Molecularly Imprinted Dispersive Solid-phase Extraction Coupled With High Performance Liquid Chromatography For The Determination Of Pyraclostrobin In Ginseng

In this paper,determination of pyraclostrobin in ginseng samples by molecularly imprinted dispersive solid-phase extraction（MIDSPE）coupled with high-performance liquid chromatograph（HPLC）method was developed.In this method,molecularly imprinted polymers were used as adsorbent for the dispersive solid-phase extraction process.Molecularly imprinted polymers（MIPs）were prepared by precipitation polymerization using pyraclostrobin as template,methacrylic acid（MAA）as functional monomer,ethylene glycol dimethacrylate（EGDMA）and azobisisobutyronitrile（AIBN）as cross-linker and initiator,respectively.The mixture of butanone（MEK）and n-heptane（7:3,V:V）were used as solvent and porogen.The microspheres were characterized by laser particle size analyzer,scanning electron microscopy（SEM）and fourier transform infrared spectrometry（FTIR）.The SEM images showed the morphology of MIPs and NIPs,MIPs had a more regular shape and clear surface than NIPs.The microspheres of MIPs and NIPs were both showed a normal distribution.However,NIPs had more widespread distribution.This indicated that the particle size distribution was affected by the template molecules during the polymerization of microspheres.FTIR spectra results show that the template molecule,MAA and EGDMA were successfully involved in the reaction.Binding experiments showed high binding capacity of polymers,that the maximum adsorption of MIPs and NIPs to pyraclostrobin were 73.01 mg·g^-1 and 59.14 mg·g^-1.The Scatchard analysis plots of the MIPs and NIPs were both straight lines,which indicated only one type of active site existed in the imprinted microspheres.The apparent maximum number Q_maxof MIPs was 73.01 mg·g^-1,which was higher than NIPs(59.14 mg·g^-1).And the equilibrium dissociation constants（Kd）of MIPs and NIPs were 86.58 mg·L^-1 and 502.50 mg·L^-1.The Langmuir isotherm indicated the adsorption characteristics of each adsorption site in MIPs are the same,and the adsorption of pyraclostrobin by MIPs is a monolayer adsorption.These results revealed that the adsorption cavities of MIPs were homogeneous and specific.Selective adsorption experiments verified that polymers had specific and selective recognition site for pyraclostrobin.The molecularly imprinted dispersive solid phase extraction（MIDSPE）coupled with liquid chromatography（LC）for the separation and determination of pyraclostrobin in ginseng was developed.Compare MIPs with C₁₈,the recoveries of pyraclostrobin from blank ginseng samples spiked at 0.05,0.1,1.0 mg·kg^-1 ranged between 77.60%and 93.15%with the relative standard deviations（RSDs）between 2.47%and 6.99%（n=5）.The recoveries of pyraclostrobin that used C₁₈ as sorbent were found to be 53.04-63.86%with the relative standard deviations of1.07-4.99%.The data indicated that the method for the analysis of the pyraclostrobin in ginseng samples can achieve good recoveries,repeatability and reproducibility.The linear regression equation was calculated as y=2.09935e-006x+0.0176235（R²=0.998656）.The limit of detection（LOD,S/N=3）was 0.01 mg·kg^-1.The confidence interval for the slope at the 95%confidence level was[356084.1828,899542.8563],and the confidence interval for the intercept was[-755349.2710,72645.0856].The MIDSPE-HPLC method showed specific selective separation and enrichment of trace pyraclostrobin in ginseng samples.The raw samples were tested and results were were all below the maximum Residue Limit（MRL）0.1 mg·kg^-1 in the European Union.