Electrochemical measuring system for determination of surface-active substances in aqueous solutions

Diffusion controlled adsorption of surface active substances at the stationary mercury electrode causes a time dependency of the electric capacity of the interface electrode/electrolyte. This is the basis of the analytical method proposed. A computer controlled measuring system with a controlled growth mercury electrode is shown. Well-defined conditions for the measuring procedure are managed by electronic control of mercury drop size and a specific potential switch method. Results are given for pure, tap, natural and industrial waters and related to measurements using standard procedures (UV adsorption, methylene blue method). Using sodium dodecyl sulfate (SDS) as calibration substance, the limit of detection is 0.1 mg/1. Measurements in waste water of a tenside plant made with the electrochemical and the methylene blue methods gave a good agreement of the concentrations found. The advantages of the described electrochemical system are the high sensitivity, the simple use and the velocity of measurements. The disadvantages are lack of selectivity and the use of mercury as electrode material.