Determination of Sulphate in Beverages by Spectrophotometric Flow Injection Analysis

An inexpensive FI-manifold and a minicolumn packed with cation exchanger resin with spectrophotometric detection are described for the determination of sulphate ions. It is based on the competitive reaction of SO4 2- and methythymol blue (MTB) with barium(II) in aqueous solution. Measurements were made at 610 nm. Conditions for the quantitation of sulphate ions were optimized using univariate and simplex methods. The cation exchange minicolumn was used to overcome some possible cationic inferences. Linear calibration graphs over the range of 5-25 mg/l SO4 2- were established with the regression equation (n=5) Y=2.3172X-3.6798 (r=0.9963). The detection limit of 0.81 mg/l SO4 2- respectively together with the RSD of 2.09 % for 10 mg/l SO4 2- (N=10) were obtained. The proposed method has been applied satisfactorily to the determination of SO4 2- in commercial beverages. Results obtained by the recommended method were in excellent agreement with those obtained by the reference method verified by using student t-test.