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Mercury electrode in flow systems
Abstract
The purpose of the work is the design and construction of new mercury electrodes suitable for flow systems which can be used for automated electrochemical measurements. A mercury plug electrode is suggested and designed for a flow system, in which an entire electrochemical cell is assembled on-line. The surface area of the working electrode in the 0.5 mm diameter flow line was determined experimentally to be 0.00218 cm$\sp2$. Three electrochemical analytical methods were investigated. The study of Osteryoung square-wave voltammetry with the mercury plug electrode was done to see if electrode response conformed to theory. The square-wave frequency and amplitude were examined. With a low frequency (lower than 100 Hz) and a small amplitude (smaller than 50 mV), the experimental results agreed well with those obtained by theoretical calculation. Cadmium ion solutions were determined with Osteryoung square-wave voltammetry over the concentration range from 4 $\times$ 10$\sp{-7}$ to 1 $\times$ 10$\sp{-4}$ M. The results showed a linear relationship between the peak current and the concentration of cadmium when the concentration is lower than about 7 $\times$ 10$\sp{-5}$ M. A detection limit of 0.1 $\mu$M cadmium was found. In investigations using alternating current voltammetry, an ac electrochemical instrument based on digital lock-in amplifier was used. Here, the detection limit for cadmium ion was 3 nM when the number of the cycles for the multiple up/down counting was 1. Results were also obtained using larger numbers of up/down counting cycles to increase sensitivity obviously. The determination of ethanol was performed on alcoholic beverages using tensammetry. The results showed that the mercury plug electrode cell can be used not only for the determination of electroactive materials but also for the determination of the nonelectroactive materials which are surface active. The advantages of the mercury plug electrode include: (a) a small surface area (0.00218 cm$\sp2$); (b) a small cell volume (6 $\mu$L); (c) a new mercury surface for each measurement; (d) an improvement in the reproducibility of the electrode surface area; and (e) the elimination of dispersion (since the sample solution was sandwiched between two mercury plugs. In the last part of this work, a surface renewable miniature mercury pool electrode is demonstrated which improves the stability of the mercury electrode in a flowing solution and improves the reproducibility of the electrode surface area. The procedure for renewing the electrode surface is accomplished by controlling pumps. Both of the two types of new mercury electrodes are based on using flow systems to take advantage of the liquid nature of mercury.
Subject Area
Analytical chemistry
Recommended Citation
Deng, Zhiwei, "Mercury electrode in flow systems" (1991). Doctoral Dissertations Available from Proquest. AAI9132841.
https://scholarworks.umass.edu/dissertations/AAI9132841