Showing papers in "Journal of Analytical Atomic Spectrometry in 1996"

Inter-laboratory note. Laser ablation inductively coupled plasma mass spectrometric transient signal data acquisition and analyte concentration calculation

Abstract: Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) produces complex, time-dependent signals. These require significantly different treatment both during data acquisition and reduction from the more steady-state signals produced by solution sample introduction. This paper discusses, in detail, data acquisition and reduction considerations in LA-ICP-MS analysis. Optimum data acquisition parameters are suggested. Equations are derived for the calculation of sample concentrations and LOD when time-resolved data acquisition is employed, sensitivity calibration is obtained from reference materials with known analyte concentrations and naturally occurring internal standards are used to correct for the multiplicative correction factors of drift, matrix effects and the amount of material ablated and transported to the ICP.

Application of a sequential extraction scheme to ten geological certified reference materials for the determination of 20 elements

Abstract: Methods are described for a sequential extraction scheme to dissolve selectively elements bound in soils and sediments in the following nominal forms: (1) adsorbed, exchangeable, carbonate (AEC); (2) amorphous iron oxyhydroxide (am Fe ox), including manganese oxides; (3) crystalline iron oxides (cry Fe ox); (4) organics and sulfides; and (5) residual (mainly silicates). This scheme has been applied in triplicate to a suite of ten international CRMs, i.e., soils SRM 2709–2711 and the SO-1–4 series, marine mud MAG-1, lake sediment LKSD-4 and the till sample TILL-2. Elements determined comprise: As (by HG–quartz tube AAS, HG–QTAAS); Be, Ca, Co, Cr, Cu, Ni, P, Ti and V (by ICP-AES); Mn, Fe and Zn (by FAAS); and Cd, Ce, La, Li, Tl, Pb and U (by ICP-MS). The precision obtained is excellent, generally in the range 2–10% RSD, at concentrations 10 × higher than detection limits. Most results for the element concentrations summed over the five phases agree, within statistical uncertainties, with the recommended total values for the CRMs. Those where recoveries are significantly below 90% are for elements such as Cr and V, which are known to be present in refractory minerals and would require fusion for complete dissolution. The results presented herein for samples SO-1–4 and MAG-1 do not agree well with those recently published using a scheme purported to dissolve similar phases. This highlights the need to be more definitive in describing the nature and extent of the phases actually extracted so that comparisons can be made between different laboratories and studies.

Rapid speciation of butyltin compounds in sediments and biomaterials by capillary gas chromatography-microwave-induced plasma atomic emission spectrometry after microwave-assisted leaching/digestion

Abstract: A rapid procedure for the simultaneous determination of mono-, di- and tributyltin in sediments and biological materials is described. The target compounds in sediments were subject to quantitative microwave-assisted leaching with acetic acid. Biomaterials were dissolved in a tetramethylammonium hydroxide solution under the action of a low-power microwave field in such a way that the organotin moiety remained intact. The leaching of the analytes from a sediment as well as the dissolution of a biomaterial in a focused microwave field took only 1–5 min, which is much faster than previously reported methods. It was also demonstrated that the leaching efficiency of monobutyltin from certified reference sediments was superior to that of most literature procedures. The butyltins were derivatized with sodium tetraethylborate (NaBEt4) in the aqueous phase, and simultaneously extracted into isooctane (5 min). The analysis was carried out by capillary gas chromatography (GC) with microwave-induced plasma atomic emission detection. The sample throughput was limited by the duration of the GC run (10 min). The detection limit was 2 ng g–1 for 0.2 g of sample (dry) without preconcentration; it could be improved by a factor 10 if preconcentration was applied. The developed method was applied to a variety of real samples and was validated by analysing three certified reference materials: PACS-1, CRM 462 and NIES 11.

Cloud point preconcentration and flame atomic absorption spectrometry: application to the determination of cadmium

Abstract: Cloud point methodology has been successfully used for the preconcentration of trace amounts of cadmium as a prior step to its determination by flame atomic absorption spectrometry. A procedure based on the formation of a complex with 1-(2-pyridylazo)-2-naphthol (PAN) is used for the preconcentration of cadmium in a surfactant-rich phase of Triton X-114. The chemical variables affecting the preconcentration step and the viscosity of the solution affecting the detection process have been optimized. Under the optimum conditions, a precision of 3.0% was achieved. The preconcentration of only 15 ml of sample with 0.05% Triton X-114 permits the detection of <0.4 ppb of cadmium with a concentration factor of 120.

