Determination of barium by atomic absorption spectrometry with electrothermal atomisation. Part 1. Study of the volatilisation and atomisation of solid barium phosphate, silicate, molybdate, vanadate and molybdovanadate compounds

Abstract

Molybdate, vanadate and molybdovanadate ions are recommended as chemical modifiers to suppress matrix effects in the determination of barium by electrothermal atomic absorption spectrometry (ETAAS). These ions form complexes with interfering phosphate and silicate ions and, as they are relatively involatile anions, the release of barium is favoured, thereby standardising evaporation and atomisation conditions, within certain limits. In order to investigate the conditions required to evaporate and atomise the compounds that are assumed to be formed, the most important compounds were prepared in the solid state, and 0.2–1-mg samples were placed in the graphite tube. The solid samples were heated, typically at a rate of 10 °C s^–1, and the absorbance versus time curves (volatilisation curves) were recorded. These curves, prepared with various masses of sample, are presented for 11 compounds from which the appearance temperatures (T_app) of the barium could be deduced. The T_app values were found to be in the range 1450–2150 °C. Of the compounds investigated, T_app of barium 8-hydroxyquinolinate is the lowest (1450 °C). The values for barium phosphate (1850 °C) and barium silicate (1980 °C) are significantly higher, with the highest being those for barium molybdate (2050 °C), barium molybdovanadate (2050 °C) and barium molybdophosphate (2150 °C). Barium molybdovanadophosphate and barium molybdovanadosilicate have T_app values of about 1700 °C. The results of investigations on solutions will be given in a later paper.