Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, Japan.
Rapid Commun Mass Spectrom. 2012 Apr 30;26(8):978-82. doi: 10.1002/rcm.6177.
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.
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.
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.
The carbon isotope ratios of caffeine from eight tea cultivars were determined using the protocol.
通过对提取出的咖啡因进行特定化合物同位素分析（CSIA），可以确定茶的产地的真实性。元素分析-同位素比质谱法（EA-IRMS）广泛用于测量咖啡因的碳同位素比值，但对提取咖啡因的纯度有严格的要求。为了从茶叶中获得高纯度的咖啡因，通常需要重复进行传统的提取过程，大约需要 5-6 小时。为了提高咖啡因碳同位素比值的测量精度，需要一种更快速、准确的测量方法。
我们开发了一种使用气相色谱-燃烧-同位素比质谱法（GC-C-IRMS）结合我们的提取工艺来测定茶叶中咖啡因碳同位素比值的分析方案。从提取咖啡因到测定其碳同位素比值的整个过程耗时约 1.5 小时。
该方法的标准偏差小于 0.1‰（1σ）。所测的咖啡因碳同位素比值不受咖啡因进样量（0.08-0.62μg）或咖啡因从茶叶中的提取产率的影响。
使用该方案测定了 8 个茶树品种的咖啡因的碳同位素比值。
