title: N-Alkylpyridinium isotope quaternization for matrix-assisted laser desorption/ionization Fourier transform mass spectrometric analysis of cholesterol and fatty alcohols in human hair.
abstract: Isotope-coded reagents have been developed for labeling of amino acids, phenols and fatty acids, but not for alcohols. In this work, a simple reaction based on direct N-alkylpyridinium isotope quaternization (NAPIQ) was developed for mild derivatization of cholesterol and fatty alcohols. Different from the conventional quaternary reagents with cations on themselves, two simple and charge-neutral reagents: pyridine and d(5)-pyridine directly attached N-cationic tag onto the target compounds in the presence of trifluoromethanesulfonic anhydride (Tf(2)O) without tedious sample preparation. The derivatization completed in 5 min and achieved charge labeling of the target compounds, which significantly improved the detection limits of analytes by 10(3)-folds in further analysis by matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS). The use of commercially available d(0)/d(5)-pyridine pairs facilitated isotope-coded chemical derivatization and avoided the use of isotope-labeled internal standards; the excess pyridine did not affect the signals of analytes. Utility of the NAPIQ method was examined in the identification of cholesterol and fatty alcohols in small amount of human hair sample (<0.5mg). The fluctuation of total cholesterol in human body was profiled during time by quantitatively comparing the different segments of a single strand of hair. This study combines the direct pyridinium quaternization with MALDI-FTMS, which offers a perspective and an alternative tool for the identification and quantification of substances in biological matrix by comparing d(0)/d(5) pairs, especially when isotope-labeled internal standards are unavailable.
authors.affiliation: Shanghai Mass Spectrometry Center, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, PR China.
authors.forename: Hang
authors.initials: H
authors.lastname: Wang
authors.forename: Haoyang
authors.initials: H
authors.lastname: Wang
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.forename: Yinlong
authors.initials: Y
authors.lastname: Guo
mesh_terms: D002784:Cholesterol / Q000032:analysis*; D005233:Fatty Alcohols / Q000032:analysis*; D005583:Fourier Analysis; D006197:Hair / Q000737:chemistry*; D006801:Humans; D007553:Isotope Labeling; D008698:Mesylates / Q000737:chemistry; D011726:Pyridinium Compounds / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D005233:Fatty Alcohols; D008698:Mesylates; D011726:Pyridinium Compounds; D002784:Cholesterol; C012077:trifluoromethanesulfonic acid