Jiansheng Wang

Direct analysis of solid samples by electrothermal vaporization inductively coupled plasma mass spectrometry

Abstract The direct analysis of solid samples by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) has been demonstrated. This method provides a rapid alternative to traditional means of solid sample analysis, as the sample pre-treatment procedures are eliminated or minimized. Three instrument calibration methods for the solid sample determinations such as liquid standard, standard addition and differing weights of a standard reference material have been investigated. Utilization of standard reference materials for standardization, when available, provided for the best performance for the ETV-ICP-MS system. A simple and easy to use method of introducing the solid sample, with a well-defined mass, into the graphite furnace has been developed.

Speciation of toxicologically important transition metals using ion chromatography with inductively coupled plasma mass spectrometric detection

Speciation of vanadium(IV) and (V) using a mixed mode high-performance liquid chromatography column with inductively coupled plasma mass spectrometry detection was investigated. Nickel(II), chromium(III) and (VI) were also separated using the same column. The effect on the separation by varying the pH of the mobile phase and the ionic strength were studied. The absolute detection limits in aqueous media were 0.024 ng for vanadium(v) and 0.114 ng for vanadium(IV). The speciation of vanadium in National Institute of Standards and Technology Standard Reference Material (SRM) 2670 (Toxic metals in Freeze-Dried Urine, Elevated Level) was also accomplished. Using a slight modification of the mobile phase, the speciation of chromium(III) and (VI), as well as nickel(II) was accomplished. Absolute detection limits for chromium(III) at m/z 52 and 53 were 0.042 and 0.017 ng, respectively and for chromium(VI) at the same masses were 0.055 and 0.022 ng, respectively. Absolute limits of detection for nickel obtained were 0.031 ng and the speciation of nickel(II) in SRM 2670 was also demonstrated.

Addition of molecular gases to argon gas flows for the reduction of polyatomic-ion interferences in inductively coupled plasma mass spectrometry

Addition of 1% N2 to the coolant Ar gas flow at a nebulizer gas flow rate of 0.95 dm3 min–1 can eliminate 40Ar35Cl+ and dramatically reduce 35Cl16O+ and 37Cl16O+, without losing sensitivity for a representative analyte, In. Addition of 3% N2 to the central channel gas flow, at a nebulizer gas flow rate of 0.70 dm3 min–1, has the same effects on polyatomic-ion interferences but also results in a loss in sensitivity to some extent. No significant effects on oxides (48Ti16O+, 140Ce16O+, 238U16O+) and doubly charged (138Ba2+) species were observed with or without N2 addition. Addition of CH4 to the Ar gas flows has a similar effect to that of N2 addition, but results in carbon deposition on the sampling cone and a more complicated spectrum. Results of analyte determination for a reference material confirmed that addition of N2 could be applied to real samples.

Graphite furnace hydride preconcentration and subsequent detection by inductively coupled plasma mass spectrometry

Abstract Preconcentration of multi-element volatile hydrides in a graphite furnace and the subsequent determination by inductively coupled plasma mass spectrometry (ICP-MS) is a relatively new method for elemental analysis. This method offers several advantages over direct hydride generation sample introduction. In this technique the excess hydrogen generated as a by-product of the reduction of the analytes was not introduced into the plasma with the analytes, thus giving the plasma greater stability. The hydrides of arsenic, bismuth, and tellurium were trapped in the presence of metallic palladium inside the graphite tube of an electrothermal vaporization unit, and subsequently determined by the ICP-MS in a single run. The linearity obtained using this method was limited to a sub-ng/ml concentration range. The preliminary limit of detection calculated for arsenic is 0.002 ng ml −1 , this value was based on the slope value of the linear portion of the calibration curve. Effectiveness of the trapping method was determined by analysis of a standard reference material.

Extraction of trace elements in coal fly ash and subsequent speciation by high-performance liquid chromatography with inductively coupled plasma mass spectrometry. Plenary lecture

The speciation of arsenic in coal fly ash is reported. The amounts of AsIII and AsV were found and these values, released into water from coal fly ash, are dependent on the pH of extracted solution and the type of coal fly ash (e.g., location collected, type of coal and combustion conditions). A small amount of arsenic conversion from AsIII to AsV was found, especially from the lower pH extractions. The arsenic conversion may be caused by co-existing high oxidation states elements in the extracted solution, and may be promoted by the grinding process. Oxygen from the atmosphere was found to be an unlikely source for the arsenic conversion. A preliminary investigation for speciation of vanadium and nickel in coal fly ash shows that VV, VIV and NiII exist in the extracted solutions. This extraction–speciation approach can provide some basic information for predicting the hydrolytic behaviour of trace elements in the coal fly ash–water systems and can be extended to the speciation of other elements.

