FLUOROMETRIC-DETERMINATION OF AMMONIA IN SEA AND ESTUARINE WATERS BY DIRECT SEGMENTED FLOW-ANALYSIS

A direct automated method for routine determination of ammonia in sea and estuarine waters has been developed using segmented flow analysis. The method, based on the reaction of ammonia with orthophtaldialdehyd e (OPA) and sulfite, is easy to use, sensitive and highly reproducible . The combination of reagents makes it highly selective, thus eliminat ing the need for the gas diffusion cell commonly used to remove amino acid interference. Results on kinetics, on reagent composition and lig ht effects and on pH and salinity changes are presented. The salt-effe ct does not exceed 3% in the 0-35 salinity range. Interference from pr imary amines is < 0.5%. Among the naturally occurring inorganic specie s tested, only sulfide presents a significant, depressive effect. The method can be used in oligotrophic areas (detection limit 1.5 nmol l(- 1)); specific recommendations are provided accordingly. Repeatability of 0.01 mu mol l(-1) was achieved in marine samples with ammonia conce ntrations ranging from 0.5 to 5 mu mol l(-1). Using on-line dilution. ammonia determination can be performed up to 250 mu mol l(-1) and salt effect becomes negligible. Comparison of the present CPA-method with the indophenol blue method yielded fully comparable results. (C) 1997 Elsevier Science B.V.