Electrospray ionization mass spectrometry (ESI-MS) is a powerful method to monitor organometallic reactions. It is fast at generating spectrum, soft to fragile organometallic compounds and sensitive to intermediates in low concentration. When coupled with the pressurized sample infusion (PSI) that helps to continuously inject reacting solution to the MS, both an inert-gas atmosphere and real-time reaction monitoring can be achieved. Also collision induced dissociation (CID) of MS can be used to probe the relative binding affinities of phosphine ligands in ruthenium complexes. PSI ESI-MS can be coupled with Fourier transform infrared spectroscopy (FTIR) to monitor the rhodium-catalyzed hydroacylation simultaneously. This technique expands the dynamic range to 5 magnitudes. The effect of mass-transfer in heterogeneous hydrogenation of charge-tagged alkyne was also studied by PSI ESI-MS. In this study cross area, stirring effect, catalyst loading and hydrogen concentration were considered and tested. Also in the study an interesting finding reveals in heterogeneity of the solution. Relative binding affinities of different phosphine ligands were attained from comparing the relative intensities of fragmentation products from MS/MS. And the phosphine ligand substitution reaction was monitored by the ESI-MS in a real-time manner. A competitive dissociative substitution mechanism was proposed and confirmed by the simulation and modeling of COPASI. / Graduate

Challenges encountered in pathogen identification and detection include the genetic heterogeneity of strains within species of some foodborne pathogens, isolation of injured cells, mixed strains or mixed species contamination of foods, and differentiation between viable and dead cells. The first objective of this research was to evaluate an isolation medium that was based on time-delayed release (5 to 6 h) of selective agents in tablet format to a modified Listeria recovery enrichment broth (mLRB) medium for enhanced and rapid recovery of injured Listeria. The second objective involved the use of Fourier transform infrared (FT-IR) spectroscopy and chemometric analysis for the differentiation of: Listeria monocytogenes epidemic clones (ECs); viable versus heat-killed populations; different mixed strains and mixed species of Listeria; and different injury treatments and repair in Listeria populations. Nitrite- or acid-injured Listeria at approximately 10 CFU/ml were recovered in mLRB medium, and cell populations enumerated at various times (12 to 48 h) of incubation at 37oC. Analysis of variance revealed that acid-injured Listeria populations in mLRBS6 (mLRB plus the selective agents at 6 h) were significantly higher (P < 0.05) than those in mLRBS0 (mLRB plus the selective agents at 0 h) at 24 h; however, the differences in populations on these two media were not significant for nitrite-injured Listeria. Cell populations of four strains of Listeria recovered in mLRBTD (mLRB plus the time-delayed release tablets of the selective agents) were significantly higher than when those strains were enriched in the U.S. Food and Drug Administration (FDA), International Organization for Standardization (ISO), and U.S. Department of Agriculture (USDA) broths at 24 h. Comparison between artificially contaminated milk and meat samples with a four-strain cocktail of Listeria resulted in cell populations that were significantly higher (P < 0.05) on mLRBTD for contaminated meat than on mLRBTD for contaminated milk at 24 h. FT-IR spectroscopy in the mid-infrared region (4000 to 600 cm-1) and chemometrics was successfully applied to discriminate L. monocytogenes strains belonging to the same EC (ECII or ECIV) (100% accurate spectral classification), intact and heat-killed populations of each EC strain (100% accurate spectral classification), and spectral wavenumbers 1650 to 1390 cm-1 were used to differentiate heat-killed from intact populations. FT-IR spectroscopy and chemometrics in the wavelength region 1800 to 900 cm-1 could successfully discriminate different mixed strains of L. monocytogenes (98.15% accurate spectral classification) and different mixed species of L. monocytogenes and L. innocua (92.06% accurate spectral classification) from individual strains; Wavelength range 1800 to 900 cm-1 was successfully used to discriminate between intact, acid-injured, and heat-injured Listeria, with repaired cells from acid and heat treatments clustering closer to intact cells (93.33% of spectra accurately classified). Delayed-addition of selective agents to broth medium improves recovery of injured Listeria by allowing repair time, could minimize contamination through manual addition of selective agents, and saves analyst time; FT-IR spectroscopy is a highly discriminatory and reproducible technique that can be used for the differentiation of strains and various physiological states of Listeria.