Distribution and accumulation of a mixture of arsenic, cadmium, chromium, nickel, and vanadium in mouse small intestine, kidneys, pancreas, and femur following oral administration in water or feed.

Manufactured gas plant (MGP) sites are contaminated with coal tar and may contain metals such as arsenic (As), cadmium (Cd), chromium (Cr), nickel (Ni), and vanadium (V). These metals are known to cause cancer or other adverse health conditions in humans, and the extent and cost of remediating MGP sites may be influenced by the presence of these metals. Studies assessed the distribution of these metals in female B6C3F1 mice ingesting (1) a metal mixture in water or (2) an MGP mixture in NIH-31 feed. The highest metal levels were measured in the small intestine and kidneys of mice receiving the metal mixture in water. For mice receiving the metal mixture in water, levels of As, Cd, and Cr, in the small intestine, levels of As, Cd, Cr, and V in the kidneys, levels of As and Cd in the pancreas, and levels of Cr and V in the femur were significantly greater than controls at 4, 8, 12, 16, and 24 wk. Except for Ni levels in the small intestine and femur and Cr levels in the kidneys, levels of metals were much lower in mice administered the MGP mixture in feed. The highest concentrations of metals in mice ingesting the MGP mixture in feed were found in the small intestine and kidneys, but few were significantly greater than controls. Levels of As in the small intestine at 6 and 18 wk and levels of Cr in the kidneys at 12, 18, and 24 wk were significantly greater than in controls. The data suggest that tissue burdens in small intestine, kidneys, pancreas, and femur of arsenic, cadmium, chromium, and vanadium are less when metals are present as an MGP mixture in feed than as a mixture in water. The reduced distribution and accumulation of metals in the organs of mice ingesting the MGP mixture in feed compared to the levels in organs of mice ingesting the metal mixture in water suggests that metals may be less likely to accumulate in humans ingesting MGP mixtures, thereby presenting a lower overall human health risk. The data presented indicate that the matrix in which metals are present will affect the uptake of individual metals and the organ specificity.

Effect of ion-lens tuning and flow injection on non-spectroscopic matrix interferences in inductively coupled plasma mass spectrometry

The effects of various matrix constituents, Co, Pb and synthetic ocean water, on analyte signal have been studied. Suppression of the 138Ba+ signal was observed in the presence of each matrix, with the Pb matrix having the greatest effect. These matrix-induced suppressions of analyte signal were compensated for in part by the use of In as an internal standard, and by initially tuning the ion lenses for maximum analyte signal in the presence of the matrix, rather than for a simple acidified standard solution. The severity of matrix-induced suppression was compared for flow injection and continuous sample introduction. No significant differences in suppression of analyte signal between the two methods were observed because of the relatively large sample volume used for flow injection. The experimental procedure adopted, continual reference of analyte signals with and without the matrix present, effectively eliminated any bias in the results due to nebuliser and cone blockage.

Utilization of metallic platforms in electrothermal vaporization inductively coupled plasma mass spectrometry

A method to improve the analytical performance of hydride trapping on Pd inside a graphite furnace and subsequent determination by ICP-MS was investigated. Strips of tungsten, tantalum, molybdenum and rhenium were coated (electroplated/sputtered) with palladium and used as platforms inside the graphite furnace. A typical pyrolytic graphite-coated graphite platform was also coated with Pd in the same manner, for performance comparisons. Scanning electron microscopy (SEM) and X-ray fluorescence spectrometry were used to characterize the surfaces. SEM showed a smoother Pd layer covering the metallic substrates when compared with the graphite. An analyte signal reproducibility study revealed that Ta, Re and Mo were not ideal substrates for this purpose. The As peaks obtained from trapping on the graphite platform were broadened with a decrease in intensity after a few firings. The Pd-sputtered tungsten platform showed superior performance over the other platforms. The linear dynamic range obtained using this platform was improved by one order of magnitude in the upper limit (from 1 to 100 ng ml–1) over that reported using a graphite platform in previous work. The limit of detection of arsenic was found to be 0.01 ng ml–1, within the same range obtained from the graphite platform.

Minimization of non-spectroscopic matrix interferences for the determination of trace elements in fusion samples by flow injection inductively coupled plasma mass spectrometry

The efficiency of various ion lens tuning strategies, flow injection and the use of an internal standard has been investigated for the determination of trace elements in real samples. Spike recoveries indicated that internal standardization was always preferable if 100% recovery was to be obtained. However, good recoveries were also obtained by tuning the ion lenses for a maximum 115In+ signal in a matrix blank solution containing 100 ng g–1 of In, while using continuous nebulization sample introduction. Results indicated that tuning the ion lenses in the presence of the matrix yielded improved analyte recoveries when compared with tuning the lenses for a standard solution.