Lessons From the NIST Micronutrients Quality Assurance Program for Vitamin C, 1993 to 2015: Sample Stability, Assay Reproducibility, and Use of Controls to Improve Comparability
David L. Duewer, Jeanice M. Brown Thomas, Katherine E. Sharpless, S A. Margolis
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 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 past-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.
, Brown, J.
, Sharpless, K.
and Margolis, S.
Lessons From the NIST Micronutrients Quality Assurance Program for Vitamin C, 1993 to 2015: Sample Stability, Assay Reproducibility, and Use of Controls to Improve Comparability, Analytical and Bioanalytical Chemistry, [online], https://doi.org/10.1007/s00216-020-03021-9
(Accessed May 18, 2021)