Preparation of a novel RAM-MIP for selective solid-phase extraction and gas chromatography determination of heptachlor, endosulfan and their metabolite residues in pork†
A novel method was established using a restricted access material combined with a molecularly imprinted polymer (RAM-MIP) as the sorbent material in solid phase extraction (SPE) for clean-up of α-endosulfan, β-endosulfan, endosulfate, endosulfan-ether, endosulfan lactone, heptachlor, heptachlor-exo-epoxide, and heptachlor-endo-epoxide in pork and gas chromatography (GC) for determination. The RAM-MIP was prepared by precipitation polymerization by using endosulfan as the template, methacrylic acid (MAA) as the monomer, glycidyl methacrylate (GMA) as the pro-hydrophilic co-monomer, ethylene glycol dimethacrylate (EGDMA) as the crosslinker, azobisisobutyronitrile (AIBN) as the initiator, and toluene as the porogen. Ultraviolet spectroscopy (UV) and 1H-nuclear magnetic resonance (1H-NMR) analysis verified that MAA interacted specifically with endosulfan in a ratio of 1 : 1 in the pre-polymerization solution. The RAM-MIP exhibited specific adsorption performance for endosulfan and efficiently avoided the deposition of macromolecules on the surface of polymers. The residues of endosulfan, heptachlor and their metabolites in pork were extracted with acetone : n-hexane (2 : 8, v/v), cleaned up by using a SPE cartridge packed with the RAM-MIP, and determined by GC. The limits of quantification (LOQs) for endosulfan, heptachlor and their metabolites in pork samples were confined to 0.005 mg kg−1. The recoveries of target compounds spiked at 0.005–0.05 mg kg−1 were 51.17–107.73% with relative standard deviations (RSDs) of 1.4–15.9%. Thus, this novel method can be successfully applied to the determination of heptachlor, endosulfate and their metabolite residues in pork samples.