Investigation of selenium speciation in in vitro gastrointestinal extracts of cooked cod by high-performance liquid chromatography–inductively coupled plasma mass spectrometry and electrospray mass spectrometry

Abstract: As part of an ongoing study of Se bioavailability from the human diet, Se was determined in cooked cod and in enzyme extracts of cooked cod. Total Se was measured by direct nebulization ICP-MS and standard additions, following digestion with HNO3 in stainless steel pressure decomposition vessels. The concentration of Se in the cod was 1.52 mg kg–1 with an LOD of 0.008 mg kg–1. An in vitro gastrointestinal enzymolysis procedure was used to extract Se species from the cooked cod. HPLC, using an anion-exchange column, was used to separate Se standards (selenomethionine, selenocystine, sodium selenite and sodium selenate) and the species soluble in the gastrointestinal extract (pH 6.8). The 82Se signal was used to quantify the individual Se species. In the extracts of cooked cod, approximately 12% of total Se was thought to be selenite whilst the remaining Se eluted at a retention time different to that of any of the Se standards measured. However, as the retention time was close to that of selenomethionine, it was suggested that the Se-containing species was organic rather than inorganic. A similar peak was also found in the enzyme blanks. In order to gain further information as to the identity of the unknown species, the samples and standards were subjected to electrospray-MS (ES-MS) in both positive and negative ionization modes. Although the four standards were amenable to analysis by ES-MS, more work is required to improve the sensitivity of the system. This will involve modifying the chromatography for both ICP-MS and ES-MS.

Application of inductively coupled plasma mass spectrometry for total metal determination in silicon-containing solid samples using the microwave-assisted nitric acid–hydrofluoric acid–hydrogen peroxide–boric acid digestion system

Abstract: The microwave-assisted conventional HNO3–HF–H2O2–H3BO3 digestion system has been explored for direct ICP-MS analysis of total metals in silicon-containing solid samples. In closed Teflon PFA vessels under microwave heating with temperature/pressure regulation, a 0.25 g portion of sample containing ⩽ 33% silicon was digested in 1.5 ml of HF (48%), 5 ml of concentrated HNO3 and 2 ml of H2O2(30%), followed by a second digestion stage with 12 ml of 5% m/v boric acid. The amount of HF used was approximately twice the stoichiometric requirement for 33% silicon contained in the samples, assuming all silicon exists as silica. The amount of boric acid used was the stoichiometric requirement for the HF added. With a sample dilution factor of 2000 (v/m), the end solution contained ⩽ 0.17% total dissolved solids for ICP-MS analysis. The ICP-MS system was calibrated by the method of external standards prepared in reagent blank solutions with in as the internal standard. The sensitivity of the In signal in a 5–8 h operation was only decreased by 5–10%. Background interferences from the digestion reagents were studied and corrected. The method developed is simple and rugged and suitable for routine analysis of at least 25 elements: Al, Ag, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Mo, Ni, Pb, Sb, Sn, Sr, Th, Ti, Tl, U, V and Zn. The recoveries for most of these elements in standard reference materials including coal fly ash, urban particulate matter, sediment and soil were within 90–110%, and the relative standard deviations were within 5%. The method cannot determine B and is not suitable for Hg determination. The detection limits for Be and Se determination are not adequate.

Determination of rare earth elements in wine by inductively coupled plasma mass spectrometry using a microconcentric nebulizer

Abstract: A method for the direct determination of REEs in undiluted wine by ICP-MS was developed. The performance of a microconcentric nebulizer (MCN) was optimized regarding the nebulizer gas flow rate and sample uptake rate for all the REEs in terms of signal intensity and signal-to-noise ratio. The effect of ethanol on the sensitivity was also studied. Possible spectral interferences were identified and are discussed in detail. The MCN was shown to reduce the sample consumption to 30–50 µl min–1 and to decrease the matrix signal suppression by a factor of 2–5 in comparison with a de Galan nebulizer. Polyatomic interferences were found to be negligible except for those of BaO on 151Eu, 153Eu and 155Gd and of 139La16O on 155Gd. Data obtained with three different ICP-MS instruments were compared. Several wines from different vineyards in France, California and Australia were analysed for REEs. The REE concentration patterns showed inter-continental and inter-regional variations, whereas no difference was observed for different vintages from the same vineyard over a period of several years.

Arsenic speciation by liquid chromatography coupled with ionspray tandem mass spectrometry

Abstract: Ionspray mass spectrometry, a well established organic analysis technique, has been coupled to high-performance liquid chromatography for speciation of organic arsenic compounds. The ionspray source and differentially pumped interface of the mass spectrometer were operated in dual modes for elemental and molecular analysis. Tandem mass spectrometry was employed to increase selectivity. Dual mode detection was applied to demonstrate the utility of the technique for analysis of nine organoarsenic standards, including four dimethylarsinylriboside derivatives (arsenosugars). Structural fragmentation patterns showing molecular dissociation through an expected common product ion were obtained for the four arsenosugars. Molecular mode detection was utilized for qualitative verification of speciation analysis by high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry of organoarsenicals in plaice and for analysis of an arsenosugar in extracts of oyster and mussel.

