How it began
In 1918, during Jaroslav Heyrovský's doctoral examination at the university in Prague, the physicist Bohumil Kučera asked him about measuring the surface tension of mercury with a dropping mercury electrode and suggested he pursue an unsolved anomaly. After the war Heyrovský weighed mercury drops collected in solutions under different voltages. On the afternoon of February 10, 1922, he connected a sensitive mirror galvanometer to the circuit and measured the current as well. The curve he obtained in a sodium chloride solution could be reproduced exactly.
Before it existed
Chemists such as Max Le Blanc had studied electrode processes with polarization curves on solid electrodes, but they could not get satisfactorily reproducible results. The dropping mercury electrode already existed. C. F. Varley and Gabriel Lippmann had created it, and Kučera was the first to use it as a research tool, for measuring surface tension.
How it works
Mercury drips at a regular rate from a fine glass capillary into the solution. Each new drop offers a fresh surface that does not depend on what happened before, so measurements can be repeated exactly. A changing voltage is applied between this electrode and a second, unpolarizable one, and the current is recorded. The resulting curve of current against voltage shows steps that reveal which substances are in the solution and how much of each.
How it spread
In 1924 Heyrovský and the Japanese chemist Masuzo Shikata designed the polarograph, which recorded the curves automatically on photographic paper and cut the time from hours to minutes. Shikata took one of the first instruments to Japan in 1925. Visitors from Italy and Poland learned the method in Prague, and Heyrovský lectured in the United States for five months in 1933. By 1940 the literature on polarography had reached 900 publications.
What lasted
Heyrovský received the 1959 Nobel Prize in Chemistry for his discovery and development of the polarographic methods of analysis. An Institute of Polarography was founded in Prague in 1950 with him as director. Later workers developed oscillographic, pulse and square-wave forms of the method, and stripping techniques with hanging mercury drops.
Where it stands today
Computer-controlled electrochemical instruments based on renewed mercury electrodes are used in research ranging from materials science to biophysics. A conference on modern electroanalytical methods held in Prague in 2009 commemorated the method. Radio Prague International marked 100 years of polarography in February 2022.
