| Bisphenol A (2, 2-bis (4-hydroxyphenyl) propane, BPA) is known to be one ofthe environmental hormones and has estrogenic effect. BPA is a monomer used inthe chemical industry for the manufacture of numerous plastic products includingfood packaging, infant feeding bottles, inner surface coating of cans and dentalsealants. When these plastic products are reused and exposed to high temperature,BPA will be released into the environment and produce adverse effects on humanhealth. Consequently, there is a significant demand for the strict monitoring of BPA.As the concentration of BPA is usually very low and the sample matrices inbiological and environmental samples are often very complex, so samplepretreatment steps which could attain analyte enrichment and matrix removal areessential. Consequently, it is of great significance to develop a sensitive and highselective sample pretreatment method for the determination of BPA in theenvironment.Molecular imprinting technique (MIT) is a novel developing technique for thepreparation of molecularly imprinted polymers (MIPs) which have a predeterminedselectivity toward a given analyte or a group of structurally related species. For thegreat qualities of high selectivity, chemical stability, high mechanical strength,resistance to extreme conditions and easy preparation, the MIPs are often used as theextraction sorbent packed in the solid-phase extraction column for samplepretreatment.In this study, a molecularly imprinted polymer layer was synthesized on thesilica nanoparticle surface via a sol-gel process, using BPA as the template, aminopropyltriethoxysilane (APTES) as the functional monomer, tetraethoxysilane(TEOS) as the cross linking agent and methanol as the porogen. After thepolymerization procedure, molecularly imprinted nanopaticles with regular size andshape were obtained. The prepared molecularly imprinted nanopaticles each hadnumerous binding sites in its surface layer and a small dimension with extremelyhigh surface/volume ratio, providing more complete removal of templates, better siteaccessibility, lower mass-transfer resistance and higher extraction capacity.In addition, the molecular imprinting technique was used for the research of stirbar sorptive extraction(SBSE). SBSE is a novel solvent-free sample pretreatmentmethod that is based on the solid-phase microextraction (SPME). In SBSE, a glassstir bar with an iron bar sealed in it is used as the support of coating, and coated withan absorbent layer as the stationary phase.The major advantage of the stir bar technique is its large amount of extractionphase, leading to a high enrichment factor and hence a better recovery and samplecapacity, which is suitable for the trace analysis of samples. Besides, the coated stirbar could stir itself during the extraction step, which could avoid the competitiveadsorption of the trace component resulted from the addition of an extra stir bar.Currently, the applications of SBSE in different areas including environmentalanalysis, biological analysis and food contaminant analysis have attractedconsiderable attention.In this study, sorptive extraction stir bars based on the molecular imprintingtechnique were prepared by a sol-gel process, which were expected to extract thetarget compounds selectively with their molecularly imprinted coatings. The stir barwas prepared using BPA as the template, APTES as the functional monomer,methytrimethoxysilane (MTMS) as the sol-gel precursor, hydroxyl-terminatedpoly(dimethylsiloxane) (OH-PDMS) as the sol-gel active organic polymer, a MIP layer was immobilized on the activated glass bar with Si-O-Si covalent bond througha sol-gel process. In the experiment process, several reactants were compared andselected, the experimental conditions were optimized, the cracking and dryingproblems of the coating were successfully solved, and finally a molecularlyimprinted polymer layer was coated firmly on the surface of the glass bar, which wasof certain solvent resistance and could stay well in methylene chloride, water andmethanol. But the problem of template bleeding still exists and remains to be solved.Finally, the BPA-imprinted nanoparticles were packed in the solid-phaseextraction cartridges as the extraction sorbent for the determination of BPA in fishsamples. The MIP-SPE column showed higher recovery to BPA (97%) and exhibitedexcellent selective extraction efficiency to its competitive structural analogues (4-tert-butylphenol (BP) and 3, 3, 5, 5-tetrabromobisphenol A (TBBPA)) comparedwith the commercial C18-SPE column, which demonstrated good qualities of thepacked BPA-imprinted polymers. When the same MIP-SPE column was sequentiallyused for six times, an average recovery of 92.0% was obtained with relative standarddeviation of 12.2%, which indicated acceptable repeatability and reusability of thecolumn.The calibration curves for detection of the target compounds were obtained byperforming a linear regression analysis on standard solution covered the range of 0.7-114.1μg·L-1 using a weighted calculation method, with correlation coefficients ofr>0.997.The BPA concentration of 4ng·g-1 was detected in bream with an averagerecovery of 74.5%(n=5), and the BPA concentration detected in crucian was belowthe LOQ. The proposed MISPE-HPLC method could be applied for determination ofBPA in fish samples.
|
PDF Full Text Request