DETERMINATION OF OXALATES IN CORK STOPPERS BY HPLC WITH ELECTROCHEMICAL DETECTION

For oxalate quantification in cork stoppers an automated HPLC method u sing an ion exchange organic acid column and an electrochemical detect or was performed. The study was conducted on cork stoppers in three st eps of their manufacture: untreated cork stopper (corresponding to nat ural cork), whitened stopper, and final stage (ready for commercial de livery). The oxalate determinations may be performed in a linear range from 0.1 mu g/mL (detection limit) to 20 mu g/mL. The identification of the chromatographic peak corresponding to oxalic acid was proved by the specific action of oxalate oxidase. Satisfactory recovery for the extraction procedure (recoveries of oxalic acid in the additions meth od between 92.85% +/- 3.70% and 103.65% +/- 7.70%) and precision for t he over-all procedure (relative standard deviation between 5.90% and 8 .20%), and low time consuming (30 min for the HPLC analysis) were obse rved. It makes this procedure suitable for monitoring residual oxalate s in cork stoppers either by the industry itself or by government qual ity control. Quantification of oxalic acid in 60 randomly obtained sam ples from the market gave the value of 173.8 +/- 15.4 mu g/g (X +/- SE ).