Determination of Cephalexin Crystallinity and Investigation of Formation of its Amorphous Solid by Chemoinformetrical near Infrared Spectroscopy

Abstract

The crystallinity of cephalexin (CEX) was evaluated by chemoinformetrical near infrared (NIR) spectroscopy. The molecular interaction of ground amorphous solid of CEX was investigated by the method. Six kinds of standard material with various degree of crystallinity were prepared by the physical mixing of crystalline and ground amorphous CEX. X-ray powder diffraction profiles and NIR spectra were recorded for the standard samples. Chemoinformetric analysis was performed on the NIR spectral data sets by principal component regression (PCR). The correlation between the actual and the predicted crystallinity of CEX using the conventional X-ray diffraction method showed a straight line relationship with a slope of 1.000, an intercept of −5.77 × 10−4 and a correlation coefficient of determination ( R2) of 0.986. A NIR spectrum of amorphous CEX showed significantly different peaks at 1530 and 1620 nm due to the NH2 group from those of crystalline CEX. PCR was performed on various kinds of pre-transformed NIR spectral data sets of standard samples of CEX. To minimise the standard error of cross-validation ( SECV), the spectral data sets were subjected to the leave-one-out method. The combination of normalization and multiplicative scatter correlation treatments yielded the lowest SECV values. Based on a three-components model, a plot of the calibration data between the actual and CEX crystallinity predicted by the NIR method was obtained. The plot showed a straight line ( Y = 0.993X + 0.262; R2 = 0.992; n = 18). The mean bias for the NIR and X-ray powder diffraction methods were calculated to be 3.40 and −1.58% and their mean accuracy were 7.70 and 5.76%, respectively. NIR spectral changes of crystalline CEX during grinding suggested the intermolecular hydrogen bonds between the amino and the carboxyl groups are destroyed and the crystals are transformed into the amorphous CEX.