SOURCES OF ERROR IN THE DETERMINATION OF NONIONIC SURFACTANTS IN ENVIRONMENTAL-SAMPLES

The analytical procedures for the determination of non-ionic surfactan ts (NS) consist of sampling, multistage separation and final determina tion. Each of these stages is a potential source of error. 33% of an i nitial amount of 100 mu g NS may be lost due to adsorption on the wall s of glass vessels during storage or 55% in the case of polyethylene v essels. Ineffective preservation of samples leads to very quick biodeg radation of NS and incorrect results. Chloroform, frequently used for this purpose, is ineffective, whereas formaldehyde gives satisfactory results. Also during the separation procedure substantial fractions of NS are lost. The currently used methods enable the determination of N S having 5-30 oxyethylene subunits only. In the extraction with ethyl acetate NS having long oxyethylene chain remain in the water phase or are caught at the interface. If looked at carefully these analytical p rocedures show serious drawbacks. The washing of the precipitate in th e BiAS procedure causes a dramatic loss of precipitate. The recommende d use of G4 glass filters also leads to loss of precipitate. Instead, the use of G5 gives satisfactory results. The choice of one surfactant as the standard, necessary for the determination of the total concent ration of a mixture of unknown composition, possibly consisting of sev eral hundred of individual compounds, can be also a serious source of error. The higher is the difference between the slopes of the calibrat ion curves of the mixture components, the higher is the error. Two new ly developed techniques, namely the indirect tensammetric method (ITM) and the BIAS procedures combined with the ITM give better results tha n the procedures currently recommended.