Optimization for Decocting Later of Menthae Herba in Eungyo-San, a Herbal Formula, Using Response Surface Methodology with Gas Chromatography/Mass Spectrometry

BACKGROUND: “Decocting later” is important procedure for the extraction of herbal medicines containing volatile compounds. OBJECTIVE: This study was performed to investigate optimal conditions for “Decocting later” of Menthae herba in Eungyo-san (EGS) and correlation between extraction variables and the yields of d/l-menthol, a marker compound of Menthae herba. MATERIALS AND METHODS: The decocting temperature, total decocting time, and decocting later time were chosen as individual variables, and the yield of d/l-menthol was set as the response value which were calculated by using a Box-Behnken design (BBD). The amount of d/l-menthol was quantified using gas chromatography/mass spectrometry. RESULTS: Response surface methodology (RSM) was used to predict optimal conditions for decocting later of Menthae herba into the formula. Optimal conditions for “Decocting later” from RSM were as follows: 100.63°C of decocting temperature; 82.95 min of total decocting time; 19.11 min of decocting later time. Both decocting temperature and total decocting time showed significant correlation with the yield of d/l-menthol. CONCLUSIONS: These results suggest that the decocting temperature and total decocting time were influential factors, and RSM can be applied for optimizing the conditions of “Decocting later” of Menthae herba in EGS. SUMMARY: Gas chromatography/mass spectrometry method developed was applied to quantify the d/l-menthol, a volatile compound in Menthae Herba, in Eungyo-san decoction (EGS); d/l-Menthol was extracted in the chloroform layer of the partition between EGS decoction and chloroform. A Box-Behnken design produced the predicted response values (yield of d/l-menthol in EGS) from the actual response values with individual variables including decocting temperature, total decocting time, and decocting later time. Optimal conditions for “Decocting later” of Menthae Herba in EGS obtained from the response surface methodology were 100.63°C of decocting temperature, 82.95 min of total decocting time, and 19.11 min of decocting later time. Abbreviations used: KM: Korean medicine; EGS: Eungyo-san; GC/MS: Gas chromatography/mass spectrometry; RSM: Response surface methodology; SIM: Selected ion monitoring; LOD: Limits of determination; LOQ: Limits of quantification; RSD: Relative standard deviation; ANOVA: Analysis of variance; BBD: Box-Behnken design.