Comparison of differently coated SPME fibres applied for monitoring volatile substances in vegetable oils

Abstract

Solid-phase microextraction (SPME) was developed to determine volatile substances from liquid, gas or even solid materials. This technique has been successfully applied for soil, waste water, blood and urine samples, but in spite of its advantages there are still few applications for vegetable oils. SPME is applicable to determine the aroma and other volatile compounds of the oil, which are characteristic to its origin and oxidative status. In this study the sensitivity and selectivity of some commercially available SPME adsorption materials (polydimethylsiloxane, divinylbenzene, carboxen) were compared. The diverse types of stationary phases were investigated by applying standard oils containing volatile substances from 9-90 mg/kg concentrations. SPME fibre was placed into the headspace of an oil sample in a 30-ml headspace vial thermostated at 80°C for 45 min. The extracted volatile materials were desorbed from the fiber in the injection port of the gas chromatograph at 250°C. Identification of the extracted compounds is based on pure standards and mass spectra. The reliability of the SPME sampling method was studied by parallel measurements. The 2-cm long fibre coated with divinylbenzene (50 μm) and carboxen (30 μm) proved to be the most appropriate to determine the volatile oxo-materials from vegetable oils. The method was successfully applied to follow up the formation of volatile substances (e.g. hexanal, t-2-hexenal, t-2-heptenal, t-2-octenal, nonanal, t,t-2,4-nonadienal, t-2-nonenal, t-2-decenal, t,c- and t,t-2,4-decadienal, 2-pentylfuran, 1-octen-3-ol) during deep frying in sunflower oil.