Communication. Selective removal of plasma matrix ions in plasma source mass spectrometry

Abstract: We report a new method for selective removal of argon ions and other plasma matrix ions in plasma source MS. The method consists of sampling the plasma and reacting the sampled plasma and analyte ions with hydrogen gas. Reactions have been studied in three instruments: in the ion trap of a plasma source ion trap (PSIT) mass spectrometer and in the post-skimmer region of both a conventional ICP mass spectrometer and a second PSIT. In the ion trap, the reaction between Ar+ and H2 proceeds at nearly the collisional rate whereas reaction of most other atomic ions is four to five orders of magnitude slower. For modest H2 pressures and reaction times in the ion trap [10–4 Torr (1 Torr = 133.322 Pa) and 10 ms], the Ar+ signal is reduced by six orders of magnitude. We have examined reactions of H2 with 33 different atomic ions; the only ions for which a reaction was evident were N+, O+, Cl+, and Ar+. The decrease in Ar+ occurs by a sequence of fast reactions resulting in charge transfer from Ar+ to form the low m/z ions H2+ and H3+, which are rapidly ejected from the ion trap. The net effect is the selective removal of Ar+ chemically, not by virtue of its mass-to-charge ratio only, as in resonant ion ejection methods. In the conventional ICP-MS experiments the reaction time is short, limiting the decrease in Ar+ to about 40-fold in preliminary and unoptimized experiments. However, the reaction is still selective: simple scattering by H2 reduces the 45Sc+ signal at only 5% of the rate of reactive loss of Ar+. Production of H2+ and H3+ is observed directly in the conventional ICP-MS experiments, indicating that the chemistry in the post-skimmer region is consistent with that observed in the ion trap. We discuss methods by which the magnitude of Ar+ reduction observed in the ion trap might be realized in conventional ICP-MS, thus possibly allowing a greater analyte ion transmission efficiency and reduced space-charge effects.

Evaluation of a commercially available microconcentric nebulizer for inductively coupled plasma mass spectrometry

Abstract: The performance of a commercially available microconcentric nebulizer (MCN-100, CETAC Technologies, USA) operated at flow rates ranging from ⩽0.001 up to 0.65 ml min–1 was evaluated using a Perkin-Elmer Sciex ELAN 5000 ICP-mass spectrometer. The observations made were compared with those for the standard GemTip cross-flow nebulizer. Registration of signal behaviour plots (signal intensity as a function of the nebulizer gas flow rate) at different rf powers and at different sample uptake rates allowed firstly, a systematic optimization of the operation parameters, and secondly, a comparison of the signal behaviour observed when using both types of nebulizer. The stability of the MCN-100 was evaluated at different sample uptake rates and the occurrence of memory effects was checked for a number of elements. Also, the level and the behaviour of oxide and doubly charged ions was studied. Furthermore, the susceptibility to matrix effects was investigated using synthetic matrices of different origin (acid, organic and high salt content) and it was demonstrated that, generally, matrix effects observed with both nebulizers are comparable and the MCN-100 can be used with NaCl concentrations up to 4 g l–1 without capillary blocking. Finally, it is illustrated that the MCN-100 can be applied at sample flow rates of < 5 µl min–1, as are encountered when coupling capillary zone electrophoresis to ICP-MS for elemental speciation studies.

Integrated sample preparation and speciation analysis for the simultaneous determination of methylated species of tin, lead and mercury in water by purge-and-trap injection-capillary gas chromatography-atomic emission spectrometry

Abstract: A sensitive and interference-free automated method for the simultaneous speciation analysis of methylated species of mercury, tin and lead, and also inorganic mercury in water, using purge-and-trap injection–gas chromatography–atomic emission spectrometry, was developed. The ionic species are volatilized from the sample after ethylation, using sodium tetraethylborate, in acetate buffer medium of pH 5 and preconcentrated on a capillary cryogenic trap. Desorption is effected by linear heating of the trap, followed by separation of the analytes by capillary gas chromatography and selective simultaneous detection by microwave-induced plasma atomic emission spectrometry. Detection limits of 0.15, 0.20 and 0.60 ng l–1 for methylated tin, lead and mercury species, respectively, and 2 ng l–1 for inorganic mercury can be obtained, on the basis of a 10 ml sample volume. Examples of results for the analysis of river- and soil run-off water samples are given.

