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Determination of Total Potassium, Sodium, Calcium, and Magnesium in Plant Materials by Ion Chromatography¹

ABSTRACT

A simple, accurate, and precise ion chromatographic (IC) method for determination of total K, Na, Ca, and Mg in plant materials was developed. It involves dry ashing approximately 0.1 g of plant material, followed by dissolution of the residue in 5 mM HCl and determination of K, Na, Ca, and Mg in the digest by using a Dionex Model 10 IC. The IC method is based on separation of the cations by a separator column containing low-capacity, cation-exchange resin in the H⁺ form and on converting the various cations to their corresponding hydroxide forms by a suppressor column in the OH^- form. The eluent used for determination of K and Na was 5 mM HCl, and that used for determination of Ca and Mg was 2.5 mM HCl + 2.5 mM m-phenylenediamine dihydrochloride. Electrical conductivity is used as the mode of detection. Results showed that the average total K values in 25 plant materials by IC, atomic absorption spectrophotometry (AA), and flame photometry (FP) were 3.08, 3.08, and 3.07%, respectively. The corresponding average total Na values were 0.258, 0.264, and 0.256%. The average total Ca values in the same plant samples by the IC and AA methods were 1.20 and 1.19%, respectively. The corresponding average total Mg values were 0.327 and 0.331%. The IC method developed has the same degree of precision as that of AA or FP method. The IC method has an excellent sensitivity with detection limits of 0.1, 0.05, 0.1, and 0.03 mg L^–1 of K, Na, Ca, and Mg, respectively. With the IC method, K and Na can be determined simultaneously in 6 min, or Ca and Mg can be determined in 7 min. A single operator can perform about 40 analyses of K and Na or Ca and Mg in a normal working day.

¹ Journal Paper no. J-11489 of the Iowa Agric. & Home Econ. Exp. Stn., Ames, IA. Projects 2112 and 2601. Received 6 June 1984. Approved 20 Aug. 1984. Presented before Div. S-4, Soil Sci. Soc. Am., Las Vegas, NV. 28 Nov. 1984.

² Graduate Research Assistant and Professor of Soil Chemistry, respectively. Dep. of Agronomy, Iowa State Univ., Ames, IA 50011.