Showing papers in "Journal of Analytical Atomic Spectrometry in 1999"

Enhanced sensitivity in laser ablation-ICP mass spectrometry using helium-argon mixtures as aerosol carrier

Abstract: Laser ablation-ICP-MS is a sensitive and accurate technique for major to trace multi-element analysis at high spatial resolution on the scale of 10 µm. A wide variety of samples can be studied quantitatively, including minerals and their solid, liquid or melt inclusions as required for geochemical studies. As the desired spatial resolution increases, however, detection limits become severely constrained by the total amount of sample material reaching the ICP. Detection limits are therefore determined by the ablation rate and by the efficiency of removal of ablated aerosol particles from the ablation spot and their transport into the plasma. Properties of the carrier gas are known to affect the ablation process and the efficiency of particle transportation. This study explores the effects of different ablation-cell configurations and the use of helium, dry argon and argon moistened with water for the transport of aerosols into an ICP-MS, using a prototype 193 nm ArF excimer laser. Deposition of visible particles deposited around the ablation pit is significantly reduced when helium is used instead of argon. A moderate flux of helium through the chamber, mixed with moistened argon immediately downstream from the ablation chamber, leads to at least a 2-3-fold increase in the signal intensities across the entire mass range when compared with argon gas only. Background intensities above mass 85 are significantly reduced, but polyatomic interferences in the low mass region increase by an order of magnitude, owing to oxide formation caused by the water load. A high flux of helium, mixed just behind the ablation cell with dry argon, yields a 2-3-fold sensitivity enhancement, in addition to greatly reduced background intensity across the entire mass range. This results in one order of magnitude improvement in detection limits for most elements. These modifications permit the routine determination of minor concentrations of chlorine in microscopic fluid inclusions or the analysis of minerals, such as trace element concentrations in quartz (e.g., Na and Li down to 500 ng g –1 , using a 40 µ ablation pit). Furthermore, this improved sensitivity has recently yielded the first quantitative determination of gold concentrations (∼0.1 µg g –1 ) and full rare-earth element patterns in single 25 µm fluid inclusions.

Laser ablation inductively coupled plasma mass spectrometry: achievements, problems, prospects

Abstract: 1 Introduction 2 Evolution of LA-ICP-MS 3 Laser principles 3.1 Ruby 3.2 Nd:YAG 3.3 Excimer 4 Laser ablation systems 5 Laser–solid interactions 6 Particle transport 7 Optimization 8 Calibration strategies 9 Performance and problems 10 Growth areas 10.1 Fingerprinting 10.2 Geological microprobe analysis 10.3 Isotope ratios 11 Prospects 12 References

A critical assessment of laser ablation ICP-MS as an analytical tool for depth analysis in silica-based glass samples

Abstract: Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a versatile technique for trace element analysis with respect to depth in solid samples. The high sensitivity of ICP-MS makes it possible to determine most elements in the periodic table at trace levels (<1 µg g –1 ). Recent trends in the development of instrumentation have led to the possibility of analysing craters of smaller diameter with variable depth. However, a major limitation to this approach for depth profiling, preventing accurate and precise analysis, is element-selective, non-reproducible ablation. The ability for representative sampling during depth analysis is tested in this study by ablating into homogeneous silica-based glass materials. Elemental relative response deviations of up to 300% are observed for selected elements during progressive ablation into the glass target. The geometry of the ablation crater controls the accuracy of sampling of the material at depth. Elemental fractionation becomes significant for some elements (e.g., Zn, Pb) when the depth/diameter ratio of the ablation crater is >6, corresponding to a 50% reduction in analyte response. Large diameter craters, if ablated with sufficient laser power density, reduce elemental fractionation and give a larger signal for a longer period of time, providing more suitable conditions for representative analysis. LA-ICP-MS can be a powerful technique for depth profiling provided that optimum analytical conditions are selected.

Comparison of the ablation behaviour of 266 nm Nd:YAG and 193 nm ArF excimer lasers for LA-ICP-MS analysis

Abstract: The ablation characteristics of a 266 nm Nd:YAG laser and a 193 nm excimer laser were compared by successive experiments by inductively coupled plasma mass spectrometry (ICP-MS), using the same ablation cell without changing the carrier-gas flows within comparative experiments. Both laser-optical systems have a fairly flat-topped lateral energy distribution yielding pan-shaped ablation pits on the sample. Comparative experiments with the two optical systems were carried out with argon and with helium+argon as carrier gases. For both lasers and both gas set-ups, signals of 40 s duration were recorded with a pulse rate of 10 Hz, with similar fluence adjusted to give comparable rates of material ablation. ICP-MS signal intensities were normalised to the total ablated volume, to compare the effects of lasers and gases on transport efficiency, ionisation efficiency and response and time-dependent element fractionation. The accuracy of trace element results was tested using two materials that allow stable ablation with both lasers but have significantly different matrix compositions (SRM 612 silicate glass from NIST and AGV-1 geological reference material in lithium tetraborate fusion). The time-averaged rate of material ablation is similar for both lasers and independent of the carrier gas in the sample chamber, but decays more rapidly with the 266 nm system. In argon, the signal unit response per volume of ablated material is similar with both lasers. In helium, the signal intensity with the 266 nm laser is enhanced slightly (maximum two-fold) compared with argon, but with the 193 nm system a consistent 2-3-fold signal enhancement is achieved. The use of helium reduces the amount of visible (>1 µm size) particle deposition in the ablation cell, irrespective of laser wavelength, and tests with successive ablations of chemically contrasting samples indicate memory effects with the 266 nm system that are absent in the same experiment with the 193 nm system. The limits of detection for both lasers were further improved by the use of He owing to the decrease in background intensities. Time-dependent element fractionation during a 40 s single-spot ablation is almost eliminated with the 193 nm system (<10%), but with the 266 nm laser inter-element intensity ratios comparing the first and the second halves of the ablation period varied by up to 60% for some elements. Results for the cross-calibration between silicate (SRM 612) and borate glasses (AGV-1) obtained with both lasers indicate that the fractionation with the 266 nm system is similar for these two matrices, but this is not generally true for silicate minerals. The 193 nm system gives slightly better reproducibility between multiple analyses of one sample compared with the 266 nm system, yielding 2-5% RSDs for major and minor elements and 7-15% for concentrations below 10 ppm.

