Analysis of triglycerides in food items by desorption electrospray ionization mass spectrometry

Abstract

The triglyceride composition and oxidation behavior of edible oil and margarine samples were analyzed by desorption electrospray ionization mass spectrometry (DESI-MS). For the characterization of the lipids, the chain length and the degree of unsaturation of the fatty acids were determined. The measurements were carried out in positive ion mode; the triglycerides were detected as alkali metal or ammonium adducts. The DESI solvent was water/methanol 1:1 (v/v); measurements were carried out both with and without the addition, as an ionizing agent, of ammonium acetate that enhances the signal intensity of the ammonium adduct ions. The spectra were interpreted for both cases and intensities were compared. Triglyceride monomers and dimers were observed in the spectra. Tandem mass spectrometric (MS/MS) measurements were carried out to determine the structure of the triglycerides. It was demonstrated that the terminal fatty acids in the sn1- or sn3-position are more likely to be cleaved than the internal fatty acid (sn2-position). Characteristic triglyceride patterns were obtained using a simple and rapid sample preparation protocol comprising the simple deposition of samples onto a glass carrier surface. The triglyceride data was analyzed by principal component analysis (PCA). The different edible oils were clearly separated and the hydrogenated derivatives were identified by their triglyceride spectra. The oxidation of the oil samples was observed and the oxidation products were detected and identified. This method provides a fast and simple technique for the detection and analysis of triglycerides in oil- or fat-containing samples ranging from food items to tissue samples. The potential application areas include nutritional studies, the food industry and cosmetics.