Application of a Quantitative Proton Nuclear Magnetic Resonance Method for the Determination of Protopine in Radix Dactylicapnotis

Background: The Bai ethnologic herb Radix Dactylicapnotis, the root and tuber of Dactylicapnos scandens (Papaveraceae), is used for clearing heat, relieving pain, and achieving hemostasis and antihypertensive effects. Objective: The study aimed to develop a quantitative method for determining the protopine content in Radix Dactylicapnotis by using proton nuclear magnetic resonance (¹H NMR) spectroscopy. Methods: The deuterium solvent, internal standard, and NMR parameters were optimized. The quantitative method was validated by linearity, precision, accuracy, repeatability, and stability, as well as limit-of-detection (LOD) and limit-of-quantitation (LOQ) assays. Results: A mixture solution consisting of 500 μL of DMSO-d6 and 20 μL of D2O enabled satisfactory separation of the signals to be integrated into the ¹H NMR spectrum. Trimethyl benzene-1,3,5- tricarboxylate (TMBT) was selected as an internal standard. The integration of δ 6.05-6.08 corresponding to OCH2O was selected to quantify protopine. The developed quantitative method was found to be precise and accurate and to exhibit excellent linearity and range. The protopine content in Radix Dactylicapnotis could be quantified accurately using the featured signal. Conclusion: This is the first study to report quantitative ¹H NMR determination of protopine in Radix Dactylicapnotis. The study results indicate that quantitative ¹H NMR represents a feasible alternative to HPLC-based methods for the quantitation of protopine in Radix Dactylicapnotis, and is suitable for the quality control of Radix Dactylicapnotis.