Measurements of buffer capacities of reducing gases against oxygen using a zirconia oxygen pump-gauge Original Research Article

A small amount of a reducing gas, H2, CO or CH4, in Ar was titrated with oxygen over a wide range of oxygen partial pressures using a zirconia oxygen pump-gauge in a similar way to the pH titration in aqueous solutions. Concentrations of the reducing gases in Ar were determined from the equivalence points in the titration curves. The buffer capacities against oxygen were theoretically formulated for the mixtures, and were compared with those analyzed from the measured titration curves. Precise values of the buffer capacity were obtained for the reducing gases above a total oxygen demand of 100 ppm, and the measured buffer capacities deviated from theoretical ones at much lower reducing gas concentrations. Several factors influencing the measurement of the buffer capacity and the limit of the measurement were discussed.