Infrared microspectroscopic identification of marker ingredients in the finished herbal products based on the inherent heterogeneity of natural medicines.

Finished herbal products (FHPs) are preparations made from one or more herbs. The first stage in assuring the quality, safety, and efficacy of FHPs is to identify the herbs in the products. A new simple and quick method is developed in this research to detect the marker ingredients in FHPs. The inherent chemical heterogeneity of herbs and FHPs makes it possible to resolve different ingredients, without any additional separation or labeling, by infrared microspectroscopic imaging. Therefore, multiple marker ingredients in FHPs can be recognized directly and simultaneously by the infrared microspectroscopic identification method. As an example, all six kinds of herbs in Liuwei Dihuang Wan are identified through the following steps: (1) Each herb is characterized by infrared spectroscopic imaging, then the spectra of the main ingredients are calculated by the combination of principal component analysis, independent component analysis, and alternating least squares. (2) One marker ingredient is chosen for each herb. Ten typical pixels, the spectra of which best match the calculated spectrum of the marker ingredient, are selected by partial least squares target. The average spectrum of the typical pixels is taken as the marker spectrum. (3) Correlation coefficients between the typical pixel spectra and the marker spectrum are calculated. The acceptance correlation threshold is determined through the beta distribution function and then validated by positive and negative samples. (4) Using the above marker spectra and correlation criteria, herbs in the model mixture and the commercial product are identified. Good recognition results reveal the potential of the infrared microspectroscopic identification method in the quality control of herbs and FHPs.