Determination of ammonium in seawater by column-switching ion chromatography

A system which combines column switching and concentration was developed. A binary eluent mechanism was developed to study the effect of high sample c oncentration matrix on retention time shifts of the trace analyte. Separati on conditions were chosen according to this mechanism to reduce the retenti on time shift of ammonium in the presence of high concentration sodium ion: high concentration sulfuric acid (25 mmol/l) was used as the eluent, and a hydronium-selective column of high capacity - a CS12 column, was employed. Since the retention time shift was reduced, the interval between onset and the complete elution of a high concentration ammonium standard (10 mg/l) w as directly defined as the column-switching time window, which greatly simp lified the procedure for determining the time window. Results showed that f or ammonium below 1 mg/l, 90% ammonium was introduced and concentrated. Det ection limits of 12.8 mu g/l were obtained for ammonium with sodium at 1000 mg/l. (C) 2000 Elsevier Science B.V. All rights reserved.