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.