Pharmacognostic specification of Acorus calamus rhizomes in Thailand

Acorus calamus Linn. dried rhizomes has been traditionally used as crude drug in Thai remedies such as Pra-Sa-Plai, Pra-Sa-Karn-Plu and Wi-Sum-Pa-Ya-Yai. This study aimed to report the current information on the pharmacognostic properties of A. calamus dried rhizomes and analysed the chemical constituents of calamus oil by gas chromatography–mass spectrometry (GC/MS). The rhizomes were collected from 15 habitats located at various regions throughout Thailand. The whole plant of A. calamus was illustrated in detail. The crude drug was traditionally prepared by cleaning, cutting and drying in a hot air oven. The macroscopic characters were cylindrical pieces, variable in size, pale brown with longitudinal furrows and circular, with pitted scars of rootlets, internally whitish and spongy and odor aromatic. The anatomical and histological characterizations were starch granules, secretory sac containing volatile oil and prismatic crystal of calcium oxalate. The total ash, acid insoluble ash, loss on drying, ethanol–soluble extractive, water–soluble extractive water content and volatile oil content of 4.49 ± 0.15, 0.83 ± 0.07, 12.23 ± 0.34, 7.32 ± 0.29, 9.53 ± 0.45, 13.15 ± 0.46 and 1.37 ± 0.11 % dry weight respectively. Thin-layer chromatographic fingerprints of ethanolic extracts of A. calamus dried rhizomes were studied using toluene and ethyl acetate (9:1) as mobile phase. Detection under ultraviolet light (254 nm and 365 nm) as well as spraying with anisaldehyde-sulfuric acid reagent showed the dominant band of α-asarone and β-asarone at Rf = 0.58. The calamus oil consisted of β-asarone (67.5 %) and α-asarone (22.4%) as main components. Linearity range of β-asarone was 0-0.5 mg/ml with correlation coefficient (r2) of 0.997 and α –asarone was 0-0.1 mg/ml with correlation coefficient (r2) 0.998.. LOD and LOQ for β-asarone were 0.0280 and 0.0850 mg/µl of injected sample, 0.0126 and 0.0382 mg/µl of injected sample for α-asarone respectively. The precision was evaluated by the % RSD of repeatability and intermediate precision. β-Asarone was between 1.45-4.67 % RSD and 0.95-2.21 % RSD and α-ssarone showed 2.48-6.58 % and 1.29-3.00 % RSD respectively. The average recoveries were 100.11-100.40 % in β-asarone and 100.17-100.80 % in α-asarone. The quantitative results showed that β-asarone was the highest content in calamus oil (0.259 ± 0.035 mg/µl of oil) whereas α-asarone was found at 0.120 ± 0.020 mg/µl of oil. This study provides scientific information for the quality control of A. calamus dried rhizomes including calamus oil composition in Thailand that leads to safe use of this crude drug.