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Effect of Oxygen Ashing on Analyte Transport Efficiency Using ETV-ICP-MS

Volume 51, Number 12 (Dec. 1997) Page 1800-1806

Fonseca, R.W.; Miller-Ihli, N.J.; Sparks, C.; Holcombe, J.A.; Shaver, B.

Oxygen ashing has been used in electrothermal atomic absorption spectroscopy to eliminate organic matrix sample components and is particularly useful when doing direct solids analysis of biologicals using ultrasonic slurry sampling. Oxygen ashing has also proven to be useful for the analysis of slurry samples using ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS). In this work, the effect of oxygen ashing on analyte transport in USS-ETV-ICP-MS was evaluated. Oxygen ashing in the presence of Pd modifier (Pd/O2) en- hances analyte transport efficiency, possibly as a result of an increase in the number of carbon particles present in the graphite furnace during the vaporization step. These carbon particles act as a physical carrier, providing a surface on which the analytes can condense to be transported more efficiently. The carbon produced at earlier times, with Pd/O2, may be the result of either dissociation or fracture of the graphite during the rapid heating of the furnace. Pd, which was initially added to act as a physical carrier, also seems to be acting as a catalyst for carbon oxidation. The shift in the carbon signal toward earlier times when using oxygen ashing was observed only when Pd was present. In addition, scanning electron micrographs of a home-made graphite platform revealed that portions of the graphite substrate were missing when Pd/O2 was used and that clearly visible pits were found in the graphite. Oxygen ashing combined with 1 mu g Pd improves quantitative results by removing the organic part of the matrix present in slurry samples while enhancing analyte transport efficiency by providing carbon particles that serve as a physical carrier.