TENSAMMETRIC DETERMINATION OF NONIONIC SURFACTANTS COMBINED WITH THE BIAS SEPARATION PROCEDURE - PART 3 - DETERMINATION IN THE PRESENCE OF HYDROCARBONS

A method for the determination of non-ionic surfactants (NS) in the pr esence of an excess of hydrocarbons is developed. The modified BiAS pr ocedure combined with the indirect tensammetric method (BiAS-ITM) is a pplied for this purpose. The method consists of extraction of NS into ethyl acetate, precipitation of ethoxylates with modified Dragendorff reagent, removal of adsorbed hydrocarbons by washing with isooctane an d the determination of NS in the dissolved precipitate by the ITM. The method is characterised by 96-100% recovery and RSD of 0.02-0.04 at a 1000-fold excess of hydrocarbons. The detection limit of the procedur e is 1.5 mu g and the linear dynamic range is 2-20 mu g in the sample, which facilitates work within the range of 2-1000 mu g through the us e of aliquots. The non-modified version of the BiAS-ITM exhibits a los s of NS due to their extraction by droplets of residual hydrocarbons t rapped in the precipitate. Isooctane as a washing agent is found to be the best among eight tested media: methanol, ethyl acetate, diisoprop yl ether, chloroform, water, glacial acetic acid, benzene and isooctan e. (C) 1998 Elsevier Science B.V. All rights reserved.