“No-prep” Analysis of Lipids in Cooking Oils and Detection of Adulterated Olive Oil
Dietary fats are categorized according to the level of unsaturation. Oils are a mixture of triglycerides and free fatty acids. Olive oil contains a high concentration of monounsaturated fatty acids, while other oils such as Canola and safflower oil contain larger amounts of polyunsaturated fatty acids. Characterizing the type of lipids present is important for quality control and for detecting adulteration of more expensive oils (e.g. olive oil) with cheaper products. Analysis by HPLC is time consuming and requires solvents and consumables. DART provides a convenient alternative: no solvents are required and the analysis can be completed in seconds.
Analysis was carried out by using a JEOL AccuTOFDART™ mass spectrometer operated in positive-ion mode at a resolving power of >6000 (FWHM). The DART source was operated with helium and the gas heater was set to 375°C. Melting point tubes were dipped in oil samples and placed in front of the DART ion source for a few seconds. A cotton swab dipped in dilute ammonium hydroxide was placed nearby to enhance formation of [M+NH4]+ from triglycerides. A spectrum of PEG 600 was measured between samples to permit exact mass measurements.