Chlorhexidine gluconate as a urine preservative in analysis for oxalic acid.

Chborhexidine, a potent antiseptic (1), has been used as a preservative for urine (2, 3) in which oxabic acid and calcium were to be measured. We recently described a biquid-chromatographic method for determining oxalic acid in urine (4) and wish to describe our results when using chlorhexidine gluconate (CG) to replace HCI in the preservation of urine in which oxalic acid was measured. Our method for determining oxalic acid is based on the formation of 2,3dihydroxyquinoxabine by reaction of oxalic acid in urine with o-phenybenediamine and the isolation and quantitation of this derivative by reversedphase liquid chromatography. In this method, the formation of the quinoxaline from compounds other than oxalic acid is corrected for by use of samples incubated with oxalate decarboxylase (EC 4.1.1.2) before the reaction with o-phenylenediarnine (4). Also, in those studies, urine was acidified with HCI and stored frozen. We saw no statistically significant change in the oxalic acid content of urine during frozen storage for as bong as 35 days (4). Subsequently, other studies indicated that oxalic acid is unchanged in acidified urines stored at room temperature. Because 24-h urine specimens are Table 1. Influence of Preservative on UrInary Oxalic Acid OxaIIc acId (sg/mL) In urine preserved wIth