Use of reagent in suspension in flow injection analysis. Spectrophotometric determination of sulphate in natural water.

This paper presents an automatic procedure employing a reagent in the form of a slurry in a flow-injection system. The feasibility of the proposal is demonstrated by sulphate determination in water using the Barium Chloranilate method, which is based on the precipitation of barium sulphate, The release of a stoichiometric amount of highly colored chloranilic ions is monitored at 528 am. The reaction is carried out in alcoholic medium in order to reduce the solubility of the reagent. A considerable improvement in the sensitivity is attained by adding ferric ions to the released chloranilic ions. An on-line filtration step to separate the excess reagent from the released chloranilic ions was necessary. In addition, a column containing a cation exchange resin was included in the manifold to remove potentially interfering ions, The proposed procedure is suitable for 30 determinations per hour and the relative standard deviation is less than 2%, The analytical curve is linear between 0.0 and 40 mg L-1 and the determination limit is about 2.0 mg (L-1SO42). Accuracy was confirmed by running several samples already analysed by a standard turbidimetric procedure.