Vaporization of Pb, As and Ga alone and in the presence of Pd modifier studied by electrothermal vaporization-inductively coupled mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) with electrothermal vaporization (ETV) was used to study the processes taking place in a graphite furnace for atomic spectroscopy. Monitoring of carbon release during the pyrolysis stage provided information on the solid-state reduction processes. Among three carbon species studied (12C, 13C and 28CO), 13C was found to be the most suitable. Gallium and arsenic oxides practically do not reduce during the pyrolysis stage. According to the data on carbon release, two reduction processes of lead species (at about 690-915 and > 1000 °C) were found to take place in the furnace. Two separate peaks of Pb (at the end of the pyrolysis stage and in the vaporization stage) were observed, probably related to vaporization of unreduced lead oxide and elemental Pb, respectively. A pre-reduced palladium modifier suppresses the low-temperature Pb losses so that the high-temperature Pb peak is increased. In the absence of modifier, a gaussian-shaped As signal was formed only if small arsenic masses were introduced into the vaporizer. Increase of the arsenic mass resulted in formation of a pronounced plateau after the peak, in spite of the very high vaporization temperature applied (2500 °C). In the presence of pre-reduced palladium modifier, a gaussian-shaped As signal was formed already at 1700 °C with a 4-15-fold increase in sensitivity depending on the analyte mass. The palladium modifier apparently prevents strong interaction of arsenic with graphite. The obtained data support very high potential of ETV-ICP-MS for detailed investigation of processes occurring in graphite furnaces used in analytical atomic spectroscopy, especially during the pyrolysis stage.