Ligang Chen

Magnetic molecularly imprinted polymer extraction of chloramphenicol from honey.

A rapid and selective method was successfully developed using magnetic molecularly imprinted polymer (MMIP) as sorbent for the extraction of chloramphenicol from honey samples. The extraction process was carried out in a single step by blending and stirring the sample, extraction solvent and polymers. When the extraction was completed, the MMIPs adsorbing the analyte were separated from the sample matrix by an external magnet. The analyte eluted from the MMIPs by methanol under ultrasound assisted was analysed by liquid chromatography-tandem mass spectrometry. Various parameters affecting the extraction efficiency were evaluated for achieving optimal recovery and reducing non-specific interactions. Under optimal conditions, the detection limit of CAP was 0.047 ng g(-1). The relative standard deviations of intra- and inter-day ranging from 4.1% to 5.3% and from 2.9% to 7.1% were obtained, respectively. The method was applied to determine CAP in six honey samples. The recoveries of CAP in these samples from 84.3% to 90.9% were obtained.

Fast and selective extraction of chloramphenicol from soil by matrix solid-phase dispersion using molecularly imprinted polymer as dispersant.

The molecularly imprinted polymer (MIP) was synthesized and used as dispersant of matrix solid-phase dispersion (MSPD) for the extraction of chloramphenicol (CAP) in soil samples. The satisfactory recovery of CAP was obtained by the optimized extraction conditions: 1:2 as the ratio of sample to MIPs; 5 min as the dispersion time; 30% aqueous methanol as washing solvent and methanol as elution solvent. The CAP extracted from soil was determined by LC-MS/MS. The slight ion suppression phenomenon was observed for the CAP when the sample was cleaned up by MSPD with MIP as dispersant, when compared with C18 as MSPD dispersant, which caused significant ion suppression. LOD of CAP is 4.1 ng/g. RSDs of intra- and inter-day tests ranging from 3.1 to 6.2% and from 3.9 to 8.3% are obtained. At all three fortified levels (20, 100 and 500 ng/g), recoveries of CAP are in the range of 86.9-92.6%. The effect of ageing time of spiked soil sample on the CAP recovery was examined. The CAP recovery decreased from 91.0 to 36.9% when the ageing time changed from 1 day to 4 wk.

Analysis of melamine in milk powder by using a magnetic molecularly imprinted polymer based on carbon nanotubes with ultra high performance liquid chromatography and tandem mass spectrometry

A new magnetic molecularly imprinted polymer was coupled with ultra high performance liquid chromatography and tandem mass spectrometry for the selective determination of melamine in milk powder. The magnetic molecularly imprinted polymer has been prepared by using carbon nanotubes as the matrix, Fe3 O4 particles as the magnetic ingredient, melamine as the template molecule, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker and polyvinylpyrrolidone as the dispersant. The polymer was characterized with scanning electron microscopy, Fourier transform infrared spectroscopy and a physical property measurement system. The isothermal adsorption, kinetics adsorption, and selectivity were studied to evaluate the rebinding properties of the magnetic molecularly imprinted polymer. Various parameters affecting the extraction efficiency such as the amount of polymer, extraction time, and eluting solution were evaluated. The limit of detection was 0.00075 mg/kg. The relative standard deviations of the intraday and interday precision are 0.4-2.7 and 2.3-5.1%, respectively. The proposed method was successfully applied to determine melamine in different milk powder samples from different provenances, and satisfactory recoveries of 89.0-95.6% were obtained. This method has great significance for quality control and is simple and suitable for the rapid determination of melamine in milk powder.

Preparation of a magnetic molecularly imprinted polymer by atom-transfer radical polymerization for the extraction of parabens from fruit juices.

A silica-based surface magnetic molecularly imprinted polymer for the selective recognition of parabens was prepared using a facile and general method that combined atom-transfer radical polymerization with surface imprinting technique. The prepared magnetic molecularly imprinted polymer was characterized by transmission electron microscopy, Fourier transform infrared spectrometry and physical property measurement. The isothermal adsorption experiment and kinetics adsorption experiment investigated the adsorption property of magnetic molecularly imprinted polymer to template molecule. The four parabens including methylparaben, ethylparaben, propylparaben, and butylparaben were used to assess the rebinding selectivity. An extraction method, which used magnetic molecularly imprinted polymer as adsorbents coupled with high-performance liquid chromatography for the determination of the four parabens in fruit juice samples was developed. Under the optimal conditions, the limits of detections of the four parabens were 0.028, 0.026, 0.021, and 0.026 mg/L, respectively. The precision expressed as relative standard deviation ranging from 2.6 to 8.9% was obtained. In all three fortified levels, recoveries of parabens were in the range of 72.5-89.4%. The proposed method has been applied to different fruit juice samples including orange juice, grape juice, apple juice and peach juice, and satisfactory results were obtained.

Magnetic molecular imprinting polymers based on three-dimensional (3D) graphene-carbon nanotube hybrid composites for analysis of melamine in milk powder

A novel analytical method for melamine in milk powder has been developed and exploited with three-dimensional (3D) magnetic molecularly imprinted polymers (MMIPs) combining with liquid chromatography-tandem mass spectrometry. The 3D MMIPs were synthesized with graphene-carbon nanotube hybrid composite as carrier which can increase the accessible surface area. The products were characterized, and the binding affinity was investigated by isothermal absorption, kinetic adsorption and selective adsorption. The results showed that the 3D MMIPs exhibited high adsorption capacity with maximum adsorption capacity of 123.1 mg g-1, fast adsorption rate (10 min) and high selectivity toward melamine. Various affecting extraction parameters were evaluated. The limit of detection was 0.00045 mg kg-1 and the recoveries were ranged from 90.3% to 95.7%. The precisions (RSDs) were lower than 4.7%. This method was applied for analyzing six milk powder samples. The result was in agreement with that obtained by the state standard method used in China.