Fig. 1 (A) HPLC chromatogram of Compound D and (B) six Thai herbs in the Thai Herbal Compress ball
Previous publications reported that compound D was the main active compound. Therefore, compound D was used to prepare the calibration curve of linearity, accuracy, and precision. The linearity of compound D was determined by using five different concentrations of the crude extract of Zingiber cassumunar Roxb. in the ranges of 1-10 μg/mL.