Luke Chimuka

On-line solid-phase extraction of triazine herbicides using a molecularly imprinted polymer for selective sample enrichment.

A coupled-column system, consisting of a combination of a molecularly imprinted polymer (MIP) and a C(18)-silica column, was used for selective triazine detection in the HPLC mode. Complex aqueous samples, spiked with triazines, were selectively extracted by the MIP followed by subsequent identification by analytical reversed-phase chromatography. The MIP showed good performance for selectively discriminating triazines from humic acid, whereas urine and apple extract had some tendency to be retained by the MIP. Enrichment was observed in all cases, and triazine-enrichment factors of up to 100 could be recorded, with good extraction efficiency (74-77%). The results indicate that the high selectivity of MIPs can be favorably used for selective sample enrichment in conjunction with reversed-phase HPLC.

Selective extraction of triazine herbicides from food samples based on a combination of a liquid membrane and molecularly imprinted polymers.

A selective extraction technique based on the combination of liquid membrane (microporous membrane liquid-liquid extraction) and molecularly imprinted polymers (MIP) was applied to triazines herbicides in food samples. Simazine, atrazine and propazine were extracted from aqueous food 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 molecularly imprinted polymers particles in the organic acceptor phase, extraction time, and type of organic acceptor solvent and desorption solvent. An extraction time of 90 min and 50mg of MIP were found to be optimum parameters. 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. The selectivity of the technique was demonstrated by extracting spiked lettuce and apple extracts where clean chromatograms were obtained compared to liquid membrane extraction alone or to the microporous membrane liquid-liquid extraction - non-imprinted polymer combination. The MIP showed a certain degree of group specificity and the extraction efficiency in lettuce extract was 79% (0.72) for simazine, 98% (1.55) for atrazine and 86% (3.08) for propazine.

Selective extraction of triazine herbicides based on a combination of membrane assisted solvent extraction and molecularly imprinted solid phase extraction

A selective extraction technique based on the combination of membrane assisted solvent extraction and molecularly imprinted solid phase extraction for triazine herbicides in food samples was developed. Simazine, atrazine, prometon, terbumeton, terbuthylazine and prometryn were extracted from aqueous food samples into a hydrophobic polypropylene membrane bag containing 1000μL of toluene as the acceptor phase along with 100mg of MIP particles. In the acceptor phase, the compounds were re-extracted onto MIP particles. The extraction technique was optimised for the type of organic acceptor solvent, amount of molecularly imprinted polymers particles in the organic acceptor phase, extraction time and addition of salt. Toluene as the acceptor phase was found to give higher triazine binding onto MIP particles compared to hexane and cyclohexane. Extraction time of 120min and 100mg of MIP were found to be optimum parameters. Addition of salt increased the extraction efficiency for more polar triazines. The selectivity of the technique was demonstrated by extracting spiked cow pea and corn extracts where clean chromatograms were obtained compared to only membrane assisted solvent extraction or only molecularly imprinted solid phase extraction. The study revealed that this combination may be a simple way of selectively extracting compounds in complex samples.

Critical parameters in a supported liquid membrane extraction technique for ionizable organic compounds with a stagnant acceptor phase

The reviews cover important critical parameters that are often optimized in a supported liquid membrane extraction technique in both flat sheet and hollow fibre designs for ionizable organic molecules. Understanding of these parameters can enable one to predict the behavior of the compound before hand and thus reduce the number of optimization experiments. Moreover, less number of experiments can be also generated using statistical techniques which are now becoming more commonly used. Supported liquid membrane extraction optimal parameters such as the conditions of the pH of the acceptor and donor phases should easily be fixed from the pKa values of the compounds. Other parameters, including the polarity of the compound can help to predict the partitioning into the membrane and the behavior of the compound. The influence of parameters such as temperature on the mass transfer in supported liquid membrane depends on the design of the module, experimental design and type of mass transfer controlling the extraction process.

Molecularly imprinted polymers targeting quercetin in high-temperature aqueous solutions.

