Specific Enrichiment Of OPs From Water By Molecularly Imprinted Polymers

Organophosphorus pesticides(OPs) are used extensively in agriculture due to their relatively low persistence in the environment. With great toxicity to human health OPs are one of the main pollutants in the river, lake and ocean. Determination of OPs in environment has received considerable attention in recent years. The concentration of OPs in water is too low to be determined directly , therefore the samples should be enriched before analyzing. Solid phase extraction(SPE) is gradually substituting for the traditional liquid-liquid extraction(LLE) for its simplicity, low-in-price, easily automation, etc. But the ordinary SPE sorbents are not highly selective which hinders its development. The molecular imprinting technique has been paid more and more attention for its predetermination, selective recognition and widely applications. And molecularly imprinted polymers (MIPs) have developed rapidly and been used widely because of their good affinity, selectivity and stability. Molecularly imprinted solid phase extraction (MISPE) is an efficient technology for the purification, enrichment and separation of analogs in environment samples.In this article, MIPs using methyl parathion as the template are prepared. And the conditions of synthesis are studied. Results from this study show that the MIPs may get higher selectivity and affinity when use 35ml chloroform as solvent. Higher selectivity has also been obtained using 4-vinylpyridine (4VP) rather than methacrylic acid (MAA) or acrylamide (MA) as monomer. The affinity capacity and selectivity is much higher when the template to monomer ratio is 1:4.Moreover, we discuss the binding and rebinding mechanism by UV and infrared spectrum. Results indicate that all three monomers can form complexes with the template. There are two binding sites between 4-vinylpyridine and the template, the P-O-C and the -NO2 site. While the other two monomers can only associate with the template at the P-O-C site. Infrared spectrum study of the polymers also confirmed the existence of the functional groups which may interact with the template. Afterwards, the selective binding characteristics of the imprinted polymers are evaluated by Scatchard ananlysis. The results show that there are different bingding sites with various affinity characteristics in the MIPs. According to the Langmuir isotherm, the maximum adsorption capacity of MIP-4VP, MIP-MA and MIP-MAA are estimated to be 625.5μmol/g, 256.7μmol/g and 106.5μmol/g respectively.MIPs show high and stable affinity to methyl parathion in seawater. And influences of temperatures and pH of seawater are not obvious on the affinity. Then a new analytical methodology is developed for the analysis of three OPs (methyl parathion, malathion and chlorpyrifos) in seawater incorporating a molecularly imprinted solid phase extraction process using MIPs prepared. Eluating the MISPE columns with 10ml methanol, the OPs can be concentrated efficiently. The recoveris are above 80%, and the OPs can be enriched by 8~12 times, which are much higher than that of traditional LLE and SPE using C18 as the adsorbent. In order to improve the selectivity of MISPE, washing conditions are also optimized. Washed with hexane MIP-MAA show different selectivity to three OPs studied.Conclusively, MIPs prepared with methyl parathion have high selectivity and affinity to the template. The molecularly imprinted solid phase extraction is likely to become an efficient means of sample pretreatment for selective separation and enrichment of OPs in seawater.