title: Development of a methodology using gas chromatography-combustion-isotope ratio mass spectrometry for the determination of the carbon isotope ratio of caffeine extracted from tea leaves (Camellia sinensis).
abstract: BACKGROUND
  Compound-specific isotope analysis (CSIA) of the extracted caffeine can be used to determine the authenticity of the origin of tea. Elemental analysis-isotope ratio mass spectrometry (EA-IRMS), which is widely used to measure the carbon isotope ratio of caffeine, has a strict requirement for the purity of the extracted caffeine. To obtain high-purity caffeine from tea leaves, the conventional extraction process has to be repeated and usually takes about 5-6 h. To improve the measurement of the carbon isotope ratio of caffeine, a more rapid and accurate measuring method is needed.
  
  
  METHODS
  An analytical protocol was developed for the determination of the carbon isotope ratio of caffeine from tea leaves using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) combined with our extraction process. The procedure to extract caffeine and determine its carbon isotope ratio takes around 1.5 h.
  
  
  RESULTS
  The standard deviation of the method is less than 0.1‰ (1σ). The measured carbon isotope ratios were not influenced by the amount of caffeine injected (0.08-0.62 µg) or by the extraction yield of caffeine from the tea leaves.
  
  
  CONCLUSIONS
  The carbon isotope ratios of caffeine from eight tea cultivars were determined using the protocol.
authors.affiliation: Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, Japan. chenwu.violet@gmail.com
authors.forename: Chen
authors.initials: C
authors.lastname: Wu
authors.forename: Keita
authors.initials: K
authors.lastname: Yamada
authors.forename: Osamu
authors.initials: O
authors.lastname: Sumikawa
authors.forename: Akiko
authors.initials: A
authors.lastname: Matsunaga
authors.forename: Alexis
authors.initials: A
authors.lastname: Gilbert
authors.forename: Naohiro
authors.initials: N
authors.lastname: Yoshida
mesh_terms: D002110:Caffeine / Q000032:analysis*; D028241:Camellia sinensis / Q000737:chemistry*; D002247:Carbon Isotopes / Q000032:analysis; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D010936:Plant Extracts / Q000032:analysis*
chemical_list: D002247:Carbon Isotopes; D010936:Plant Extracts; D002110:Caffeine