Molecularly imprinted polymers (MIPs) targeting quercetin were prepared from 4-vinylpyridine and ethylene dimethacrylate (EDMA) under various solvent systems with the aim to form MIPs with high recognition for the quercetin molecule in aqueous systems at high temperature. A MIP prepared from the three-component solvent mixture of THF/H(2)O/MeOH showed potential in its application for the determination of quercetin in plants (onion). The polymer particles before and after washing were characterized by infrared spectroscopy and thermogravimetric analysis. Surface morphology was recorded by scanning electron microscopy. The binding capacity of the MIPs was investigated at 25 and 84 °C, respectively, in batch mode. Parameters, including the influence of pH, extraction time and binding capacity, were evaluated. The slopes for the effect of extraction time revealed that the mass transfer of the analytes was higher at 84 °C than at 25 °C. Also, the binding capacity for the most promising MIP and its corresponding NIP was higher at 84 °C. The binding capacity for the MIP was ~30 μmol g(-1) at 25 °C and ~120 μmol g(-1) at 84 °C, while for the corresponding NIP, it was ~15 and ~90 μmol g(-1), at 25 and 84 °C, respectively. A demonstration of MIP selectivity at higher temperature using standard solutions of selected flavonols showed that the MIP still retained its selectivity for quercetin. Similar selectivity was observed when preliminary application studies on aqueous yellow onion extracts were investigated.

Potential of combining of liquid membranes and molecularly imprinted polymers in extraction of 17β-estradiol from aqueous samples.

The potential of combination of liquid membranes (microporous membrane liquid-liquid extraction) and molecularly imprinted polymers (MIPs) was performed using 17beta-estradiol (E2) as model compound. The model compound was extracted from aqueous sample through a hydrophobic porous membrane that was impregnated with hexane/ethyl acetate (3:2), which also formed part of the acceptor phase. In the acceptor phase, the compound was bound onto MIP particles that were also part of the organic phase. The potential of such combination was optimised for the type and amount of MIP particles in the organic acceptor phase, the extraction time, and the type of organic acceptor solvent. Ultrasound assisted binding of E2 onto MIP particles was also investigated. MIPs prepared by precipitation polymerization were found to be superior to those prepared by bulk polymerization. Increase in the extraction time and the amount of MIP particles in the acceptor phase led to more E2 binding onto the MIP particles. Hexane/ethyl acetate (3:2) as an organic acceptor was found to give higher E2 binding onto MIP particles compared to toluene, diethyl ether, and hexane. Ultrasound was furthermore found to increase the binding of E2 onto MIP particles. The selectivity of the technique was demonstrated by extracting wastewater and where clean chromatograms were obtained compared to liquid membrane extractions (SLMs) alone.

Determination of ibuprofen, naproxen and diclofenac in aqueous samples using a multi-template molecularly imprinted polymer as selective adsorbent for solid-phase extraction

This study describes the application of multi-template molecularly imprinted polymer (MIP) as selective sorbent in the solid-phase extraction (SPE) of naproxen, ibuprofen and diclofenac from wastewater and river water. MIP was synthesized at 70°C by employing naproxen, ibuprofen and diclofenac as multi-templates, ethylene glycol dimethacrylate, 2-vinyl pyridine and toluene as cross-linker, functional monomer and porogen, respectively. Wastewater and river water samples (pH 2.5) were percolated through SPE cartridge packed with 50mg of the MIP. The cartridge was washed with 2mL of methanol-water 10:90% (v:v) prior to elution with 2mL of acetic acid-acetonitrile 20:80% (v:v). Quantification of eluted compounds was performed with high performance liquid chromatography equipped with photo diode array detection. The detection limits were 0.15, 1.00 and 0.63μgL(-1) for naproxen, ibuprofen and diclofenac, respectively. Recoveries for naproxen, ibuprofen and diclofenac in deionized water spiked at 5 and 50μgL(-1) were greater than 80%. Ibuprofen was the most frequently detected compound with maximum concentrations of 221, 67.9 and 11.4μgL(-1) in wastewater influent, effluent and river water, respectively.

