One-step microwave-assisted extraction and derivatization followed by flow-modulation GC×GC-FID for rapid determination of fatty acid in a variety of food samples

Fatty acid profile is an important analysis to answer a multiplicity of questions, for instance related to nutritional quality and authenticity of foods. Fatty acids are mainly present in esterified forms, therefore derivatization to transform them in the corresponding fatty acid methyl ester (FAMEs) is needed for the further chromatographic analysis. Moreover, for many matrices the prior lipid extraction is needed before derivatization.
The goal of this work was to optimize a fast and accurate method for preparation of FAMEs using one-step microwave-assisted extraction and derivatization by transesterification of fatty acids. The method performance was evaluated by comparing fatty acid profiles with those resulting from conventional FAMEs preparation (AOCS Official Method Ce 2b-11; Cruz-Hernandez et Al.: Journal of AOAC International Vol. 87, No. 2, 2004). Microwave- assisted method was rapid, simple and universally effective across complex samples ranging from milk to fish oil. FAMEs were subsequently analysed by flow-modulation comprehensive two-dimensional gas chromatography (GC×GC) coupled to FID to identify and quantify the individual fatty acid. GC×GC analysis is more sensitive than monodimensional one thus allowing to achieve lower LOQ. The instrument repeatability evaluated in terms of first and second dimension retention times was highly satisfactory, i.e. RSD% < 0.5% and < 2.5%, respectively. The repeatability of entire method procedure was lower 3% in terms of area percentage of the different FAMEs evaluated in different samples.