Microwave-assisted volatilization of silicon fluorides for the determination of trace impurities in high purity silicon powder and quartz by ICP-MS

Closed vessel microwave-assisted volatilization of silicon as fluoride in presence of vapors of HF and HNO3, for the determination of trace impurities in high purity silicon powder and quartz, is reported. The volatilization of the matrix element from Si powder is 98.7% using vapors generated from 2:1 ratio of HF:HNO3 whereas vapors generated from 5:1 ratio of HF:HNO3 are used to volatilize 99% of Si from quartz. The recoveries of Mg, K, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ag, Cd, Ba and Pb after volatilization of matrix element are in the range 83-103% and 94-116% for Si powder and quartz, respectively, except for Ag (60-77% in both types samples). Determinations are carried out using inductively coupled plasma mass spectrometer with Dynamic Reaction Cell™ (DRC ICP-MS). The interferences due to the tailing of 40Ar+, 38Ar1H+, 40Ar12C+ and 40Ar16O+ on the determination of 39K+, 52Cr+ and 56Fe+, respectively, have been reduced to insignificant levels in DRC mode using NH3 as the reaction cell gas. Matrix volatilization using in situ-generated acid vapors in closed containers resulted in sub ng ml−1 experimental blanks. The method detection limits computed based on 3σ variation in blank measurements (n = 5) are in the low or sub ng g−1 level. The methods developed have been applied to determine trace impurities in high purity silicon powder and quartz samples.