title: The methanol method for the quantification of ascorbic acid and dehydroascorbic acid in biological samples.
abstract: We present a fast to perform spectrophotometric method for the quantification of ascorbic acid and its oxidized form dehydroascorbic acid in biological samples. The assay detects a chromophore formed during the reaction of dehydroascorbic acid with methanol in phosphate/citrate buffer. This reaction can also be employed for the determination of ascorbate (vitamin C) in the presence of ascorbate oxidase. The major advantage of the developed protocol for the determination of both forms of vitamin C is a simple spectrophotometrical single end point determination. It is demonstrated that the methanol method is an improvement compared with a commercially available test kit for the determination of vitamin C. Using the methanol method, a dose-dependent increase in intracellular ascorbic acid was determined upon incubation of L-929 cells and RAW 264.7 macrophages with increasing concentrations of extracellular ascorbate. In blood serum, vitamin C was determined at concentrations between 46 and 97 microM. Supplementation with different amounts of ascorbate showed satisfying recovery. In L-929 cells, even unphysiologically high amounts of reactive nitrogen species were unable to completely oxidize intracellular vitamin C.
authors.affiliation: Institut für Physiologische Chemie, Universitätsklinikum Essen, Hufelandstrasse 55, 45122 Essen, Germany.
authors.forename: Curd-David
authors.initials: CD
authors.lastname: Badrakhan
authors.forename: Frank
authors.initials: F
authors.lastname: Petrat
authors.forename: Maren
authors.initials: M
authors.lastname: Holzhauser
authors.forename: Anke
authors.initials: A
authors.lastname: Fuchs
authors.forename: Elena E
authors.initials: EE
authors.lastname: Lomonosova
authors.forename: Herbert
authors.initials: H
authors.lastname: de Groot
authors.forename: Michael
authors.initials: M
authors.lastname: Kirsch
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000097:blood* / Q000737:chemistry; D002460:Cell Line; D003683:Dehydroascorbic Acid / Q000097:blood* / Q000737:chemistry; D007700:Kinetics; D000432:Methanol; D051379:Mice; D010084:Oxidation-Reduction; D010710:Phosphates; D012680:Sensitivity and Specificity; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*
chemical_list: D010710:Phosphates; D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid; D000432:Methanol