|Fonseca, Rodney - GENERAL ELECTRIC|
|Sparks, C. - UNIVERSITY OF TEXAS|
|Holcombe, J. - UNIVERSITY OF TEXAS|
|Shaver, B. - UNIVERSITY OF TEXAS|
Submitted to: Journal of Applied Spectroscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 2, 1997
Publication Date: N/A
Interpretive Summary: In this work, ultrasonic slurry sampling has been combined with inductively coupled plasma mass spectrometry (ICP-MS) to provide rapid, multielement analyses of solid samples. An important consideration in using electrothermal vaporization (ETV) is the efficiency of transport of the sample into the plasma of the ICP-MS. This work revealed that foods and biological samples which contain significant amounts of carbon, provide enhanced analyte transport, making it impossible to do calibration using external aqueous calibration and requiring the method of additions be used for quantitation. In-situ oxygen ashing was done in the electrothermal vaporizer to get rid of the organic sample matrix so that analyte transport would be the same for samples and aqueous standards. This worked extremely well and an added benefit was that oxygen ashing combined with the addition of palladium led to increased sensitivity overall. This work is important to anyone interested in doing ETV-ICP-MS and points out the need for consideration of the carbon content of samples. It also supports the importance of considering theories and mechanisms associated with electrothermal atomic absorption spectrometry when doing ETV-ICP-MS.
Technical Abstract: 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 enhances analyte transport efficiency due to an increase in the number of carbon particles coming off of the graphite furnace during the vaporization step. These carbon particles act as a physical carrier providing a surface on which analytes can condense to be transported more efficiently. The carbon produced at earlier times, when oxygen ashing is used in combination with Pd, may be the result of either dissociation or fracture of the graphite during the rapid heating of the furnace. Pd which is 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 due to oxygen ashing was only observed 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 oxygen ashing was used in the presence of Pd. Oxygen ashing combined with 1 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 which serve as a physical carrier.