Use of a solid-phase extraction disk module in a FI system for the automated preconcentration and determination of surfactants using potentiometric detection

The global determination of anionic surfactants is proposed by using flow injection potentiometry, and by employing specifically developed tubular flow-through ion selective electrodes (ISEs). The low concentration requirements needed for the environmental application are obtained with an on-line preconcentration stage embedded in the flow system, which has as its goal the unattended monitoring of anionic surfactants in surface waters. The on-line preconcentration is achieved by employing an octadecylsilica extraction disk in the FIA system. This stage performs the solid phase extraction (SPE) for the enrichment and purification of the target analytes from common interfering anions. The outlined procedure improves the detection limit of a direct injection system, which is decreased from 10 to 0.25 μM by using a preconcentration volume of 3.0 mL and 50 μL of 75% acetonitrile in water as the eluent. Precision was estimated as 2.9% relative standard deviation (n = 20) for a 0.25 μM (0.070 mg·L− 1) sodium docecylsulfate standard.