Evaluation and Comparison of the Cobalt Thiocyanate and Modified Dragendorf Reagent Test Methods for Nonionic Detergents,

摘要

Studies were undertaken to evaluate a modified Dragendorf reagent test method for the determination of nonionic surfactants in influents and effluents of biological wastewater treatment plants and to compare its sensitivity with that of the cobalt thiocyanate method for nonionic detergents. The WICKBOLD method is based on the precipitation of the surfactant with a modified Dragendorf reagent (K2BiI4 + BaCl2 +acetic acid). The filtered precipitate is washed with acetic acid and dissolved in ammonium tartrate solution. The bismuth from the bismuth-surfactant complex in solution is then titrated potentiometrically at pH 4 - 5with 0.0005 N pyrrolidine dithiocarbamate solution using a platinum and calomel electrode. The cobalt thiocyanate method involves the treatment of the detergent with ammonium cobalt thiocyanate solution,chloroform extraction of the surfactant-cobalt thiocyanate complex and the spectrophotometric analysis of the complex in chloroform at 318nm. The three nonionic surfactants used in the studies were: (1) fatty alcohol ethoxylate with 30.7ethylene oxide units, (2) fatty alcohol ethoxylate with 10.6ethylene oxide units,and (3) nonyl phenol ethoxylate.