Nerea Aguinaga

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 C(18) column (50 mm x 4.6 mm, I.D., 1.8 microm) thermostated at 50 degrees 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 degrees C for 30 min with stirring at 1700 rpm in the presence of a 0.1M acetate/acetic acid buffer (pH 5) and 20% (m/v) sodium chloride. Liquid desorption was performed with 100 microL 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 microgL(-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.

Stir bar sorptive extraction coupled to liquid chromatography for the analysis of strobilurin fungicides in fruit samples

A stir bar microextraction (SBSE) procedure for the determination of seven strobilurin fungicides in fruit samples using liquid chromatography (LC) and diode array detection (DAD) has been developed. The samples were sonicated in the presence of ethanol before submitting the extracts to SBSE. The incorporation of drazoxolon as an internal standard before SBSE allowed calibration without the need to use the standard additions method. Under the optimized conditions, detection limits were in the 0.3-2 ng g(-1) range, corresponding to trifloxystrobin and metominostrobin, respectively. The SBSE-LC-DAD procedure showed good repeatability (RSD below 11% in all cases) and provided recoveries of 80-105% from spiked samples. The method was applied to fifteen fruit samples, and low levels of pyraclostrobin and trifloxystrobin were found in two of them.

Solid-Phase Microextraction Coupled to Gas Chromatography-Mass Spectrometry for the Analysis of Famoxadone in Wines, Fruits, and Vegetables

ABSTRACT A sensitive, selective, and solvent-free method based on direct immersion solid-phase microextraction (DI-SPME) followed by gas chromatography with mass spectrometry (GC-MS) is proposed for the determination of trace amounts of famoxadone in wines, fruits, and vegetables. Parameters affecting the sample enrichment step, such as sample mass, ionic strength, adsorption and desorption times, and temperatures were carefully optimized. A polar 85 µm polyacrylate fiber was found to be suitable for extraction at 60°C in 20 min under continuous stirring. Desorption was carried out at 270°C for 5 min. Undiluted wine samples and diluted extracts obtained from the solid samples submitted to an ultrasound treatment in the presence of ethanol were quantified against external aqueous standards prepared in 12% ethanol (v/v). Under the optimized conditions, detection limits of 5 ng L−1 and 10 pg g−1 were obtained for liquid and solid samples, respectively. SPME-GC-MS analysis yielded good repeatability (RSD under 10% in all cases). The method provided recoveries of 91.6–110.9% from spiked samples. The method was applied to different samples, and none of them was found to contain famoxadone at concentrations above the corresponding detection limits.