Application of gas-liquid chromatography to the analysis of essential oils. Part VII. Fingerprinting of essential oils by temperature-programmed gas-liquid chromatography using a carbowax 20M stationary phase
Problems of obtaining reproducible results in the “fingerprinting” of essential oils by temperature-programmed gas-liquid chromatography have been examined; in particular an absorption-coating technique for the column packing is described. The requirements for standardisation of column efficiency, selectivity and reproducibility have been worked out using as a basis the method of column characterisation described by van den Dool. This column characterisation is referred to as the “g-pack” value and is determined from experimentally determined relative retention indices for a set of test substances using the even carbon numbered n-alkanes from C8 to C24. A collaborative study with Carbowax 20M as stationary phase, and a specification of g-pack values for the column packing, has resulted in the production of a method that yields reproducible relative retention indices for the test substances limonene, linalol, linalyl acetate, acetophenone, naphthalene and cinnamyl alcohol, and has been applied with satisfactory results to oils of bergamot, Jamaican ginger, Nigerian ginger, West Indian nutmeg and East Indian nutmeg. A recommended method is given for the reproducible temperature-programmed gas-liquid chromatographic finger-printing of essential oils when Carbowax 20M is used as a stationary phase.