INDIRECT TENSAMMETRIC METHOD FOR THE DETERMINATION OF NONIONIC SURFACTANTS .2. INVESTIGATION AND IMPROVEMENT OF TOLERANCE TO MAN-MADE ANIONIC SURFACTANTS

Non-ionic surfactants can be determined by means of their lowering effect on the tensammetric peak of ethyl acetate. Representative man-made anionic surfactants were investigated in order to check the tolerance to this group during the determination of non-ionic surfactants. Both the ''normal'' procedure (recording in the cathodic direction starting from - 1.200 V) and ''reverse'' recording (scanning in the anodic direction starting from - 1.400 V) were used. Sodium salts of dodecylbenzene sulphonate (DBS), dodecyl sulphate (DSA), dodecyl sulphonate (DSO) and stearate (S) and the commercial products Kosulfonat 40 (KOS) and Sulforokanol L-3 (lauryl ether sulphate) (LES) were investigated. The interference of the anionic surfactants increases in the order DSA, DBS < LES < DSO, S < KOS with ''normal'' recording and in the order DSA, DBS, S < LES, DSO < KOS with ''reverse'' recording. The tolerance to anionic surfactants is substantially better if ''reverse'' recording is used. On the other hand, the signals of non-ionic surfactants having 1-3 oxyethylene subunits are slightly lower in this case. The real tolerance to anionic surfactants is better than expected presuming additivity of analytical signals. A 2-mug amount of Triton X-100 can be determined in the presence of 20 and 50 mug of DBS with ''normal'' and ''reverse'' recording respectively. However, only 2.7 and 7 mug of KOS, respectively, are tolerated under the same conditions.