A shipboard fluorometric flow analyzer has been developed for near-real-time, high-resolution underway measurement of ammonium in seawater. The fluorometric method is based on the reaction of ammonium with o-phthaldialdehyde (OPA) and sulfite. The reagents used in this method have been modified to suit seawater analysis. This method shows no refractive index and salinity effect from seawater samples. The potential interferences in seawater have been studied, and their effects have been reduced. The instrument response is linear over a wide range of ammonium concentration. The limit of detection of 1.1 nM was estimated in laboratory using ammonium standards prepared in distilled water. It should be noted that application of this method to lowlevel ammonium measurement requires a correction of interference species, such as amino acids. The sample throughput is 3600 h -1 . The system can be used for both freshwater and seawater samples and has been used to monitor the distribution of ammonium in Florida coastal waters around an oceanic wastewater outfall.Ammonium is an essential nutrient in the marine environment. Phytoplankton generally prefer ammonium over nitrate, which requires additional energy to reduce to ammonium during assimilation. 1-3 However, high concentrations of ammonia are toxic to marine organisms such as fish, 4 shrimp, 5 abalone, 6 and sea urchin, 7 especially larvae or juveniles of these species. Water quality monitoring requires accurate measurements of the concentration of ammonium in the coastal environment; 8 however, both physical and biological processes, such as biological uptake and release, 9,10 atmospheric deposition, air-sea gas exchange, 11,12 and wastewater discharge, 13 rapidly change the ammonia concentrations in both space and time. Development of a shipboard analyzer that can perform near-real-time, high-resolution underway measurements of ammonium in coastal water is urgently needed.The most common technique used to measure ammonia in seawater is the indophenol blue method using the Berthelot reaction; 14,15 however, this technique has low sensitivity (LOD 0.6 µM) and a high reagent blank. [16][17][18] An ammonia electrode was found easy to operate, 19 but it requires long equilibration times and provides low sensitivity (LOD 0.2 µM). To increase sensitivity, a solvent extraction method 20 was developed, but the procedure is time-consuming and labor-intensive. Recently, a long-path liquid waveguide capillary cell 21 was used to improve the sensitivity (LOD 5 nM), but the problems associated with the indophenol blue still remained. In 1971, Roth 22 developed a fluorescent method for determination of amino acid and ammonia in which o-phthaldialdehyde (OPA) reacts with mercaptoethanol to produce a strongly fluorescent compound. This method has been adapted for a variety of applications. [23][24][25]26 In 1989, Dasgupta 27 modified this method by replacing mercaptoethanol with sulfite and provided a method with higher sensitivity for ammonia and greater selectivity over amino ac...

We present a new fully automated instrument for the measurement of acid gases and soluble anionic constituents of atmospheric particulate matter. The instrument operates in two independent parallel channels. In one channel, a wet denuder collects soluble acid gases; these are analyzed by anion chromatography (IC). In a second channel, a cyclone removes large particles and the aerosol stream is then processed by another wet denuder to remove potentially interfering gases. The particles are then collected by one of two glass fiber filters which are alternately sampled, washed, and dried. The washings are preconcentrated and analyzed by IC. Detection limits of low to subnanogram per cubic meter concentrations of most gaseous and particulate constituents can be readily attained. The instrument has been extensively field-tested; some field data are presented. Results of attempts to decipher the total anionic constitution of urban ambient aerosol by IC-MS analysis are also presented.