Abstract: Electrochemical method for determining the concentration of a carbon source and L-amino acid in a fermentation medium or cultured broth by contacting a microbial electrode consisting of an oxygen-sensitive electrode or a carbon dioxide gas-sensitive electrode combined with fixed microbial cells of a micro-organism capable of assimilating said carbon source or decarboxylating said L-amino acid with a sample solution and sensing electrically the rate of current decrease which is caused by the consumed oxygen in the solution in proportion to the concentration of carbon source; or the electric motive force which is caused by the liberation of carbon dioxide in the sample solution in proportion to the concentration of L-amino acid. Microbial electrodes and systems useful in carrying out the aforementioned method.

Abstract: The concentration of ammonia in an aqueous liquid is determined by contacting a sample of the liquid with dissolved oxygen and with a microbial electrode comprising an oxygen-sensitive electrode, a porous membrane, and nitrifying bacteria confined or immobilised by the membrane which are in direct or close contact with the diaphragm of the electrode. The rate of oxygen consumption under otherwise uniform conditions is as precise a measure of concentration of ammonia as a conventional colorimetric method and distillation-titration method.

Abstract: The microbial activity in a liquid medium is determined by measuring the electric current values or potential values generated by the microorganisms. Also disclosed herein is apparatus for carrying out such measurement comprising two electrodes or two electrolytic electrode systems constructed and arranged to be immersed in a culture liquor.