Preparation Of Pirimicarb Molecularly Imprinted Polymers Grafted On Silica Bead And Study Of Its Absorption Property

Pirimicarb,2-(dimethylamino)-5,6-dimethyl-4-pyrimidinyl-dimethylcarbamate, an extensively used carbamate insecticide, has been widely applied in fruits and vegetables protection from aphid. The maximum residue limit of contaminants in green food of China is 1.0mg/kg. Due to the overuse of pirimicarb, the pressure on environment and food safety has been increasingly serious. A quick and sensitive analytical methodology for the quantification of pirimicarb becomes desirable.In this study, different kinds of molecularly imprinted polymers based on modified silica gel were prepared on the theoretical basis of surface polymerization. The thermal polymerization was initiated by azo-initiator grafted on silica surface. The MIPs were prepared from trifiuoromethacrylic acid (TFMAA), methacrylic acid (MAA), 4-vinylpyridine (4-VP) and acrylamide (AM) as functional monomers, with acetonitrile and heptane as porogens. Aqueous solutions of pirimicarb and propoxur were applied to an MIPs-SPE column. After reaching adsorption equilibrium, the concentrations of pirimicarb and propoxur in the remaining sample were measured by high performance liquid chromatography (HPLC). The results indicated that TFMAA formed a stronger interaction with pirimicarb than other monomers and heptane was a better solvent for this complexation. The selectivity coefficient of the MIPs for pirimicarb/propoxur mixtures was 7.3-fold greater than that of non-imprinted polymers (NIPs). The 1H of Nuclear Magnetic Resonance (NMR) experiment testified that there existed stronger hydrogen bond or ion pairing effort between pirimicarb and TFMAA in D-heptane. Thus, the results of the NMR study were consistent with the results of the selectivity study. According to the adsorption performance of MIPs produced at different temperature, the temperature of polymerization was determined at 70℃.It was deduced from different loading solutions results that MIPs displayed a better absorption ability in aqueous solution. Thus, in aqueous medium, intermolecular hydrogen bond and electrostatic interaction existed between TFMAA and pirimicarb, and the synergy between the two interactions leads to the strong adsorption of MIPs towards pirimicarb. Because of carboxyl dissociation and N-atom protonation, the adsorption rate of pirimicarb was highest in aqueous solution when pH was 6. The MIPs had better selectivity and absorption ability for pirimicarb in further comparison with other SPE columns.It was found that MIPs-SPE column behaved superior selectivity when loading real samples, and the adsorption rate could be more than 80%. This result proved MIPs could separate and concentrate the substance for quick and sensitive determination. This study would provide reference and basis for the further improvement of rapid detection for pirimicarb in fruits and vegetables by MIPs-SPE coupled with HPLC.