Tensammetric determination of non-ionic surfactants combined with the BiAS separation procedure Part 3. Determination in the presence of hydrocarbons

摘要

A method for the determination of non-ionic surfactants (NS) in the presence of an excess of hydrocarbons is developed. The modified BiAS procedure combined with the indirect tensammetric method (BiAS-ITM) is applied 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 and the determination of NS n 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 procedure is 1.5 μg and the linear dynamic range is 2-20 μg in the sample, which facilitates work within the range of 2-1000 μg through the use of aliquots. The non-modified version of the BiAS-ITM exhibits a loss of NS due to their extraction by droplets of residual hydrocarbons trapped in the precipitate. Isooctane as a washing agent is found to be the best among eight tested media: methanol, ethyl acetate, diisopropyrl ether, chloroform, water, glacial acetic acid, benzene and isooctane.