Single Column Ion Chromatography: II. Analysis of Ammonium, Alkali Metals, and Alkaline Earth Cations in Soils

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Abstract
Single column ion chromatography (SCIC) was evaluated as an effective analytical method for the determination of soluble ammonium, alkali metals, and alkaline earth cations in soil extracts. Eluents chosen for determination of the mono‐and divalent cations were 10 mM nitric acid (pH 2.1) and 5 mM ethylenediammonium dinitrate (pH 6.1), respectively. Separation was carried out on a commercially available, low‐capacity, cation exchange column, with conductimetric detection. SCIC can utilize very small sample sizes (≤ 500 µL), and yields linear, reproducible relationships between peak area and concentration of cations. Simultaneous determination of Li+, Na+, NH+4, and K+ or Mg2+, Ca2+, Sr2+ and Ba2+ was performed in < 7 min with precision ranging from 3 to 8%. Determinations can be made against a background of various ions and organic constituents without interferences. Minimum detectable concentrations of the selected cations using a 500 µL loop were: Na2+, Ca2+, and Mg2+ (0.05 mg/L), Li+ and Ba2+ (0.10 mg/L), NH+4‐N (0.5 mg/L), and K+ and Sr2+ (1 mg/L). Results obtained by SCIC agreed closely with those obtained by other methods: NH+4‐N, steam distillation (r = 0.996***); Na+, atomic emission spectrometry (AES) (r = 0.992***); K+, AES (r = 0.999***); Mg2+, atomic absorption spectrometry (AAS) (r = 0.995***); Ca2+, AAS (r = 0.996***). Simplicity of this method makes it feasible to construct a HPLC instrument dedicated for the analysis of cations.

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