An Enzymic Colorimetry of Citric Acid with Pymvate Oxidase

Abstract

Studies are reported on a colorimetric microdetermination of citric acid using pyruvate oxidase. The method is based on formation of a red quinone compound in a reaction of citric acid together with citrate lyase, oxalacetate decarboxylase, pyruvate oxidase and peroxidase.
The optimum pH (0.2 M Tris-HCI buffer) was 8.8, and the color product was measured at 505nm. in this method the calibration graph was rectilinear in the range of 50 to 200 nmol of citric acid and the detection limit was 13nmol.
This enzymic method wouid be more advantageous in some applied sciences than that with citrate lyase and malate dehydrogenase because of the visible colordevelopment.