Multipesticide residue analysis in maize combining acetonitrile-based extraction with dispersive liquid-liquid...

A fast and simple gas chromatography-mass spectrometry (GC-MS) method for determination of forty-one pesticide residues in maize is introduced. The sample preparation involves liquid-liquid partitioning with acetonitrile in presence of anhydrous MgSO(4) and NaCl (QuEChERS) followed by dispersive liquid-liquid microextraction (DLLME) using carbon tetrachloride as extractive solvent and the extract obtained by QuEChERS as dispersive solvent. The main factors influencing DLLME efficiency including extractive solvent type and volume as well as the volume of dispersive solvent were evaluated in this study. The DLLME procedure effectively provides an enrichment of the extract and a cleanup of certain polar matrix components, which can maximize the sensitivity when a single quadrupole MS is used. For validation purposes, recoveries studies were carried out at two concentration levels, yielding recovery rates in the range 70-120% for 82% of the analytes. A good linearity and precision, with relative standard deviations generally below 20% were obtained for all forty-one pesticides. The limits of detection obtained were lower than 19 μg kg(-1) for more than 63% of the analytes. In two of a total of ten samples of maize, residues of lindane, tefluthrin, pirimicarb, folpet and bifenthrin were found, although at levels below the maximum limit established for this kind of samples.