| Abstract
| - A highly fluorescent vitamin B12 derivative was readilyprepared with a fluorescent reagent [6,7-dimethoxy-1-methyl-2(1H)-quinoxaline-3-propionylcarboxylicacid hydrazide] specific for carboxylicacids. Hydroxovitamin B12 was reduced byNaBH4, and then 4-chlorobutyric acid was addedtoform carboxypropyl vitamin B12, which was labeled with thefluorescent reagent in the presence ofcarbodiimide. An assay for vitamin B12 with thefluorescent vitamin B12 derivative and hogintrinsicfactor was devised. Vitamin B12 could be assayed overa range of 0.2−10 μg/L by this method,which was useful for vitamin B12 assay infoods. Keywords: Vitamin B12; cobalamin; fluorescence assay; intrinsicfactor
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