TENSAMMETRIC DETERMINATION OF NONIONIC SURFACTANTS COMBINED WITH BIASSEPARATION PROCEDURE (WICKBOLD) .2. OPTIMIZATION OF THE PRECIPITATIONAND INVESTIGATION OF INTERFERENCES

The precipitation step in the developed procedure (BiAS-ITM) was optim ised with the aim of achieving a lower detection limit. Losses during filtration using Triton X-100 as representative non-ionic surfactant ( NS), the indirect tensammetric method (ITM) and adsorptive stripping t ensammetry (AdST) for the determination of the concentration of the su rfactant in the precipitate and in the filtrate were investigated. The G4 glass filter recommended up to now was found to be insufficiently effective and a source of loss. The new version of the procedure devel oped works within the range 2-1000 mu g of NS in the sample, and thus two orders of magnitude lower than the former version of the procedure , showing satisfactory recovery and precision. The detection limit (3 x S.D.) was found to be below 1.5 mu g in the sample. Interferences of anionic surfactants (ASs) e.g. sodium dodecylbenzenesulphonate and so dium lauryl sulphate, lipids, e.g. glycerol trioleate (GTO), and chlor ophyll were investigated. GTO and AS show no effect on the BiAS-ITM re sults although strong adsorption of ASs on the glass filter as well as a slight adsorption on the precipitate was found. Chlorophyll does no t interfere with the determination up to 30 mu g in the sample, wherea s higher concentrations produce results that are too high.