Electrogravimetric trace analysis on a piezoelectric detector

Abstract

The fundamental frequency of a piezoelectric crystal is dependent upon its mass. Very small changes in the active mass of the crystal can be observed by following the frequency of an oscillator controlled by that crystal. Quartz crystals with vacuum-plated metallic film electrodes are commercially available, and when these electrodes were used as the working electrode in an electrodeposition circuit, the frequency changes of the crystals were found to be proportional to the amount of material deposited. When electrodeposition was conducted over constant time intervals, the amount of metal deposited during an interval was proportional to the initial metal ion concentration. Linear working curves showing frequency changes as functions of the initial metal ion concentrations, for given sets of conditions, were found to be suitable for quantitative analysis. A detailed procedure based on these observations is presented in this dissertation which describes a novel method for the determination of very low concentrations of cadmium, nickel, zinc, indium, and lead in aqueous solutions. Cadmium was used as the model for the most extensive study. Cadmium concentrations covering the range from 5.0 x 10��M to 5.0 x 10��M were determined, and similar results should be attainable for the other metals listed. The accuracy of the method for cadmium varied from 0.42% at the larger concentrations to 8.7% at the lower end of the range. An investigation was conducted to examine the influence of different electrodeposition time intervals on the sensitivity of the method for metal determinations. A similar study was carried out to test the prediction that smaller mass changes are detectable with higher frequency crystals. Numerous calibration curves are shown illustrating analyses under different conditions for-these two variables. Results from the analysis of binary mixtures are presented. A discussion of some of the limitations of the method is given, along with suggestions for some possible improvements.