THE DETERMINATION OF AQUEOUS AMMONIA BY ION MOBILITY SPECTROMETRY

A novel aqueous ammonia analyzer, based on an ion mobility spectromete r (IMS) is described. Ammonia is thermally purged from an aqueous samp le stream into the IMS through a silicone membrane. Studies were under taken to establish the limit of detection of the unit and evaluate the effect of ammonium ions. Following this work the system was assessed under simulated process monitoring conditions. Data indicate that the IMS response is to aqueous ammonia, and the limit of detection of the configuration used was found be 1.2 mg l(-1), although lower concentra tions were dearly attainable. The ability to determine ammonium ion co ncentration through pH adjustment of the sampled material was also dem onstrated; emphasising the importance of accurate definition of the an alyte's chemical state. The system was shown to be capable of monitori ng accurately, changes in aqueous ammonia concentration over a simulat ed ammonia concentration excursion for a period of approximately 24 h. Further, no measurement artifacts attributable to memory effects with in the membrane were observed.