Measurement of vitamin C by capillary electrophoresis in biological fluids and fruit beverages using a stereoisomer as an internal standard.

scorbic acid (or vitamin C) is an important component of many biological systems and various physiological roles have been described for it. A rapid and simple capillary electrophoresis method for ascorbic acid measurements in biological fluids as well as in beverages was developed. A stereoisomer of ascorbic acid, isoascorbic acid, not normally found in nature, was used as the internal standard for this assay. The analysis was performed in a 30 cm x 75 microns I.D. fused-silica capillary with 100 mM tricine buffer, pH 8.8, and measured by UV absorbance at 254 nm. The method was sensitive to 1.6 micrograms/ml and linear to 480.1 micrograms/ml. Within-run R.S.D. was 3.2% (93.5 +/- 3.0 micrograms/ml, mean +/- S.D., n = 18) and run-to-run R.S.D. was 3.3% (35.6 +/- 1.2 micrograms/ml, mean +/- S.D., n = 10) and 1.9% (149.4 +/- 2.8 micrograms/ml, mean +/- S.D., n = 10). Average spiked recovery from human plasma samples was 98.0%. The technique has been demonstrated to be suitable for assay of vitamin C in biological samples and some fruit juices.