Determination of total sulfur at microgram per gram levels in geological materials by oxidation of sulfur into sulfate with in situ generation of bromine using isotope dilution high resolution ICPMS

We have developed a new, simple, and accurate method for the determination of total sulfur at microgram per gram levels in milligram-sized silicate materials with isotope dilution high-resolution inductively coupled plasma mass spectrometry equipped with a now injection system. In this method, sulfur can be quantitatively oxidized by bromine into sulfate with achievement of isotope equilibrium between the sample and spike. Detection limits for S-32(+) and S-34(+) in the ideal solution and silicate samples were 1 and 6 ng mL(-1) and 0.07 and 0.3 mug g(-1) respectively. The total blank was 46 ng, so that a 40-mg silicate sample containing 10 mug g(-1) sulfur can be measured with a blank correction of < 10%. This total blank can be lowered to 8 ng if a low-blank air system is used for evaporations. To evaluate the applicability of this method, we analyzed not only silicate reference materials with sulfur content of 5.25-489 mug g(-1) and sample sizes of 13-40 mg but also the Allende meteorite with a sulfur content of 2%. The reproducibility for various rock types was <9%, even though blank corrections in some samples of low sulfur content were up to 24%, This method is suitable for analyzing geological samples as well environmental samples such as soils, sediments, and water samples.