Measurement of ascorbic acid in human plasma and serum: stability, intralaboratory repeatability, and interlaboratory reproducibility.
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%.
Margolis
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SA
Analytical Chemistry Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA. Sam.Margolis@NIST.gov
Duewer
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DL
D001205:Ascorbic Acid / Q000097:blood*; D002845:Chromatography / Q000379:methods / Q000706:statistics & numerical data; D003683:Dehydroascorbic Acid / Q000097:blood; D004229:Dithiothreitol; D004355:Drug Stability; D005615:Freezing; D006801:Humans; D007700:Kinetics; D007753:Laboratories / Q000592:standards*; D010655:Phenylenediamines; D010659:Phenylhydrazines; D010757:Phosphorous Acids; D010949:Plasma; D015203:Reproducibility of Results; D013048:Specimen Handling; D013237:Stereoisomerism; D013997:Time Factors
D010655:Phenylenediamines; D010659:Phenylhydrazines; D010757:Phosphorous Acids; C004787:2,4-dinitrophenylhydrazine; C034193:1,2-diaminobenzene; C043639:metaphosphoric acid; D001205:Ascorbic Acid; D004229:Dithiothreitol; D003683:Dehydroascorbic Acid