A flow system for the determination of cationic surfactants in the presence of anionic surfactant is proposed. The system consists of a microcolumn packed with anion-exchange resin and a surfactant-selective polyvinyl chloride membrane electrode detector. The membrane was plasticized with phthalic acid di(2-ethylhexyl) ester. Anionic surfactants were removed by the anion-exchange resin column. The cationic surfactant was eluted by methanol/H2O = 50/50(v/v, %) and detected. The electrode detector showed the linear response with a potential slope of 45 mV/decade for dodecyltrimethylammo-nium (DTA) ion from 5×10-7 to 1×10-5M. The detection limit for DTA was 1.0×10-8 M. The proposed method was free from interferences from coexisting inorganic electrolytes, anionic surfactants and nonionic surfactants. By this method, a trace level of cationic surfactants in river water could be determined.
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