Development of HPTLC method for determination of α-terpinyl acetate, and evaluation of antioxidant properties of essential oils in Elettaria cardamomum

Purpose: To develop a simple and reliable protocol for high performance thin layer chromatography (HPTLC) quantification of α-terpinyl acetate in oils extracted from Elettaria cardamomum, and to study relative antioxidant potential of oils obtained from three varieties of fruits of E. cardamomum. Methods: Essential oil was extracted separately from the fruits of three varieties of E. cardamomum, viz, Valley-green, Palakuzhi, and ICRI-2, using hydro-distillation method. In the development of an HPTLC method, standard α-terpinyl acetate was subjected to chromatography on aluminium-backed silica gel 60 F₂₅₄ plates using a mobile phase of n-hexane: ethyl acetate (8:2, v/v), and quantified at 665 nm through densitometric analysis. The antioxidant property of essential oil of each cultivar was determined with respect to 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical scavenging assays, as well as ferric reducing assay. Results: The developed HPTLC method showed a good resolution for α-terpinyl acetate, with Rf of 0.64 ± 0.01, and also showed good linearity of the calibration plots (r² = 0.9982). The HPTLC method was validated as per ICH guidelines, and used for the determination of α-terpinyl acetate in the essential oils. The valley green variety of E. cardamomum had the highest content of α-terpinyl acetate (55.36 ± 1.33 %w/w). The inhibitory capacity (IC₅₀ value) for the oil of valley green variety as determined using DPPH and ABTS methods was 378.2 and 19.87 μg/mL, respectively. Conclusion: The proposed HPTLC method is suitable for routine analysis of α-terpinyl acetate in medicinal herbs, and it reveals the role of α-terpinyl acetate in the antioxidant efficacy of cardamom oil.