紫外分光光度法快速测定果蔬及饮料中维生素C含量的研究

Study of Direct Ultraviolet Spectrophotometry on the Determination of Ascorbic Acid in Fruits, Fruit Juices and Soft Drinks

维生素C在紫外（UV）谱区243，267nm处有吸收峰，且在碱性条件下不稳定，当pH达12～13时，10min其破坏率达95％以上，利用碱处理前后吸光度的变化可以消除背景干扰测定VC含量。比色液VC含量在0．3～25μg·mL－1服从Beer－Lambert定律，准确度、精确度、回收率等实验表明，本法快速、准确、可靠，适用于大多数果蔬和除了含有高浓度咖啡因、糖精、焦糖和单宁以外饮料VC含量的测定。

Direct ultraviolet spectrophotometry through alkaline treatment as a fast and simple analytical method for the determination of ascorbic acid in fruits, fruit juices and soft drinks was developed. The optical maximum absorption of vitamin C was 243 nm at pH2. The detection limit was 0. 3~50μg·mL－1. It was found that the alkaline treatment method can be used as a background correction in blank, because more than 95% vitamin C was destroyed in 10 min after alkaline treatment (pH12 ~ 13). The interferences in about fourty components of the fruit juices, mainly the natural substances and additives were studied. No significant interferences were observed for most of the samples tested.This method was found to be applicable to most fruits, fruit juices and soft drinks except those that were unstable to alkaline treatment , and were deeply colored, or contained high concentration of caffeine, saccharin, caramel and tannic acid.