Background: Lanthanum carbonate hydrate is used to treat hyperphosphatemia in patients with end-stage renal disease. Impurities of lanthanum carbonate in the form of decarboxylated bases may be generated during manufacture or storage, often at low levels of 1%. If analyzed by the XRPD single-peak method, the detection limit cannot be met.

Solution: The Rietveld full-spectrum fitting method can avoid sources of error such as meritocratic orientation by mathematical correction, and its quantitative accuracy and reliability far exceed those of the traditional single-peak method, and it can be tested without standards and pre-made calibration curves. However, this method needs to know the crystal structures of all phases in advance. Currently, only the crystal structure of the impurity alkali carbonate Form II is available in the database, and the crystal structure of the main phase hydrated carbonate is still missing, which needs to be analyzed by MicoED first.

Process: 

1. Through MicroED, it is fast and accurate enough to obtain the crystal structure information of lanthanum hydrate carbonate.
2. Combined with the existing structural data of lanthanum carbonate in the database, quantitative analysis was performed by Rietveld full-spectrum fitting method, and the results showed that the content of lanthanum carbonate impurities in the base form was 1.04%.