Conventional Methods of Sample Preparation for Quality Control of Chinese Medicines

Sample preparation is an important and time-consuming step in quality control of herbal medicine. Due to the state of most solid samples, their constituents should be transferred to solvents from the matrix before analysis. One of the traditional sample preparation techniques is called "solid–liquid extraction". The classical solid–liquid extraction methods include decoction, reflux extraction, steam distillation, Soxhlet extraction, and ultrasonic-assisted extraction. Those classical extraction methods are even more widely used in routine quality control of herbal medicines than some modern extraction methods due to low investment in equipment and easy operation. In this paper, the classical extraction methods used for sample preparation in quality control are summarized, which may provide some ideas for the development of new quality control methods for herbal medicine in the future.