Theses and dissertations (Applied Sciences)

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Hollow fibre liquid phase microextraction of pharmaceuticals in water and Eichhornia crassipes
(2019) Mlunguza, Nomchenge Yamkelani; Madikizela, Lawrence Mzukisi; Chimuka, Luke; Mahlambi, Precious N.
This work describes a simple and rapid method for the simultaneous isolation, enrichment, and quantitation of selected pharmaceuticals in aqueous environmental samples and Eichhornia crassipes. This was achieved by developing a hollow fiber liquid phase microextraction (HF-LPME) technique coupled with ultra-high-pressure liquid chromatography-high resolution mass spectrometry for the simultaneous extraction, pre- concentration and quantitation of four non-steroidal anti-inflammatory drugs (NSAIDs) and three antiretroviral drugs (ARVDs) from aqueous matrices and different segments of water hyacinth plant species. The target compounds for NSAIDs were naproxen (NAP), fenoprofen (FENO), diclofenac (DICLO) and ibuprofen (IBU) whereas the selected ARVDs included emtricitabine (FTC), tenofovir disoproxil (TD) and efavirenz (EFV). A multivariate approach by means of a half-fractional factorial design was used to optimize the HF-LPME technique focusing on six factors; donor phase (DP) pH, acceptor phase (AP) pH, extraction time, stirring rate, supported liquid membrane carrier composition (SLM carrier comp.) and salt content. Four of these factors (DP pH, AP pH, stirring rate and extraction time) were identified as vital for an enhanced enrichment of each of the selected NSAIDs and four of the previously mentioned vital factors including the SLM carrier composition were classified as significant for the selected ARVDs from aqueous samples into the hollow fiber. These essential factors were further paired according to their level of significance. The paired significant factors were then optimized using central composite designs (CCD) where empirical quadratic response models were used to visualize the response surface through contour plots, surface plots and optimization plots of the response outputs. The optimized factors for individual analytes belonging to each class were then altered to universal conditions for their simultaneous extraction from same sample solution. The acceptability of the universal conditions was defined using desirability studies. A composite desirability value of 0.7144 was obtained when the optimum factors of the three ARVDs were applied for their simultaneous extraction while a simultaneous extraction of NSAIDs had a desirability value of 0.7735. This implied that the set conditions were ideal for a combined extraction of the target compounds from the donor phase into the acceptor phase across a supported liquid membrane impregnated with a carrier molecule. For the simultaneous extraction of ARVDs, the universal optimum HF- LPME conditions were found to be DP pH of 4, AP HCl conc. of 200 mM (pH = 0.4) with SLM carrier comp. set at 4.5 (%w/w) and stirring at 1000 rpm. Under optimum conditions, the enrichment factors (EF) for ARVDs from aqueous phase were 78 (FTC), 111 (TD) and 24 (EFV). These conditions yielded recoveries in the range of 96 to 111%. The sensitivity of the analytical method through limits of quantification (LOQ) for the selected ARVDs in wastewater samples were 0.033 μg L-1 (FTC), 0.10 μg L-1 (TD) and 0.53 μg L-1 (EFV). The LOQ values were computed for surface water samples using the same target ARVDs were 0.169 μg L-1 (FTC), 0.018 μg L-1 (TD) and 0.113 μg L-1 (EFV). For NSAIDs, the overall conditions were DP pH of 10, AP pH of 3 at an extraction time of 60 min with stirring rate at 1000 rpm. The recoveries yielded under these optimum conditions for the target compounds ranged from 86 to 116%. The EF for the target NSAIDs from aqueous media were 49 (NAP), 126 (FENO), 93 (DICLO) and 156 (IBU). The LOQ values for each target NSAID in wastewater samples were 0.47 μg L-1 (NAP), 0.09 μg L-1 (FENO), 0.59 μg L-1 (DICLO) and 0.49 μg L-1 (IBU). The specific universal conditions were then used in the analysis of ARVDs in wastewater and surface water whereas for NSAIDs analysis, only wastewater samples were analysed. The surface water samples were obtained from North of Johannesburg in Hartbeespoort dam and the wastewater samples were collected from various wastewater treatment plants located in Durban, KwaZulu-Natal. The technique was also applied in the analysis of the target compounds in plant samples obtained from Hartbeespoort dam in North of Johannesburg, Umgeni river located in Springfield (Durban in KwaZulu-Natal) and Mbokodweni river