Synthesis, adsorption and selectivity studies of N-propyl quaternized magnetic poly(4-vinylpyridine) for hexavalent chromium

The ability of solid N-propyl quaternized magnetic poly(4-vinylpyridine) for the extraction of chromium(VI) in aqueous solutions was investigated. For the synthesized Cr(VI) magnetic polymers, the optimum pH obtained was 4 for both the magnetic ion imprinted polymer (IIP) and the corresponding non-ion imprinted polymer NIP. The amount of the adsorbent which gave the maximum adsorption was determined to be 20 and 65 mg for the magnetic IIP and NIP, respectively. A Cr(VI) concentration which was adsorbed maximally was 5 mg L(-1) which was therefore taken as the optimum. The maximum adsorption capacities for the magnetic polymers were 6.20 and 1.87 mg g(-1) for the magnetic IIP and NIP, respectively. The optimum time for the adsorption of the Cr(VI) analyte was determined as 40 min. The prepared magnetic ion imprinted polymer showed good selectivity towards Cr(VI). The order of selectivity of the investigated anions followed the sequence: Cr2O7(2-)>SO4(2-)>F(-)>NO3(-).

Molecular imprinted polymer for solid-phase extraction of flavonol aglycones from Moringa oleifera extracts

Molecular imprinted polymer produced using quercetin as the imprinting compound was applied for the extraction of flavonol aglycones (quercetin and kaempferol) from Moringa oleifera methanolic extracts obtained using heated reflux extraction method. Identification and quantification of these flavonols in the Moringa extracts was achieved using high performance liquid chromatography with ultra violet detection. Breakthrough volume and retention capacity of molecular imprinted polymer SPE was investigated using a mixture of myricetin, quercetin and kaempferol. The calculated theoretical number of plates was found to be 14, 50 and 8 for myricetin, quercetin and kaempferol, respectively. Calculated adsorption capacities were 2.0, 3.4 and 3.7 μmol/g for myricetin, quercetin and kaempferol, respectively. No myricetin was observed in Moringa methanol extracts. Recoveries of quercetin and kaempferol from Moringa methanol extracts of leaves and flowers ranged from 77 to 85% and 75 to 86%, respectively, demonstrating the feasibility of using the developed molecularly imprinted SPE method for quantitative clean-up of both of these flavonoids. Using heated reflux extraction combined with molecularly imprinted SPE, quercetin concentrations of 975 ± 58 and 845 ± 32 mg/kg were determined in Moringa leaves and flowers, respectively. However, the concentrations of kaempferol found in leaves and flowers were 2100 ± 176 and 2802 ± 157 mg/kg, respectively.

Preparation, characterization and application of NaHCO3 leached bulk U(VI) imprinted polymers endowed with γ-MPS coated magnetite in contaminated water.

A new type of ion imprinted polymer (IIP) embedded with γ-methacryloxypropyltrimethoxysilane (γ-MPS) coated magnetic particles for selective extraction of uranyl ions was synthesized by bulk polymerization. The performance of the magnetic sorbent on the extraction of U(VI) was evaluated by various parameters which included the influence of pH, amount of the magnetic polymers, contact time and initial U(VI) concentration. The adsorption capacity of the magnetic polymers was found to be 1.1 and 0.95mgg(-1) for the IIP and its control ion non-imprinted polymer (NIP), respectively. The optimum amount of the sorbent was 50mg for an initial concentration of 2.5mgL(-1). The prepared magnetic imprinted sorbent displayed an uptake with a time of 45min considered optimum. The magnetic polymer displayed good selectivity and exhibited good reusability. Studies from binary mixtures of metal ions in aqueous solutions showed that the magnetic adsorbent selectivity following the order: U(VI)>Ni(II)>Pb(II). Experimental results illustrated the potential application of magnetic ion imprinted polymer sorbents for selective removal of U(VI) from contaminated water.