Sample preparation and HPLC separation approaches to speciation analysis of selenium in yeast by ICP-MS

Abstract: Eight solid-liquid extraction procedures were evaluated for the recovery of selenium species from yeast. Speciation of Se in the extracts was characterized by different types of HPLC, including size-exclusion, anion-exchange and reversed-phase chromatography with ICP-MS detection. The results obtained depended critically on the sample preparation procedure used. Leaching with water and with methanol led only to 10-20% recoveries of Se, split into eight compounds, among which Se(IV) and selenomethionine could be identified. Leaching with pectinolytic enzymes released an additional 20% of selenomethionine. Leaching with sodium dodecyl sulfate solution allowed the solubilization of a selenoprotein that accounted for ca. 30% of the total Se present. Leaching with proteolytic enzymes led to recoveries of Se above 85%, the majority as selenomethionine. Hydrolysis of the yeast with tetramethylammonium hydroxide solubilized the sample completely but the Se species present were entirely degraded to selenomethionine and inorganic selenium. A sequential leaching procedure is proposed for the evaluation of selenium speciation in yeast without the need for a coupled technique.

A dynamic reaction cell for inductively coupled plasma mass spectrometry (ICP-DRC-MS). Part 1. The rf-field energy contribution in thermodynamics of ion-molecule reactions

Abstract: The existing vast database of ion-molecule reaction kinetics may, with advantage, be used to overcome spectral interference in ICP-MS. To be directly applicable to an rf multipole reactor, it must be shown that the multipole provides a controlled thermal environment. The contribution of the rf field energy to the ion energy is modeled for a quadrupole reaction cell. It is shown that the rf field contribution increases with increasing rf amplitude and decreasing rf frequency (i.e., towards the high-q side of the quadrupole stability region). A thermodynamic ladder is proposed as a convenient measure of the thermal characteristics of the reactor, and should serve as a benchmark for comparison of various reaction cell designs. Experimental results for charge transfer reactions are presented. These indicate that the configuration reported is near-thermal, with an rf field energy contribution less than about 0.4 eV. The rich variety of ion-molecule processes which might be studied is demonstrated by examples of condensation, simple association and complex ligation reactions.

Speciation of arsenic in fish tissue using microwave-assisted extraction followed by HPLC-ICP-MS

Abstract: The use of microwave-assisted extraction for the extraction of arsenic species from fish tissue is described. Quantitative extraction of arsenic from spiny dogfish muscle (CRM, DORM-2) was achieved using methanol-water (80+20, v/v) with microwave heating at 65 °C in a closed-vessel microwave system. Extractions were performed with a variety of solvents including water, two different methanol-water mixtures, and a 5% tetramethylammonium hydroxide solution. Extracted arsenic species were separated using both ion-exchange and ion-pair chromatography with ICP-MS detection. The DORM-2 along with three different varieties of fish purchased from a local market were analyzed for arsenic. In all samples, the majority of arsenic present was in the form of arsenobetaine, a non-toxic arsenic species.

Determination of platinum, rhodium and palladium in exhaust fumes

Abstract: With the introduction of catalytic converters for reducing emissions of CO, NO x and HC, a higher concentration of Pt, Pd and Rh is being observed in environmental samples. These platinum group elements (PGE) are the main active components of catalytic converters and they are mainly released as a result of surface abrasion of the catalyst during car operation. The present work reports the procedure employed for sampling, mineralization and determination of PGE by quadrupole ICP-MS in three different types of catalysts. Whole raw exhaust fumes were collected directly from the end of the exhaust pipe following the 91441 extra urban drive cycle (EUDC) using a newly developed sampling device. The sampling procedure allows the further differentiation between a soluble and particulate (insoluble) sample fraction. The release of pollutants such as Hf, Cu, Y, Rb, Sr and Pb present in the catalyst washcoat or in the fuel was also monitored since these elements cause spectral interferences in the determination of PGE. These spectral interferences, 179 Hf 16 O + on 195 Pt, 40 Ar 65 Cu + and 89 Y 16 O + on 105 Pd and 40 Ar 63 Cu + , 87 Rb 16 O + , 87 Sr 16 O + and 206 Pb 2+ on 103 Rh, were considered and mathematically corrected. The sampling procedure was applied to quantify the PGE released from two different types of fresh gasoline catalyst (Pt/Pd/Rh and Pd/Rh), a diesel catalyst (Pt only) and a 18 000 km aged Pt/Pd/Rh gasoline catalyst. Most of the released PGE is in particulate form (Pt >95%, Pd >85% and Rh >90%). Release was found to vary from catalyst to catalyst and between samples of the same catalyst. The determination of PGE in the exhaust fumes shows that they are released at the ng km –1 level.

