Spectrophotometric determination of dimethyl sulphoxide

Abstract A spectrophotometric method for the determination of milligram quantities of dimethyl sulphoxide in aqueous solutions has been developed. The method is based on the medium effect on the visible absorption spectra of metal salt solutions. Out of several compounds investigated, iron(III) alum was chosen as most suitable for this purpose. Beer's law is obeyed for dimethyl sulphoride concentrations up to 20 mg ml at 410 nm. Dimethyl sulphone does not interfere and dimethyl sulphide can be tolerated in amounts up to 25 % of the sulphoxide present. Possible interferences caused by metal cations can be avoided by passing the sample through a cation-exchanger before adding the reagent. The molar absorptivity is 3 l.mole −1 .cm −1 at 410 nm, and the average relative error ± 0.5%.