Speciation of inorganic selenium and selenoaminoacids by on-line reversed-phase high-performance liquid chromatography–focused microwave digestion–hydride generation-atomic detection

Abstract: A high-performance liquid chromatographic–microwave digestion–hydride generation system coupled on-line with three atomic detectors (atomic absorption, inductively coupled plasma atomic emission and inductively coupled plasma mass spectrometry) has been developed and investigated for selenium species separation and determination. Total inorganic selenium, selenomethionine and selenoethionine are separated by reversed-phase chromatography prior to on-line microwave digestion of selenocompounds with a KBrO3–HBr mixture to form continuously SeIV, which is finally transformed into H2Se, also in a continuous manner, with a merging flow of sodium borohydride. Detection limits obtained for each Se species in water and urine using the three atomic detectors have been worked out and compared (i.e., for SeIV DLs were 6.8 µg l–1 by AAS, 30 µg l–1 by ICP-AES and 0.16 µg l–1 by ICP-MS).The integrated flow system, HPLC–MW digestion–HG-atomic detection, proposed here allows, in a single injection, reliable speciation in urine of the selenoaminoacids tested versus total inorganic selenium. Further speciation of the overlapped inorganic SeIV and SeVI peaks is accomplished by a second injection of the urine sample to determine only SeIV by avoiding microwave heating. Results on Se speciation in human urine have shown that more speciation information of the actual species, perhaps unknown, present in real samples could be gathered by resorting to the use of two, or more, atomic detectors coupled to the same separation scheme.

Determination of mercury in filtered sea-water by flow injection with on-line oxidation and atomic fluorescence spectrometric detection

Abstract: A flow injection (FI) atomic fluorescence method incorporating an on-line bromide–bromate oxidation step to determine mercury in filtered sea-water samples at the ng l–1 level is described. A heated reaction coil was incorporated in the FI manifold to increase the conversion of organic mercury into inorganic mercury(II) chloride from 50 to approaching 100%. Detection limits (3σ) for mercury(II) chloride and methylmercury chloride were 25 and 23 ng l–1 Hg, respectively. The FI manifold could also be used to determine the total mercury concentration in biological materials and was validated by analysing the CRM TORT-1 Lobster Hepatopancreas. Good agreement with the certified (330 ± 60 µg l–1) value was achieved (353 ± 64 µg l–1). The analysis of coastal water samples from Sutton Harbour, Plymouth, showed that mercury levels ranged from 24 ± 5 to 54 ± 10 ng l–1.

Speciation of organic selenium compounds by high-performance liquid chromatography–inductively coupled plasma mass spectrometry in natural samples

Abstract: The importance of selenium in the environment and in biological systems is now well recognized. Its biochemical functions, e.g., its anti-oxidant role and therefore cell protecting function, as an essential constituent of the enzyme glutathione peroxidase, has provoked a growing interest in the determination of this element. Selenoamino acids are essential for the understanding of the biogeochemical cycle of Se and TMSe+ is a known urinary metabolite present at high levels when Se is taken in excess. In this work we present a hyphenated technique (HPLC–ICP-MS) available for the separation of the organic Se compounds (selenocystine, selenomethionine and trimethylselenonium ion). The choice of column and solvents has been a critical parameter. Good repeatability and excellent detection limits (less than 1 µg l–1 for each species) have been reached for standard solutions and the application to some natural samples (enriched yeast, human serum and urine) has shown quite promising results.

On-line solid-phase chelation for the determination of eight metals in environmental waters by inductively coupled plasma mass spectrometry

Abstract: A low-pressure method for the on-line preconcentration of analytes and elimination of matrix elements prior to determination by inductively coupled plasma mass spectrometry (ICP-MS) is described. The method reduces the concentrations of matrix elements in samples to levels that do not interfere with the determination of the first row transition elements at trace levels. The method also reduces biases caused by differences between samples and standards by delivering the analytes to the ICP-MS instrument in a consistent nitric acid matrix. A commercially available low-pressure sample manipulation system was used to perform solid-phase chelation on an iminodiacetate column. The effectiveness of the method is demonstrated for the determination of Cd, Co, Cu, Mn, Ni, Pb, U and Zn in the certified reference materials CASS-2, Near Shore Sea-water; NASS-4, Open Ocean Sea-water; and the Standard Reference Material 1643b, Trace Elements in Water. The volume of sample preconcentrated was varied in order to optimize the analyte signal. The detection limits for 10 ml samples ranged from 0.8 ng l–1 for Co to 40 ng l—1 for Cu and Zn.

