Simultaneous Determination of Phosphorus, Sulfur, and Selenium in Rocks and Stream Sediments by Inductively Coupled Plasma-Tandem Mass Spectrometry (ICP-MS/MS) with Sealed Acid Digestion

In the geochemical analysis of rocks and stream sediments, phosphorus (P), sulfur (S), and selenium (Se) are important tracer elements, providing critical insights into diagenetic and metallogenic processes, redox conditions and ecotoxicity assessment, respectively. The unique physical and chemical properties of these three elements as well as the complex matrix of the samples make their simultaneous determination using a single method challenging. Typically, multiple analytical techniques must be combined, which results in a lengthy sample pretreatment process and cumbersome operation. In this work, a mixed acid system of nitric acid and hydrofluoric acid was used for sample digestion under sealed conditions at 185℃ for 24 h, followed by determination using inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS). In tandem mass spectrometry mode, oxygen (O₂) was selected as the reaction gas to convert ³¹P⁺ to ³¹P¹⁶O⁺, ³²S⁺ to ³²S¹⁶O⁺, and ⁸⁰Se⁺ to ⁸⁰Se¹⁶O⁺, effectively eliminating polyatomic ion interferences. The results indicated that P exhibited excellent linearity within the range of 0–500 μg/L, while S and Se showed excellent linearity within 0–200 μg/L, with correlation coefficients greater than 0.9999. The detection limits were 0.16 μg/g (P), 1.64 μg/g (S), and 0.004 μg/g (Se). The accuracy and reliability of the method were validated by analyzing certified reference materials (CRMs) for rock and stream sediments. Good agreement was observed between the measured and certified values, and spiked recoveries ranged from 95.0% to 115.0%. This method is simple to operate, yields accurate and reliable results, and provides a new solution for the high-throughput analysis of P, S, and Se in geological samples.