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 electrotherm al 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 v arying amounts of sulphate added. Prereduced palladium was a better modifie r since it tolerated higher amounts of interferent. For high levels of inte rferent, the kinetic parameters approached that of selenium without modifie r. It was postulated that the interference was caused by the formation of p alladium sulphate which reduces the number of active palladium sites availa ble for selenium stabilization. The poorer performance of the unreduced mod ifier was explained in that the formation of stabile palladium sulphate hin dered the reduction of Pd(II) to palladium metal which was needed for the s elenium stabilization. Sulphate only interfered on the high temperature sta bilization process; the low temperature stabilization, linked to the format ion of a [Pd,Se,O] compound, was unaffected. The results support earlier li terature reports that selenium loss occurs by covolatilization with the mat rix and gives a reason why palladium modifiers are rendered useless by the sulphate interferent. (C) 1999 Elsevier Science B.V. All rights reserved.