Fast and low-cost online detection of critical micelle concentration based on impedance spectroscopy

The dosage of detergents in washing processes is decisive for efficiency. The optimal dosage can be determined by a measurement of the critical micelle concentration (CMC). Classical methods are not suitable for online applications in washing machines with automatic dosage because detergent concentrations c_det highly above the CMC are also needed and automatic dosage cannot be stopped in time. Optical methods are commonly used for such applications but they are expensive or imprecise. A new online detection method of CMC using impedance spectroscopy (EIS) is developed. Impedance values at selected frequencies are used to detect c_cmc. The new method detects the CMC immediately and precisely when c_cmc is reached so that automatic detergent dosing can be stopped in time and online measurement is possible.