A direct injection nebulizer (DIN) is used with packed microcolumns for anion chromatography (AC) and size exclusion chromatography (SEC). Two Se species (SeOs2-and Se0d2-) are separated by AC with detection limits of 15 pg of Se. The isotope ratio 74Se/78Se can be measured with a relative standard deviation of 0.5% on 25 ngof each Se species during the actual chromatographic separation. Proteins in human serum are separated by SEC without sample pretreatment. The metals present in each molecular weight fraction are determined by ICP-MS with detection limits of 0.5-3 pgof metal. Theseabsolute detection limits are 1-2 orders of magnitude better than those obtained with conventional nebulizers.
Various cationic species of Hg (Hg2+, MeHg+, EtHg+, and PhHg+) and Pb (Pb2+, (Me)3Pb+, and (Et)3Pb+) are separated as Ion pairs by reversed-phase liquid chromatography. Lead Is detected at =0.2 pg and Hg at ~7 pg by Inductively coupled plasma mass spectrometry. A direct Injection nebulizer minimizes band broadening and yields good sensitivity by Injecting all the sample Into the plasma. Chromatographic conditions such as mobile-phase composition and the compound used for Ion pairing are selected based on the mutual requirements of chromatographic performance and detection sensitivity. The Inorganic lone Pb2+ and Hg2+ can be monitored directly In human urine by simply diluting and Injecting the liquid sample. The organolead and organomercury Ions were not concentrated enough to be seen directly In urine, but good separations were obtained when these compounds were spiked Into the sample.
A new version of the direct injection nebulizer (DIN) is used to interface liquid chromatographic (LC) separations with element-selective detection using inductively coupled plasma mass spectrometry (ICP-MS). The DIN injects all of the sample into the ICP and has a dead volume of less than 1 microliter. Charged species of arsenic and tin are separated as ion pairs on a micro-scale (1 mm i.d.), packed, reversed-phase column. Detection limits are 0.2-0.6 pg for arsenic and 8-10 pg for tin. For methanol + water eluents, the signal is highest at 25% methanol and stays within 25% of this maximum as the methanol fraction is varied from 20 to 80%. Compared with LC-ICP-MS with conventional nebulizers, the absolute detection limits and chromatographic resolution are substantially superior, and the dependence of analyte signal on solvent composition is somewhat less severe with the DIN.
Aerosol droplet sizes and velocities from a direct injection nebulizer (DIN) are measured with radial and axial spatial resolution by phase Doppler particle analysis (PDPA). The droplets on the central axis of the spray become finer and their size becomes more uniform when ≍ 20% methanol is added to the usual aqueous solvent. This could explain why the analyte signal is a maximum at this solvent composition when the DIN is used for inductively coupled plasma-mass spectrometry (ICP-MS). Mean droplet velocities are 12 to 22 ms−1 with standard deviations of ±4 to ±7 ms−1. The outer fringes of the aerosol plume tend to be enriched in large droplets. The Sauter mean diameter ( D3,2) and velocity of the droplets also vary substantially with axial position in the aerosol plume.
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