Initial separation and preservation for long-term storage of non-ionic surfactants from raw and treated sewage

Interlaboratory comparison of analytical methods requires that analyte concentrations in the sample are stable. Consequently, stable samples may be analysed when needed rather than immediately. Stability of non-ionic surfactant (NS) concentration in raw and treated sewage samples preserved with 1% formaline is investigated over 28 months. Apart from preserved water samples their raw and processed ethyl acetate extracts are also investigated. The indirect tensammetric method with ethyl acetate as monitoring substance is used for NS determination. The following conclusions may be drawn: (i) raw and treated sewage samples preserved with 1% formaline are insufficiently stable for long-term maintenance of NS concentration; (ii) raw ethyl acetate extracts of sewage samples demonstrate limited long-term stability of NS concentration; and (iii) dried ethyl acetate extracts of sewage samples mixed with chloroform (1:2) exhibit stable NS concentration over a minimum of 28 months. This manner of sewage sample preparation may be recommended for long-term storage.