentrations, cross-sectional and longitudinal distributions were measured in hair from haemodialysis patients and controls | 63 |
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Footnote |
| † *Review co-ordinator, to whom correspondence should be addressed and from whom reprints may be obtained. |
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