Abstract
Vitamin‐enriched, lyophilized serum (VES) was prepared for an inter‐laboratory study to compare vitamin assays. The VES contained water‐soluble vitamins (vitamin B1, vitamin B12, vitamin C, and folate), fat‐soluble vitamins (vitamin A and vitamin E), and cholesterol. We performed stability studies and determined vitamin concentrations and total cholesterol in VES stored at −20°C for 12 months. Our recovery of the water‐soluble vitamins in reconstituted VES was 70–142%, but we recovered only 33–45% of the fat‐soluble vitamins. Physicochemical properties, such as specific gravity and viscosity of the reconstituted VES did not affect manual or automated measurements of these vitamins. Vial‐to‐vial differences found for the VES were the same as the within‐day analytical variations. There was no evidence of degradation of vitamin A, vitamin B1, vitamin B12, vitamin C, folate, and cholesterol over 12 months in VES stored at −20°C. Following deproteinization, vitamin C concentration was found to be lower than when not deproteinated. Vitamin E was less stable in VES, however, and the degradation during 12 months was lower than the between‐day analytical variation of the assay. Our VES is the first preparation of lyophilized control serum that contains water‐soluble and fat‐soluble vitamins. J. Clin. Lab. Anal. 18:240–246, 2004. © 2004 Wiley‐Liss, Inc.
Keywords: vitamins, reference value, lyophilized serum, standard reference materials 968c (SRM 968c)
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