Isolation of a Zinc-chelating Compound from Instant Coffee by the Tetramethyl Murexide Method

Abstract

Tetramethyl murexide, which is a chelating reagent that shows a shift in the absorption maximum due to the formation of a complex, was used as an indicator for the purification of a zinc-chelating compound in instant coffee. A soluble coffee solution was purified principally by ion exchange, gel filtration, and reversed-phase column chromatographic methods. An active compound was isolated and identified as citric acid by nuclear magnetic resonance and mass spectroscopic analyses. One mole of citric acid bound 1 mol of zinc, and its apparent dissociation constant was 3.5 × 10 -8 mol/L.