Comparison of tubular polymeric pH and ammonium ion electrodes as detectors in the automated determination of ammonia

Abstract

The analytical response properties of two types of flow-through ammonia gas sensing electrode systems are examined and directly compared under the same experimental conditions. Both detection systems involve the use of continous flow gas dialysis in conjuction with tubular polymer membrane electrode detectors. In one method, the pH of the flowing recipient stream leaving the dialyser is monitored; in the second, ammonium ions are detected. For each of five sample diluents studied, the latter method is shown to offer a greater than 100-fold improvement in detection limits over the more classical pH monitoring technique. Further studies clearly show that the ammonium electrode detection mode also offers superior selectivity over volatile amines (e.g., methylamine, ethylamine, etc.). The reasons for these enhanced analytical characteristics are discussed in terms of ammonia flux through the gas-permeable membrane of the dialyser and appropriate solution equilibria.