Structural studies of impurities of risperidone by hyphenated techniques

During the impurity profile of risperidone (RSP), a more polar impurity (RSP-1) and a more non-polar impurity (RSP-2) were detected in LC-MS with respect to risperidone. These impurities were isolated, enriched and were subjected to mass and NMR spectral studies. Based on the spectral data, RSP-1 and RSP-2 were characterized as risperidone N-oxide and 9-methylene risperidone, respectively. The formation of these impurities is rationalized. The structures of both the impurities were unambiguously confirmed by single crystal XRD Studies.