Optimization of UA-DLLME by experimental design methodologies for the simultaneous determination of endosulfan and its metabolites in soil and urine samples by GC–MS

Abstract

A simple, economical, rapid and sensitive analytical method has been developed for the simultaneous determination of endosulfan (α- and β-) and its metabolites (endosulfan ether, endosulfan hydroxy ether, endosulfan lactone, endosulfan alcohol and endosulfan sulphate) in complex samples, such as soil and urine, based on ultrasound assisted dispersive liquid–liquid microextraction (UA-DLLME) followed by gas chromatography–mass spectrometric (GC–MS) analysis. The method parameters have been optimized using response surface design experiments. Trichloroethylene (TCE) and acetone were chosen as extraction and disperser solvents respectively. After UA-DLLME, the sediment phase obtained was directly analyzed by GC–MS without any further cleanup and preconcentration procedure. Several factors which can affect the UA-DLLME extraction were screened and optimized by 2^7–4 Plackett–Burman design (PBD) and central composite design (CCD) experiments respectively. Based on these experiments the optimized parameters for UA-DLLME extraction were as follows: extraction solvent, (TCE, 58 μL), disperser solvent (acetone, 1.27 mL) and ionic strength (Na₂SO₄, 7%, w/v). Intra- and inter-day precision were expressed as percent relative standard deviation (% RSD) and were found to be less than 6.33%. The limit of detection (LOD) of all the analytes in soil and urine were found to be in the range of 0.316–2.494 ng g⁻¹ and 0.049–0.514 ng mL⁻¹ respectively. The proposed method was successfully applied in the analysis of soil samples contaminated with endosulfan. The method may find wide application for the routine determination of endosulfan and its metabolites in environmental and biological samples.