Comparison of stir bar sorptive extraction and membrane-assisted solvent extraction for the ultra-performance liquid chromatographic determination of oxazole fungicide residues in wines and juices

The present study compares two new sample preparation methods, stir bar sorptive extraction (SBSE) and membrane-assisted solvent extraction (MASE) coupled to the novel technique of ultra-performance liquid chromatography (UPLC) for the sensitive, selective and solvent-free determination of six oxazole fungicide residues (hymexazol, drazoxolon, vinclozolin, chlozolinate, oxadixyl and famoxadone) in wine and juices. The analytes were separated on a rapid resolution C18 column (50 mm × 4.6 mm, I.D., 1.8 μm) thermostated at 50 °C with isocratic elution using a 50/50 (v/v) water/acetonitrile (ACN) mobile phase at a flow-rate of 1 mL min−1 and detected by diode-array detection (DAD). The UPLC method rapidly separates the fungicides (7 min). The best results as regards sensitivity, repeatability and analyte recovery were obtained using SBSE with a polydimethylsiloxane (PDMS) twister, at 60 °C for 30 min with stirring at 1700 rpm in the presence of a 0.1 M acetate/acetic acid buffer (pH 5) and 20% (m/v) sodium chloride. Liquid desorption was performed with 100 μL of a 80/20 (v/v) ACN/water solution in a desorption time of 15 min. With the PDMS polymer, an apolar phase, hymexazol and oxadixyl were not extracted. Consequently, the SBSE procedure can only be applied to the other four fungicides. Detection limits ranged from 0.05 to 2.5 μg L−1 at a signal to noise ratio of 3, depending on the compound. Recoveries obtained for spiked samples were satisfactory (83–113%) for all compounds. The proposed method was successfully applied to the analysis of different samples, residues of chlozolinate and drazoxolon being found in samples of red wine and grape juice, respectively.