分光光度法测定茶叶中茶单宁含量的研究

Determination of Tea Tannin by UV Spectrophotometry

建立了测定茶叶中茶单宁质量分数的分光光度测定方法。利用茶单宁具有的还原性,将Fe3+还原为Fe2+,以邻二氮菲为显色剂,在酸性介质中测定茶单宁的质量分数。考察了检测波长、邻二氮菲加入量、Fe^(3+)用量、pH等对测定结果的影响。最佳测定条件为:检测波长为510nm,邻二氮菲加入量为5.0mL,抗干扰剂EDTA的加入量为1.0mL,pH为4.4,反应时间为30min。在此条件下其标准曲线在0~2.0mg/L范围内呈线性关系,回归方程为:A=0.4827C+0.009,线性相关系数R=0.9891,摩尔吸光系数ε510nm=1.1×104 L/(mol·cm)。加标回收率在99.14%~102.07%之间,RSD为2.71%。该方法操作简便,灵敏度高,费用低廉,可用于茶叶中茶单宁质量分数的分析。

A UV Spectrophotometric method for the determination of tea tanninwas established in this paper. The method was based on the fact that Fe3＋ can be restored by tannin to Fe2＋ , and Fe2＋ canreact with o-phenanthroline to form salmon pink complexin acid medium, by whichthe tea tannin was determined. In order to obtain the optimal determination results, 4 crucial deter- mination parameters, including detection wavelength.pH、 amounts of chromogenic reagent and Fe3＋ concentration, were investigated. Results showed that the optimal values of the above parameters were as follows： detection wavelength 510 nm, o-phenanthroline amount 5.0 mL, hy- droxylamine hydrochloride amount 2.0 mL, EDTA amount 1.0 mL, pH 4.4, and Fe3＋ concentration 0.010 moL/L. Under such conditions, a good liner relationship between absorbance（A） and tannin concentration（C） in the range 0～ 2.0 mg/L was observed, which could be expressed as A = 0. 482 7C＋0. 009, （r = 0. 989 1）, recovery rate was 99. 14%- 102.07%, RSD was 2.71%. The method is easy to operate, owning good sensitivity, and low cost, which could be applied to the indirect determination tannin in tea.