Quantitative determination of anionic surfactants using optical sensors with microtiter plate reader

In this study, it is shown that anionic surfactants can be readily determined by using polymer film-based optodes containing an appropriate chromoionophore. The optodes are prepared with poly(vinyl chloride) (PVC), polyurethane (PU), bis(2-ethylhexyl) sebacate (DOS), and 2′,7′-dichlorofluorescein octadecylester (DCFOE). These optodes exhibit reproducible and sensitive absorbance changes in response to the varying titrant concentrations. Three different cationic surfactants, cetyltrimethylammonium bromide (CTAB), benzyldimethyltetradecylammonium chloride (zephiramine, Zeph), and benzyldimethylhexadecylammonium chloride (CDB), are employed as titrants to determine anionic surfactant concentrations. In addition, membrane electrodes were also employed for estimating the interactions between the cationic and anionic species. The reaction stoichiometries are compared based on the electrode measurements and Scatchard plots are prepared to estimate the strength of binding interaction of titrants with the target surfactants.