Robert C. Hutton

Characterization of polyatomic ion interferences in inductively coupled plasma mass spectrometry using a high resolution mass spectrometer

The effect of common interferences on the ICP-MS of the elements from Li through to Ge has been catalogued. The study utilizes the resolving power available from a double focusing mass spectrometer and provides definitive information regarding the nature and potential origin of such species. The study investigates several common anion matrices typical of the normal acids used in practical analysis (sulfate, nitrate and chloride) as well as the concomitants present from atomospheric entrainment into the argon plasma (C, N, H and O). The resulting database should provide a useful reference guide as to which interferences need to be considered in any practical analysis, whether using a quadrupole or a sector-based instrument.

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

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.

Role of aerosol water vapour loading in inductively coupled plasma mass spectrometry

The influence of aerosol water loading has been shown to be of great significance in inductively coupled plasma mass spectrometry (ICP-MS). The resultant spectra from both singly charged M+, oxide MO+ and doubly charged M2+ species have a strong dependence on the water loading in the plasma. Similarly the levels of polyatomic species, whether derived directly or indirectly from water components (O+, H+) are also significantly improved when loadings are lowered. At low water loadings, the mean ion energies are reduced to low but reasonably constant levels (ca. 4 eV) for a wide range of elements facilitating more predictable plasmas and minimising mass dependent ion focusing.

Evaluation of inductively coupled argon plasma mass spectrometry (ICP-MS) for simultaneous multi-element trace analysis in clinical chemistry

The suitability of inductively coupled plasma mass spectrometry (ICP-MS) for the determination of trace amounts of inorganic elements in clinical samples has been investigated. Protein solutions, which were known to be free from biohazards, were obtained in sufficient amounts to allow the preparation of three pools of material of differing trace metal content. Freeze-dried portions were distributed to four different laboratories with established expertise in trace element analysis.The elements Mg, Al, Cr, Mn, Fe, Ni, Cu, Zn and Se as determined by ICP-MS showed reasonable agreement with the values obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES), simultaneous multi-element atomic absorption continuum source (SIMAAC) spectrometry and by established flame and graphite furnace atomic absorption spectrometry (FAAS and GFAAS) procedures.A commercial source of freeze-dried urine with assigned values for a range of trace elements was analysed by ICP-MS. Acceptable results were obtained for elements with mass numbers greater than 81 (e.g., Pb, Cd, Hg and Tl). However, with the exception of Co, results obtained for the first row transition elements, as well as for As and Se, were severely degraded by polyatomic interferences. Acid digests of dried bovine liver (NBS SRM 1577) were also analysed by ICP-MS and acceptable agreement with the certified values found for Mn, Fe, Cu, Co, Rb, Zn, Sr and Mo. Modification of the sample preparation procedure by precipitation of chloride prior to analysis by ICP-MS has been found to offer advantages for some elements.

Communication. Isotope ratio measurement by inductively coupled plasma multiple collector mass spectrometry incorporating a high efficiency nebulization system

Isotope ratio analysis by inductively coupled plasma multiple collector mass spectrometry has been performed utilizing a high efficiency desolvating nebulization system for sample introduction. The high accuracy and high precision analysis of uranium, lead and hafnium reference materials at a concentration of 50 ng ml–1 are reported. Use of the high efficiency device has increased sample transmission and hence increased ion-signal levels by a factor of ten compared with conventional nebulization. The analysis of each uranium and lead solution required 29 ng of sample while the analysis of each hafnium solution required 290 ng of sample. The accuracy and precision of the measurements are comparable with those obtained by thermal ionization mass spectrometry. Transmission calculations indicate an ion:atom ratio of 1:5500 for each of the three elements. This is superior to that observed with other plasma source mass spectrometers and in the case of hafnium, exceeds that achieved with thermal ionization mass spectrometers.

