Analytical Sciences

Identification of Al(III) Species in a Solution Containing Equimolar Concentrations of Al(III) and Citric Acid Using Varying-Temperature ²⁷Al NMR Spectrometry

Etsuro YOSHIMURA,*  Mariko AKASHI,** Tomonari UMEMURA,** and Kin-ichi TSUNODA**

*Department of Applied Biological Chemistry, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
**Department of Chemistry, Gunma University, Kiryu, Gunma 376-8515, Japan

²⁷Al NMR spectra of an equimolar (10 mM) Al(III)-citrate system were obtained at different temperatures. The linewidths of the signals decreased in the spectra recorded at elevated temperatures, which enabled us to unequivocally identify the resonance lines. From the spectrum recorded at 65°C, a mononuclear Al(III)-citrate complex was identified at a solution pH of 3.0 in addition to trinuclear Al(III)-citrate complex, which dominated at pH 4.0.

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