Diffusion tensor imaging in biomechanical studies of skeletal muscle function

Abstract: In numerical simulations of skeletal muscle contractions, geometric information is of major importance. The aim of the present study was to determine whether the diffusion tensor imaging (DTI) technique is suitable to obtain valid input with regard to skeletal muscle fibre direction. The accuracy of the DTI method was therefore studied by comparison of DTI fibre directions in the rat tibialis anterior muscle with fascicle striation patterns visible on high‐resolution magnetic resonance imaging (MRI) and with fibre directions in an actual longitudinal section (ALS) through the same muscle. The results showed an excellent qualitative agreement between high‐resolution MRI and DTI. Despite less accurate quantitative comparison with ALS, it was concluded that DTI does indeed measure skeletal muscle fibre direction. After the experiment, it was possible to determine an appropriate voxel size (0.9 mm3) that provided enough resolution and acceptable accuracy (5°) to use DTI fibre directions in biomechanical analyses. Muscle deformation during contraction, resulting from a finite element simulation with a mesh that was directly generated from the experimental data, has been presented.

High-precision measurement of calcium isotopes in carbonates and related materials by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS)

Abstract: Multi-collector ICP-MS has been used for the precise measurement of natural variations in the isotopic composition of Ca. The interference of Ar in the Ca mass region is assessed and the repeatability of the 44Ca/42Ca ratio of a sample calcium solution relative to the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 915a Calcium Carbonate (Clinical) standard is better than 0.1‰ at 95% confidence. Variations in sample 44Ca/42Ca ratio are expressed as δ44Ca units, which are deviations in parts per 103 from the same ratio in the NIST SRM 915a Ca standard. Measurements of δ44Ca are presented for terrestrial and marine carbonates, which show a variation of up to 0.7‰, in agreement with previous studies by thermal ionisation mass spectrometry (TIMS).

Determination of plutonium concentration and its isotopic ratio in environmental materials by ICP-MS after separation using and extraction chromatography

Abstract: An analysis method for 239 Pu and 240 Pu in environmental samples (including four certified reference materials) by ICP-MS was studied. Two types of chromatographic resin, Dowex 1X8 and TEVA, were examined for their applicability to the separation of Pu from the matrix elements. Sufficient decontamination factors (10 4 -10 5 ) for many matrix elements including U, which interferes with the detection of mass 239, were obtained with both resins. The detection limit of Pu by ICP-MS was about 0.02 pg ml –1 (0.05 mBq ml –1 for 239 Pu; 0.17 mBq ml –1 for 240 Pu) in the sample solution or 0.1 pg in the sample. Analytical results of 239+240 Pu in certified reference materials (IAEA-135, -SOIL-6, -368 and -134) indicated that the accuracy of the method was satisfactory. Data on the 240 Pu/ 239 Pu atom ratios in these reference materials, which are scarce in the literature, were also obtained, i.e., 0.211 for IAEA-135, 0.191 for IAEA-SOIL-6, 0.043 for IAEA-368 and 0.200 for IAEA-134. Compared with alpha-spectrometry, the ICP-MS method has significant advantages in terms of its simple analytical procedures, prompt measurement time and capability of determining the 240 Pu/ 239 Pu ratio.

Determination of mercury in potable water by ICP-MS using gold as a stabilising agent

Abstract: A method for the routine determination of mercury in potable water samples was developed that uses addition of gold to samples to preserve mercury by amalgamation and subsequent analysis by inductively coupled plasma mass spectrometry (ICP-MS). The method was validated using the guidelines of the NS 30 document and shows compliance with the analytical performance criteria required by the UK's Drinking Water Inspectorate over the range 0-1.2 µg l –1 Hg. The prescribed concentration or value (PCV) for mercury is 1.0 µg l –1 . A limit of detection 0.032 µg l –1 and a recovery of 99.0% at the PCV were obtained. Gold was added off-line to both samples and standard solutions. It was also added to the ICP-MS wash water to eliminate any memory effects from mercury in previous samples. The details of gold addition and the operating conditions of the Perkin-Elmer SCIEX Elan 6000 ICP-MS instrument are described. This work forms part of a project to enable the routine determination of all the low-concentration metals in potable water samples to be achieved in a single run using ICP-MS.

Application of double-focusing sector field ICP mass spectrometry with shielded torch using different nebulizers for ultratrace and precise isotope analysis of long-lived radionuclides

