2-4-dinitrophenylhydrazine and metaphosphoric-acid

We demonstrate that total ascorbic acid (TAA, the sum of ascorbic acid and dehydroascorbic acid) in properly prepared human plasma is stable at -70 degrees C for at least 6 years when preserved with dithiothreitol. TAA in human plasma or serum preserved with metaphosphoric acid degrades slowly, at the rate of no more than 1% per year. As assessed from our stability data and from data obtained from 23 laboratories over a period of > 2 years, the intralaboratory repeatability of TAA measurement is approximately 2 mumol/L, irrespective of TAA concentration. Nonchromatographic analytical methods involving dinitrophenylhydrazine and 0-phenylenediamine yield biased results relative to chromatographic methods. Within groups of laboratories that use roughly similar analytical methods, the interlaboratory measurement reproducibility CV for TAA is 15%.

Topics: Ascorbic Acid; Chromatography; Dehydroascorbic Acid; Dithiothreitol; Drug Stability; Freezing; Humans; Kinetics; Laboratories; Phenylenediamines; Phenylhydrazines; Phosphorous Acids; Plasma; Reproducibility of Results; Specimen Handling; Stereoisomerism; Time Factors