Kinetics of selenium atomization in electrothermal atomization atomic absorption spectrometry (ETA-AAS). Part 3: Chemical interference of sulphate using palladium modifiers

The interference caused by sulphate las the sodium salt in the electrothermal atomization atomic absorption analysis of selenium was investigated for prereduced and unreduced palladium nitrate modifiers. Kinetic parameters of the selenium atomization were calculated for both types of modifier with varying amounts of sulphate added. Prereduced palladium was a better modifier since it tolerated higher amounts of interferent. For high levels of interferent, the kinetic parameters approached that of selenium without modifier. It was postulated that the interference was caused by the formation of palladium sulphate which reduces the number of active palladium sites available for selenium stabilization. The poorer performance of the unreduced modifier was explained in that the formation of stabile palladium sulphate hindered the reduction of Pd(II) to palladium metal which was needed for the selenium stabilization. Sulphate only interfered on the high temperature stabilization process; the low temperature stabilization, linked to the formation of a [Pd,Se,O] compound, was unaffected. The results support earlier literature reports that selenium loss occurs by covolatilization with the matrix and gives a reason why palladium modifiers are rendered useless by the sulphate interferent. (C) 1999 Elsevier Science B.V. All rights reserved.