Simple determination of nonionic surfactants using an ion association reaction

Nonionic surfactants, such as TritonX-100 and Brij-35, form cationic compounds in the presence of monovalent metal ions, which associate with an anionic tetrabromophenolphthalein ethyl ester dye (TBPE) to produce an extractable blue ion associate. When tetrakis(4-fluorophenyl)borate (BF4) is added to an aqueous phase, BF4 forms a colorless ion associate with cationic compounds, and the associate is rapidly extracted into 1,2-dichloroethane. At the end point, BF4 takes the cationic compound from the blue ion associate. As a result, a blue color in the organic phase turns out to be yellow because TBPEH is produced. In this work, the addition of 5 ml of 4 M KCI gave a clear end point and RSD with KCI was 0.2%. 1,2-Dichloroethane was suitable in the titration system. Since the ion association formation is stoichiometric, nonionic surfactants can be determined simply and conveniently.