Quantitative analysis of four major diterpenoids in Andrographis paniculata by 1H NMR and its application for quality control of commercial preparations

A quantitative proton nuclear magnetic resonance technique (qHNMR) has been successfully introduced to quantify andrographolide, dehydroandrographolide, deoxyandrographolide and neoandrographolide in Andrographis paniculata, a commonly used important traditional Chinese medicine. Creative use of trifluoroacetic acid-d, which satisfactorily resolved the overlapping signals of these compounds in crowded regions of δ 4.5-5.6 ppm in 1H NMR spectrum, made their quantification possible. Optimization of other experimental conditions, including internal standard, NMR pulse sequence, and NMR relaxation delay time, finally established the 1H NMR based quantification approach, which was validated with satisfactory accuracy, precision, repeatability, and recovery. Except for deoxyandrographolide and neoandrographolide in two compound recipes, this method was successfully applied to quantify the four major components in fourteen raw herb materials and five commercial preparations, providing quantification results in good agreement with those determined by HPLC. The inherent advantages of qHNMR, such as its rapidity and simplicity, make itself a feasible alternative to HPLC for the quality control of A. paniculata raw material and herbal preparations.