Application Of Capillary Electrophoresis And Molecularly Imprinted Solid-phase Extraction In Analysis Of Phenoxy Acid Residues

Phenoxy acid herbicides are a category of commercial herbicides widely used in the world. Their metabolites degradate slowly and some of them can interfere with endocrine of human and animals. They can also be transferred into crops and aquatic products through water and soil ecosystems, and further threaten human health. EU,US, Japan, China and other countries have set the residues standards of this type of herbicide. Therefore, the establishment of sensitive and reliable detection method for monitoring such herbicide residues in food samples is very necessary. The complex components in food matrices makes it hard for determination of trace herbicide redidues. Thus, how to remove the interferences of impurities in complex matrices is critical to the analysis of trace residues. In this paper, determination and pre-treatment of 2,4-D, Clofibric acid, Picloram and Clopyralidresidues were studied and the contents were as follows:A fast, efficient and environmentally friendly new method was developed for the determination of 4phenoxy acid herbicides in cereals by capillary electrophoresis(CE)combined with online enrichment technology. The effects of buffer pH, phosphate concentration, SDS concentration, separation voltage, injection time, the pH and concentration of sample buffer and enrichment voltage on separation and concentration of the analytes were studied. 4 phenoxy acid herbicides were injected by 3.5kPa×200s, separated in the optimized buffer composition: 20mmol/L phosphate,60mmol/L SDS, pH of 7.5 at 25℃, concentrated by the enrichment voltage of-20 kV in a sample buffer containing 20mmol/L phosphate with pH of 7.5 and detected at220 nm. Under the optimum conditions, 4 phenoxy acids were enriched by 510~620folders.The detection limits of them were 0.20~0.38μg/kg, the intra day precision were 0.9~1.3% and the day to day precision were 1.8~2.4%; the average recoveries in creals were 81.3-96.7% at 5~50μg/kg spiked levels, with a 2.1~5.0% of RSD. This method can meet multinational requirements of phenoxy acid herbicides maximum residue limits and can be used for determination of phenoxy acid residues in cereals.The molecularly imprinted polymer microspheres(MIPs) was prepared by using clofibric acid as a template. The amounts of functional monomer, organic solvent and crosslinking agent were optimized. The best conditions for preparation of the MIPs were as follows: the molar ration of clofibric acid, methacrylic acid(MAA),ethyleneglycol dimethacrylate(EDMA) was equal to 1:4:20, that was n(clofibric acid):n(MAA):n(EDMA)=1:4:20; the amount of AIBN was 25mg; the volume of acetonitrile was 30 mL; the preparation temperature and time were 60℃ and 17 h,separately. The prepared MIPs showed good adsorbtion on clofibric acid with an imprinting-induced promotion of binding(IPB) value of 117.26%. These MIPs had two kinds of binding sites on the template. The dissociation contants(Kd) and the max apparent bingding capacities(Qmax) of the high affinity’s binding sites were respectively 0.923mmol/L and 29.063μmol/g, the Kd and Qmax of the low affinity’s binding sites were 10.059mmol/L and 146.814μmol/g, respectively.The prepared MIPs showed good adsorption performance on 4 phenoxy acid herbicides and had good reusability.The method of using solid-phase extraction column filled with clofibric acid MIPs for application in purification and enrichment of phenoxy acid herbicides in rice and oatmeal samples was established and was used as pre-treatment of CE dection. The pre-treatment conditions were as follows: 5mL of acetonitrile was used as sample solvent and the loading flow rate was 0.6mL/min; The washing solvent was 5mL methanol-acetonitrile(25:75,V/V); The eluting solvent was 6mL methanol-acetic acid(90:10,V/V). The results showed that recoveries of 4 phenoxy acid herbicides spiked at 0.05~0.2mg/kg after treating with molecularly imprinted solid phase extraction(MISPE) column and C18 column were 81.9~97.7% and 80.3~91.7%, respectively. It was demonstrated that MISPE column was superior to C18 column in purification and can be used for purification and off-line concentration in cereals.