title: N-alkylpyridinium quaternization for assisting electrospray ionization of sterols in oil by quadrupole-time of flight mass spectrometry.
abstract: BACKGROUND
  The illegal cooking oil has become a serious social problem and raised widespread alarm recently. However, an efficient and sensitive technique for identifying the potential illegal cooking oil is still unavailable, especially when mixed with the ordinary ones; there is an urgent need to develop an efficient method for identifying the illegal cooking oil. Sterols in the cooking oil could be used as an indicator to identify the source and quality of oil by detecting the kinds of phytosterols and zoosterols. However, those sterols are difficult to be ionized by electrospray ionization, which resulted in the low sensitivity in electrospray ionization (ESI)-mass spectrometric (MS) analysis.
  
  
  METHODS
  N-alkylpyridinium isotope quaternization was extended to charge label sterols in different cooking oil and attached N-cationic pyridinium tag onto the sterols in the presence of trifluoromethanesulfonic anhydride (Tf2 O); the kinds of sterols were identified and quantified by comparing d0 /d5 pairs and product scan from ESI-quadrupole-time of flight (Q-TOF) MS analysis.
  
  
  RESULTS
  The derivatized sterols were attached with permanent charge, resulting in the significant enhancement of ionization in ESI-Q-TOF MS analysis. The detection limits of analytes were improved to 0.02-0.05 ng/mL; different kinds of phytosterol, zoosterol and oxides were identified and quantified by comparing d0 /d5 pairs from full scan and product scan. The method was applied in the detection of zoosterol for identifying the potential recycled cooking oil, even when the illegal oil has been blended into the ordinary one. More zoosterol was detected in the recycled oil compared with other cooking oil.
  
  
  CONCLUSIONS
  The use of N-alkylpyridinium isotope quaternization method provided an alternative method for identifying the potential illegal cooking oil.
authors.affiliation: Shanghai Mass Spectrometry Center, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Lingling Road 345, 200032, Shanghai, China; Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Zuchongzhi Road 555, 201203, 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: Jiapeng
authors.initials: J
authors.lastname: Leng
authors.forename: Tingting
authors.initials: T
authors.lastname: Cai
authors.forename: Yinlong
authors.initials: Y
authors.lastname: Guo
mesh_terms: D004042:Dietary Fats, Unsaturated / Q000032:analysis*; D005504:Food Analysis / Q000379:methods*; D057230:Limit of Detection; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013261:Sterols / Q000032:analysis*
chemical_list: D004042:Dietary Fats, Unsaturated; D013261:Sterols
keywords: chemical derivatization; illegal cooking oil; isotope-coded reagent; pyridinium quaternization; quadrupole-time of flight mass spectrometry