Stabilization of ascorbic acid in human plasma, and its liquid-chromatographic measurement

We describe two independent HPLC procedures for the rapid, accurate analysis for ascorbic acid in human plasma. No sample extraction or phase separation is required. We also describe a procedure for preparing a human plasma reference material for use in clinical laboratory analysis for ascorbic acid. The ascorbic acid in plasma can be determined in 15 min, with as little as 50 microL of sample. Analytical recoveries are near 100% with direct injection of deproteinized plasma. Extensive stability data under several conditions, with dithiothreitol as a preservative (antioxidant), indicate that ascorbic acid remains stable in stored plasma for as long as 57 weeks. CVs for round-robin analysis of 11 normal human blood samples by two independent methods were between 0.1% and 5.3%. These clinical samples appear to be stable for at least 50 days under the described conditions of stabilization and sample treatment. Finally, because ascorbic acid prepared by the described procedures is stable at room temperature for at least 18 h, these methods can be readily adapted to clinical laboratory automation at room temperature.