VAPRIZATION OF ACIDS AND THEIR EFFECT ON ANALYTE SIGNAL IN ELECTROTHERMAL VAPORIZATION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

The vaporization properties of HCl and HNO3 under various furnace heating conditions were investigated. Drying-step temperatures of 140-degrees-C (50 s) and pyrolysis-step temperatures of 400-degrees-C (10 s) were effective in volatilizing most of the chloride from 10 mul of 1% v/v HCl, however, a small amount (40 ng) of acid was retained on the graphite even after pyrolysis at 400-degrees-C. Under the same experimental conditions, HNO3 was completely volatilized from the graphite tube. The effect of a range of concentrations of HCl, HNO3, H2SO4 and H3PO4 on analyte signals was studied for Co, Cu, Ag, Cs, Pb, Bi and U. Analyte signals were enhanced by as much as a factor of two in the presence of 1% v/v HNO3 and H2SO4. Phosphoric acid suppressed analyte signals for Ag and Bi and the use of HCl resulted in relatively small changes in analyte sensitivity. The use of a pyrolysis step in the heating programme reduced the effects associated with acid matrices, but at the expense of signal intensity. A mixed modifier-carrier reduced the matrix effects associated with H2SO4 and H3PO4 and essentially eliminated them for HNO3 and HCl.