A new sensitive photometric procedure for the determination of sulfate in fuel ethanol without sample preparation exploiting a flow-batch strategy

A simple, accurate, and fast flow-batch procedure employing photometric detection for the determination of sulfate in fuel ethanol was developed. After the formation of soluble barium sulfate in alcoholic medium, the remaining barium forms a product with dimethylsulfonazo III (DMS), the absorbance of which was monitored at 655 nm directly in the reaction chamber. The proposed procedure does not require any sample treatment such as dilution. Under the optimized conditions, the technique offers the advantages of low waste generation (< 5 mL), sampling throughput of 35 h(-1), linear response from 0.1-1.5 mg L-1 sulfate, and a limit of detection (95%) and coefficient of variation (n = 6) of 48 mu g L-1 and 1%, respectively. The accuracy was assessed by comparison of results with those obtained by ion-chromatography; no significant difference was observed at the 95% confidence level.