Rapid Determination of Sulfur in Sixty Geological Reference Materials by High Resolution Inductively Coupled Plasma‐Mass Spectrometry

Abstract

In this study, a rapid method for the quantification of sulfur mass fractions in geological materials using high‐resolution sector field‐inductively coupled plasma‐mass spectrometry (SF‐ICP‐MS) was developed. The effects of HNO3, Lefort, aqua regia, and HCl on the recoveries of sulfur in three different geological samples were evaluated. It was found that 0.5‐1 h digestion at 90 °C was enough to completely recover sulfur from BCR‐2 (basalt rock), GSS‐25 (loess), and GSD‐7 (stream sediment) using 2 ml aqua regia in both closed and open vessels. Compared with that of traditional digestion methods (e.g., HF‐HBr‐HNO3 acid digestion method), the efficiency of this proposed aqua regia digestion is improved by a factor of approximately 20. No loss of sulfur was observed because sulfur released from geological materials is directly oxidised to sulfate, which inhibits the volatilisation of sulfur. In addition, the effect of the heating‐condensing system combined with two different skimmer cones on the analytical sensitivity of sulfur was investigated. Compared with that of the normal sampling mode, the signal intensity of sulfur is enhanced by a factor of approximately 22 and 10 at a temperature of 140 °C using the S + X cone combination and S + H cone combination, respectively. This improvement is of importance for the determination of sulfur in samples with low sulfur content. The developed method was successfully applied to the determination of sulfur in geological reference materials. Most of the measured sulfur values of sixty geological materials, using both closed and open vessel digestion, are in good agreement with reference values. Compared with closed vessel digestion, the more flexible open vessel acid digestion is simple, fast, and shows great potential for the rapid quantification of sulfur in a large batch of geological and environmental samples.