Radioactivity coulometers:

A microcoulometer based on counting deposits of ¹¹⁰Ag has been defined. The unknown silver solution is spiked along with a known amount of radioactive silver ¹¹⁰Ag and then deposition is made on a platinum wire in a cell in series with one containing only radioactive silver.  Equivalent amounts of silver are plated on every cathode. The ratio of the radioactivities gives the amounts of silver in the unknown solution. The cell holding the radioactive silver is the radioactivity coulometer.

The method is meaningful for small quantities and plating required not be taken to quantitative completion, as it includes the measurement of the ratio of the radioactivities in the two cells.

The above kinds of coulometers can be put in series in an electrolytic reaction and could be used as a current measuring device.