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-labeled bacterial synthesized folate internal standard, The GC-MS method exploits the fact that the common feature of all folate molecules is ap-aminobenzoic acid moiety sandwiched between a pteridine ring and a polyglutamate chain of varying length, In this method, red blood cell folates together with a folate internal standard are specifically purified using bovine folate binding protein and the folates are subsequently chemically cleaved to p-aminobenzoic acid, pteridines, and glutamic acids, Since all six carbon atoms of the benzene ring in the p-aminobenzoic 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 sensitive, 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.