ABSTRACT

We present a simplified method for simultaneous determinations of fluorine (F), chlorine (Cl), and sulfur (S) contents and isotopic abundances in rock samples. After using pyrohydrolysis to extract F, Cl, and S from a sample and transfer it into a sodium hydroxide (NaOH) solution, concentrations of F, Cl, and S as sulfate are measured by ion chromatography. The method is applicable to a variety of rock materials, including peridotite, basalt, gabbro, andesite, rhyolite, sulfide minerals, and possibly to sea salt, with F, Cl, and S contents of several μg g^-1 to several tens of weight percent in 40 to 250 mg of rock powder. F, Cl, and S contents obtained by 5-7 repeated analyses of each of nine geological reference materials were in good agreement with previously reported values. In certain reference materials, sulfite peaks were observed, indicating incomplete oxidation to sulfate during S extraction by pyrohydrolysis. However, total S contents in those samples analysed by ICP-AES were also in good agreement with previous reported values. The RSDs of F, Cl, and S contents in reference materials were <6%, except for samples with F content <10 μg g^-1 (∼20%) or S content <∼20 μg g^-1 (<20%). In addition, Cl isotope compositions of seawater (IAPSO Standard Seawater and Pacific Ocean water) from sample solutions in this study were identical within error to reported values, indicating that Cl isotopes do not fractionate during pyrohydrolysis. After small isotopic fractionation corrections, multiple isotope compositions of S (³²S, ³³S, ³⁴S and ³⁶S) in solutions of sulfide (IAEA-S-1, IAEA-S-2, and IAEA-S-3), IAPSO Standard Seawater, and gabbro (JGb-1), also agree well with their respective reported values. Thus, this method is applicable to obtain accurate Cl and S contents as well as their isotopic compositions from a single aliquot of sample.