polarography (pōˌlərŏgˈrəfē) [key], in chemistry, method for analyzing the composition of a dilute electrolytic solution (see electrolyte). Two electrodes are placed in the solution: One has a fixed potential (voltage) and is called the reference electrode, and the other has a variable potential and is called the polarizable electrode. As voltage is applied to the polarizable electrode, the resulting change in the current through the solution is monitored. By plotting the pairs of values for voltage and current, a series of current-voltage curves (polarograms) can be generated. The general name for this method is voltametry ; the term polarography was formerly restricted to those cases where the polarizable electrode is a dropping mercury electrode, though now this distinction is often disregarded. Current-voltage curves, which look like a series of steps called polarographic waves, can be used to determine the reduction potentials of any reducible species present in the solution, e.g., inorganic ions or complex organic intermediates (see oxidation and reduction; electromotive series). Conversely, unknown substances can be identified by their characteristic reduction potentials. Quantitative titrations of an oxidizing agent by a reducing agent can be performed using a polarographic cell to determine the equivalence point by monitoring changes in the current.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.