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 t he determination of low levels of anionic surfactants in river water and wa stewater. The system uses especially constructed tubular now-through ion-se lective electrodes (ISEs) as potentiometric sensors and on-line preconcentr ation techniques. The anionic surfactant ISEs employed are of the all-solid -state type with a plasticized PVC membrane. They show a general response t o anionic surfactants with a lower limit of linear response of similar to 1 0(-5) M, when used in direct determinations. However, their specificity is limited, which hampers their direct use with environmental samples. Therefo re, the FIA. system presented here includes a solid-phase extraction proced ure for purification and preconcentration of analytes, Breakthrough curves were constructed to characterize different sorbents and different eluents w ere tested to optimize the preconcentration process. The FIA system was fir st applied to the determination of different types of anionic surfactant st andards. 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 similar to 10(-7) M (0.03 ppm ) of sodium dodecyl sulfate could be detected in the nonlinear response reg ion when 3 mt of sample was preconcentrated and eluted with 50 mu L of a 75 % acetonitrile/water (v/v) solution. Precision was 2% RSD (n = 31) for a 1 x 10(-6) M sodium dodecyl sulfate standard solution and the sample throughp ut was 10 h(-1). The FIA system was then used for the determination of tota l anionic surfactants in river water and wastewater.