Determination of total sulfur and sulfate sulfur in geological materials of rocks, soils, and sediments by ICP-OES after sample digestion using alkali flux

Abstract

Sulfur in geological materials is generally determined by an elemental analyzer or by wet chemical methods (after fusion with alkali flux or acid digestion) viz. gravimetry, turbidimetry, and titrimetry. A method has been developed for the determination of total sulfur and sulfate sulfur in rocks, soils, and sediments by ICP-OES. The samples are decomposed with potassium carbonate in the presence of MgO, leached with water, acidified with perchloric acid, most of the salt is removed by filtration, and analyzed for total sulfur by ICP-OES. Another aliquot of sample is leached with HCl for the determination of sulfate sulfur. The quantity of flux and MgO, combinations of fluxes, temperature and duration for fusion for complete attack and recovery was critically evaluated and optimized. The salt content of the sample solution was reduced by precipitating potassium as Perchlorate. Interference effects of the matrix elements were investigated and the emission line of 181.978 nm was used for analysis under nitrogen purging. The method was validated by analyzing CRMs UTS-1, UTS-2, MA-lb, DS-1, WMS-la, RTS-1, RTS-2, RTS-4 (CANMET, Canada) and ASK-3 (Analytic Sporelement Romite, Scandinavia). The recoveries were > 95% for sulfur. The RSD of the method was < 3% for n=10. The method is very simple, does not involve acid fuming or require a special apparatus for sample decomposition.