[Application of qNMR in Standard Materials Used for the Crude Drugs]

Crude drugs and Kampo formulations derived from natural materials such as plants, animals, and minerals are multicomponent medicines that contain numerous chemical constituents. Quantitative determination of characteristic constituents for quality control is crucial for the standardization and quality assurance of natural medicines. Quantitative assays to determine marker compound contents are commonly performed using HPLC systems. In order to achieve accurate quantitative determination, it is essential to use standard materials with well-defined purities corresponding to the target analytes. Many marker compounds used as standard materials must be purified and isolated from natural products while ensuring sufficient purity. However, the composition of impurities in the standard material differs among different batches due to differences in the raw materials and their extraction, separation, and purification processes. Therefore, controlling the purity of standard materials derived from natural products is more complex than that of synthetic substances. Quantitative NMR (qNMR), which has become widely used as an absolute quantitative method for low-molecule organic compounds, makes it possible to solve these issues. qNMR has been introduced into the crude drug section of the Japanese Pharmacopoeia (JP) for evaluating the purity of standard materials used for the assay. This review outlines an example of quantitative determination using relative molar sensitivity (RMS) based on qNMR adopted in the JP and introduces the latest efforts toward the application of qNMR to standard materials used for crude drugs in this context.