Abstract: The capability of double-focusing sector field ICP-MS with a plasma-shielded torch using different nebulizers (a Meinhard nebulizer with a Scott-type spray chamber with a solution uptake rate of 1 ml min –1 ; a MicroMist microconcentric nebulizer used with a minicyclonic spray chamber with a solution uptake rate of 0.085 ml min –1 ; an ultrasonic nebulizer with a solution uptake rate of 2 ml min –1 ; and a direct injection high-efficiency nebulizer with a solution uptake rate of 0.085 ml min –1 ) for the introduction of radioactive sample solutions into the ICP was investigated. The total amount of analyte for each long-lived radionuclide ( 226 Ra, 230 Th, 237 Np, 238 U, 239 Pu and 241 Am; concentration of each was 1 ng l –1 in the aqueous solution) using different nebulizers was 5 pg for the Meinhard nebulizer, 0.4 pg for the MicroMist microconcentric nebulizer and 10 pg for the ultrasonic nebulizer. The application of the shielded torch yielded an increase in sensitivity for all these nebulizers of up to a factor of 5 compared with the original configuration without a shielded torch. Sensitivities of about 2000 MHz ppm –1 were measured for the radionuclides investigated (except for 226 Ra) using the MicroMist microconcentric nebulizer with a shielded torch. The detection limits were in the sub-pg l –1 range and the precision ranged from 1 to 2% RSD (n=5) for the 1 ng l –1 concentration level (0.4 pg sample size). A further increase in sensitivity for long-lived radionuclides of nearly one order of magnitude in comparison with the MicroMist microconcentric nebulizer was observed using ultrasonic nebulization, but the amount of analyte required was significantly higher (by a factor of 25). In contrast, the direct injection high-efficiency nebulizer (DIHEN) in double-focusing sector field ICP-MS (DF-ICP-MS) with a shielded torch resulted in a decrease in sensitivity in comparison with the unshielded torch because of a higher water load due to the direct injection of aqueous solution into the plasma. At low solution uptake rates (down to several µl min –1 ), the uranium solutions were analyzed by DIHEN-ICP-MS using a double-focusing sector field instrument with higher sensitivity than quadrupole-based ICP-MS. Flow injection was used for sample introduction to measure small sample volumes of radioactive waste solutions (20 µl). The determination of 237 Np at a concentration of 10 ng l –1 by flow injection DF-ICP-MS was possible with a precision of 2.0% (RSD, n=5). In order to avoid mass spectral interferences and matrix effects long-lived radionuclides (e.g., of U, Th and 99 Tc) were separated from the radioactive waste matrix by liquid-liquid extraction or ion exchange. The methods developed for the precise determination of the concentration and isotopic ratios of long-lived radionuclides were applied to aqueous standard solutions and radioactive wastes by double-focusing sector field ICP-MS. The precision of Pu isotopic analysis by double-focusing ICP-MS with a shielded torch was 0.2, 2 and 14% for 1000, 100 and 10 pg l –1 (amount of analyte: 500, 50 and 5 fg), respectively.

Stability of inorganic arsenic (III) and arsenic (V) in water samples

Abstract: The objective of this study was to formulate a protocol for the collection and preservation of natural water samples (lakes and streams) to be analysed for the inorganic species As(III) and As(V) The analytical technique employed was HPLC-ICP-MS, using a proprietary anion exchange resin (ANX-1606-AS from Cetac) as the basis for separation of the two species Initial experiments carried out at room temperature, where de-ionised water and Ottawa River water samples were spiked at low (05-20) µg l –1 concentrations of As(III) and As(V), demonstrated that As(V) is actually reduced to As(III) within a few days This reduction is matrix and concentration dependent and was confirmed by independent analysis using HGAAS with hydride generation at pH 45 and <1 Such conversion of As(V) to As(III) does not occur in spiked deionised water maintained at 5 °C but is evident in the Ottawa River sample at this temperature A time and temperature study of a filtered (045 µm) natural water sample, with a total As concentration of 21 µg l –1 , showed that immediate storage in a filled bottle at about 5 °C will preserve As (III) and As(V) concentrations for about 30 d If kept at room temperature, changes for this particular sample occur after about 5 d, with As(V) becoming the dominant species via oxidation and gradually declining thereafter Although acidification to 01% HNO 3 stabilises the As species for at least 15 d at 22 °C, its effect is immediately to alter the species distribution With the natural water sample, this effect was to increase the concentration of As(III) substantially and, to a lesser extent, that of As(V), at the expense of other forms of the element Acidification to 01% HCl also produced these results The study of spiked de-ionised water and Ottawa River samples at 01 and 04% in HNO 3 and HCl demonstrated that both acids cause the oxidation of As(III) to As(V) but HNO 3 showed a higher degree of oxidation with greater acid strength, as expected

Direct determination of 10 trace metals in 50 µL samples of coastal seawater using desolvating micronebulization sector field ICP-MS

Abstract: Understanding the trace metal marine geochemistry of temporally variable coastal systems requires intensive sampling programs with attendant analytical burdens. Most established techniques for multi-element trace metal determinations are slow, require a skilled chemist, and are not easily automated. Advances in sample introduction systems and ICP-MS instrumentation now provide marine chemists with the sensitivity and mass resolution necessary to determine many trace metals at natural concentrations in coastal seawater. A new method has been developed for the rapid (10 samples h –1 ) determination of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb in diluted seawater, requiring just 50 µL of seawater and no reagents other than pure nitric acid. A sensitivity of 800 000-1 200 000 cps ppb –1 86 Sr in a 10% sea water matrix is obtained when microconcentric desolvating nebulization is combined with a shielded torch and hot plasma high resolution ICP-MS. Analyses are standardized by a matrix-matched external calibration curve with variations in sensitivity corrected by normalizing to the natural internal standard Sr, a conservative ion in seawater. The method thus depends on mass bias stability for each analyte relative to Sr, which was examined as a function of forward power and matrix and found to be optimized at 1100-1350 W. Precision and accuracy are limited by appropriate correction for blanks, which derive mainly from the ICP-MS introduction system, and are equivalent to about 10% of typical coastal seawater concentrations for these metals. Preliminary evaluation of a new low-flow nebulizer (µFlow, Elemental Scientific, Omaha, NE, USA) suggested lower blanks and compatibility with solutions high in total dissolved solids compared with standard microconcentric designs. Determination of dissolved concentrations in reference seawater (CASS-3) demonstrate very good agreement with certified values (within 95% confidence limit) and a precision of 3-12% (1σ) for all elements except Cr (15%). The utility of the method is demonstrated by the determination of spatial trends for these metals in a transect of seawater samples from shelf waters off southern New Jersey, USA. The new technique is sufficiently sensitive to determine some of these metals in open ocean seawater and, with minor modifications, should be applicable to a larger suite of analytes in a wide variety of natural waters.

