A new method, free from interference of cationic surfactants, is proposed for the determination of polyoxyethylene non-ionics in waters at ultra-trace levels. The procedure involves (i) a pre-extraction from water sample with dichloromethane, and (ii) the determination of non-ionics as potassium picrate active substances (PPAS). In aqueous phase the polyether chain reacts reversibly with potassium cation (in large excess) to form a positive complex, which is extracted and concentrated in 1,2-dichloroethane (1,2-DCE) through ion-pairing with the chromophoric picrate. The yellow colour of ion-pairs extracted into organic layer disappears immediately by extraction with water, which lowers drastically the concentration of reagents. The difference between the absorbances gives the PPAS attributable to polyoxyethylene non-ionics only, because PPAS due to cationics are not extractable. The method was tested in sea waters polluted by urban liquid wastes.
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Favretto et al. (1983) studied this question.
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