| 1. |
- Amdany, Robert, et al.
(författare)
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Assessment of bioavailable fraction of POPS in surface water bodies in Johannesburg City, South Africa, using passive samplers : an initial assessment
- 2014
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Ingår i: Environmental Monitoring & Assessment. - : Springer Netherlands. - 0167-6369 .- 1573-2959. ; 186:9, s. 5639-5653
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the semipermeable membrane device (SPMD) passive samplers were used to determine freely dissolved concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in selected water bodies situated in and around Johannesburg City, South Africa. The devices were deployed for 14 days at each sampling site in spring and summer of 2011. Time weighted average (TWA) concentrations of the water-borne contaminants were calculated from the amounts of analytes accumulated in the passive samplers. In the area of interest, concentrations of analytes in water ranged from 33.5 to 126.8 ng l(-1) for PAHs, from 20.9 to 120.9 pg l(-1) for PCBs and from 0.2 to 36.9 ng l(-1) for OCPs. Chlorinated pesticides were mainly composed of hexachlorocyclohexanes (HCHs) (0.15-36.9 ng l(-1)) and dichlorodiphenyltrichloromethane (DDT) with its metabolites (0.03-0.55 ng l(-1)). By applying diagnostic ratios of certain PAHs, identification of possible sources of the contaminants in the various sampling sites was performed. These ratios were generally inclined towards pyrogenic sources of pollution by PAHs in all study sites except in the Centurion River (CR), Centurion Lake (CL) and Airport River (AUP) that indicated petrogenic origins. This study highlights further need to map up the temporal and spatial variations of these POPs using passive samplers.
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| 2. |
- Amdany, Robert, et al.
(författare)
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Investigating the temporal trends in PAH, PCB and OCP concentrations in Hartbeespoort Dam, South Africa, using semipermeable membrane devices (SPMDs)
- 2014
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Ingår i: Water S.A.. - : South African Water Research Commission. - 0378-4738 .- 1816-7950. ; 40:3, s. 425-436
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Tidskriftsartikel (refereegranskat)abstract
- The seasonal variability of persistent organic pollutants in Hartbeespoort Dam, South Africa, was investigated using semipermeable membrane devices (SPMDs) as passive samplers. Freely dissolved waterborne polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were sampled to investigate seasonal changes in their concentrations. Exposure of the passive samplers was done for 14 days at the same sampling site in each of the four seasons of the year, in 2011. The SPMD-derived analyte amounts enabled the calculation of time-weighted averages of free dissolved waterborne levels of the contaminants. Concentrations ranged from 30.0 ng.l(-1) to 51.5 ng.l(-1) for PAHs, 38 pg l(-1) to 150 pg.l(-1) for PCBs, 9.2 to 10.4 ng.l(-1) for HCHs and 0.3 to 0.8 ng.l(-1) for DDTs, respectively. It was also noted that the winter season generally exhibited higher contaminant concentrations for most compounds studied, which likely reflects the seasonality of their atmospheric deposition. An attempt was also made to identify possible sources of PAH contaminants in the dam by examining PAH ratios. These diagnostic ratios were inclined towards pyrogenic sources of pollution, except for the winter season where both pyrogenic and petrogenic sources likely contribute to the contamination pattern.
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| 3. |
- Chimuka, Luke, et al.
(författare)
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Application of membrane-based extraction techniques to food and agricultural samples
- 2006
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Ingår i: Modern extraction techniques; food and agricultural samples (ACS symposium series). - 0097-6156. - 9780841239401 - 0841239401 ; 926, s. 149-162
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The use of membrane-based extractions are increasingly seen as offering an alternative to conventional sample preparation procedures in analysis of chemical species in both food and agricultural samples. In this article, emphasis is placed on the attractiveness of membrane based extraction techniques to a variety of food and agricultural samples such as circulating nutrient solutions, fruit juices, fruits, beverages, vegetables, food oils and others. Examples of membrane based applications demonstrating how selective these techniques are even for food and agricultural samples are given.
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| 4. |
- Mhaka, Byron, et al.
(författare)
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Selective extraction of triazine herbicides from food samples based on a combination of a liquid membrane and molecularly imprinted polymers
- 2009
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1216:40, s. 6796-6801
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Tidskriftsartikel (refereegranskat)abstract
- 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 50 mg 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.
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| 5. |
- Nemulenzi, Olga, et al.
(författare)
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Potential of combining of liquid membranes and molecularly imprinted polymers in extraction of 17 beta-estradiol from aqueous samples
- 2009
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Ingår i: Journal of Separation Science. - : Wiley. - 1615-9306 .- 1615-9314. ; 32:11, s. 1941-1948
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Tidskriftsartikel (refereegranskat)abstract
- The potential of combination of liquid membranes (microporous membrane liquid-liquid extraction) and molecularly imprinted polymers (MIPs) was performed using 17 beta-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.
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| 6. |
- Nuapia, Yannick, et al.
(författare)
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Selective pressurized hot water extraction of nutritious macro-nutrients vs. micro-nutrients in Moringa oleifera leaves—a chemometric approach
- 2020
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Ingår i: Analytical and Bioanalytical Chemistry. - : Springer Science and Business Media LLC. - 1618-2642 .- 1618-2650. ; 412:11, s. 2495-2503
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Tidskriftsartikel (refereegranskat)abstract
- Moringa oleifera leaves are widely used in traditional medicine as a food supplement because they are high in essential and nutritious content. Pressurized hot water extraction (PHWE), which is a green approach, was used for the recovery of the macro-nutrient and micro-nutrient elements from dried leaf powder of Moringa oleifera. In this study, response surface methodology was applied to assess the influence of temperature (50–200 °C) and time (5–60 min) on the extractability pattern of macro-nutrient and micro-nutrient elements from the leaves of Moringa oleifera when processed by PHWE. The quantification of macro-nutrient elements such as Ca, K and Mg and micro-nutrient elements like Al, Co, Cr, Cu, Fe, Ni and Zn from the leaves was determined using inductively coupled plasma optical emission spectroscopy (ICP-OES). Obtained results revealed that the extraction of macro-nutrient elements from the Moringa oleifera leaves was enhanced by increasing the extraction time more than the extraction temperature. On the contrary, the amounts of extractable micro-nutrient elements were increased by increasing the extraction temperature. Hence, the recovery for macro-nutrient elements ranged from 88 to 98% while for micro-nutrients it ranged from 21 to 46%. This implies that macro-nutrient elements are extracted with relatively high selectivity in relation to micro-nutrient elements in Moringa dried leaf powder using the PHWE technique.
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| 7. |
- Pakade, Vusumzi, et al.
(författare)
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Molecular imprinted polymer for solid-phase extraction of flavonol aglycones from Moringa oleifera extracts
- 2013
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Ingår i: Journal of Separation Science. - : Wiley. - 1615-9314 .- 1615-9306. ; 36:3, s. 548-555
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Tidskriftsartikel (refereegranskat)abstract
- 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 mu mol/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.
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