A flow system exploiting multicommutation for speciation of inorganic nitrogen in waters Original Research Article

A flow system for the speciation of inorganic nitrogen in waters is described. Multicommutation and binary sampling approaches are exploited to perform the sequential determination of nitrate, nitrite and ammonium without changing the manifold. Gravitational flow of solutions is employed in the sampling steps in order to avoid the effect of pulsation of the peristaltic pump on precision. A homemade photometer based on a dual-color (red/green) LED and a photodiode is employed to detect the reaction products. The repeatability was estimated as 0.32, 0.42 and 0.72% for nitrite, nitrate, and ammonium, respectively. A sampling rate of 60 determinations per hour was attained and the reagent consumption was reduced to 25% (ammonium) and 45% (nitrate and nitrite) relatively to conventional flow injection analysis (FIA) procedures. Detection limits of 5 μg l−1 NO2−, 15 μg l−1 NO3−, and 25 μg l−1 NH4+ were estimated at the 99.7% confidence level. Results for river water samples agreed with those obtained by conventional FIA or ion chromatography at the 95% confidence level.