Development of a Stirring-Dependent Magnetic Dispersive Solid Phase Extraction Method Coupled with Ferrofluid-Based Dispersive Liquid–Liquid Microextraction for the Extraction of Some Pyrethroid Pesticides from Fruit Juices

In the present work, a new and efficient sample treatment method based on the combination of stirring-dependent magnetic dispersive solid phase microextraction and ferrofluid-based dispersive liquid–liquid microextraction has been developed for the extraction of some pyrethroid pesticides (bifenthrin, phenothrin, tetramethrin, cyhalothrin, permethrin, and cypermethrin) from fruit juices prior to their determination with gas chromatography–mass spectrometry. For this purpose, a few milligrams of a synthesized magnetic sorbent (Fe3O4@polythiophene) is added into a sample solution containing the analytes and stirred at high rate. By this action, particles of the magnetic sorbent are detached from the magnetic stir bar surface and completely dispersed throughout the solution. After stopping stirring, the particles containing the adsorbed analytes are rapidly returned onto the stir bar. Then, the stir bar is taken and eluted with an appropriate solvent to desorb the analytes. Afterward, the eluent is mixed with a few microliters of a synthesized ferrofluid and the mixture is rapidly injected into deionized water placed in a conical glass test tube for more enrichment of the analytes. In the next step, the ferrofluid settled down at the bottom of the tube in the presence of an external magnet and the supernatant is discarded. After back-extraction of the analytes with n-hexane, an aliquot of the extract is injected into the determination system. Under optimal conditions, the developed method offered high enrichment factors (1380–1660) and extraction recoveries (69–83%), and low limits of detection (4.0–12 ng L−1) and quantification (14–40 ng L−1). The relative standard deviations were ≤ 7.1% for intra-day (n = 6) and inter-day (n = 4) precisions at a concentration of 250 ng L−1 of each analyte. Finally, six different fruit juice samples were successfully analyzed by the introduced method and cypermethrin was detected in apple juice at a concentration of 110 ± 0.5 ng L−1.