New methods for the determination of L-asparagine and arginine are described. Solutions containing L-asparagine were pumped through an asparaginase tube, which catalyzed the hydrolysis of L-asparagine to L-aspartic acid and ammonium ion. For L-arginine determination, solutions containing L-arginine were pumped through an arginase–urease tube. This dual enzyme tube catalyzed the conversion of L-arginine to L-ornithine, carbon dioxide, and ammonium ion. The ammonium ion concentrations in the effluent of the enzyme tubes were determined quantitatively by an ammonium-ion-selective electrode. The potentiometric response of the electrode was directly proportional to the logarithm of the concentration of L-asparagine and L-arginine in the range of 0.1–50 mM. An equation relating the electrode response and the substrate concentration is derived.
The Selectivity Evaluation of an Ion-selective Electrode with a Liquid Membrane by Electrode Response to a Foreign Ion