Comparison of different injection modes in edible oil minor components analysis

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.