A methodology for the determination of reductive sulphur in optical and technical glass

This paper describes an analytical method for the determination of reductive sulphur (S(IV), S(-II)) in glass. The glass sample is dissolved in hydrofluoric/hydrochloric acid mixture and the sulphur is separated via distillation in an apparatus made of polyfluoralkoxyethylene (PFA). The distilled hydrogen sulphide is trapped in buffered boric acid–zinc acetate solution and subsequently determined after conversion to an ethylene blue dye. The range of the method lies within a range of 2–1200 μg g−1 reductive sulphur. The quantification limit for reductive sulphur is 2 μg g−1. ent analysed glass types show either no detectable reductive sulphur or up to 30% of the total sulphur content reductive sulphur. The inter-laboratory standard deviation shown by a round robin test performed is excellent (±4 μg g−1; average 59 μg g−1). Sources of error of the methodology are discussed.