located in south of Durban city, KwaZulu-Natal. The plant samples were first cut and separated into different segments (roots, stems and leaves) and the target analytes then extracted into 20 mL water using an optimized microwave assisted extraction technique (MAE). The HF-LPME technique initially optimized for water samples was then applied for pre-concentration of the target pharmaceuticals from the MAE water extract. Factors that were optimized for MAE technique were irradiation time and temperature for ARVDs whereas irradiation time and solvent volume were optimized for the extraction of NSAIDs. For extraction of both ARVDs and NSAIDs, the optimum irradiation time was 20 min while the irradiation temperature was set at 90 ̊C during the extraction of ARVDs and 100 ̊C for NSAIDs. Generally, the studied ARVDs were all detected in most samples with concentrations for FTC (0.11 – 3.10), TD (0.10 – 0.25) and EFV (1.09 up to 37.3) μg L-1 recorded in wastewater samples. EFV had the highest concentration of 37.3 μg L-1 in the wastewater effluent. The concentration of ARVDs in the roots of the water hyacinth ranged from 7.4 to 29.6 μg kg-1, 0.97 to 11.42 μg kg-1 in the stem and 0.98 to 9.98 μg kg-1 in the leaves of the aquatic plant. Roots of the water hyacinth plant had higher concentrations of the investigated ARVDs. Lastly, the NSAIDs were also detected in various wastewater samples with concentration for NAP (1.15 to 3.30) μg L-1, FENO (
Optimization of extraction techniques for the isolation and pre-concentration of pharmaceuticals in aquatic environments
(2021) Sigonya, Sisonke; Mdluli, Phumlane Selby; Chimuka, Luke
The occurrence of pharmaceuticals in South African aquatic environments has been reported in several studies. However, most of these reports focused on the occurrence of organic compounds in wastewater and surface water. There are very few studies reporting the presence and concentration of these compounds in seawater and coastal areas. Further, most studies have looked at only on one season. This study focussed on the optimisation of a SPE extraction method using Bond Elut Plexa cartridges for the identification and quantification three nonsteroidal anti-inflammatory drugs (NSAIDs), three antiretroviral drugs (ARVs) and a lipid regulator in coastal area of Durban city, South Africa covering four seasons. The optimised SPE conditions were as follows: 500 mL sample volume and at pH 5.8, 5 and 5 mL as conditioning and elution volumes, respectively. The flow rate ranging from 5 to 10 mL/min 10 and 5 mL/min as sample and elution flow rates. The extracted compounds were qualitatively and quantitatively detected by a high-performance liquid phase chromatographic instrument coupled to a photodiode array detector (HPLC-PDA). The recoveries ranged from 62 -102% with RSD values of 0.56 to 4.68% respectively for the determination of emtricitabine, tenofovir, naproxen, diclofenac, ibuprofen, efavirenz, and gemfibrozil. The analytical method was validated by spiking estuarine water samples with 5 µg L-1 of a mixture containing the target pharmaceuticals and the matrix detection limits (MDL) were established to be 0.62- 1.78 µg L-1 for the target compounds. The optimized method was applied to seasonal monitoring of pharmaceuticals at chosen study sites from winter and spring of 2019 and summer and autumn of 2020.The sum of emerging pollutants (ƩEP) were calculated based on each study site. The influent of the Kingsburgh WWTP (EFK) had the highest ƩEP of 144.88 µg L-1 in winter between the two wastewater treatment plants area in this study. The Northern WWTP influent (INN) had a total ƩEP of 117.11 µg L-1 in autumn, the Kingsburgh WWTP effluent (EFK) had a concentration 63.8 µg L-1 in autumn and a concentration 63.8 µg L-1 in summer and the Northern (EFN) had a total ƩEP of 43.97 µg L-1 in winter. A comparison between UMgeni (UR) and Kingsburgh river (KR) showed that the KR had the highest concentration of total ƩEP of 22.66 µg L-1 and UR with the total ƩEP of 18.3 µg L-1 both in winter and spring, respectively. The seawater EPs Blue Lagoon (BL) had the highest ƩEP of 46.75 µg L-1 in spring, subsequently Warner Beach bottom (WBB), Glen Ashley (GA) and Warner Beach top (WBT) with concentrations of 24.96 µg L-1 in summer, 13.29 µg L-1 in spring and 6.94 µg L-1 in autumn, respectively. Estuarine EPs had concentrations of 37.9 µg L-1 and 20.97 µg L-1 for Warner beach estuary (WE) and UMgeni estuary (UE) in winter. WBE having the highest concentration between the two. This showed a significant variation on the presence of these pharmaceuticals in different season.
