Optimization and validation of a new pesticide residue method for cucumber and tomato using acetonitrile-based extraction-dispersive liquid-liquid microextraction followed by liquid chromatography-tandem mass spectrometry

A multiclass and multi-residue method was optimized and validated for analysis of 19 pesticides of 16 chemical classes in greenhouse cucumber and tomato followed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). In this study a dispersive liquid-liquid microextraction (DLLME) technique was applied for extraction and pre-concentration of pesticide residues from QuEChERS (quick, easy, cheap, effective, rugged and safe) extracts. The DLLME method was carried out using carbon tetrachloride as the extraction solvent and QuEChERS extract as the dispersive solvent. The main parameters affecting DLLME efficiency including the type and volume of extraction solvent and the volume of dispersive solvent and salt addition were optimized for the proposed method. To validate this developed method, recovery studies were carried out at two concentration levels, yielding mean recovery rates in the range of 86 to 104% with relative standard deviations below 12%. Good linearity and precision, with relative standard deviations generally below 10%, were obtained for all 19 pesticides. The method limits of detection (LOD) between 3.4 and 10.4 mu g kg(-1) and method limits of quantification (LOQ) in the range of 11.2-34.5 mu g kg(-1) were obtained for the proposed method. Recovery rates and method LODs and LOQs of the validated method were compared with those of the routine QuEChERS method and results indicated the efficiency of the proposed method for routine analysis of 19 pesticide residues in cucumber and tomato.