J. Electroanal. Chem., 179 (1984)99-106 99 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands AN ACCURATE MERCURY ELECTRODE DROP-TIME MEASURING INSTRUMENT BASED ON A PIEZOELECTRIC TRANSDUCER * IVANO G.R. GUTZ Instituto de Quimica, Universidade de S~o Paulo, Cx. P. 20,780, 01498-S~o Paulo (Brazil) (Received 15th February 1984) ABSTRACT A simple and reliable instrument for the digital measurement of the drop-time of a dropping mercury electrode accurate within 1/100 s is described. The detection is independent of the electrode polarization circuit and is made by a piezoelectric transducer interposed in the path of the drop fall. The instrument is of general use. An application to the measurement of interfacial tension by the drop-time method is presented as well as a brief discussion of the error sources and some modifications to minimize or eliminate them. INTRODUCTION The precise detection of drop fall is one of the critical points of the drop-time method, frequently used to obtain interfacial tension data in adsorption studies at the mercury/solution interface [1]; it is also important for other techniques. Many alternatives have been described in the literature to substitute the tedious and inaccurate procedure of the visual detection of the drop fall and manual control of a stopwatch [2-8]. The detection methods of most of the described instruments fall into one of the following classes and can present the indicated shortcomings: (a) Superimposition of an alternating signal on the potential applied to the electrode and detection of the sudden impedance change that takes place at the drop fall. It has been argued that this procedure can exert some disturbance on the measurement. (b) Observation of the change of the natural electrode potential at the drop fall, requiring an inconvenient disconnection of the excitation signal near the end of the drop life. (c) Observation of the sudden change of the current at the drop fall. Near the pzc, the necessary high sensitivity measuring circuit must be carefully adjusted. (d) Opto-electronic detection of the drop fall. The main advantage over the * Presented in part at the II Brazilian Symposium of Electrochemistry and Electroanalytical Chemistry, Sao Paulo, June 1980. 0022-0728/84/$03.00 © 1984 Elsevier Sequoia S.A.