Determination of Ammonium and Other Major Cations in River and Rain Water by Ion Chromatography Using Silica Gel as an Ion Exchanger

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The separation of NH₄⁺ from Na⁺, K⁺, Mg²⁺ and Ca²⁺ on silica gel columns was investigated using natural water samples and lithium oxalate as a retention modifier. The pore size of silica gels was found to be the most important factor affecting the retention of the cations. When a 0.0025mol dm^-3 lithium oxalate solution of pH 7 was used as the mobile phase these cations could be completely separated on a short silica-gel column (Develosil 30-3, 35mm×4.0 mm i.d.) within about 20min. NH₄⁺ contents in river (0.01-0.27ppm) and rain (1-1.8ppm) water samples were determined successfully.