Mixed liquids for single-drop microextraction of organochlorine pesticides in vegetables

A new approach for the extraction of nine kinds of organochlorine pesticides (OCPs) from vegetable samples coupling single-drop microextraction with gas chromatography–mass spectrometry was presented. Experimental parameters, such as organic solvent, exposure time, agitation and organic drop volume were controlled and optimized. An effective extraction was achieved by suspending a 1.00 μL mixed drop of p-xylene and acetone (8:2, v/v) to the tip of a microsyringe immersed in a 2 mL donor aqueous solution and stirred at 400 rpm. The approach was applied to the determination of OCPs in vegetable samples with a linearity range of 0.05–20 ng mL−1 for α-, β-, γ-, δ-hexachlorobenzene (BHC) and dicofol, 0.5–20 ng mL−1 for dieldrin and 2,2-bis(4-chlorophenyl)-1,1-dichloroethane (DDD) or 0.5–50 ng mL−1 for 2,2-bis(4-chlorophenyl)-1,1-dichloroethylene (DDE) and 2-(2-chlorophenyl)-2 (4-chlorophenyl)-1,1,1-trichloroethane (p,p′-DDT). Correspondingly, the determination limit at an S/N of 3 ranged from 0.05 ng mL−1 for α-, β-, γ-, δ-BHC to 0.2 ng mL−1 for dicofol, dieldrin or p,p′-DDT. The relative recoveries were from 63.3 to 100%, with repeatability ranging from 8.74 to 18.9% (relative standard deviation, R.S.D.). The single-drop microextraction was proved to be a fast and simple approach for the pre-concentration of organochlorine pesticides in vegetable samples.