Solid-phase extraction of selected acidic pharmaceuticals from wastewater using a molecularly imprinted polymer
(2017) Zunngu, Silindile Senamile; Mdluli, Phumlane S.; Madikizela, Lawrence Mzukisi; Chimuka, Luke
In this study, molecular modeling was used to investigate the intermolecular interactions between the functional monomer and ketoprofen which is an acidic pharmaceutical that possesses anti-inflammatory and analgesic activities. Ketoprofen is widely employed in medical care for treating musculoskeletal injury. This led to rational design of a molecularly imprinted polymer (MIP) that is selective to ketoprofen. Density functional theory (DFT) at B3LYP/6-31 level was used to investigate the intermolecular interaction between functional monomers and ketoprofen. Binding energy, ΔE, was used as an indication of the strength of the interaction that occurs between functional monomers and ketoprofen. 2-vinylpyridine (2-VP) as one of the functional monomers gave the lowest binding energy when compared to all the functional monomers investigated. Monomer-template interactions were further experimentally investigated using spectroscopic techniques such as Ultraviolet-visible and Fourier transform infrared (FTIR). A selective MIP for ketoprofen was synthesized using 2-vinylpyridine, ethylene glycol dimethacrylate, 1,1’-azobis(cyclohexanecarbonitrile), toluene/acetonitrile (9:1, v/v), and ketoprofen as a functional monomer, cross-linker, initiator, porogenic mixture, and template, respectively. The polymerization was performed at 60 °C for 16 h, and thereafter the temperature was increased to 80 °C for 24 h to achieve a solid monolith polymer. The non-imprinted polymer (NIP) was synthesized in a similar manner with the omission of ketoprofen. Characterization with thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD) showed that the synthesized polymers were thermally stable and amorphous. Morphology of the particles were clearly visible, with MIP showing rough and irregular surface compared to NIP on the scanning electron microscopy (SEM). The characterization of the prominent functional groups on both MIP and NIP were performed using FTIR and nuclear magnetic resonance (NMR). The existence of hydroxyl was observed in the MIP; this was due to the presence of ketoprofen in the cavity. Prominent carbonyl group was an indication of the cross-linker present in both polymers. The synthesized MIP was applied as a selective sorbent in the solid-phase extraction of ketoprofen from the water. The extracted ketoprofen was monitored by high performance liquid chromatography (HPLC) coupled with UV/Vis detector. Several parameters were investigated for maximum recovery of ketoprofen from the spiked deionized water. The optimum method involved the conditioning of 14 mg MIP sorbent with 5 mL of methanol followed by equilibrating with 5 mL of deionized water adjusted to pH 2.5. Thereafter, 50 mL sample (pH 5) was loaded into the cartridge containing MIP sorbent followed by washing and eluting with 1% TEA/H2O and 100% methanol, respectively. Eluted compounds were quantified with HPLC. MIP was more selective to ketoprofen in the presence of other structural related competitors. The analytical method gave detection limits of 0.23, 0.17, and 0.09 mg L-1 in wastewater influent, effluent, and deionized water, respectively. The recovery for the wastewater influent and effluent spiked with 5 µg L-1 of ketoprofen was 68%, whereas 114% was obtained for deionized water. The concentrations of ketoprofen in the influent and effluent samples were in the ranges of 22.5 - 34.0 and 1.14 - 5.33 mg.L-1, respectively. The relative standard deviation (RSD) given as ± values indicates that the developed analytical method for the analysis of ketoprofen in wastewater was rapid, affordable, accurate, precise, sensitive, and selective.