测定抗坏血酸的亚甲蓝褪色光度法

Determination of Ascorbic Acid by Spectrophotometry with Fading Reaction of Methylene Blue

确定了亚甲蓝与抗坏血酸褪色反应的最佳条件 ,在pH=2的缓冲溶液和对氨基苯磺酸存在的条件下 ,抗坏血酸能够很快还原亚甲蓝并使之褪色 ,褪色反应的体系具有很好的稳定性。该反应的摩尔吸光系数为2.0×103 L·mol-1·cm-1,线性范围0.4～40.0mg/L。该法具有优良的选择性 ,常见的能够与抗坏血酸共存的阴、阳离子和还原剂、表面活性剂不干扰测定 ,应用于药品、饮料、蔬菜中抗坏血酸的测定 。

Methylene blue is reduced and faded by ascorbic acid in the medium of dilute hydrochloric acid(pH=2) with sulfanilic acid as a catalyst. The optimal conditions of the fading reaction were investigated in detail. Based on this fading reaction a new spectrophotometric method for the determination of ascorbic acid was established. The apparent molar absorptivity of the system was ε660=2.0×103 L·mol-1·cm-1, whereas the linear range was 0.4～40.0 mg/L for ascorbic acid. The method is rapid, sensitive and selective. Common coexisting ions, reducing agents and surfactant do not interfere with the determination. This method was used to determination of ascorbic acid in pharmaceuticals, soft drinks and vegetables with satisfactory results.