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| - Quantitation of Monosaccharide IsotopicEnrichment in Physiologic Fluids by ElectronIonization or Negative Chemical Ionization GC/MSUsing Di-O-isopropylidene Derivatives
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| - The aldonitrile pentaacetate and other derivatives lackions in the electron ionization (EI) spectra possessing anintact hexose structure and thus must be analyzed bychemical ionization GC/MS in order to study multipleisotopomers. We report methods for quantitation of hexose di-O-isopropylidene acetate (IPAc) or pentafluorobenzoyl (PFBz) esters. These were prepared in a two-stepprocedure using inexpensive reagents that do not adversely impact the isotopomer structure of the sugar. Theacetate derivative possesses an abundant [M − CH3] ionin the EI spectrum which is suitable for quantitativeanalysis of isotopomers. The negative chemical ionization(NCI) spectrum of the corresponding pentafluorobenzoylderivative has a dominant molecular anion. Moreover, thePFBz derivative is about 100-fold more sensitive than theacetate, which offers some advantages for analysis ofminor hexoses found in plasma. Isotopic calibrationcurves of [U-13C]glucose are linear over the 0.1−60%tracer/tracee range tested. The useful range for isotopictracer studies is 25−2500 pmol for EI analysis of theacetate derivative and 0.1−55 pmol for NCI analysis ofPFBz derivative (sample amount injected). For moststudies where sample size is not limited, EI-GC/MSanalysis of the IPAc derivative is preferred. NCI-GC/MSanalysis is reserved when sample size is limiting or whenstudies involve hexoses other than glucose that arenormally present at low concentration.
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