An improved direct Injection nebulizer (DIN) Is used In a continuous-flow mode for Inductively coupled plasma mass spectrometry (ICP/MS). Precision In cases where the signal Is not limited by counting statistics Is typically 0.5% relative standard deviation (RSD), an Improvement by a factor of 4 over the precision obtained with conventional nebulizers. A rlnse-out time of only 15 s Is sufficient to reduce the analyte signal to 0.1% of Its steady-state value, even for memoryprone elements such as Hg and I. Relative detection limits are similar to those obtained with conventional pneumatic nebulizers. Since the sample flow rate Is only 120 µ min"1, the absolute detection limits are Improved by up to an order of magnitude. The refractory oxide Ion ratios (MO+/M+) are 3 times higher than with other nebulizers. Matrix effects caused by Na are comparable to those observed with other nebulizers.

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A sensitive technique for speciation and quantification of Cr(III), Cr(VI), and total chromium has been developed using high-pressure liquid chromatography (HPLC) combined with direct injection nebulization (DIN) and inductively coupled plasma mass spectrometry (ICP-MS). A characterization and optimization of a microcolumn specifically designed for chromium speciation has been conducted. The direct injection nebulizer (DIN) was optimized to produce the best possible sensitivity for the system. Parameters affecting the column component of the system such as sample pH, eluent strength, sample size, flow, and pressure characteristics were studied in addition to optimal DIN-ICP-MS parameters. The detec-ACKNOWLEDGMENT Many thanks to Lian Shan Liu, George Wood, and other staff of the Laboratory Services Branch of Ministry of the Environment and Energy for their invaluable help in making this publication possible.

gle-column approach (29) and in a column-switching approach (30). ACKNOWLEDGMENTWe thank L. Bowers and P. Froehlich for helpful discussions and perspective, as well as C. Galgano and J. Newman for their assistance with the preparation of the manuscript.

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