Determinations of citric acid by differential pulse polarography with immobilized enzymes

Summary Citrate lyase and oxaloacetate decarboxylase can be rapidly and simply immobilized in polyacrylamide gel to provide a selective and sensitive reactor. Conversion ratio of citric acid to pyruvic acid comes up to 90% under the optimal conditions. Generated pyruvic acid can be determined by differential pulse polarography. The bioreactor can be used for thirty determinations over several weeks. Samples of sports drinks and wine were successfully tested without pretreatment; the relative standard deviation with 1.0×10^-5 mol l^-1 citric acid in polarographic solutions was 1.17% and the detection limit was 6.6×10^-7 mol l^-1 (=2).