Determination of Ag, Pb and Sn in aqua regia extracts from sediments by electrothermal atomic absorption spectrometry using Ru as a permanent modifier

Abstract: Ruthenium, deposited on a L’vov platform, is proposed as a permanent modifier for the determination of Ag, Pb and Sn in aqua regia extracts from sediments by electrothermal atomic absorption spectrometry. The coating process is simple: a solution containing Ru is pipetted repeatedly on to the platform inserted in a graphite tube and is submitted to a temperature program. In a 50% v/v aqua regia solution, high pyrolysis temperatures could be used: 1200 °C for Ag and Pb, and 1500 °C for Sn. At these temperatures, similar characteristic masses to those found for a nitric acid medium, using a Pd–Mg modifier, were obtained, showing that the high concentration of chloride does not interfere with the determination. In the aqua regia medium, the permanent modifier is much superior in comparison with Pd or Pd + Mg, modifiers applied as a solution, which could not stabilize the analytes satisfactorily. Very long tube lifetimes, around 1700 cycles, were obtained for Pb and Sn in this medium. Three sediment reference materials were partially dissolved using a mixture of aqua regia and hydrogen peroxide in a microwave oven. The results for Ag and Pb were in agreement with the recommended values, demonstrating the efficiency of the extraction. However, for Sn, the precison was less satisfactory, indicating that the extraction may be less efficient and reproducible for this analyte. Other advantages of the permanent Ru modifier are the low blanks due to in situ cleaning of the modifier and the shorter analysis time in comparison with the modifiers in solution.

Speciation analysis for iodine in milk by size-exclusion chromatography with inductively coupled plasma mass spectrometric detection (SEC-ICP MS)

Abstract: A method allowing the determination of iodine species in milk and infant formulas was developed. It was based on the coupling of size-exclusion chromatography (SEC) with on-line selective detection of iodine by ICP MS. Iodine species were quantitatively eluted with 30 mM Tris buffer within 40 min and detected by ICP MS with a detection limit of 1 µg l–1 (as I). A systematic study of iodine speciation in milk samples of different animals (cow, goat) and humans, of different geographic origin (several European countries) and in infant formulas from different manufacturers was carried out. Whey obtained after centrifugation of fresh milk or reconstituted milk powders contained more than 95% of the iodine initially present in milk in all the samples investigated with the exception of the infant formulas in which only 15–50% of the total iodine was found in the milk whey. An addition of sodium dodecyl sulfonate (SDS) improved considerably the recovery of iodine from these samples into the milk whey. Iodine was found to be principally present as iodide in all the samples except infant formulas. In the latter, more than half of the iodine was bound to a high molecular (>1000 kDa) species. The sum of all the species recovered from a size-exclusion column accounted for more than 95% of the iodine present in a milk sample. For the determination of total iodine in milk a rapid method based on microwave-assisted digestion of milk with ammonia followed by ICP MS was optimized and validated using CRM 151 Skim Milk Powder.

Determination of element species at trace levels using capillary electrophoresis-inductively coupled plasma sector field mass spectrometry

Abstract: The development and analytical characterization of a coupled capillary electrophoresis-inductively coupled plasma sector field mass spectrometer (CE-ICP-SFMS) system for the simultaneous determination of different species of As, Sb, Se and Te at trace levels are described. The species are separated by CE using a 55 cm×75 µm id fused silica capillary column. A newly developed interface with a special, low dead volume spray chamber allows the optimization of the fluid mechanical properties, thus preventing a suction effect between the nebulizer and the CE capillary. The ICP-SFMS instrument runs in the low resolution mode and is equipped with a grounded platinum electrode at the ICP torch in order to achieve the highest possible sensitivity. The CE-ICP-SFMS system developed provides stable electrophoretic conditions and allows reproducible separations to be obtained with RSDs below 3% for the migration times and below 8% for the peak areas. Excellent peak shapes down to 4 s and short analysis times of a few minutes are other important features of this combined instrument. Detection limits in the low µg L –1 region for compounds and in the picogram to femtogram range for the isotopes are achieved from standard solutions.

