Solid-State Characterization of Buspirone Hydrochloride Polymorphs

The purpose of this study was to characterize Form 1 and Form 2 of buspirone hydrochloride, an anxiolytic medicine. The techniques used for characterization included microscopy (optical, hot stage, and scanning electron microscopy), thermal analysis (differential scanning calorimetry and thermogravimetric analysis), solid-state Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffractometry (XRPD), and Raman spectroscopy. Morphologically, Form 1 and Form 2 consist of plate and columnar crystals, respectively, with good filterability. Thermal analysis showed that the two forms are enantiotropic over the studied temperature range. The FTIR method was used successfully for the quantification of Form 1 in a mixture of Forms 1 and 2. The ratio of a characteristic peak to a reference peak and the chemometric method were used to obtain the calibration curve. The Raman peak shifts showed the difference between the two forms especially for the n-butyl group. The large number of distinguishable XRPD peaks in the region of 5° to 30° 2θ of the two polymorphs demonstrated that XRPD is a useful tool for quantitative and qualitative analysis of polymorphs.