Determination of Cationic Surfactants in Environmental Samples by Flow Injection Analysis

A new simple flow injection analysis (FIA) procedure for the spectrophotometric determination of cationic surfactants (CSs), i.e. dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB), and cetylpyridinium chloride (CPC), is described. The method is based on absorptivity enhancement of the Bi(III)-I− complex in the presence of CSs. Among the investigated compounds, highest sensitivity is obtained with CPC, so it was selected for detailed study. The apparent value of molar absorptivity of the complex in terms of CPC is (6.00)×103 L mol−1 cm−1 at λmax 505 nm for FIA determination. The detection limit (3σ criterion) of the method for FIA determination is 110 µg L−1. The sample throughput is >140 samples h−1. The effect of analytical and FIA variables in the determination of CPC is described. The composition of the complex is discussed. The method is free from interferences of common ions. The method has been applied to the analysis of surfactant contamination in environmental samples, i.e. pond water, municipal/industrial wastewater, sewage, sediment and soil.