TENSAMMETRIC DETERMINATION OF NONIONIC SURFACTANTS COMBINED WITH BIASSEPARATION PROCEDURE (WICKBOLD) .1. PRECIPITATION OF DIFFERENT ETHOXYLATES WITH MODIFIED DRAGENDORFF REAGENT IN THE PROPOSED AND CLASSICAL BIAS PROCEDURES

The proposed procedure (BiAS-ITM) combines BiAS separation scheme of n on-ionic surfactants with their determination by indirect tensammetric method (ITM). The method is based on (i) gas stripping separation of ethoxylates, (ii) their precipitation with modified Dragendorff reagen t and (iii) determination of their concentration in the dissolved prec ipitate using ITM. Washing of the precipitate with glacial acetic acid , necessary in classical BiAS procedure which is a source of serious e rror, is omitted in the proposed separation scheme. The presented meth od determines the non-ionic surfactants instead of bismuth in the clas sical BiAS. The precipitation of 12 oxyethylated alcohols, four oxyeth ylated alkylphenols and four other ethoxylates were investigated accor ding to the proposed procedure. Adsorptive stripping tensammery (AdsT) was applied for additional control of investigated surfactants in the precipitate and in the filtrate. Simultaneously 13 ethoxylates were p recipitated and determined according to classical BiAS procedure. The BiAS-ITM procedure shows significantly better recoveries and lower sen sitivities vs. the chemical structure of the determined surfactants an d thus BiAS-ITM is less sensitive to the composition of determined mix ture than classical BiAS procedure. It enables the determination of et hoxylates having three or more oxyethylene subunits, while classical B iAS determines only those having five or more.