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Evaluation of Three Aluminum Assay Techniques for Excluding Aluminum Complexed with Fluoride or Sulfate

Dep. of Agronomy, Coastal Plain Exp. Stn., P.O. Box 748, Tifton, GA 31793-0748

M. E. Sumner and W. P. Miller

Dep. of Agronomy, Univ. of Georgia, Athens, GA 30602

Y. C. Li

Shandong Cotton Research Center, Jinan City, People's Republic of China

* Corresponding author.

ABSTRACT

Aluminon, 8-hydroxyquinoline and ferron reagents are often used to measure Al in solutions. Since Al complexed with F^- or SO^2-₄ is less phytotoxic, in solutions containing these ligands an estimate of Al excluding that complexed with F^- and/or SO^2-₄ represents predominantly phytotoxic Al. In the present study, the capacity of the above reagents to exclude Al complexed with F^- or SO^2-₄ was evaluated in solutions containing 40 µM Al with 20 to 640 µM F^- or 40 to 5120 µM SO^2-₄ at pH 4.5. The effects of varying reaction time from 15 s to 30 min on the recovery of Al by the respective reagents was also investigated. The sum of predicted (by MINTEQ speciation model) concentrations of Al³⁺ and hydroxy-Al monomers decreased to 45% or to 0.6% of total Al in solutions with 5120 µM SO^2-₄ or 80 µM F^-. The concentration of Al measured by 8-hydroxyquinoline (15- or 60-s reaction) or aluminon (15-s reaction) appeared to exclude entirely Al complexed with F^-. All three reagents, however, regardless of reaction time, failed to exclude Al complexed with SO^2-₄. Therefore, 8-hydroxyquinoline (15- or 60-s reaction) aluminon (15-s reaction) reactive Al would accurately represent phytotoxic Al in the presence of F^-, while ferron reagent is likely to overestimate the phytotoxic Al. In the presence of SO^2-₄, however, all three reagents are likely to overestimate the phytotoxic Al.

Contribution from the Dep. of Agronomy, Univ. of Georgia. Research supported by Florida Inst. of Phosphate Research, and the Georgia Agric. Exp. Stn.

Received for publication March 22, 1988.