Pre-analytical factors affecting ascorbic and uric acid quantification in human plasma.

We have recently described a new capillary electrophoresis assay to measure serum ascorbic and uric acids in which a baseline separation of peaks was obtained in less than 4 min by using a 60.2 cm x 75 microm uncoated capillary with a 100 mmol/L sodium borate running buffer pH 8. Since during sample preparation AA is rapidly oxidized, we employed our new capillary electrophoresis method to analyze the pre-analytical factors affecting its stability. In particular we evaluated how the standard mix preparation, the blood collection (plasma EDTA or serum) and the plasma protein precipitation influence the results of analysis. Our data suggest that standard ascorbate must be dissolved in a solution containing cysteine and EDTA in order to avoid oxidation and that EDTA blood collection is better than serum for AA measurement. Moreover, the type and the quantity of the precipitating compound are critical parameters to obtain a complete recovery of analytes. We performed AA and UA analysis in 32 healthy volunteers with the optimized experimental conditions by using our capillary electrophoresis method and a reference CE assay. Obtained data were compared to Bland-Altman test to verify the accuracy of our CZE method.