Analyte Transport Studies of Aqueous Solutions and Slurry Samples Using Electrothermal Vaporization ICP-MS

Abstract

Analyte transport of both aqueous solutions and slurry samples was studied with the use of ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS). The elements studied included V, Mn, Ni, Cu, and Pb, and the materials analyzed included NIST SRM 1548 Total Diet, SRM 1632a Coal, SRM 1566a Oyster Tissue, and NRCC LUTS-1 Lobster Hepatopancreas. The effect of microgram amounts of Pd as well as the effect of oxygen ashing on analyte transport were studied. Slurry samples were found to have better analyte transport in comparison to aqueous solutions when no physical carriers were added. Under these experimental conditions, the determined slurry concentrations were apparently high when quantified with the use of external calibration. Microgram amounts of Pd were used to investigate whether it was possible to reduce the difference in analyte transport between slurry samples and aqueous standards. The use of microgram amounts of Pd resulted in signal intensity suppression. Such a signal reduction could be related to the presence of space charge effects or losses of analyte due to condensation of the physical carrier together with the analyte on different parts of the ETV cell or the transfer line. On the other hand, quantitation for slurry samples was improved by the use of Pd as a physical carrier. Pd by itself was not completely effective for samples with high carbon content; therefore the effect of oxygen ashing combined with Pd was studied. An enhancement of signal intensities was observed when oxygen ashing was used, as well as a shift in the carbon signal to earlier times. In this case, signal enhancement was associated with an improvement in analyte transport caused by an increased number of carbon particles leaving the furnace at the same time as the analytes studied. With oxygen ashing, slurry samples behaved more similarly to aqueous solutions, facilitating quantitation with aqueous standards.