Synthesis and the application of molecularly imprinted polymers as solid-phase extraction and dispersive solid-phase extraction sorbents in the extraction of antiretroviral drugs in water.

Abstract

A multi-template molecularly imprinted polymer was synthesized, characterized, and applied to real water samples for the specific extraction of antiretroviral drugs (ARVDs), abacavir, nevirapine, and efavirenz. A MIP was synthesized by bulk polymerization at 60 ºC using abacavir, nevirapine and efavirenz (templates), 2-vinylpyridine (functional monomer), 1,1’- azobis-(cyclohexanecarbonitrile) (initiator), ethylene glycol dimethacrylate (cross-linker) and toluene: acetonitrile (9:1, v/v) (porogenic solvent mixture) for 16 hours. The temperature was then increased to 80 ℃ for 24 hours to ensure complete polymerization. The synthesized MIP was washed with acetic acid: acetonitrile (1:9, v/v) via soxhlet extraction until all three ARVDs were undetected in the washing solvent using high performance liquid chromatography coupled with a photo-diode array detector. A non-imprinted polymer (NIP) was synthesised using the same reagents and quantities except for the templates. Both MIP and NIP were characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscope (SEM), N2 physisorption analysis, and elemental analysis. The FTIR results showed that the polymers were similar in structure and BET showed that they were mesoporous. The SEM showed that the MIP surface was rougher when compared to the NIP and characterization with TGA showed that they were both thermally stable. The synthesized MIP was used to study its adsorption kinetics and isotherms. Kinetics modelling revealed that the Pseudo-second-rate order kinetics was the best fitting model with correlation coefficient of 1 compared to Pseudo-first-rate order kinetics which had a correlation efficient of 0.81-0.983 for all target analytes. The best fitting adsorption isotherm was the Freundlich model with a correlation range of 0.9451-0.986 for compared to the Langmuir model which had correlation efficient of 0.6692-0.93390.0198-0.6782 for all target analytes. The traditional solid phase extraction and the MIP-based solid phase extraction methods were applied in distilled water samples spiked with 1 mg.L-1 of ARVDs and recoveries obtained were ranging from 91.68-94.59% and 97.20 to 99.68%, respectively. The MIP-based dispersive solid phase extraction method was successfully optimized with recoveries ranging from 100.28% to 102.60% for all three analytes. Selectivity studies were conducted using both the NIP and MIP with lamivudine and diclofenac as competitors. The recoveries obtained for the MIP ranged between 92% to 98% for the target analytes while they were 63% to 79% for competitors. These results showed good selectivity and strong affinity of the polymer towards the target analytes than the competitors. This is justified by the presence of imprinted recognition sites that have the same functional groups, size, and shape as the target analytes/templates hence recoveries were low for competitors. The MIP was more selective towards analytes of interest compared to the NIP (recoveries ranged from 87.9% to 91%) for the analytes of interest which indicates successful imprinting on the MIP. Reusability studies showed that the MIP can be reused for up to 8 cycles with recoveries above 92% for all target analytes. The developed, adopted, and validated methods were then applied to wastewater, tap water and river water samples from around KwaZulu-Natal. The concentrations obtained for abacavir, nevirapine and efavirenz were 10.65-295.90 μg.L-1 in wastewater, 1.95-13.15 μg.L-1 in river water, and 2.17-6.27 μg.L-1 in tap water. Efavirenz was the most dominant and consistently detected ARVD in all samples. The MIP-DSPE was the most sensitive and selective extraction technique compared to SPE and MIP-SPE. Umhlathuzana and Amanzimtoti were the most ARVD’s polluted wastewater treatment plants, whilst Northern wastewater water works was the least polluted. Camps Drift was the most ARVD’s polluted sampling point in Msunduzi river. Napierville and Scottsville showed the most contaminated tap water samples from suburbs around Pietermaritzburg.