Abstract: An ultra-high performance liquid chromatography (UPLC) method for the simultaneous determination of 17 amino acids in the dried rhizome of Lycopus lucidus Turcz. var. hirtus Regel collected from six different habitats in China was established using pre-column derivatization with phenyl isothiocyanate (PITC). The chromatographic separated was achieved on an ACQUITY UPLC BEH C18 column (2.1 mm × 150 mm, 1.7 μm) within 19 minutes using a mobile phase composed of 0.1 mol/L sodium acetate solution and 80% acetonitrile solution (adjusted to pH 6.5 with acetic acid). The detection wavelength was set at 254 nm, the column temperature at 40 ℃, and the flow rate of sample loading at 0.2 mL/min. The results showed for all the 17 amino acids, a good linear relationship (r ≥ 0.999 0) was obtained within their respective concentration ranges. The average recoveries were 89.69%–106.02% with relative standard deviations (RSDs) ranging from 0.44% to 2.60%. The limits of detection (LODs) were 0.020–0.110 μg/mL, and the limits of quantitation (LOQs) were 0.067–0.368 μg/mL. The 17 amino acids were all detected in the hydrolysate of L. lucidus Turcz. var. hirtus Regel, including seven essential amino acids and nine medicinal amino acids. The ratios of essential amino acids (EAAs) to total amino acids (TAAs) were between 23.99% and 29.36%, and the ratios of medicinal amino acids (MAAs) to TAAs ranged between 68.44% and 74.16%. There existed a significant difference in the contents but not types of amino acid among rhizome samples from different geographical origins. Aspartic and glutamic acid were the most abundant amino acids in all the samples, and their average contents were 13.338 and 8.478 mg/g, accounting for 26.32% and 16.73% of TAAs, respectively. The habitats were divided into 3 categories by cluster analysis. Among the habitats, the samples collected from Heze, Shandong province and Wanzhou district, Chongqing had the highest and lowest amino acid contents (81.663 and only 19.463 mg/g), respectively. In conclusion, the dried rhizome of L. lucidus Turcz. var. hirtus Regel has high nutritional and medicinal value, and this study can provide basic data for the quality evaluation and utilization of this plant.

Key words: Lycopus lucidus Turcz. var. hirtus Regel; amino acids; phenyl isothiocyanate; ultra-high performance liquid chromatography; essential amino acids; medicinal amino acids