Development of a high-sensitivity inductively coupled plasma mass spectrometer for actinide measurement in the femtogram range

Abstract: A quadrupole inductively coupled plasma mass spectrometer was modified and developed to achieve very low detection limits, down to a few femtograms in the actinide range. This type of performance was achieved through improvements in the interface pumping system of a conventional ICP-MS instrument, resulting approximately in a 3-fold gain in sensitivity, a 3-fold reduction in background noise, a 2-fold reduction in protenated uranium abundance and a 4-fold reduction in detection limits. A further gain in sensitivity and detection limits, by a factor of 7, was obtained using a high-efficiency desolvating nebulizer which further reduces protenated uranium abundance. The detection limit achieved with good reproducibility, using the high-efficiency desolvating nebulizer on standard solutions, is close to 1.2 fg. The performance of the new instrument is discussed and compared with that of radiometric techniques, with particular reference to plutonium, using standard solutions and real samples. The ‘half-life cut off’ between ICP-MS and alpha-spectrometry is close to 650 years. Intercomparison of plutonium measurements from 300 pg down to 35 fg in 16 environmental samples shows good agreement. The plutonium detection limits in real matrices are greater than those in clean samples and vary from 1.5 to 3 fg. The high-sensitivity ICP-MS system gives access to environmental contamination of other long-lived radionuclides, e.g., 99Tc, 237Np and uranium isotopes, which are sometimes difficult to measure at very low levels using conventional techniques.

Determination of copper, cadmium and lead in biological samples by isotope dilution inductively coupled plasma mass spectrometry after on-line pre-treatment by anodic stripping voltammetry

Abstract: Flow injection isotope dilution ICP-MS was applied to the determination of Cu, Cd and Pb in several biological samples after on-line pre-treatment by anodic stripping voltammetry. The isotope ratios for each injection were calculated from the areas of the flow injection peaks. The influence of the operating conditions of the electrochemical system on the analyte signals was studied. The influence of non-spectroscopic and spectroscopic interferences caused by the matrix on the precision and accuracy of isotope ratio determinations was also investigated. The precision for isotope ratio determinations was better than 2%. Detection limits were 0.07, 0.01 and 0.07 ng ml–1 for Cu, Cd and Pb, respectively. The isotope dilution ICP-MS method was successfully applied to the determination of Cu, Cd and Pb in National Research Council of Canada CRMs DORM-1 Dogfish Muscle and DOLT-1 Dogfish Liver and NIST SRM 2670 Toxic Metals in Freeze-Dried Urine.

Low-flow interface for liquid chromatography–inductively coupled plasma mass spectrometry speciation using an oscillating capillary nebulizer

Abstract: The application of a novel nebulizer, the oscillating capillary nebulizer (OCN), is described for use in speciation studies. The nebulizer has certain features which make it very suitable for this application, without modification, at both micro-flows (1 µl min–1) and macro-flows (1 ml min–1). Short- and long-term precision at typical operating flows are comparable to a normal (1 ml min–1) concentric glass nebulizer. Column-to-nebulizer dead volume is approximately 1 µl. The narrow drop size distribution for the nebulizer at low flows leads to excellent sensitivity when coupled to a micro-LC column. Post-column peak broadening introduced by the interface is minor at flows 5 µl min–1, but widens the peaks noticeably at flows between 1 and 5 µl min–1. The very high efficiency of the nebulizer at flows <50 µl min–1 is exemplified by the fact that no drain is necessary at these flows in the open spray chamber, as no visible liquid condenses on the chamber walls. The ICP-MS response for the OCN (counts per ng of Se injected) does not change when water is replaced by methanol as solvent, whereas with a conventional nebulizer, a solvent change of this type inevitably results in a significant change in response. The OCN was used for the reversed-phase LC separation of a mixture of five organic Se compounds of pharmacological significance, at flows of 12, 50 and 400 µl min–1. With use of a 0.5 mm id column, a flow rate of 12 µl min–1 and a 60 nl injection, good peak separation was found, with an average efficiency of ≈ 10000 plates and a detection limit of around 30 pg.

Simple method for the dissolution of atmospheric aerosol samples for analysis by inductively coupled plasma mass spectrometry

Abstract: A dissolution method for atmospheric aerosol samples should be simple and quantitative with the least possibility for contamination as the trace element concentrations and masses in these samples are very low; the masses are often between 100 and 1000 µg. A simple procedure, in which the aerosol sample is dissolved at room temperature in a disposable test-tube in an HNO3–HF mixture (3 + 1), is presented. There are no evaporative losses, the elements are dissolved quantitatively and the possibilities for contamination are minimized. The elemental concentrations are determined by ICP-MS. The blank values for the aerosol collection membrane filters, reagents and test-tubes are presented. The accuracy and precision of the method were assessed with SRMs. For NIST SRM 1633a Coal Fly Ash, the recoveries for As, Cd, Cr, Cu, Fe, Ni, Pb, U, V, Zn, Be, Ca, Co, Mg, Mn, Mo, Sb, Sr, Ti and Tl were over 90%. For NIST SRM 1648 Urban Particulate Matter, the recoveries varied between 80 and 98% for the elements Al, As, Cd, Cu, Fe, K, Ni, Pb, Se, U, V and Zn. The results for real atmospheric samples dissolved by this method were compared with results for Al, Mn, Na and V obtained by instrumental NAA. The results showed good agreement, with correlation coefficients ranging from 0.970 to 0.988 and slopes from 0.92 to 1.10.

