DETERMINATION OF AMMONIA AMMONIUM ION IN WATER BY CONTINUOUS-FLOW CHEMILUMINESCENCE AFTER DERIVATIZATION TO AN ISOINDOLE

In order to determine ammonia (H-3)/ammonium ion in water, a continuou s-flow chemiluminescence (CL) system based on an aryl oxalate was deve loped using the conversion of NH3 into a fluorescent isoindole derivat ive. On-line derivatization of NH3 was carried out in a 200-s reaction coil by mixing with an OPA reagent containing 10 mM o-phthaldialdehyd e, 15 mM 2-mercaptoethanol and 10 mM phosphate (pH 10.5). A 0.5 mM bis (2,4,6-trichlorophenyl)oxalate (TCPO) acetonic solution and 0.5% hydro gen peroxide (H2O2) solution were used as an oxalate CL system. The fl ow rates of the sample, OPA reagent, TCPO and H2O2 solutions were 0.48 , 0.24, 2.10 and 0.24 ml min-1, respectively. The detection limit (SIN =3) was 2.9 ng ml-1 and the CL intensity was linearly proportional to the NH3 concentration up to 6 mug ml-1. Although primary amines were d erivatized and detected as well as NH3, the chemical species usually f ound in rainwater samples did not interfere with the measurement.