Simple Electrochemical Determination of Surface-Active Substances in Natural Waters

A simple electrochemical determination of surface-active substances by using time-dependent variation of the capacitive current in a.c. voltammetry at the HMDE is described. Surface-active substances were accumulated by stirring solution at the deposition potential of -0.6V versus Ag/AgCl (sat. NaCl). The capacitive current was recorded for different deposition times in the range 0-120 s, wherefrom the linear calibration plot is constructed. The proposed method was verified for model surfactant TritonX-100 in the concentration range 0.02-0.25 mg/L and for humic acid in the concentration range 1.65-20 mg/L. The application of the method was demonstrated for freshwater samples of the Drava river, Danube river, and the wetland Kopacki Rit, Croatia. The shape of the i(ac)-E curves as well as the obtained concentrations of surface-active substances by using humic acid as the calibration substance are quite well describing the type and the nature of organic matter in the freshwater samples.