Thiosulfate-dechlorination interference with the folin-ciocalteu reagent method for protein determination

Abstract Sodium thiosulfate is employed routinely for dechlorination of water and wastewater disinfectants. A study was conducted to evaluate the interference with the Lowry method using the Folin-Ciocalteu reagent for protein determination by the dechlorination products of chlorine or monochloramine. Free chlorine, monochloramine or sodium thiosulfate alone did not cause color formation with the test. However, when the disinfectants were dechlorinated with thiosulfate, the reaction products yielded false positives for protein. These false positives were detected at disinfectant concentrations as low as 0.3 mg l −1 as available chlorine.