CITRATE IN URINE DETERMINED WITH A NEW CITRATE LYASE METHOD

An enzyme-spectrophotometric method to determine citrate in biological fluids is proposed, based on citrate lyase-catalyzed and phenylhydraz ine reactions. The enzyme converts citrate into oxaloacetate, which, i n the presence of phenylhydrazine, is transformed into the correspondi ng phenylhydrazone. The ultraviolet-absorbing product is determined by absorbance measurement at 330 nm. The method is more precise and twic e as sensitive as the traditional citrate lyase method and, because it does not require the use of additional enzymes and coenzymes, is chea per and simpler. Mean analytical recovery of citrate averaged 100.7% /- 2.2%, imprecision (CV) of the assay for citrate at 0.96 mmol/L (uri ne) was 2.0%, and the lower limit of quantification was 0.08 mmol/L. R esults correlated well with those by both ion-chromatographic and trad itional citrate lyase methods.