Modifier effects from palladium and iridium in the determination of arsenic and antimony using electrothermal vaporisation inductively coupled plasma mass spectrometry

A study was made of the stabilising and carrying effects of palladium and iridium as modifiers in the determination of arsenic and antimony by electrothermal vaporisation inductively coupled plasma mass spectrometry. The signal intensities of arsenic and antimony were found to increase with decreasing volume (50-10 mu l) and concentration (40-5 mu g ml(-1)) of the palladium modifier solution. Similar effects were not observed for iridium. Palladium and iridium had about the same stabilising effect on the analytes; significant loss of the analyte occurred at pyrolysis temperatures above 900 degrees C. The two modifiers gave rise to about the same increase in signal intensity, but the transport mechanism is probably different. The results indicate that iridium interacts with the graphite surface such as to make carbon the main carrier. In contrast, palladium probably acts as an active carrier. (C) 1999 Elsevier Science B.V. All rights reserved.