Abstract: Molecularly imprinted polymers (MIPs) with high selectivity to ractopamine (RAC) were prepared by using RAC as template, acrylamide (AM) as monomer, and ethylene glycol dimethacrylate (EGDMA) as cross-linker. The effects of four porogens (methanol, acetonitrile, acetone, and chloroform-methanol) with triethylamine (30:1, v/v) on the recognition capability of MIPs to RAC and the morphological characteristics of the polymers were investigated. Orthogonal test was used to optimize the preparation of MIPs, and the optimal compositions were as follows: 1.0 mmol RAC, 4.0 mmol AM, 20.0 mmol EGDMA, 6.0 mL acetonitrile-triethylamine (30:1, v/v), and 50.0 mg azobisisobutyronitrile. A high performance liquid chromatographic method based on molecularly-imprinted solid-phase extraction (MISPE) was developed for the determination of ractopamine in feed samples. The limit of detection (LOD, S/N=3) of ractopamine was 0.1 mg/kg. The linear range was 0.50~100 mg/L (r=0.9994). Mean recoveries of RAC spiked in 3 kinds of feed samples at 1.0, 10 and 100 mg/kg were above 80% with the relative standard deviations of less than 10%. The clean-up efficiency of MISPE was ideal for feed samples. The method is more sensitive and reproduciable than the standard analytical method for the determination of RAC in feed matrices.

Key words: feeds, high performance liquid chromatography (HPLC), ractopamine, solid-phase extraction (SPE), molecularly imprinted polymers (MIPs)