摘要：A spectrophotometric method for the determination of citric acid (Cit) was established by ternary complex formation among Cit, o-hydroxyhydroquinonephthalein and iron (III), and the method was applied to the assay of Cit in foods. Beer's law held up to ca. 7μg of Cit (as citrate ion) in the final volume of 10ml, the apparent molar absorptivity at 610nm and the relative standard deviation being 3.2×105 1·mol-1·cm-1 and 0.91% (n=8) for 3.8 μg of Cit. Though tartaric acid, malic acid, ascorbic acid, phosphoric acid and quinic acid in small amounts affected the determination of Cit, the effects of these substances could be minimized by the standard addition method. The coexistence of monocarboxylic acids, such as acetic acid and lactic acid, and polycarboxylic acids having no hydroxy groups, such as maleic acid, succinic acid and oxalic acid, scarcely interfered with the assay, even in 20-to 100-fold molar excess over Cit. Recovery of Cit from various samples were satisfactory (95-103%). Compared with the values obtained by the pentabromoacetone method and the enzymatic method, the values determined by this method were somewhat larger, but the present method is simple and highly sensitive, and may be useful and convenient for the determination of Cit in foods.
