Measurement of diffusive flux of ammonia from water.

An instrument was developed for the measurement of gaseous ammonia concentration, NH3(sw,eq), in equilibrium with surface waters, notably ocean water. The instrument measures the ammonia flux from a flowing water surface under defined conditions and allows the calculation of NH3(sw,eq) from the principles of Fickian diffusion. The flux collector resembles a wetted parallel plate denuder previously developed for air sampling. The sample under study runs on one plate of the device; the ammonia released from the sample is collected by a slow flow of a receptor liquid on the other plate. The NH3 + NH4+ (hereinafter called NT) in the effluent receptor liquid is preconcentrated on a silica gel column and subsequently measured by a fluorometric flow injection analysis (FIA) system. With a 6-min cycle (4-min load, 2-min inject), the analytical system can measure down to 0.3 nM NT in the receptor liquid. Coupled with the flux collector, it is sufficiently sensitive to measure the ammonia flux from seawater. The in...