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 ma terials with isotope dilution high-resolution inductively coupled plasma ma ss spectrometry equipped with a now injection system. In this method, sulfu r can be quantitatively oxidized by bromine into sulfate with achievement o f 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 n g 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 mea sured 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 ap plicability of this method, we analyzed not only silicate reference materia ls with sulfur content of 5.25-489 mug g(-1) and sample sizes of 13-40 mg b ut also the Allende meteorite with a sulfur content of 2%. The reproducibil ity for various rock types was <9%, even though blank corrections in some s amples of low sulfur content were up to 24%, This method is suitable for an alyzing geological samples as well environmental samples such as soils, sed iments, and water samples.