Microwave digestion of plant and grain standard reference materials in nitric and hydrofluoric acids for multi-elemental determination by inductively coupled plasma mass spectrometry

Abstract: A microwave-assisted HNO 3 -HF digestion system was explored for the total dissolution of biological plant and grain materials followed by multi-elemental determination using ICP-MS, in order to improve the low recoveries of several elements observed in a previous study using a microwave-assisted nitric acid digestion system. NIST standard reference materials (SRMs), including Apple Leaves (1515), Peach Leaves (1547), Wheat Flour (1567a), Rice Flour (1568a), Tomato Leaves (1573) and Pine Needles (1575), were analyzed. Approximately 0.5 g of sample was digested in 5 ml of HNO 3 and 0.1 ml of HF, with or without a subsequent digestion stage with boric acid. The matrix effect for boron was evaluated for an ICP-MS system and signal enhancement was observed for all the elements tested. Potential spectral interferences in ICP-MS with HNO 3 -HF, boron and biological matrices are discussed and the spectral interferences on Co, As and Se are tabulated. The ICP-MS system was calibrated using external standards prepared in undigested reagent blanks with In as an internal standard. It was found that with a low but sufficient amount of HF in the digestion, the possible precipitation of metal fluorides in the digestate (without boric acid) was not significant. The recoveries for some silicon-bound elements, such as Al, Co, Cr, Ni, Th, U and V, were significantly improved compared with those from digestions with HNO 3 alone. Using the HNO 3 -HF digestion procedure, the ICP-MS results for 30 elements, Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Se, Si, Sr, Th, Ti, Tl, U, V and Zn, agreed well with the certified values in leaf and grain SRMs. The recoveries were mostly within the range 85-115%. Hence, the use of boric acid in the digestion was not necessary, which simplified the procedure, minimized the content of the total dissolved solids in solution for ICP-MS analysis and allowed the determination of boron.

Determination of sulfur isotope ratios and concentrations in water samples using ICP-MS incorporating hexapole ion optics

Abstract: Sulfur isotope ratios are difficult to determine by quadrupole ICP-MS due to interfering O 2 + and NO + molecular ions of high signal intensity at isotopes 32 S and 34 S. Rf-only hexapole devices have recently been introduced into ICP-MS instrumentation to facilitate ion transfer from interface to analyser. By introducing a mixture of ‘reactive’ gases into the hexapole, a series of ion-molecule reactions can be induced to reduce or remove interfering polyatomic species. The effects of various gas mixtures (He, H 2 and Xe) on the transfer of sulfur ions through the hexapole and the breakdown of interfering O 2 + and NO + molecular ions at m/z=32 and m/z=34 were investigated. A rapid charge transfer reaction between O 2 + and Xe gives at least a factor of 10 improvement in the S + /O 2 + ratio. A further reduction in O 2 + is achieved by the addition of H 2 . δ 34 S variations were investigated in crater-lake waters and waters obtained from springs and rivers on the flanks of volcanoes in Java, Indonesia. Under optimum conditions (S=10-50 mg l –1 ), the 34 S/ 32 S measurement precision for standards and samples was <0.3% RSD. Mass bias errors were corrected by using a concentration-matched in-house standard of average North Atlantic sea-water (δ 34 S=20.5). Results compare favorably against published data measured by standard gas source mass spectrometric techniques. The proposed technique is potentially useful as a survey tool due to the large δ 34 S variation (±20) encountered in nature and the accuracy and reproducibility of the technique (±3-5).

Speciation of six arsenic compounds using capillary electrophoresis-inductively coupled plasma mass spectrometry

Abstract: Capillary electrophoresis (CE) was used to separate four anionic {arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid and dimethylarsinic acid} and two cationic forms (arsenobetaine and arsenocholine) of As in a single run. At sufficiently high concentrations, the determination of these compounds could be accomplished by means of UV detection. The determination of low concentrations (<10 µg l –1 ) of these compounds of interest was accomplished by coupling CE on-line with inductively coupled plasma mass spectrometry (ICP-MS). To accomplish this coupling, a microconcentric nebulizer was used. The modifications necessary to make a conventional CE system compatible with ICP-MS, the optimization of the operation parameters and of sample stacking conditions together with the effect of the sheath liquid and of an induced laminar flow are discussed. The analytical figures of merit of the method were assessed and the limit of determination (based on the peak height of a peak for which the signal-to-noise ratio is 10:1) was found to be 1-2 µg l –1 As for each species. The recovery for the compounds of interest was determined using a spiked mineral water sample. Samples of mineral water, soil leachate and urine were analyzed with the CE-ICP-MS combination.

Infrared laser ablation and atomic emission spectrometry of stainless steel at high temperatures

Abstract: Laser-induced breakdown spectrometry has been evaluated at high temperatures for stainless steel samples. A Q-switched Nd:YAG laser operating at 1064 nm was used to create a microplasma on an AISI 304L stainless steel sample placed inside a laboratory oven. The steel sample was 51.5 cm away from the focusing lens. The temperature of the samples ranged from 25 to 1200 °C. The plasma light was collected by means of a fiber optic bundle, spectrally resolved and then detected by a CCD camera. The effects of sample temperature in the formation of a laser-induced plasma have been studied in terms of its spectral features as well as the morphology of the ablated craters in air at atmospheric pressure. A noticeable dependence of signal emission intensity on sample temperature has been found. Depth profiling of stainless steel samples for several temperature conditions was performed. Results have revealed changes in the superficial composition at temperatures above 600 °C due to the formation of a slag layer of variable thickness, mainly composed of chromium, iron and manganese oxides.

