Determination of trace levels of anionic surfactants in river water and wastewater by a flow injection analysis system with on-line preconcentration and potentiometric detection.

The authors present an automated flow injection analysis (FIA) system for the determination of low levels of anionic surfactants in river water and wastewater. The system uses especially constructed tubular flow-through ion-selective electrodes (ISEs) as potentiometric sensors and on-line preconcentration techniques. The anionic surfactant ISEs employed are of the all-solid-state type with a plasticized PVC membrane. They show a general response to anionic surfactants with a lower limit of linear response of ∼10(-)(5) M, when used in direct determinations. However, their specificity is limited, which hampers their direct use with environmental samples. Therefore, the FIA system presented here includes a solid-phase extraction procedure for purification and preconcentration of analytes. Breakthrough curves were constructed to characterize different sorbents and different eluents were tested to optimize the preconcentration process. The FIA system was first applied to the determination of different types of anionic surfactant standards. Potentially interfering substances such as chloride, nitrate, and nonionic surfactants were checked to verify that they did not interfere on the response of the system. Concentrations of ∼10(-)(7) M (0.03 ppm) of sodium dodecyl sulfate could be detected in the nonlinear response region when 3 mL of sample was preconcentrated and eluted with 50 μL of a 75% acetonitrile/water (v/v) solution. Precision was 2% RSD (n = 31) for a 1 × 10(-)(6) M sodium dodecyl sulfate standard solution and the sample throughput was 10 h(-)(1). The FIA system was then used for the determination of total anionic surfactants in river water and wastewater.