THE ELECTROCHEMICAL QUARTZ-CRYSTAL MICROBALANCE AS AN ANALYTICAL TOOL- PROBLEMS AND SOLUTIONS

In using the EQCM as a gravimetric sensor, three general problems are identified and solutions proposed. First, a means of identifying non-r igid films is required: crystal impedance provides a diagnostic. Secon dly, gravimetry is not species selective: the variations of EQCM respo nse with electrolyte concentration and with time (under thermodynamica lly and kinetically controlled conditions, respectively) enable indivi dual species to be resolved. Thirdly, modified electrodes commonly giv e irreproducible responses: a scheme-of-cubes model can rationalize a range of film history and experimental time scale effects.