Instrumental development of an inexpensive double-layer capacitance meter for studying surface adsorption phenomena

Abstract

The design, development, and calibration of an inexpensive double-layer capacitance meter is reported. The instrument measures the impedance response from a small-amplitude sinusoidal voltage applied across the electrical double layer. The two elements of the signal, the in-phase and the quadrature, are distinguished by two phase-sensitive detectors. The relationship between the quadrature voltage and the double-layer capacitance is established by using standard capacitances. Once calibrated, this capacitance meter was used to measure the change in double-layer capacitance as the protein lysozyme is adsorbed on a metal/solution interface.