Advances in sample introduction for inductively coupled plasma spectrometry

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1991
Authors
Wiederin, Daniel
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Chemistry
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Abstract

A two-step desolvation system for a continuous-flow ultrasonic nebulizer reduces the load from organic solvents on an argon inductively coupled plasma (ICP). The aerosol is first heated above the boiling point of the solvent. Subsequently, solvent vapor is removed in two condensers kept at -10°C and ~eq -80°C. No special plasma ignition procedures are required. The plasma is stable to a forward power as low as 0.5 kW when methanol, acetone, acetonitrile, or ethanol are nebulized. Detection limits for metals range from 0.2 [mu]g L[superscript]-1 for Fe to 5 [mu]g L[superscript]-1 for Pb. The detection limits for each element are approximately the same regardless of the organic solvent nebulized and are comparable to those obtained during ultrasonic nebulization of aqueous solutions;An improved direct injection nebulizer (DIN) is used for inductively coupled plasma mass spectrometry (ICP-MS). Precision is typically 0.5% relative standard deviation (RSD), a factor of 4 lower than the precision obtained with conventional nebulizers. A rinse-out time of only 15 seconds is sufficient to reduce the analyte signal to 0.1% of it steady state value, even for memory-prone elements such as Hg and I. Relative detection limits are similar to those obtained with conventional pneumatic nebulizers, but the absolute detection limits are improved by up to an order of magnitude;A direct injection nebulizer (DIN) produced a finer aerosol with a narrower drop size distribution than a glass concentric nebulizer. The droplets from the DIN were slightly larger, however, than those leaving a Scott-type spray chamber with a glass concentric nebulizer. The droplet size distribution became narrower and shifted to lower diameters as the aerosol gas flow rate increased;A flow injection method for on-line standard additions is described. A 500 [mu]L sample solution is injected into a flowing stream via a flow injection valve. Standards (50 [mu]L) are sequentially introduced through a second valve. The two streams mix in a tee prior to nebulization. The time-consuming solution preparation steps for conventional standard additions are eliminated through use of flow injection techniques and a direct injection nebulizer. Nine toxic elements in undiluted urine are determined in less than 5 minutes. ftn *This work was performed at the Ames Laboratory under contract no. W-7405-ENG-82 with the U.S. Department of Energy. The United States government has assigned DOE report no. IS-T-1528 to this dissertation.

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Chemistry, Analytic, Chemistry
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