QUANTITATION OF RED-BLOOD-CELL FOLATES BY STABLE-ISOTOPE DILUTION GAS-CHROMATOGRAPHY MASS-SPECTROMETRY UTILIZING A FOLATE INTERNAL STANDARD

We report a new gas chromatography-mass spectrometry (GC-MS) method of measurement of red blood cell folates utilizing a stable isotope-labe led bacterial synthesized folate internal standard, The GC-MS method e xploits the fact that the common feature of all folate molecules is ap -aminobenzoic acid moiety sandwiched between a pteridine ring and a po lyglutamate chain of varying length, In this method, red blood cell fo lates together with a folate internal standard are specifically purifi ed using bovine folate binding protein and the folates are subsequentl y chemically cleaved to p-aminobenzoic acid, pteridines, and glutamic acids, Since all six carbon atoms of the benzene ring in the p-aminobe nzoic acid moiety of the folate internal standard are labeled with [C- 13], it is possible to use selected ion monitoring and stable isotope dilution GC-MS to quantitate folates, The method appears to be sensiti ve, specific, and accurate, The method has been applied to generate a reference range of red blood cell folates based on assay of 25 normal individuals, (C) 1995 Academic Press, Inc.