Analysis of solutions containing high levels of dissolved solids by inductively coupled plasma mass spectrometry

Solutions used for analysis by inductively coupled plasma mass spectrometry (ICP-MS) are often restricted to those containing low amounts of dissolved solids (0.2%m/V). This is primarily due to problems associated with matrix deposition on the sampler orifice. The effect of the volatility of the matrix is considered in relation to this problem. Techniques which utilise the injection of limited sample volumes into the ICP system such as flow injection (FI) are shown to be particularly effective in minimising such effects when refractory matrices are to be analysed. Data are presented illustrating the analysis of two different matrix types, i.e., brine and aluminium. The results indicate that such samples can be routinely analysed by ICP-MS at up to 1.5–2.0%m/V of total dissolved solids if suitable sampling procedures are employed.

Elimination of chloride interference on the determination of selenium in serum by inductively coupled plasma mass spectrometry

The presence of chloride ions in sample solutions may cause interferences in the determination of certain elements (particularly V, Cr and As) by inductively coupled plasma mass spectrometry (ICP-MS). This may be problematic in clinical samples such as tissue, protein and urine where the measurement of elements, present at physiologically active levels, can be impaired by these spectral interferences. A procedure is described whereby a chromatographic separation is employed to de-salt serum samples, rendering a sample solution free of chloride. Using this procedure, ICP-MS can be used to measure the Se content of serum solution accurately without interference.

Application of multi-element time-resolved analysis to a rapid on-line matrix separation system for inductively coupled plasma mass spectrometry

A rapid on-line matrix separation system for ICP-MS, using multi-element time-resolved analysis, was developed for the determination of several trace elements in complex matrix samples. A flow injection manifold was constructed consisting of a mini-column of 8-hydroxyquinoline covalently immobilized on to controlled pore glass. Analytes retained on the column were eluted using 0.1 ml of 2.0 mol l–1 nitric acid. Sample volumes of 0.5 ml were analysed, yielding a preconcentration factor of 5 in addition to matrix separation. The system was optimized with respect to the variables of buffer concentration, buffer pH and eluent acid volume and concentration. Calibrations from both pure water and synthetic sea-water compared well and showed good linearity, with correlation coefficients of 0.988–0.999 for a range of analytes. The method showed good within-run reproducibility with precisions (sr) at the 1 ng ml–1 level of typically <3%. In general, recoveries between 89 and 104% were obtained, with the exception of Ni, which showed a recovery of 78% under the compromise conditions used. The method was validated by the analysis of estuarine (SLEW-1) and coastal (CASS-2) certified reference materials. Good agreement with the certified values was obtained for both of these materials.

Optimization of quantitative depth profiling with glow discharge mass spectrometry. Part 1. Optimization studies on crater shape and time–depth conversion

Investigations have been performed using glow discharge mass spectrometry to determine the effect of glow discharge parameters such as voltage, current and pressure on the sputter rate and sputtered crater shape. Optimization of these parameters has been carried out on a multi-layer sample and is shown to produce a flat-bottomed sputter crater and a depth profile resolution as good as 0.03 µm (300 A). Sputter rates can be controlled to within ± 10%, and by establishing a library of such values for a wide variety of materials, the crater depth can be calibrated against analysis time to provide accurate depth quantification. Different sputter rates can be used for routine depth profiling of various coating thicknesses from 0.1 to 200 µm.

Investigations into the direct analysis of semiconductor grade gases by inductively coupled plasma mass spectrometry

Silane is the main gas used in the field of electronics to produce compounds of silicon. The direct analysis of silane by inductively coupled plasma mass spectrometry has been found to be a practical proposition for both the measurement and indentification of elemental impurities at the sub-parts per billion level. Several steps, however, need to be taken to optimise commercial instrumentation further for this task. Firstly, in order to minimise the amount of matrix material being deposited on the sampler orifice, an alloy sample cone was used which operated at a higher temperature than that of the commercially available nickel cones; additionally, the optimum carrier gas flow-rate with silane was found to be significantly lower than that required to achieve maximum sensitivity in argon alone. This too reduced sample deposition around the orifice. A further increase in sensitivity was achieved when the argon carrier gas was supplemented by the addition of hydrogen; the detection limits for 75As and 127l were 0.55 and 0.65 p.p.b., respectively, with a precision of 2–5%. In order to quantify impurities in the silane two techniques were employed. The first used the silicon matrix as an internal standard and the second involved direct comparison with a calibration graph obtained by the addition of impurities to the silane.