Ion exchange in flow injection analysis: Determination of Ammonium Ions at the μg 1-1 level in Natural Waters with Pulsed Nessler Reagent

Ion exchange is incorporated in flow injection analysis by using a resin column in the sample loop of an electronically operated proportional injector. Effects of sample aspiration rate, sampling time, eluting agent concentration, pumping rate of the sample carrier stream, resin column size and sample acidity, were investigated to develop a preconcentration procedure for ammonium ion determination in natural waters at the μg 1^-1 level with pulsed Nessler reagent. The possibility of sample buffering before the adsorption step was studied. The proposed method is characterized by a precision of about 2%, a sampling rate of about 40 samples per hour. and a reagent consumption of 40 μl per sample, and is almost free of interferences. Recoveries from 95 to 105% were achieved in analysing rain-water samples with ammonium contents of less than 200 μg 1^-1. Alternative flow diagrams and the injector command unit are discussed.