Waxes and fatty acid alkyl esters are minor components used as official parameters to control the authenticity and quality of a high-value olive oil product. A poor measurement can lead to a misleading classification of the oil. The official method requires their analysis together by capillary gas chromatography equipped with a flame ionization detector and an on-column injector to avoid discrimination and thermal degradation. The degradation can occur to a different extent if different (and not properly optimized) injectors are used. However, other injection techniques, such as programmed-temperature vaporizer, are much more versatile and more widespread. The aim of the present work was to compare the performance of a programmed-temperature vaporizer injector, in on-column and splitless mode, with the on-column injector to analyze alkyl esters and waxes. Discrimination among high-boiling compounds was evaluated, as well as the occurrence of thermal degradation, especially of sterols and diterpene alcohol (phytyl and geranylgeraniol) esters. A proper optimization of a programmed-temperature vaporizer injection, with particular attention to the liner selection, was proven to provide comparable results to the traditional on-column injection. A performance comparison was carried out both on standard mixtures and on real oil samples.
Keywords: Byproducts; Injection modes; Minor components; On-column injector; Programmed-temperature vaporizer injection.
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