Evaluations of commercial ion selective electrodes:3. The ammonia gas-sensing membrane probe

Two makes of ammonia gas sensing membrane probes were evaluated. Calibration curves were determined repeatedly during three months both in separate solutions and in flowing solutions and in the air gap mode.Response times by a step change of analyte concentration were determined.Only minor differences between different makes were found.The measuring range of the probe is about from 1 mol/dm3 to 10 6 mol/dm3.The response time is dependent on concentration level so that at higher concentrations the probes respond considerably faster than at lower concentrations.A marked decrease in response time occurs at the concentration range of 10 4 10 5 mol/dm3.Response times are of few seconds to several minutes.The ammonia probes were found convenient and useful devices though their manipulation requires a certain degree of care