Spectrophotometric flow-injection determination of sulfate in rainwater

A flow-injection system is proposed for the spectrophotometric determination of low concentrations of sulfate in rainwater using barium dimethylsulfonazo(III) (Ba-DMSA). Selectivity is enhanced by including a Dowex 1-X8 anionic resin mini-column into the manifold, aiming at sulfate in-line concentration and separation from potential interfering chemical species. The proposed system is robust and provides precise results (r.s.d. < 5.0%) at an analytical frequency of 40 h−1. About 0.09 mg DMSA is consumed per determination. The analytical curve is linear up to 2.0 mg L−1 SO42− and the detection and quantification limits were estimated as 0.01 and 0.04 mg L−1 SO42−, respectively. Results are in agreement with those obtained by ion chromatography at the 95% confidence level.