Essential oils from eleven Mentha species were obtained by Deryng hydrodistillation and analysed by GC-MS: 44 compounds were identified. The most abundant were menthone, isomenthone, menthol, carvone, piperitone oxide, D-limonene and eucalyptol. Chemometric similarity measures and principal component analysis were calculated, allowing comparisons based on secondary metabolite content. The fingerprints may be helpful in chemotaxonomy.
Micro-thin-layer chromatography in two-dimensional (2D-mTLC) mode in normal- (NP) and reversed-phase (RP) systems by use of cyanopropyl-bonded stationary phases was applied to make fingerprints of 11 species of Mentha genus and two finished pharmaceutical products. Non-aqueous eluents were used in the NP systems. Mixtures of acetonitrile with water and methanol with water were used in the RP chromatographic systems. Optimization of one-dimensional systems was performed by determining RM vs. composition of mobile phase dependencies for standards occurring in various Mentha sp. On the basis of these dependencies, the most selective chromatographic systems for each run were chosen. Then most selective eluents were applied to optimize two-dimensional systems by creating RF in NP systems vs. RF in RP systems correlations. The best two-dimensional systems were chosen on the basis of R(2) values for RF vs. RF correlations (the lowest values of R(2) coefficients). The 2D-mTLC optimized systems were applied to separate phenolic compounds and make fingerprints of the examined plant materials.
The dried aerial parts of 12 plants of Ocimum spp. were extracted with the Soxhlet apparatus using dichloromethane and methanol as solvents. A micro-TLC system with silica and a normal-phase solvent system (propan-2-ol-n-heptane-formic acid) was used for the chemometric analysis of 12 selected basil methanolic extracts. Some indices of similarity (Pearson's correlation coefficient, determination coefficient, congruence coefficient, and Euclidean, Manhattan (city-block), Chebyshev, and Hausdorff distances) were calculated on the basis of thin-layer chromatograms using ImageJ software. Principal component analysis was also performed. The method allowed the comparison of the analyzed extracts and confirmed the identities of two selected unknown plants.
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