Determined by high performance liquid chromatography (Chinese Pharmacopoeia 2000, Appendix VI D). Chromatographic conditions and system suitability test Octadecyl silane bonded silica gel was used as filler; methanol-0.1% phosphoric acid solution (55:45) was used as mobile phase; the detection wavelength was 278 nm; the theoretical plate number should not be less than 1500 according to the calculation of the peak of cinnamic acid. Preparation of the control solution Appropriate amount of cinnamic acid control was taken, weighed accurately, and made into a solution of 2.0 μg per 1 ml by adding water. Preparation of test solution Take 1.0ml of this product, put it in 100ml measuring flask, dilute it with water to the scale, shake well, it is obtained. Determination method: Take 20μl each of control solution and test solution, inject into liquid chromatograph, and then determine, it is obtained. Each 1ml of this product contains not less than 0.05mg of cinnamic acid (C9H8O2).