Application of an indirect tensammetric method for the determination of non-ionic surfactants in surface water

Three alternative procedures for the determination of non-ionic surfactants (NS) in surface water have been developed. The simplest one consists of the filtration of water samples, the extraction of NS with ethyl acetate, the evaporation of the solvent and the determination of NS using an indirect tensammetric method (ITM). The detection limit is 15 μg l−1. The procedure using gas-stripping separation of NS shows a detection limit of 1.5 μg l−1. Chlorophyll extracted from water plants causes a serious interference. Therefore the sample must be filtered before extraction. The extractive procedure shows good precision and recovery of spiked surfactants from river water samples. Comparative studies of the newly developed and the classical BiAS procedures were performed. The ITM procedure shows a detection limit of two orders of magnitude better than the BiAS procedure. Therefore the required volume of water sample is reduced from 5000 to 100 ml. Due to the simpler separation procedure the ITM is substantially less time-consuming, cheaper and requires no sophisticated equipment or well-trained staff. An additional advantage of the ITM compared with the BiAS procedure is the lower sensitivity to the choice of standard surfactant and the broader “spectrum” of NS that can be determined. The results of a half year current analysis of NS in river water have been included.