Combination of homogeneous liquid–liquid extraction and dispersive liquid–liquid microextraction for extraction of some organochlorine pesticides from cocoa

Abstract

ABSTRACT In present work, a sample pre-treatment method based on a combination of homogenous liquid–liquid extraction and dispersive liquid–liquid microextraction has been proposed for the extraction of some organochlorine pesticide residues in cocoa powder before their quantification by gas chromatography–electron capture detection. To extract the analytes, a mixture of acetonitrile and potassium hydroxide solution is added to cocoa powder. In the following, an appropriate amount of sodium chloride as a phase separation agent is added and the mixture is vortexed. After centrifugation, the supernatant phase (acetonitrile containing the extracted analytes) is separated and mixed with chloroform (as an extraction solvent). This mixture is rapidly injected into the deionised water which its pH is 6.4. By this action, a cloudy solution is obtained and after centrifugation, an aliquat of the sedimented phase is removed and injected into the quantification system. Under optimum conditions, limits of detection and quantification of the analytes were found to be in the ranges of 0.024–0.041 and 0.081–0.138 ng g–1, respectively. The obtained extraction recoveries varied between 50 and 89%. Also, intra – (n = 6) and inter–day (n = 4) precisions, experiments as relative standards deviations were less than 8.9% for the studied pesticides at different concentrations (0.2, 1.0, 100 and 250 ng g−1, each analyte). Finally, the suggested method was applied to determine the studied organochlorine pesticide residues in various cocoa powders gathered from groceries in the East Azerbaijan Province, Iran. Abbreviations: DLLME, Dispersive liquid–liquid microextraction; ECD, Electron capture detector; ER, Extraction recovery; EF, Enrichment factor; GC, Gas chromatography; HLLE, Homogenous liquid–liquid extraction; LOD, Limit of detection; LOQ, Limit of quantification; LR, Linear range; RSD, Relative standard deviation; OCP, Organochlorine pesticide