Thermally stabilized iridium on an integrated, carbide-coated platform as a permanent modifier for hydride-forming elements in electrothermal atomic absorption spectrometry. Part 2. Hydride generation and collection, and behaviour of some organoelement species

Abstract: The in situ collection of volatile hydrides in an electrothermal atomizer with an integrated platform pre-treated with 110 µg of Zr or 240 µg of W and 2 µg of Ir for permanent modification was studied An optimization study of the performance characteristics of an automated FI-HG–ETAAS system based on an FI hydride generator interfaced with a transverse-heated graphite atomizer and longitudinal Zeeman-effect background correction was elaborated The HG step for AsIII, AsV, BiIII, SbIII, SbV, SeIV, SnIV and TeIV, as well as for several alkylated species of As and Sn, was optimized by means of a full factorial 32 design, the factors being the concentrations of acid and tetrahydroborate (or their supply rates in µmol s–1)The corresponding regression equations are tabulated, and representative response surfaces and contour diagrams are plotted All inorganic hydrides except for SnH4, are generated and collected with high efficiency at tetrahydroborate concentrations of 025–04% m/v, sample acidity of 15–3 mol l–1 HCl, trapping temperatures of 400 °C and a purge gas flow of argon of 100–130 ml min–1 The optimum conditions for stannane and alkyltin hydrides are: pH 1–4, tetrahydroborate concentrations of 02–04% m/v, trapping temperatures between 400 and 600 °C and argon flow rates of 60–120 ml min–1 Arsine, monomethylarsine and dimethylarsine are effectively collected on both coatings at temperatures between 400 and 500 °C and purge gas flow rates of 70–120 ml min–1 Optimum HG conditions differ strongly for AsIII, AsV, monomethylarsonate and dimethylarsinate species with this FI system, unless L-cysteine is added Organoelement species of As, Sn and Se are thermally stabilized in a similar manner on both Ir–Zr- and Ir–W- treated platforms, the least stable species being selenornethionine and trimethylselenonium The best levelling-off effect on the integrated absorbance for different analyte species (isoformation) is observed for As and the worst for organotins, particularly for trialkylated species such as tributyltin, trimethyltin and trimethylselenonium Relatively better isoformation is achieved for organotins on Ir–W- and for organoselenium on Ir–Zr-treated platforms The long-term stability of the Ir–Zr and Ir–W modifier coatings during at least 600–700 thermal cycles is demonstrated The Ir–Zr treatment is preferred to Ir–W for hydride trapping, owing to lower atomization temperatures, longer lifetime of the atomizer and an absence of double peaks Such peaks persist for Bi and Te on Ir–W-treated platforms The best characteristic masses in integrated absorbance measurements with Ir–Zr-treated platforms are close to those for the direct injection mode, viz, 35, 107, 83, 43, 104, 48, 31, 32, 153, 146, 148, 145 and 152 pg for ASIII, BiIII, SbIII, SeIV, SnIV, TeIV, monomethylarsonate, dimethylarsinate, monomethyltin, dimethyltin, trimethyltin, diethyltin and monobutyltin, respectively Analytical results for As, Sb and Se in certified reference materials (water and autoclave-decomposed sediments) are in good agreement with the certified contents

Development of a gas chromatography inductively coupled plasma isotope dilution mass spectrometry system for accurate determination of volatile element species. Part 1. selenium speciation

Abstract: The determination of element species in the environment is often especially difficult due to their presence at low concentrations. The coupling of GC with ICP-MS offers the advantage of transferring the total analyte into the ICP-MS instrument without any loss of analyte by nebulization. The application of IDMS results in relatively accurate results. The described GC–ICP-IDMS system consists of a gas chromatograph fitted with a capillary column, for analytical separation, and a diffusion cell that is used to exactly determine the mass discrimination factor for the isotope ratio measurement and to perform an element specific optimization of the plasma conditions. The construction of a relatively simple and low cost transfer line as well as the interface between GC and ICP-MS is described in detail. The applicability of the developed GC–ICP-IDMS system for the determination of volatile element species is demonstrated by the determination of selenite. Selenite is converted into a volatile piazselenol prior to determination. Selenate is determined after conversion into selenite. By applying 62% enriched 82Se selenite spike solution for the isotope dilution step, the 77Se: 82Se and 78Se: 82Se ratios, respectively, could be used for content calculation. Selenite (10 ng ml–1) was determined in a water sample with good agreement (within 1%) between the results obtained using the two isotope ratios. The accuracy of the results was demonstrated by the analysis of standard reference materials. The detection limit of the described method was found to be 0.02 ng ml–1.

