Quantitation of Monosaccharide Isotopic Enrichment in Physiologic Fluids by Electron Ionization or Negative Chemical Ionization GC/MS Using Di-O-isopropylidene Derivatives

• Published in: Analytical chemistry (Washington) 1999-10, Vol.71 (20), p.4734-4739
• Main Authors: Hachey, David L, Parsons, W. Reed, McKay, Siripoom, Haymond, Morey W
• Format: Article
• Language: English
• Subjects: Alkenes - analysis; Alkenes - blood; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Blood Glucose - analysis; Carbohydrates; Fundamental and applied biological sciences. Psychology; Gas Chromatography-Mass Spectrometry; Humans; Indicators and Reagents; Monosaccharides - analysis; Monosaccharides - blood; Oses; Other biological molecules
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac990724x

The aldonitrile pentaacetate and other derivatives lack ions in the electron ionization (EI) spectra possessing an intact hexose structure and thus must be analyzed by chemical ionization GC/MS in order to study multiple isotopomers. We report methods for quantitation of hexose di-O-isopropylidene acetate (IPAc) or pentafluorobenzoyl (PFBz) esters. These were prepared in a two-step procedure using inexpensive reagents that do not adversely impact the isotopomer structure of the sugar. The acetate derivative possesses an abundant [M − CH3] ion in the EI spectrum which is suitable for quantitative analysis of isotopomers. The negative chemical ionization (NCI) spectrum of the corresponding pentafluorobenzoyl derivative has a dominant molecular anion. Moreover, the PFBz derivative is about 100-fold more sensitive than the acetate, which offers some advantages for analysis of minor hexoses found in plasma. Isotopic calibration curves of [U-13C]glucose are linear over the 0.1−60% tracer/tracee range tested. The useful range for isotopic tracer studies is 25−2500 pmol for EI analysis of the acetate derivative and 0.1−55 pmol for NCI analysis of PFBz derivative (sample amount injected). For most studies where sample size is not limited, EI-GC/MS analysis of the IPAc derivative is preferred. NCI-GC/MS analysis is reserved when sample size is limiting or when studies involve hexoses other than glucose that are normally present at low concentration.