A new application of X-ray scattering using principal component analysis – classification of vegetable oils

Abstract

This work describes an innovative technique based on X-ray scattering applied to classify complex organic matrices of different vegetable oils. This new, very simple and rapid procedure is based on taking a 1 mL aliquot of sample, depositing it on the thin Mylar™ film of a sample cell and submitting it to irradiation for 100 s in a conventional EDXRF equipment. The resulting spectra are processed through Principal Component Analysis (PCA), a chemometric tool, and a very convenient classification is obtained as a function of the origin of the oil. This classification can be used to verify oil adulterations, for example. The X-ray fluorescence spectrometer is a common bench equipment, with a Rh tube as source of the X-rays. Vegetable oils from corn, canola, soybean, sunflower and olive (extra virgin and others) were analysed and classifications were obtained using information from the scattered radiation. For the corn, canola, soybean and sunflower oil analyses, the PC1 × PC4 score plots show distinct groups for each oil. These differences related to the variable fatty acid contents in the samples. Considering the discrimination between extra virgin and other olive oils, the PC1 × PC2 scores plot shows two groups of samples. The main difference between them can be attributed to the total absence of water in extra virgin olive oils, since this first extraction is performed at room temperature without any kind of reagent. The technique is very useful to rapidly classify vegetable oil samples at very low cost, with the possibility of performing the measurements in situ with a portable instrument.