Single reaction chamber microwave digestion coupled with ICP-MS for the determination of ultra-trace mercury in rocks

Abstract

In this study, a method for rock digestion using a single reaction chamber (SRC) microwave system was established. Nitric acid (HNO₃) and hydrofluoric acid (HF) were used as digestion agents, and the determination of mercury (Hg) in rocks was performed by inductively coupled plasma mass spectrometry (ICP-MS). The optimal conditions for the SRC microwave system were achieved at 260 °C and 70 bar, with a mixture of 3 mL of 65–68 wt% HNO₃ and 1 mL of 49 wt% HF when the sample weight is in the range of 0.025–0.05 g. The method quantitation limit (MQL) was determined to be 0.0016 mg kg⁻¹. Measurement accuracy was evaluated using five Chinese nationally certified reference materials, demonstrating good consistency between measurement results and certified values. The method was applied to two rock samples, resulting in a recovery rate ranging from 105% to 109%. This method exhibits high sensitivity, stability, and low acid consumption. Importantly, it provides a reliable and efficient determination method for Hg in rocks, which is of great significance in geochemical analysis.