2D-IR correlation analysis of deteriorative process of traditional Chinese medicine 'Qing Kai Ling' injection

The traditional Chinese medicine 'Qing Kai Ling' injection after deterioration is distinguished from the original formulation using Fourier-transform infrared spectroscopy (FTIR) and two-dimensional correlation infrared spectroscopy (2D-IR). The IR spectra of the injections before and after deterioration are so similar, that it is very difficult to distinguish them by using the conventional approach. However, the higher spectral resolution and more structural information provided by 2D-IR analysis makes the identification possible. According to the results of 2D correlation analysis, the band at 1611 cm(-1) in IR spectra, in fact, consists of the overlap of three bands at 1572, 1667 and 1729 cm(-1), which are assigned to the alkaloids (heterocyclic compounds), flavone derivatives, and carbonyl compounds in the injection, respectively. Interestingly, the autopeak at 1667 cm(-1) disappears in synchronous spectrum of the deteriorated 'Qing Kai Ling' injection. It is suggested that the deterioration of the injection in air at room temperature be due to the oxidation of the flavone compounds mainly. As all intensities of the correlation peaks involved with the band in 1059 cm(-1) decrease greatly, it is assigned to the thermal decomposition of the glucoside components. Hence, it can conclude that the oxidation of the flavone compounds and the decomposition of the glucoside components are some of the main causes concerning to the deterioration of 'Qing Kai Ling' injection at ambient temperature. Thus, the 2D-correlation analysis provides a powerful method for the quality control of the traditional Chinese medicine injection.