Detection of arsenosugars from kelp extracts via IC-electrospray ionization-MS-MS and IC membrane hydride generation ICP-MS

Abstract: The selectivity and the ability to obtain structural information from detection schemes used in arsenic speciation research are growing analytical requirements driven by the growing number of arsenicals extracted from natural products and the need to minimize misidentification in exposure assessments. Three arsenosugars were extracted from ribbon kelp utilizing accelerated solvent extraction. The three arsenosugars were separated from other arsenicals with near baseline resolution using a PRP-X100 column and a 20 mM (NH4)2CO3 mobile phase at a pH of 9 with IC-ICP-MS detection. Utilizing these chromatographic conditions, the molecular weight was determined for each arsenosugar utilizing ion chromatography-electrospray ionization-mass spectrometry (IC-ESI-MS) in the positive ion mode. The molecular weight and retention times for the three arsenicals are 328 u (4.6 min), 482 u (8.2 min) and 392 u (14.2 min). The IC-ESI-MS-MS spectra from each of the arsenosugars were compared to the spectra reported in the literature, which were obtained via direct infusion of standard materials. All three MS-MS spectra contain m/z 237, 195 and 97, which are fragments of the base dimethylarsinylriboside common to all the arsenosugars. Adequate sensitivity for each arsenical was achieved using a 6.1 ng and a 22 ng injection for IC-ESI-MS and IC-ESI-MS-MS, respectively. Given the unavailability of standards, the arsenosugar distribution was determined via relative chromatographic areas using IC-ICP-MS. The IC-ICP-MS indicated the presence of an arsenic heteroatom within the same retention windows in which the arsenosugars were detected via IC-ESI-MS. The IC-ESI-MS and IC-ESI-MS-MS detection scheme provided structural information but at reduced sensitivity. In an attempt to preserve sensitivity and improve selectivity of the IC-ICP-MS, an on-line membrane hydride generation detection scheme was evaluated. The hydride system indicated that the three unknown peaks (arsenosugars) were not hydride active, thereby simplifying the chromatographic resolution needed to quantitate the more toxicologically important arsenicals, such as MMA, DMA, As(III) and As(V), while minimizing the potential for misidentification.

A comparison of automated and traditional methods for the extraction of arsenicals from fish

Abstract: An automated extractor employing accelerated solvent extraction (ASE) has been compared with a traditional sonication method of extraction for the extraction of arsenicals from fish tissue. Four different species of fish and a standard reference material, DORM-2, were subjected to both extraction methods. Arsenicals that were extracted with 50% (m/m) methanol-18 MΩ water were speciated with chromatographic separation and inductively coupled plasma mass spectrometric (ICP-MS) detection. Both extraction methods produced extraction efficiencies of greater than 71% with RSDs on replicates of less than 5.5%. The chromatographic separation employed a PRP-X100 anion exchange column. An ammonium nitrate and ammonium carbonate buffer at pH 9.0 was used to resolve five arsenicals. The speciation data indicates that the predominant species were arsenobetaine and arsenocholine. Two unknown arsenic species were present in most of the samples. The two extraction techniques produce similar relative distribution of arsenobetaine-arsenocholine (AsB-AsC) and dimethylarsinic acid (DMA) with relative area distributions of >95% and <2%, respectively.

Inter-element fractionation and correction in laser ablation inductively coupled plasma mass spectrometry

Abstract: Inter-element fractionation in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis is one of the major challenges for using the technique for in situ trace element determination and isotopic ratio measurement of geological, environmental and biological solid samples. Attempts have been made to reduce inter-element fractionation in LA-ICP-MS analysis. However, this fractionation cannot be eliminated. The mechanism of the fractionation in LA-ICP-MS analysis is not very well understood. This study investigated the inter-element fractionation of seven elements (Ca, V, Zn, Ga, Sr, La and Nd) in three different sample matrices (NIST 613, BCR-2 and SY-4) using a UV 266 nm laser. The study showed that the inter-element fractionation depends on the sample matrices and varies with time. The inter-element fractionation behaviour of V, Zn and Ga in the synthetic silicate glass NIST 613 is different from that in the quenched glass of fused silicate rocks (BCR-2 and SY-4). Relative to Ca, V, Zn and Ga show less fractionation in NIST 613 but larger fractionation in BCR-2 and SY-4. The relative internal standard normalized element intensity (RISNEI) is not linear with time for a laser ablation period of 210 s. Therefore, data acquisition using prolonged laser ablation without a matrix match will not improve the precision and accuracy for elements whose fractionation behavior is different from that of the internal standard element. The RISNEI versus time relationship for the first 100 s laser ablation can be treated as linear to simplify the data calculation. In this paper, the internal standard normalized fractionation factor (ISNFF) is defined as the sum of the second half average RISNEI and the difference between the second and first half average RISNEI, divided by the second half RISNEI of data acquisition, for the analyte concentration calculation. The ISNFF was applied for the correction of the data reduction in LA-ICP-MS analysis. The data accuracy for these seven elements is generally improved, particularly for an element whose calibration standard normalized ISNFF is significantly greater or less than 1 (e.g., Zn and Ga in this study). Good accuracy can be obtained for elements without ISNFF correction and matrix matches only if the calibration standard normalized ISNFF of the elements is close to 1.

