Applied Chemistry Department, Faculty of Chemistry, University of the Basque Country, Manuel Lardizabal 3, 20018 Donostia-San Sebastián, Spain.
Talanta. 2003 Oct 17;61(2):139-45. doi: 10.1016/S0039-9140(03)00236-4.
This paper reports a quantitative determination method of (-)-epicatechin in apple juices by measuring of its signal at 7.05 ppm in the (1)H NMR spectrum. It is a direct method that does not need any previous derivatization. 1,3,5-Benzenetricarboxylic acid was added to the juice as internal standard for the determination of the absolute concentration of (-)-epicatechin. Ascorbic acid was also added to avoid enzymatic oxidation of the phenolics and to adjust the pH at 2.74, since the chemical shift of some compounds varies with the pH. Standard addition method accomplished with the juices of two different varieties of apples gave recoveries between 95 and 109%. The precision of the method was tested for repeatability (n=5) and reproducibility (n=13) obtaining a coefficient of variation of 5.8 and 8.6%, respectively. Limit of detection, calculated from "3S(y/x)+intercept", is 24 mg l(-1).
本文报道了一种通过测量苹果汁中（1）H NMR 谱在 7.05 ppm 处的信号来定量测定（-）-表儿茶素的方法。这是一种不需要任何衍生化的直接方法。1,3,5-苯三甲酸被添加到果汁中作为（-）-表儿茶素绝对浓度测定的内标。还添加了抗坏血酸以避免酚类的酶促氧化，并将 pH 值调节至 2.74，因为一些化合物的化学位移随 pH 值而变化。用两种不同品种的苹果汁进行的标准加入法回收率在 95%至 109%之间。该方法的精密度通过重复性（n=5）和再现性（n=13）进行测试，得到的变异系数分别为 5.8%和 8.6%。根据“3S(y/x)+intercept”计算的检测限为 24mg l(-1)。