Laser ablation–inductively coupled plasma mass spectrometry with a time-of-flight mass analyser

Abstract: Laser ablation has been employed for sample introduction into an ICP-time-of-flight (TOF) mass spectrometer. The transients generated by the ablated material are generously sampled by the 10 kHz repetition rate of the TOF instrument. A detection limit of 10 ppb for Pb in a cast-iron standard is calculated from integration of a 0.3 s transient signal generated by a single laser pulse. By simultaneously acquiring and rationing the signals from two isotopes of Zn, the substantial pulse-to-pulse power fluctuations from the laser are virtually eliminated. Although some of the data are presented in a single- or double-channel acquisition mode, the results demonstrate the sensitivity and rationing abilities available for all elements and isotopes simultaneously from a single laser pulse. Use of a digital oscilloscope provides a full elemental spectrum for each laser pulse as the laser is rastered across a lava sample that contains plagioclase crystals. The relative spatial distributions for 11 elements of interest contained in this sample are plotted over an 11 mm distance. This paper is not intended to be a display of state-of-the-art laser-ablation techniques, as the large beam divergence of the ruby laser limits the spatial resolution to 1 mm. However, the ability of the plasma-source TOF mass spectrometer for analysing transient signals is clearly demonstrated.

Determination of physiological platinum levels in human urine using magnetic sector field inductively coupled plasma mass spectrometry in combination with ultraviolet photolysis

Abstract: An extremely sensitive and reliable procedure for the determination of physiological (normal) Pt levels in human urine is described based on UV photolysis of the sample followed by the determination of Pt with magnetic sector field ICP-MS. Owing to the low blank values, which are a consequence of the minimal reagent addition required, UV photolysis was used to decompose the organic matrix components. Magnetic sector field ICP-MS operated in the low resolution mode afforded detection limits that were 100 times lower than those obtained in the high resolution mode or with conventional quadrupole ICP-MS and was found to be advantageous for the ultratrace determination of non-interfered isotopes. The detection limit in urine samples was 0.24 ng l–1 using standard nickel cones. The use of a high performance nickel skimmer cone did not result in an improvement in the detection limit, because the analyte and background signals were enhanced to a similar extent. The urinary Pt levels in 16 non-exposed persons ranged between 0.48 and 7.65 ng l–1(arithmetic mean: 1.72 ng l–1).

Determination of mercury species in sea-water by liquid chromatography with inductively coupled plasma mass spectrometric detection

Abstract: A liquid chromatographic method coupled with inductively coupled plasma mass spectrometry for the speciation of methylmercury chloride, mercury(II) chloride and ethylmercury chloride in sea-water is described. The three species were eluted from a C18 column (150 × 3.2 mm id) at 260, 340 and 750 s, respectively, with a mobile phase of 1% v/v acetonitrile and 0.005% 2-mercaptoethanol in 0.06 mol l–1 ammonium acetate pumped at 1.0 ml min–1. The total mercury determined in TORT-1 Lobster Hepatopancreas (350 ± 62 µg l–1) was in good agreement with the certified value (330 ± 60 µg l–1). The detection limits (3s) in artificial sea-water were 0.25 µg l–1 for methylmercury chloride and mercury(II) chloride and 0.75 µg l–1 for ethylmercury chloride. Off-line preconcentration using a dithiocarbamate (Dithiochel) resin gave detection limits (signal-to-noise ration = 2) of 16 ng l–1 for methylmercury chloride and 17 ng l–1 for mercury(II) chloride using a 50-fold preconcentration factor for a 1 I sample of synthetic sea-water.

Evaluation of electrochemical hydride generation for the determination of total antimony in natural waters by electrothermal atomic absorption spectrometry with in situ concentration

Abstract: A continuous-flow (timed injection) electrochemical hydride generation system was developed for the determination of total Sb in river water and sea-water. Lead was used as cathode material for the production of stibine. Both SbIII and Sbv were equally converted into their hydrides by electrochemical means with 92 ± 4% efficiency. The hydride was trapped in a Pd-coated graphite furnace prior to atomization. An absolute detection limit of 45 pg (3sblank) and a concentration detection limit of 0.02 µg l–1 were obtained using 2 ml sample volumes. The precision of replicate measurements at the 0.2 µg l–1 level (0.5 ng absolute mass level) was better than 6% relative standard deviation. The accuracy of the approach was verified through the analysis of National Research Council of Canada certified reference materials SLRS-2 and SLRS-3 River Water and NASS-4 Open Ocean Sea-water

Speciation of arsenic compounds by ion chromatography with inductively coupled plasma mass spectrometry detection utilizing hydride generation with a membrane separator

