邻苯二甲酸酐(以下简称苯酐)用途很广,常用于制药、染料、增塑剂、油漆、合成纤维等。电器行业常用它作为环氧树脂的固化剂。其中的苯二甲酸(以下称游离酸)的含量,直接影响环氧树脂浇铸质量。测定苯酐中的游离酸有多种方法。古典方法采用热苯溶解苯酐,过滤,再以水溶解游离酸,以碱滴定。该法不仅消耗大量有毒的苯,且热苯温度若稍有下降,则溶解不完全,实验精度较差。目前国外多采用英国标准方法,或国际标准协会(The InternationalOrganization for Standardization)方法,它们都是利用不含水份的三乙基胺有机溶液滴定游离酸,不过后者进而采用了电位滴定。该法最大的优点在于整个实验中没有任何机会使苯酐与水接触,避免了边滴定边水解产生邻苯二甲酸的现象,结果不致偏高.由于部分试剂和仪器的限制,国内尚未普遍采用。目前我国工厂实验室应用较多的除热苯溶解法外,是由日 Phthalic anhydride (hereinafter referred to as phthalic anhydride) is widely used, commonly used in pharmaceuticals, dyes, plasticizers, paints, synthetic fibers. It is commonly used as a curing agent for epoxy resin in the electrical appliance industry. Which phthalic acid (hereinafter referred to as free acid) content, a direct impact on the quality of epoxy casting. There are several ways to determine the free acid in phthalic anhydride. The classical method uses hot benzene to dissolve phthalic anhydride, filtering, and then dissolving the free acid in water to titrate with alkali. The method not only consumes a large amount of toxic benzene, and if the temperature of hot benzene decreases slightly, the dissolution is incomplete and the experimental precision is poor. At present, foreign countries use the British standard method, or the International Organization for Standardization (The International Organization for Standardization) method, which is the use of water-free triethylamine organic solution titration free acid, but the latter followed by potentiometric titration. The biggest advantage of this method is that there is no chance to make phthalic anhydride contact with water in the whole experiment, which avoids the phenomenon of phthalic acid hydrolysis by edge titration and the result is not too high. Due to the limitations of some reagents and instruments, it has not been widely used in China. At present, the application of more laboratories in China in addition to hot benzene dissolved outside, by the day