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)

RATIONALE: 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% (1s). The measured carbon isotope ratios were not influenced by the amount of caffeine injected (0.08-0.62 mg) 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. Copyright (C) 2012 John Wiley & Sons, Ltd.