Development of an ultrasonic and heat-assisted liquid–liquid extraction method combined with deep eutectic solvent-based dispersive liquid–liquid microextraction for the extraction of some phytosterols from cow milk butter samples

Abstract

In this study, an ultrasonic and heat-assisted liquid–liquid extraction method combined with deep eutectic solvent-based dispersive liquid–liquid microextraction procedure was developed for the extraction of four phytosterols from cow milk butters. The analytes were determined by gas chromatography-flame ionization detector without derivatization. Initially, the sample was transferred into a falcon tube and placed into a sonication bath adjusted at 50 °C. Afterward, ethanol was mixed with the butter and the mixture was sonicated. After centrifugation, the ethanolic phase collected on top of the sample was withdrawn. After addition of a few microliters, ethyl (methyl) ammonium chloride/pivalic acid deep eutectic solvent, the mixture was sucked into a glass syringe and injected hastily into deionized water. The turbid solution was centrifuged and the sedimented phase was removed. Then, it was contacted with sodium hydroxide solution to remove the extracted fatty acids. The proposed method presented high enrichment factors (340–425) and extraction recoveries (68–85%), low limits of detection (0.51–1.3 ng g−1) and quantification (1.7–4.3 ng g−1) and acceptable relative standard deviations (≤ 8.4%). The analytes contents of several cow milk butter samples were extracted and quantified with the developed method and the results were compared with ISO 23349.