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.
aldonitrile pentaacetate和其他具有完整己糖结构的衍
生物在电子离子化(EI)光谱中缺乏离子,因此必须通过
化学离子化GC/MS分析才能研究多种同位素异构体。我们报告了己糖二-O-异丙叉
乙酸酯(IPAc)或
五氟苯甲酰(PFBz)酯的定量方法。这些是通过使用廉价试剂的两步程序制备的,这些试剂不会对糖的同位素结构产生不利影响。
乙酸酯衍
生物在EI光谱中具有丰富的[M - CH3]离子,适合用于同位素异构体的定量分析。相应的
五氟苯甲酰衍
生物的负
化学离子化(NCI)光谱具有主导的分子阴离子。此外,PFBz衍
生物的灵敏度大约是
乙酸酯的100倍,这为分析在血浆中发现的次要己糖提供了一些优势。[U-13C]
葡萄糖的同位素校准曲线在测试的0.1-60%示踪剂/本体范围内是线性的。同位素示踪剂研究的有用范围是25-2500 pmol用于
乙酸酯衍
生物的EI分析,0.1-55 pmol用于PFBz衍
生物的NCI分析(注射的样品量)。对于大多数样本大小不受限制的研究,优先选择IPAc衍
生物的EI-GC/MS分析。当样本大小受限或研究涉及通常以低浓度存在的非
葡萄糖己糖时,保留NCI-GC/MS分析。