Simultaneous determination of menthol and eucalyptol by the densitometric HPTLC method in some external analgesic formulations

Several analgesic pharmaceutical formulations dispensed for external use contain menthol and eucalyptol. Simultaneous determination of the two monoterpenes was achieved utilizing high-performance thin layer chromatography (HPTLC) densitometric analysis. The stationary phase composed of silica gel 60 F₂₅₄ (E-Merck, Germany) glass-backed plates coated with 0.2 mm layers. The used mobile phase hexane: ethyl acetate 8: 2 (%, v/v) resulted in sharp, symmetrical and well-resolved peak at an R_f value of 0.34 ± 0.04 and 0.56 ± 0.04 for menthol and eucalyptol, respectively. Linearly range for menthol was 100-800 ng/spot (r² = 0.9979), whereas that for eucalyptol was 52.25-1107 ng/spot (r² = 0.9937). The developed method was validated following the International Conference on Harmonization guidelines. The method was found to be simple, accurate, time saving and enable analyses of many samples simultaneously.