Most drugs exist in the form of crystals, using X-ray diffraction, we can obtain the diffraction information of drug characteristics for each different crystal type. Even for solid preparations containing multiple components, the powder X-ray diffraction patterns corresponding to the raw material and excipients will not change, which can be used as the basis for qualitative judgment of drug crystal type. Therefore, for unknown drug samples, through PXRD, we can quickly compare the position and intensity of diffraction peaks in the measured map, and find the diffraction pattern matching the crystal structure of the raw material from the existing database, so as to accurately identify the crystal type of the drug.

The qualitative research of PXRD on drug crystal type is mainly divided into two aspects: (1) the identification of polycrystalline type of the bulk drug. (2) Identification of raw materials in solid preparations. The effect of excipients or small molecular additives on the polycrystalline form of raw materials in solid preparations was investigated by PXRD.