Development of deep eutectic solvent-based ultrasonic assisted liquid–liquid microextraction coupled with GC–MS; application in analysis of organochlorine pesticides from cheese samples

A deep eutectic solvent-based ultrasonic assisted liquid–liquid microextraction method was developed to extract organochlorine pesticides from cheese samples before their quantification with gas chromatography–mass spectrometry. A mixture of deionized water, potassium hydroxide solution, and thymol: decanoic acid deep eutectic solvent was used in the method development. Under the optimum method conditions, acceptable precision was achieved, with intra– and inter-day precisions falling within the ranges of 2.9–4.3 % and 3.5–4.7 %, respectively). A good coefficient of determination (r ≥ 0.993) was obtained over a wide concentration range (107–250,000 ng kg), with low limits of detection (32–58 ng kg) and quantification (107–193 ng kg). Additionally, acceptable extraction recoveries (57–79 %) were achieved. Method validation was conducted and the method was successfully applied to several cheese samples. Based on the results, all of the investigated samples were found to be free of investigated organochlorine residues.