Vaporization of acids and their effect on analyte signal in electrothermal vaporization inductively coupled plasma mass spectrometry

Abstract

The vaporization properties of HCl and HNO₃ under various furnace heating conditions were investigated. Drying-step temperatures of 140 °C (50 s) and pyrolysis-step temperatures of 400 °C (10 s) were effective in volatilizing most of the chloride from 10 µl of 1% v/v HCl, however, a small amount (40 ng) of acid was retained on the graphite even after pyrolysis at 400 °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.