Tensammetric determination of non-ionic surfactants combined with BiAS separation procedure (wickbold)-I. 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 non-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 reagent and (iii) determination of their concentration in the dissolved precipitate using ITM. Washing of the precipitate with glacial acetic acid, necessary in classical BiAS procedure which is a source of serious error, is omitted in the proposed separation scheme. The presented method determines the non-ionic surfactants instead of bismuth in the classical BiAS. The precipitation of 12 oxyethylated alcohols, four oxyethylated alkylphenols and four other ethoxylates were investigated according 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 precipitated and determined according to classical BiAS procedure. The BiAS-ITM procedure shows significantly better recoveries and lower sensitivities vs. the chemical structure of the determined surfactants and thus BiAS-ITM is less sensitive to the composition of determined mixture than classical BiAS procedure. It enables the determination of ethoxylates having three or more oxyethylene subunits, while classical BiAS determines only those having five or more.