Determination of rare earth elements U and Th in environmental samples by inductively coupled plasma double focusing sectorfield mass spectrometry (ICP-SMS)

Abstract: The excellent capability of high resolution inductively coupled plasma sectorfield mass spectrometry for measurements of the rare earth elements Th and U is demonstrated by investigating different materials such as geological matrices (sediments, soils), plant tissues and marine animal tissues. Appropriate digestion of the samples resulted in complex matrices, especially in the case of silicate containing samples. The elemental loss in silicate residues of plant material was found to be up to 30% and therefore required HF-containing digestion methods. The high concentration of matrix elements leads to spectral interferences, which are investigated by measuring the elements with different mass resolution. High mass resolution is shown to be a prerequisite for accurate determination of Sc and Y, respectively. Furthermore, effects of non spectral interferences are investigated and could be properly corrected for by using 115 In as internal standard. Moreover, the capability of a microconcentric nebulizer in combination with a membrane desolvation unit compared to a conventional microconcentric nebulizer is discussed with respect to suppression of spectral interferences. Oxide interferences could be reduced to a negligible amount, whereas it could be observed that high salt freight leads to a blockage of the membrane.

Precise sulfur isotope ratio measurements in trace concentration of sulfur by inductively coupled plasma double focusing sector field mass spectrometry

Abstract: Sulfur isotope ratios ( 34 S/ 32 S) were determined by means of inductively coupled plasma double focusing sector field mass spectrometry (ICP-SMS) operated in the medium resolution mode (m/Δm=4000) using a torch with a platinum guard electrode and a microconcentric nebulizer combined with a membrane desolvation unit. The guard electrode together with the nebulizing unit increased the signal intensity of the measured isotopes by two orders of magnitude. The use of the membrane desolvation unit decreased the signal intensity of the corresponding interference (mainly oxygen containing species) significantly. Detection limits in solution of 0.01 ng g –1 , limited only by blank levels, could be achieved. Moreover, sulfur isotope ratios could be determined at concentration levels down to 1 ng g –1 with a precision of better than 0.1% relative standard deviation (RSD) (n=10). A precision of 0.04% RSD could be achieved at higher concentration levels. ICP-SMS has been shown to be an excellent tool for fast and precise isotope ratio measurements in combination with a high sample throughput and minimum sample preparation prior to analysis.

Trace element determination in alpine snow and ice by double focusing inductively coupled plasma mass spectrometry with microconcentric nebulization

Abstract: Double focusing inductively coupled plasma mass spectrometry (ICP-MS) has been applied to the direct, simultaneous determination of Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mo, Ag, Cd, Sb, Ba, Au, Pb, Bi and U in recent Alpine snow and old ice at the ng g –1 and pg g –1 level. Small amounts of sample (about 1 ml) were analysed using a microconcentric nebulizer. To avoid possible spectral interferences, measurements were carried out both in medium (m/Δm≈3400) and low (m/Δm≈300) resolution modes. Clean procedures were adopted both in the field and in the laboratory in order to reduce the possibility of sample contamination to a minimum. Concentration ranges of Alpine surface snow were (in pg g –1 ): Ti (8-106×10 3 ), V (3-4601), Cr (3-2985), Mn (1-173×10 3 ), Fe (67-1058×10 3 ), Co (2-973), Cu (8-29.1×10 3 ), Zn (2-6311), Mo (11-721), Ag (0.5-107), Cd (16-218), Sb (1.7-6173), Ba (9-36.5×10 3 ), Pb (23-33.7×10 3 ), Bi (0.1-116) and U (0.1-265). Much lower concentrations were detected in high altitude sites in the Alps. Measurement repeatability, in terms of RSD, ranged between 9 and 34%, depending on the element. The reliability of the analytical method was confirmed by analysis of a certified reference material (SLRS-3, riverine water) and by determination of Cd, Pb, Cu and Zn by ETAAS. For some of the elements investigated these results constitute the first available for recent Alpine snow and old ice.

Determination of copper, iron and nickel in edible oils using emulsified solutions by ICP-AES

Abstract: The determination of copper, iron and nickel in edible oils was carried out using emulsion sample preparation followed by analysis by ICP-AES. Response surface methodology was applied in order to find the optimum emulsion and surfactant concentrations. The optimum amount of oil in the emulsion was in the range ca. 2-35% in most of the surfactants studied, except for Triton X-100, which showed a maximum response above 35% oil. The surfactant concentration in the emulsion varied between 0.5 and 9%. Good agreement was found between calibration curves for emulsified aqueous standards solutions and oil-in-water emulsions for most elements studied with Tween 80, ethoxynonylphenol and Triton X-100. The best agreement for all elements was shown when Tween 80 was used. Hence emulsified aqueous standard solutions could be used for the determination of these elements in emulsified edible oil samples using ICP-AES. Recoveries ranged from 90 to 110% for most of the elements studied, with relative standard deviations lower than 8%.

Hyphenated vapour generation atomic absorption spectrometric techniques

Abstract: 1. Aims and scope2. Modern flow techniques in VGAAS (FI-VGAAS and CF-VGAAS)3. On-line decompositions (FI-MWD-VGAAS, CF-MWD-VGAAS, FI-UV-VGAAS, etc.)4. On-line pre-reduction5. On-line preconcentration and separation (FI-VG-ETAAS, FI-ion-exchange-VGAAS, HG-CT-AAS, etc.)5.1 VG-ETAAS6. Hyphenated techniques for speciation analysis (VG-CT/GC-AAS, HPLC-VGAAS, HPLC-UV-VGAAS, HPLC-MWD-VGAAS, etc.)6.1 On-line speciation by non-chromatographic HGAAS techniques6.2 Coupling with GC6.3 Coupling with HPLC6.3.1 Scope, sensitivity and LODs6.3.2 Hardware complexity6.3.3 Mercury speciation6.3.4 Availability and validation7 Conclusion8 References