APPARATUS FOR PRECISION CONTROL OF DROP TIME OF DROPPING MERCURY ELECTRODE IN POLAROGRAPHY

An apparatus is described for the precise electromechanical control of the drop time of a dropping mercury electrode (DME) at values from 0.25 to 10 sec. A constant drop time is obtained over the entire potential range with capillaries having their orifice in the horizontal or the vertical plane. Excellent performance is most easily obtained with a Smoler 90° vertical orifice DME. Corresponding portions of controlled drop time current-time curves are essentially unchanged from uncontrolled drop time curves. The constant drop time simplifies the efficient filtering of the current fluctuations from the DME. Increased sensitivity and precision are obtained. At a 0.5-sec controlled drop time, a scan rate of 1 V/min, and with the ORNL model Q-2792 polarograph, regular or firstor second-derivative polarograms can be recorded in ∼30 sec with a relative standard deviation of 0.2% at the 10-3M concentration level. Satisfactory first- or second-derivative dc polarograms are obtained at concentrations as low as 10-7M. © 1969, American Chemical Society. All rights reserved.