Plasma ascorbic acid preparation and storage for epidemiological studies using TCA precipitation

Objectives:To introduce a procedure to validate an ascorbic acid method using trichloroacetic acid (TCA) for plasma stabilization at different storage temperatures.Methods:EDTA and heparin plasma were precipitated with TCA (1:5) containing 0.54 mol/L EDTA, or without. Samples were stored at ? 20 °C and ? 70 °C and their stability was tested at room temperature for 24 h.Results:A significant 40% loss (p < 0.001) of plasma ascorbic acid was found when EDTA samples with added EDTA were stored at ? 20 °C for 2–4 weeks compared with storage at ? 70 °C. Ascorbic acid in heparin plasma without added EDTA was most unstable and samples left at room temperature for 24 h lead to almost a total loss of ascorbic acid. Addition of EDTA to the TCA solution improved stability of samples of both plasma types at room temperature.Conclusion:The recommended procedure for ascorbic acid determination in plasma stabilized with TCA is immediate storage at ? 70 °C and inclusion of EDTA into the TCA solution.