Method for testing pyromellitic acid anhydride purity and organic impurity

The invention provides a test method for the purity of pyromellitic dianhydride and organic impurities, which is used to test the purity of PMDA products obtained after crude products of pyromellitic dianhydride are refined and organic impurities contained in the PMDA products; the method includes the preparation of color spectrum injection samples and the analysis of the chromatograph, wherein the preparation of color spectrum injection samples includes the following steps of an ethyl esterifying reaction step and a methyl esterifying reaction step; the ethyl esterifying reaction step is that pyromellitic dianhydride samples are weighed in a container, and ethanol is added for the ethyl esterifying reaction under a counterflow condition, after the reaction is ended, products together with the redundant ethanol are transferred in a watch glass, and the watch glass is transferred in a vacuum drying oven for removing the redundant ethanol, in the end, the ethyl esterifying crystals are obtained; the methyl este