A contribution to the use of thorin as an analytical reagent: spectrophotometric study of its complexation with barium and application to sulphate determination in atmospheric particulates

The complexation of Ba(2+) by Thorin in the pH range 2-9 in aqueous ethanol medium has been investigated. The dissociation constants of Thorin in the ethanolic medium have been determined spectrophotometrically and the distribution of the protonated species has been used to explain the behaviour of the apparent complexation constant. On the basis of the apparent constants found, and mass-balances, the effect of sulphate on the absorbance has been calculated, and the best conditions for determination of sulphate have been established. Cation and anion interferences have been studied and means of overcoming them are proposed. The method developed has been applied to sulphate determination in atmospheric particulates. As little as 1 mug of sulphate can be measured.