Open AccessLessons from the NIST micronutrients quality assurance program for vitamin C, 1993 to 2015: sample stability, assay reproducibility, and use of controls to improve comparability
Author(s) -
David L. Duewer,
Jeffrey J. Thomas,
Katherine E. Sharpless,
Sam A. Margolis
Publication year - 2020
Publication title -
analytical and bioanalytical chemistry/analytical and bioanalytical chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.86
H-Index - 166
eISSN - 1618-2650
pISSN - 1618-2642
DOI - 10.1007/s00216-020-03021-9
Subject(s) - reproducibility , ascorbic acid , repeatability , comparability , nist , coefficient of variation , normalization (sociology) , chemistry , chromatography , micronutrient , quality assurance , analytical chemistry (journal) , mathematics , external quality assessment , medicine , food science , computer science , pathology , organic chemistry , combinatorics , sociology , natural language processing , anthropology
Vitamin C is a necessary micronutrient that is involved in many biological processes. In preserved human plasma and serum, vitamin C is most meaningfully analyzed as total ascorbic acid (TAA). From 1993 through 2015, the National Institute of Standards and Technology (NIST) coordinated 40 interlaboratory studies (ILS) devoted to improving the between-participant comparability of TAA measurements. The results from these ILS demonstrate that the concentration of TAA ([TAA]) is stable for at least 20 years in serum diluted 1 + 1 (volume fraction) with 10% mass concentration aqueous metaphosphoric acid (MPA) and stored at -80 °C. The between-participant relative reproducibility precision, expressed as a coefficient of variation (CV), improved from over 16% to under 9% over the course of the studies. Normalization of test samples (i.e., ex post-facto recalibrating the as-submitted results) using participant-prepared serum-free calibration solutions did not improve reproducibility. Normalization to one control sample having a similar serum-based matrix as the test samples improved the CV to 7%; normalization to two such controls reduced the CV to 4%. Multicenter studies that require the highest degree of measurement comparability among the participants should consider calibrating with materials that have a serum-based matrix as similar as possible to that of the samples of interest.