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Soil Science Society of America Journal Abstract -

Determination of Mg with 1-azo-2-hydroxy-3-(2,4-dimethylcarboxanilido)-naphthalene-1′-(2-hydroxybenzene)1


This article in SSSAJ

  1. Vol. 30 No. 4, p. 443-446
    Received: Aug 18, 1965
    Accepted: May 19, 1966

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  1. D. E. Peaslee2



The reagent 1-azo-2-hydroxy-3-(2,4-dimethylcarboxanilido)-naphthalene-1′-(2-hydroxybenzene forms a soluble red complex with Mg and tolerates high concentrations of Ca. These properties suggested its usefulness as a reagent for determining Mg in soil extracts. Successful masking of interferences due to Al, Fe, Mn, and Cu permitted its use in precise spectrophotometric and rapid colorimetric determination of Mg.

The spectrophotometric method will determine 1–10 µg of Mg and tolerates the following µg quantities of diverse ions: Ca+, 1,000; Al4+3 100; Mn2+, 150; Fe3+, 150; Zn2+, 65; Cu2+, 10; 10 µg P as PO43- plus 300 µg N as NH4+. Analyses of soil extracts had a coefficient of variation of 1.5%. The colorimetric procedure is designed for soil extracts containing 5–85 µg Mg/ml and tolerates the following concentrations of diverse ions expressed as µg/ml in the extract: Ca2+, 1,000; Al3+, 150; Mn2+, 60; Fe3+, 15; Fe2+, 15; Zn2+, 65; Cu2+, 15. These methods have the advantages of sensitivity, stability, and freedom from interferences compared to most “lake” and titration methods. A semiquantitative spot test is also described.

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