Resolved and unresolved questions of analysis of surfactants in the aquatic environment

Abstract

Abstract 214 references concerning the analysis of surfactants in the aquatic environment have been reviewed. Methods for the analysis of anionic and cationic surfactants are critically discussed, but closest attention is paid to non-ionic surfactants, as this type of surfactant gives rise to the most serious unresolved questions of analysis. Typical levels of concentration of ionic and non-ionic surfactants in raw and treated sewage, surface water and river sediments are given. Recently developed tensammetric techniques, useful for the analysis of non-ionic surfactants and their metabolites, are broadly described. The following unresolved questions related to anionic surfactants are emphasised: specific determination of different classes of anionic surfactants (alkyl sulphates, alkylether sulphates), analysis of metabolites of anionic and non-ionic surfactants, and the problem of 'pseudosurfactants'. In the case of cationic surfactants, the question of inconclusive results of measurements of aquatic environment samples is selected as the most serious problem. The need to develop analytical tools for the investigation of interactions between cationic and anionic surfactants in the aquatic environment is also emphasised. The following unresolved questions are distinguished for non-ionic surfactants: selection of method for determining the total concentration of non-ionic surfactants capable of approval in interlaboratory tests, selection of the standard surfactant representative for the mixture of non-ionic surfactants in the aquatic environment, and the development of methods for determining non-ionic surfactants having less than 5 oxyethylene subunits, as well as those having more than 30 subunits. The development of methods for the specific determination of such classes of ethoxylates as oxyethylated amines, oxyethylated fatty acids, as well as methods for the specific determination of newly introduced non-ethoxylate non-ionic surfactants such as alkyl polyglucosides and metabolites of non-ionic surfactants is suggested. Methods for the trace analysis of non-ionic surfactants also require development as do methods suitable for controlling biodegradation at a realistic level of concentration. The necessity for the future development of detectors for HPLC and FIA of oxyethylated alcohols and in the automation of the analysis of non- ionic and cationic surfactants is emphasised.