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Increased Color Stability in the Determination of Magnesium¹

ABSTRACT

The method of Drosdoff and Nearpass was modified for the determination of magnesium in plant and soil extracts. One method is proposed for the analysis of ammonium acetate extracts of soils, and another method is proposed for the analysis of plant materials and water extracts of soils. These methods, which determine the magnesium content colorimetrically with the use of thiazole yellow, introduce the use of sodium bisulfite to stabilize the color obtained. Polyvinyl alcohol is used to obtain suspension stability. A procedure for the determination of magnesium with titan yellow is also presented.

A number of soil and plant samples were analyzed by the A.O.A.C. method, the proposed methods, and the method of Drosdoff and Nearpass. Values obtained for the magnesium content of the soils and plants indicate greater accuracy and reproducibility of duplicate determinations by the modified procedures than by the Drosdoff-Nearpass method. The modified methods are more sensitive to changes in magnesium concentration than is the Drosdoff-Nearpass method. Color stability of 24 hours have been obtained with the titan yellow procedure and the method used for plant analysis, and one hour of color stability has been obtained with the method used for determining exchangeable magnesium. The proposed procedures are rapid, accurate and reproducible. Stability of color and suspension, and facility of the methods adapt these procedures to mass routine analysis of samples for magnesium.

¹ Contribution of the Department of Agronomy, Nebraska Agricultural Experiment Station, Lincoln, Neb. Published with the approval of the Director as Paper No. 589, Journal Series, Nebraska Agricultural Experiment Station.

² Graduate assistant and assistant Professor of Agronomy, University of Nebraska, respectively. Assistance was given in testing the proposed procedures by Helen E. Budeit, E. J. Dennis, C. R. Krishnamurthi, J. S. Russell and a number of undergraduate students in the junior author's soil chemistry course during 1951. Paper presented before Division II, Soil Science Society of America, Cincinnati, Ohio, Nov. 19, 1952.

Received for publication December 3, 1952.