Trace element analysis of high purity arsenic through vapour phase dissolution and ICP-QMS

Abstract

Vapour phase dissolution (VPD) has been used for the dissolution of high purity arsenic through acid vapours generated by aquaregia mixture, prior to trace element characterization. Trace impurities in As were determined by employing ion-exchange and volatilization methodologies for quantitative separation of the As matrix. After dissolving the As matrix through VPD procedure, sample solution in 0.1 M HF medium was loaded on Dowex-50WX8. The sorbed elements were then eluted first with a 20 ml aliquot of 4 M HNO 3 followed by another 10 ml of 6 M HNO 3 for the elution of REE (La, Ce, Gd and Lu). In the volatilization procedure, arsenic was removed from H 2SO 4 medium as volatile bromide by three successive additions of HBr at a temperature of about 220 °C. The trace element determinations were carried out by ICP-QMS. In both the matrix separation procedures namely on Dowex-50WX8 in 0.1 M HF medium and volatilization from H 2SO 4+HBr medium showed that the removal of arsenic matrix was nearly quantitative (>99.99%). The recoveries of trace elements were found to be >95%. Good agreement was obtained for many elements in both the procedures. The VPD approach provides considerable reduction of the process blank levels for all the elements when compared with conventional open dissolution approach. The subsequent ion-exchange or volatilization steps, contribute more to the overall process blanks.