Os catalisadores eletroquímicos binários de PtSn/C, PdSn/C e PtPd/C foram sintetizados em diferentes proporções pelo método da redução via borohidreto, posteriormente estes foram caracterizados por microscopia eletrônica de transmissão, difração de raios X, espectroscopia no infravermelho por transformada de Fourier (PtSn/C e PdSn/C) e energia dispersiva de raios X. As atividades eletroquímicas dos diferentes materiais preparados foram avaliadas por intermédio de voltametria cíclica, cronoamperometria e curvas de polarização em célula a combustível alimentada diretamente por etileno glicol em eletrólito alcalino. As curvas de densidade de potência indicaram que os catalisadores eletroquímicos contendo Sn e Pd são mais ativos para a reação de oxidação do etileno glicol, especialmente a composição 70%:30% - relação molar entre os metais suportados em carbono - dos catalisadores PtSn/C, PdSn/C e PtPd/C todos superando as medidas de potência do Pt/C. Este resultado indica que a adição de Sn e Pd favorece a oxidação do etileno glicol em meio alcalino. O melhor desempenho observado para os catalisadores eletroquímicos PtSn/C, PdSn/C e PtPd/C (70%:30%) poderia estar associado à sua maior seletividade quanto a formação de oxalato, ou seja , a formação deste produto resulta em um maior número de elétrons, por consequência em maiores valores de corrente. / Binary electrochemical catalysts PtSn/C, PdSn/C and PtPd/C were synthesized in different proportions by the method of reduction via borohydride. These were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy (PtSn/C and PdSn/C) and energy dispersive X-ray. The electrochemical activities of the different materials prepared were evaluated by cyclic voltammetry, chronoamperometry and polarization curves for fuel cell powered directly by ethylene glycol in an alkaline electrolyte. Power density curves indicated that the electrochemical catalysts Sn-containing or Pd-containing are more active for ethylene glycol oxidation reaction, particularly the (70%:30%) composition of PtSn/C, PdSn/C and PtPd/C, all of them exceeding power measurements of Pt/C. These results indicate that the addition of Sn and Pd promotes the oxidation of ethylene glycol in an alkaline medium and this improved performance may be associated with a higher selectivity for the formation of oxalate that results in a larger number of electrons, consequently enhancing the current values.

Thesis (Master of Applied Sciences in Chemistry)--Cape Peninsula University of Technology, 2018. / Biosensors have been on the forefront to provide clinical diagnosis tools for various diseases. Proper selection of biomarkers as well as chemical electrode modification is key in the fabrication of electrochemical biosensors. Hence, electrode modified with nanomaterials devices to improve electroanalytical applications. These nanomaterials were functionalized to improve conductivity, accelerate signal transduction and amplify biorecognition events. Thus, resulting in novel sensing platforms that are highly sensitive and selective towards the target analyte. In this study, gold nanorods (Au NRs) capped with CTAB, zeolitic imidazole framework were synthesised using the seed mediated and hydrothermal method respectively. Composites of gold nanorods with cysteine, ZIF-8 or both were also synthesised. All synthesised materials were characterized using ultraviolet–visible (UV-Vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-Ray diffraction (XRD) and cyclic voltammetry (CV) techniques. The obtained results confirmed the synthesis of the nanomaterials and composites. Identification of the ideal platform for fabrication of a transducer with the best electrochemical response was determined by studying the combinations of the synthesised nanomaterials and composites. The studied parameters were surface coverage, conductivity, rate of electron transfer constant. Cysteine-Au NRs composites platforms, had exceptional properties hence its synthesis optimisation of was undertaken. The effect of CTAB, reaction time, volume and concentration ratio of Au:Cysteine, temperature and pH on the composite properties were assessed. However, this composite’s electrochemical properties decreased when bioconjugated with the antibodies. Hence, the choice of Au NRs CTAB functionalised ZIF-8 (CTABAu/ZIF-8) as the transducer for biosensor applications due to a more favourable biocompatibility. Biosensor fabrication was done by drop coating glassy carbon electrode with the CTABAu/ZIF-8 forming a transducer followed by immobilisation of the antibody (Ab) using a covalent attachment method with glutaraldehyde (GA) as a cross linker. The target analyte, epidermal growth factor (EGF) was interacted with the Ab binding sites via electrostatic forces. All the fabrication steps were optimized for biosensor components, immobilization technique (drop coating and immersion), concentration and incubation time of linker and bioreceptor, as well as the synthesis of the CTABAu-ZIF-8 composites where in situ and ex situ techniques were compared together with the effect of the concentration ratio of Au: ZIF-8. There was also an analysis of optimum pH. Optimum conditions were found to be immersion in 3 % GA and 2 μg/ml Ab, with incubation times of 8, 10 and 5 minutes for GA, Ab and EGF respectively at a pH of 6. The following electroanalytical techniques: cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) were utilised for EGF detection. The DPV showed better reproducibility, higher currents and better resolution hence; it was the method of choice. The technique’s optimisation involved assessments of the effect of step potential, starting potential and pulse amplitude. The optimum response for pulse amplitude, step potential and starting potential were 60 mV, 20 mV and 0.5 V respectively. The biosensor analytical parameters were linear towards EGF in the concentration range from 2 to 100 nM with a detection limit of 0.58 nM. Reproducibility and repeatability tests were acceptable, and the biosensor had a stability over 80 % within 15 days. There was no interference observed in the presence of glucose and creatine. The EGF biosensor was successfully applied in urine and saliva analysis, obtaining 67.5 and 3.12 nM respectively. This biosensor’s positive outcome strongly suggests its potential as a diagnosis tool for early detection of kidney disease as it was able to detect EGF concentration within physiological levels of EGF in normal kidney function.

