Determination of non-ionic surfactants adsorbed on particles of surface water by an indirect tensammetric method combined with the BiAS separation scheme

Procedures have been developed for the determination of non-ionic surfactants (NS) adsorbed on particles in water samples, NS dissolved in water and a total flux of NS (comprising both fractions). Two procedures for the determination of NS adsorbed on particles were developed: direct determination and a differential method. In the direct determination (detection limit of 3 μg l−1), NS adsorbed on particles are separated by filtration and subsequent extraction of NS adsorbed on particles with ethyl acetate. The further separation and quantification follows the separation scheme of the BiAS method (bismuth active substances) combined with the indirect tensammetric method (BiAS-ITM). In the differential approach (detection limit of 8 μg l−1), the concentration of NS in filtered water (as determined by the BiAS-ITM) is subtracted from the corresponding result for non-filtered water. The results for concentration of NS in non-filtered water, as determined by the BiAS-ITM, represent a total flux of NS in river water (dissolved fraction and fraction of NS adsorbed on particles). The detection limit of the determination is 6 μg l−1. In the tested samples, NS adsorbed on particles ranged from 4% to 32% (average 20%) of total concentration of NS in river water. The BiAS-ITM shows a fundamental advantage vs. the indirect tensammetric method (ITM) used as a separate procedure in the determination of NS adsorbed on particles or contained in non-filtered water samples, due to tolerance to chlorophyll. On the other hand, the ITM can be recommended for the determination of NS in filtered water samples.