Method development based on molecularly imprinted polymers for the selective extraction of organic compounds in complex aqueous matrices

Abstract

Contamination of water from organic compounds in low concentrations such as triazines herbicides and estrogens and the fact that due to complex matrix effect, the compounds are not easy to determine which call for sample preparation approaches such as MIPSE – MMLLE. A selective extraction method based on the combination of microporous membrane liquid-liquid extraction (MMLLE) and molecularly imprinted polymers (MIPs) was developed and applied to the extraction of 17 β-estradiol and selected triazines herbicides in complex aqueous samples. These pollutants were extracted from aqueous complex samples through the hydrophobic porous membrane that was impregnated with toluene, which also formed part of the acceptor phase. In the acceptor phase, the compounds were re-extracted onto MIP particles. The extraction technique was optimised for the amount of MIP particles in the organic acceptor phase, extraction time, and type of organic acceptor solvent and desorption solvent. Triazines herbicides (simazine, atrazine and propazine) and estrogenic compound (17 β-estradiol) were used as model compounds in this study. HPLC-UV was used for the determination of these organic compounds. An extraction time of 90 minutes and 10 mg of MIP were found to be optimum parameters for triazines extraction. Toluene as the acceptor phase was found to give higher triazines binding onto MIP particles compared to hexane and combinations of diethyl ether and hexane. 90% methanol in water was found to be the best desorption solvent compared to acetonitrile, methanol and water. Higher MIP mass (30 mg) was used for 17 β-estradiol (E2) because of poor binding kinetics. An extraction time of 60 minutes and 90% methanol in water were adopted. Hexane: ethyl acetate (3:2) as the acceptor phase was found to give a stable membrane and give better partitioning of the E2 from the aqueous donor. In order to improve the binding of the E2 onto the MIP ultrasound assisted rebinding was studied. The developed method proved its selectivity to the extraction of complex matrices where clean chromatograms were obtained. Furthermore samples spiked with varying amounts of humic substances were also extracted and “clean” chromatograms obtained. Reference iii materials containing ametryn, prometon, prometryn, propazine, simetryn, simazine and terbutryn were extracted to demonstrate the validity of the developed technique. The results indicated that the MMLLE – MIP could be used to reliably determine real samples. The method was then applied to spiked lettuce, apple extracts and wastewater where clean chromatograms were obtained compared to MMLLE alone or to the microporous membrane liquid-liquid extraction – non imprinted polymer combination (MMLLE – NIP). The triazine MIP showed a certain degree of group specificity and the extraction efficiency was 68 % for simazine, 74 % for atrazine and 69% for propazine, giving enrichment factors of 40, 56 and 45, respectively in deionised water. The extraction efficiency in apple extracts were 55%, 63% and 60% for simazine, atrazine and propazine respectively. The percentage relative standard deviation in plant samples ranged from 1 to 15. The E2 MIP also demonstrated high selectivity although the extraction efficiencies and enrichments factors were low due to poor E2 binding on the MIP particles.