TUT DIGITAL OPEN REPOSITORY

Recent Submissions

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    Improved derivatization protocol for simultaneous determination of alkylphenol ethoxylates and brominated flame retardants followed by gas chromatography–mass spectrometry analyses.
    (Water Research Commission, 2014-01-01) Chokwe, T.B.; Okonkwo, J.O.; Sibali, L.L.; Ncube, E.J.
    An improved derivatization protocol for the simultaneous determination of alkylphenol ethoxylates and brominated flame retardants with heptafluorobutyric anhydride under triethylamine amine base was investigated. The derivatization reaction was completed in 30 min at 50°C using hexane as solvent. Under these conditions, it was observed that alkylphenol ethoxylates and tetrabromobisphenol A were derivatized successfully in the presence of hexabromocyclododecane, lower congeners of polybrominated biphenyls and polybrominated diphenyl ethers. The improved protocol was applied to recovery of analytes of interest from simulated water samples after solid phase extraction. The recoveries achieved were above 60%. The limit of detection and limit of quantification ranged from 0.01–0.20 µg/ℓ and 0.05–0.66 µg/ℓ, respectively.
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    Hazard assessment of microcystins from the household's drinking water.
    (ALÖKI Applied Ecological Research and Forensic Institute Ltd., 2016-04-23) Mokoena, M.M.; Mukhola, M.S.; Okonkwo, O.J.
    Cyanobacteria produce toxins which are hazardous to the health of people who are using water that is contaminated. The hazard quotient suggested by United States Environmental Protection Agency (USEPA) was used to assess the human health hazard of using contaminated water containers. There was no statistically significant difference (P = 0.5511) in the level of microcystin between blooming and decaying seasons. Findings show that all treated water samples in the containers were below the 1.0 µg/L level, which underscore this important issue: drinking water from treated water in containers has no adverse health effect when compared to drinking water from non-treated water containers, whether used by adults or children. In conclusion, collecting and storing of either pre-treated or non-treated water using containers needs post-treatment before drinking.
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    Polybrominated diphenyl ethers (PBDEs) in eggshells of the southern ground-hornbill (bucorvus leadbeateri) and wattled Crane (bugeranus carunculatus) in South Africa.
    (Elsevier, 2014-09-11) Daso, Adegbenro P.; Okonkwo, Jonathan O.; Jansen, Raymond; Forbes, Patricia B.C.; Kotzé, Antoinette; Rohwer, Egmont R.
    This study was undertaken to assess the levels of eight PBDE congeners, namely: PBDE-17, 47, 100, 99, 154, 153, 183 and 209 in eggshells of Southern Ground-Hornbill (SGH) Bucorvus leadbeateri and Wattled Crane (WC) Bugeranus carunculatus obtained from different nesting sites within the eastern savanna of Limpopo Province and the midlands of KwaZulu-Natal, respectively. Analyses were performed using gas chromatography–mass spectrometry employing the electron impact ionization technique. The results obtained indicated that the lower brominated congeners were predominant in both species. The total PBDEs ranged between not detected (ND) to 264 lg g1 lipid weight and 5.98–7146 lg g1 lipid weight in the SGH and WC samples, respectively. More so, the mean recoveries of the 13C-labelled surrogate standards ranged between 40% (PBDE-100) and 136% (PBDE-99). The potential hazards to these birds via PBDEs exposure were evaluated by determining the hazard quotients (HQs) by employing the established Lowest Observed Effect Level (LOEL) values associated with impaired pipping and hatching success as well as that associated with impaired reproduction. HQs values varying from 0.58 to 0.94 and 27.71 to 45.27, respectively were obtained for SGH and WC species. This implies that the SGH populations are exposed to low to moderate hazards, while the WC populations are susceptible to high hazards. Considering the potential threats posed by PBDEs, particularly to the WC species, it is likely that exposure to the current environmental levels of PBDEs by these birds may contribute to their reduced breeding success and declining population trends.
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    Optimization of horseradish peroxidase immobilization on glassy carbon electrode based on maize tassel-multiwalled carbon nanotubes for sensitive copper(II) Ion detection.
    (Elsevier, 2013-11-16) Moyo, Mambo; Okonkwo, Jonathan O; Agyei, Nana M.
    Enzymatic procedures for measuring trace metal ions, based on the inhibitive action of these metals on horseradish peroxidase (HRP) enzyme activity, have been developed. Glassy carbon electrode (GCE) modified with maize tassel- multiwalled carbon nanotubes (MT-MWCNT) was used as an immobilizing surface of HRP through electrostatic attractions. The voltammetric and amperometric response of HRP was affected by the presence of metal ion, which caused a decrease in the current intensity. The experimental optimum working conditions of MT: MWCNT amount (10 μL, 4:1), enzyme loading (10 μL, 10 mg mL-1), nafion amount (0.5 μL, 0.3%), pH 7, and potential applied (300 mV) were established. Using Cu2+ as a model divalent metal ion, the inhibition rate was proportional to the concentration in the range from 0.068-2.0 mg L-1 with a limit of detection of 4.2 μg L-1. Representative Dixon and Cornish-Bowden plots showed that the reaction was reversible and mixed. Under these conditions, repeatability and reproducibility of HRP/MT-MWCNT biosensor was determined, reaching values below 10% in terms of relative standard deviation.
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    Optimization and simultaneous determination of alkyl phenol ethoxylates and brominated flame retardants in water after SPE and heptafluorobutyric anhydride derivatization followed by GC/MS.
    (Springer, 2012-07-02) Chokwe, Tlou B.; Okonkwo, Jonathan O.; Sibali, Linda L.; Ncube, Esper J.
    A gas chromatography–mass spectrometry (GC–MS) method was investigated for the simultaneous analysis of two types of endocrine disrupting compounds (EDCs), i.e., alkylphenol ethoxylates and brominated flame retardants (BFRs), by extraction and derivatization followed by GC–MS. Different solid phase extraction (SPE) cartridges (Cleanert PestiCarb, C18, Cleanert-SAX and Florosil), solvents (toluene, tetrahydrofuran, acetone, acetonitrile and ethyl acetate) and bases (NaHCO3, triethylamine and pyridine) were tested and the best chromatographic analysis was achieved by extraction with Strata-X (33 lm, Reverse Phase) cartridge and derivatization with heptafluorobutyric anhydride at 55 degrees C under Na2CO3 base in hexane. It was observed that APE together with lower substituted PBBs (PBB1, PBB10, PBB18 and PBB49), HBCD and TBBPA can be determined simultaneously under the same GC conditions. This simple and reliable analytical method was applied to determining trace amounts of these compounds from wastewater treatment plant samples. The recoveries of the target compounds from simulated water were above 60 %. The limit of detection ranged from 0.01 to 0.15 lg L-1 and the limit of quantification ranged from 0.05 to 0.66 lg L-1. There were no appreciable differences between filtered and unfiltered wastewater samples from Leeuwkil treatment plant although concentration of target analytes in filtered influent was slightly lower than the concentration of target analytes in unfiltered influent water. The concentrations of the target compounds from the wastewater treatment were determined from LOQ upwards.