Improvement of Official Chemical Analysis of Tea (Part 3)

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  • 茶の公定分析法の改良(第3報)
  • Examination of Tannin Determination
  • タンニン定量法の検討

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The accuracy of analysis and the personal error of analyst were examined with the Lowenthal method and the colorimetric method using ferrous tartrate reagent for determination of tannin in tea except black tea.<BR>The colorimetric method was more accurate than the Lowenthal method and the error of analytical value obtained by the colorimetric method was one-third of that by the Löwenthal method. Therefore, the colorimetric method was decided as the official method for determination of tea tannin.<BR>The accuracy of analysis was computed as C. V. 1.52%; the error accompanied with a single determination by an analyst was C. V. 5.42% and that with a mean value of double determinations by an analyst was C. V. 5.31%.<BR>Calibration curve of (-)-epicatechin gallate was shown to be suitable for measurement of tea tannin (catechins). Ethyl gallate was also able to be used as substitute for (-)-epicatechin gallate. As I mg. of ethyl gallate is equivalent to 1.5 mg. of (-)-epicatechin gallate, the amount of ethyl gallate must be converted to that of (-)-epicatechin gallate.

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