萘茜光度法直接测定茶叶中的微量铜

茶叶中含有许多对人体有益的微量元素 (如Cu ,Zn ,Mn等 )而倍受人们的青睐。在中国、日本和许多其他国家都有茶文化。因此 ,有必要对茶叶中微量元素的含量进行准确测定。目前微量铜的测定方法有火焰原子吸收光谱法1 ,2 ] 、荧光法3,4] 、分光光度法5～8] 和流动注射分析法9～ 1 2 ] 。测定铜方法很多 ,由于分光光度是一种经典的方法 ,具有快速、灵敏度高 ,选择性好 ,特别是不要求贵重仪器等特点 ,它仍是检测铜重要手段之一。本文研究发现 ,在 0 1mol·L- 1 NH4Ac介质中 ,在表面活性剂SDS的存在下 ,痕量Cu(Ⅱ )与 5 ,8 二羟基 1 ,4 萘醌 (Naph)络合具有灵敏的显色反应 ,有色络合物的最大吸收波长为 330nm ,而Naph的最大吸收波长为5 1 5nm ,建立了测定痕量Cu(Ⅱ )的分光光度法。本法快速准确、灵敏度高 ,选择性好 ,可满意地测定茶叶中的微量铜。

Direct Determination of Trace Copper in Dry Tea by Spectrophotometry with Naph

In the ethanol/water medium containing 0.1 mol.L-1 ammonium acetate (NH4Ac) and 1.5% (w/v) sodium dodecyl sulfate (SDS), the complex chromogenic reaction of trace Cu (II) with 5, 8-dihydroxy-1, 4-naphthoquinone (Naph) has been studied. Based on this study, a novel spectrophotometric method for determining trace Cu (II) has been developed. The results show that the maximum absorption of the colored complex is at 330 nm, the molar absorptivity is 1.8 x 10(4) L.mol-1.cm-1, the detection limit of the method is 0.3 mg.L-1 for Cu (II) and Beer's law is obeyed for Cu (II) in the range of 0.0-4.5 mg.L-1. The linear regress equation of A is 0.290 CCu(II) (mg.L-1) +0.015, the correlation coefficient is 0.9981, the standard recovery of Cu (II) is in the range of 97.9%-104.1% (n = 6) and the relative standard deviation (RSD) is in range of 1.6%-5.1% (n = 6). Both of the precision and accuracy are suitable to microanalysis. The method was applied to trace copper determination in dry tea samples with satisfactory results.