Abstract: Ion chromatography (IC) was used to speciate four of the environmentally significant, toxic forms of arsenic: arsenite, arsenate, monomethylarsonic acid, and dimethylarsinic acid. Hydride generation (HG) was used to convert the species to their respective hydrides. These hydride species were detected with ICP-MS. The gas–liquid separator for the HG unit was based on microporous PTFE tubing. Two novel features which reduce noise are incorporated into the membrane-based HG unit: firstly, gas is added to the liquid stream prior to entering the membrane, and secondly, the flow of carrier gas through the gas–liquid separator forms a ‘feedback’ loop. Absolute detection limits based on 3.14σ from 7 replicates for the four arsenic species listed above were 0.6, 3.1, 1.1, and 0.7 pg, respectively. The overall IC–HG–ICP-MS system produced RSD values of 1–6% over 30 min and 2–6% over a week for the four compounds. Two saline reference materials, NASS-4 and SLEW-2 (National Research Council of Canada), were analysed to determine concentrations of the four arsenic species, and the sum of the arsenic concentration was compared with the certified total arsenic value for each of the reference materials.

On-line method for inductively coupled plasma mass spectrometric determination of rare earth elements in highly saline brines

Abstract: A rapid and reliable on-line preconcentration method for the determination of REE in sea-water and highly saline brines by ICP-MS was developed. The method is based on REE separation from the saline water by adsorption on a micro-column of silica-immobilized 8-hydroxyquinoline. After adsorption on the micro-column at pH 9, the REE are eluted with a small volume of mixed acids and introduced into the ICP-MS instrument. The system operates at low pressure. Total time of preconcentration and analysis is less than 10 min. Detection limits in highly saline waters range from 0.06 ng l–1 for Tb and Ho to 0.6 ng l–1 for Ce and Nd. Since there is no REE sea-water reference, the analytical results obtained by this method were compared with those quoted in the literature.

Determination of selenocystine, selenomethionine, selenite and selenate by high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry

Abstract: An analytical method has been developed for the determination of selenocystine, selenomethionine, selenite and selenate. Separation of the four Se species was achieved by HPLC on a Spherisorb 5 ODS–AMINO column using a concentration gradient from 3.5 to 7.0 mmol l–1 phosphate buffer of pH 6.0 as the mobile phase at a flow rate of 1.0 ml min–1. Detection was carried out using an on-line inductively coupled plasma mass spectrometer. The chromatographic parameters and the chemical factors affecting the separation of the Se species were optimized. The detection limits, using a 100 µl sample loop volume and expressed as Se, were found to be 2.0, 1.0, 1.6 and 1.2 µg l–1 for selenocystine, selenomethionine, selenite and selenate, respectively. The precision was better than 5% in all instances. The method was successfully applied to the determination of the four Se species in water samples certified for selenite and selenate, to which selenocystine and selenomethionine had been added.

Interference of copper and nickel on electrochemical hydride generation

Abstract: Interferences by copper and nickel on electrochemical hydride generation of stibine, arsine and hydrogen selenide were examined using flow injection sample introduction. Direct interference or memory interference by either metal was found to be severe when using lead, pyrolytic graphite or vitreous carbon as a cathode. With a lead cathode, corresponding signal recoveries (%) for AsH3, SbH3, and SeH2 were, 20, 20 and 60 in the presence of 20, 10 and 40 µg ml–1 of NiII, respectively, and 30 and 50 for AsH3, and SbH3 in the presence of 120 and 7.5 µg ml–1 of CuII, respectively. Although nickel presented less interference on arsine production with a platinum cathode [no interference from 600 µg ml–1 NiII], arsine production efficiency is too low to be analytically useful with this material (<8%). An increase in acidity of the catholyte solution and use of thiourea or L-cysteine resulted in no alleviation of interference from copper on stibine production [50% suppression due to 7.5 µg ml–1 CuII]. A discussion is presented outlining the potential remedial action which can be undertaken to minimize or eliminate such interferences.

Preconcentration of rare earth elements on activated carbon and its application to groundwater and sea-water analysis

Abstract: Systematic investigations were carried out into the sorption of REEs, Y and Sc on activated carbon. Experimental parameters, such as the effect of pH, amount of carbon, contact time, sample solution volume and various mineral acids for desorption, were optimized for quantitative recoveries. The procedure was applied to the determination of REEs in Indian sea-water and groundwater by ICP-MS. The practical limit of determination with an enrichment factor of 400 is 0.3 pg ml–1(based on the preconcentration of 2000 ml of sample to 5 ml). The precision of the method is 10% at the 0.3 pg ml–1 level. The preconcentration method is simple, expeditious and field-oriented with a simple single-stage separation of the REEs from Ba and the salt content.