Indications of the chemical structure of oxygen-containing constituents of volatile oils by capillary gas chromatography using one or two modified beta- and alpha-cyclodextrin phases

Three modified beta-cyclodextrin (CD) and two alpha-CD phases were used at 125 and 150 degrees C to gas chromatograph 22 diverse oxygen-containing substances from volatile oils. Percentage changes with temperature in retention times relative to n-undecane were determined. Solutes showing significant decreases include acyclic geraniol and citronellol, plus three cyclic alcohols. A smaller decrease than the average 90%, or even an increase in relative retention on some phases was shown by three non-alcohol bicyclics and menthone, all saturated molecules. At 125 degrees C, results are compared for pairs of beta-CDs, the dipentyl modification proving very useful. Percentage increases in relative retentions observed against hydroxypropyl-dimethyl- or trimethyl-CDs could indicate solutes to be an alcohol (bicyclic, monocyclic or acyclic), another type of bicyclic, an aromatic or a carbonyl compound. The two methods offer good structure indications for unknown solutes using either temperature changes on one CD phase, or on two phases at one temperature.