Precise selenium isotope measurement in seawater by carbon-containing hydride generation-Desolvation-MC-ICP-MS after thiol resin preconcentration

The isotopic compositions of Se in natural materials can be measured by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in combination with hydride generation and desolvation device. Although oceans are important targets for research, precise isotopic analysis of Se in seawater is generally difficult owing to its low concentrations and the much higher concentrations of other elements. We developed a robust, accurate method for the precise determination of Se isotopic composition in seawater. A hydride generator combined with a desolvation device with methane addition was coupled to MC-ICP-MS to measure Se isotopes precisely. Two new thiol resins were used to preconcentrate and separate Se from the seawater matrix efficiently, and Se was quickly eluted by small amounts of concentrated HNO₃. No detectable Se isotope fractionation was observed during the preconcentration and separation procedure. The carbon-containing plasma increased Se sensitivity, suppressed the spectral interference signal, and improved precision by > 3 times. The precisions (2sd, n = 24) of Merck Se standard solutions for δ^82/78Se, δ^82/77Se, and δ^82/76Se were 0.07‰ 0.10‰ and 0.16‰ respectively. The δ^82/76Se values of standard solutions agreed well with results obtained by other research groups. The method was used to obtain a depth profile for dissolved inorganic Se (DISe) isotopes in seawater from the Northwestern Pacific Ocean. The range of δ^82/76DISe was 0.41‰ to 1.59‰ indicating that Se isotopes fractionate sufficiently to clarify the biogeochemical cycling of this element in the ocean.