Mathew Muzi Nindi

Development and application of a dispersive liquid-liquid microextraction method for the determination of tetracyclines in beef by liquid chromatography mass spectrometry.

A rapid, cost effective and environmentally friendly extraction method, based on dispersive liquid-liquid microextraction (DLLME) was developed for the determination of six tetracyclines in meat destined for human consumption. Meat extracts were analysed for tetracyclines using liquid chromatography tandem mass spectrometry (LC-MS/MS), a sensitive and selective analytical technique. Various factors influencing the pre-concentration of tetracyclines such as sample pH, type and volume of both disperser solvent and extraction solvent were optimized. Validation parameters such as calibration function, limit of detection (LOD), limit of quantification (LOQ), detection capability (CCα), decision limit (CCβ), accuracy and precision were established according to Commission Decision 2002/657/EC. Linearity in the range of 25-200 µg kg(-1) was obtained with regression coefficients ranging from 0.9991 to 0.9998. Recoveries of spiked blank muscle samples at three levels (50, 100 and 150 µg kg(-1)) ranged from 80% to 105% and reproducibility was between 2% and 7%. LODs and LOQs ranged from 2.2 to 3.6 µg kg(-1) and from 7.4 to 11.5 µg kg(-1) respectively while CCα ranged from 105 to 111 µg kg(-1) and CCβ ranged from 107 to 122 µg kg(-1). The proposed method compared well with the existing accepted dispersive solid phase extraction method and was successfully applied to the pre-concentration and determination of tetracyclines in meat samples. Eleven of the thirty bovine muscle samples obtained from local abattoirs and butcheries were found to contain residues of two tetracycline antibiotics (chlortetracycline and oxytetracycline), with oxytetracycline being the most detected. Concentration levels of the tetracycline residues detected in bovine muscle samples were lower (12.4 and 68.9 µg kg(-1)) than the stipulated European Union maximum residue level (MRL) of 100 µg kg(-1), hence the meat was fit for human consumption. From this work it can be concluded that the DLLME is indeed a greener sample preparation method and could be used as an alternative to dispersive solid phase microextraction (dSPE).

Chemical, structural and thermal properties of Gonometa postica silk fibroin, a potential biomaterial

In the present study, chemical, structural and thermal properties of fibroin from Gonometa postica, a wild silkmoth species were investigated. Silk from Gonometa rufobrunnea and Bombyx mori species were included in this study for comparison. The results indicated that G. postica and G. rufobrunnea silk exhibited similar properties whereas distinct differences were observed with B. mori silk. Amino acid analysis showed that glycine, alanine and serine accounted for more than 70% of the total amino acid content in all species. The amount of polar amino acids in Gonometa fibroin was significantly higher than for B. mori fibroin suggesting increased chemical reactivity of the former. The abundance of basic amino acids in Gonometa fibroin makes it a promising biomaterial in cell and tissue culture. Structural analysis revealed a unique β-sheet structure of Gonometa fibroin which is comprised of both poly-alanine and poly-glycine-alanine sequences. The maximum decomposition temperatures for Gonometa and B. mori fibroin were 350°C and 320°C respectively. The influence of amino acid composition on structural and thermal properties of the silks is also discussed.

Characterization of PM10 samples from Vanderbijlpark in South Africa.

In this study, mass concentrations and physico-chemical characteristics of suspended particulates of aerodynamic size 10 μm (PM10) were evaluated. A dual E-Sampler which combines the light scatter and the gravimetric filter methods was used. Sampling occurred between August and December 2009. Scanning Electron Microscope – Energy Dispersive Spectrometry (SEM-EDS) and Inductively Coupled Plasma 6000 were used for elemental and physical characterization. The highest daily average mass concentration measured was 0.03543 mg/m3 and was below the international and national daily limit of 0.150 mg/m3, as well as the strict Vaal Triangle regional standard of 0.075 μg/m3. Relatively high daily average mass concentrations were obtained during the winter period. Concentrations of evaluated heavy metals decreased in the following order: iron (Fe) > manganese (Mn) > zinc (Zn) > copper (Cu) > vanadium (V) > titanium (Ti) > nickel (Ni) > lead (Pb). Positive correlations were established between Zn and Pb (r = 0.916); Zn and Mn (r = 0.883); Zn and V (0.984); Zn and Ni (r = 0.877); Zn and Fe (r = 0.914), which suggests common sources. However, Zn and Ti (r = 0.522); Zn and Cu (0.781) were poorly correlated.

Fabrication and Structural Characterization of Electrospun Nanofibres from Gonometa Postica and Gonometa Rufobrunnae Regenerated Silk Fibroin

AbstractWe report the fabrication and characterization of electrospun nanofibres from Gonometa postica and Gonometa rufobrunnae silk fibroin indigenous to Southern Africa. Nanofibres were electrospun from regenerated silk fibroin (RSF) powders obtained by freeze drying or via rotary evaporation using methanol as a desiccant. Optimal electrospinning conditions employed trifluoroacetic acid as a solvent. The solution of RSF powder prepared by rotary evaporation was electrospun at a lower concentration (27% w/v) than that of freeze dried RSF powder (40% w/v). Concentration of the fibroin solution had the most influence on electrospinnability whereas voltage and flow rate mainly affected the fibre morphology. Scanning electron microscopy (SEM) showed that nanofibres from freeze dried and rotary evaporator dried RSF powders had diameters ranging from 300–760 and 400–1,000 nm respectively. Fourier transform infrared (FTIR) analysis revealed that the RSF powders were mainly composed of β-sheets, similar to degummed silk fibroin. The nanofibres, however, exhibited predominantly random coil/α-helical structure showing degradation of the native silk structure. β-sheet structure in the nanofibres was restored upon solvent treatment resulting in improved water stability. The extent of structural transformation was dependent on the type of solvent used. This study confirms the feasibility of fabricating Gonometa fibroin into stable nanofibrous structures that could be used as scaffolds in biotechnological and biomedical applications.

Environmental fate and ecotoxicological effects of antiretrovirals: A current global status and future perspectives

The therapeutic efficacy of antiretroviral drugs as well as challenges and side effects against the human immunodeficiency virus is well documented and reviewed. Evidence is available in literature indication that antiretrovirals are only partially transformed and become completely excreted from the human body in their original form and/or as metabolites in urine and feces. The possibility of massive release of antiretrovirals through human excreta that enters surface water through surface runoff and wastewater treatment plant effluents is now of environmental concern because the public might be experiencing chronic exposure to antiretrovirals. The primary concern of this review is limited data concerning environmental fate and ecotoxicity of antiretrovirals and their metabolites. The review aims to provide a comprehensive insight into the evaluation of antiretrovirals in environmental samples. The objective is therefore to assess the extent of analysis of antiretrovirals in environmental samples and also look at strategies including instrumentation and predictive models that have been reported in literature on the fate and ecotoxicological effects due to presence of antiretrovirals in different environmental compartments. The review also looks at current challenges and offers possible areas of exploration that could help minimize the presence of antiretrovirals in the environment.