Microplastics are particles that are < 5 mm in size and come from a wide range of sources. The global distribution in terrestrial and aquatic environments indicates they are likely to cause harm to living organisms. They are used in a variety of personal care products and kitchen scourers. To advance further studies, different approaches have been developed in recent years. In this research, a comparison of methods and analytical techniques were applied to characterise microplastics in two toothpastes and two facial scrubs. The analysis of microplastics was determined using light microscopy, laser diffraction, Fourier-transform infrared spectroscopy. This research reports for the first time, the application of Imaging flow cytometry to characterise microplastics, and was explored to characterise smaller sized particles in each product. The methods developed where validated by characterising particles abraded from kitchen scourers. Two market leading and three chain store brands of kitchen scourers were utilised for the characterisation of microplastics. The application of the different techniques indicated differences in the size, number and morphological characteristics of the particles analysed. The different approaches developed for particle extraction, and the analytical techniques had an apparent influence on the results produced. Currently, there are no universally accepted laboratory protocol and analytical techniques to characterise microplastics. However, this research can serve as a reference point to promote more studies on laboratory methods and analytical techniques to characterise microplastics, with the hope of understanding better these complex particles.

Os catalisadores eletroquímicos binários de PtSn/C, PdSn/C e PtPd/C foram sintetizados em diferentes proporções pelo método da redução via borohidreto, posteriormente estes foram caracterizados por microscopia eletrônica de transmissão, difração de raios X, espectroscopia no infravermelho por transformada de Fourier (PtSn/C e PdSn/C) e energia dispersiva de raios X. As atividades eletroquímicas dos diferentes materiais preparados foram avaliadas por intermédio de voltametria cíclica, cronoamperometria e curvas de polarização em célula a combustível alimentada diretamente por etileno glicol em eletrólito alcalino. As curvas de densidade de potência indicaram que os catalisadores eletroquímicos contendo Sn e Pd são mais ativos para a reação de oxidação do etileno glicol, especialmente a composição 70%:30% - relação molar entre os metais suportados em carbono - dos catalisadores PtSn/C, PdSn/C e PtPd/C todos superando as medidas de potência do Pt/C. Este resultado indica que a adição de Sn e Pd favorece a oxidação do etileno glicol em meio alcalino. O melhor desempenho observado para os catalisadores eletroquímicos PtSn/C, PdSn/C e PtPd/C (70%:30%) poderia estar associado à sua maior seletividade quanto a formação de oxalato, ou seja , a formação deste produto resulta em um maior número de elétrons, por consequência em maiores valores de corrente. / Binary electrochemical catalysts PtSn/C, PdSn/C and PtPd/C were synthesized in different proportions by the method of reduction via borohydride. These were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy (PtSn/C and PdSn/C) and energy dispersive X-ray. The electrochemical activities of the different materials prepared were evaluated by cyclic voltammetry, chronoamperometry and polarization curves for fuel cell powered directly by ethylene glycol in an alkaline electrolyte. Power density curves indicated that the electrochemical catalysts Sn-containing or Pd-containing are more active for ethylene glycol oxidation reaction, particularly the (70%:30%) composition of PtSn/C, PdSn/C and PtPd/C, all of them exceeding power measurements of Pt/C. These results indicate that the addition of Sn and Pd promotes the oxidation of ethylene glycol in an alkaline medium and this improved performance may be associated with a higher selectivity for the formation of oxalate that results in a larger number of electrons, consequently enhancing the current values.

The aim of this work was to use Fourier Transform Infrared Spectroscopy to characterize and identify bacteria of particular significance to the food industry. FT-IR spectroscopy is a rapid technique that can be applied to all groups of bacteria. The two objectives were to determine a suitable sampling procedure to record a spectrum and to determine a suitable statistical technique to identify characteristic regions of the spectrum associated with the genus and, potentially, the species. Pure cultures of bacteria were grown in broth, suspended in saline and dried to produce a film on a halide salt crystal. These films were then used to produce FT-IR spectra. In total, 80 spectra were recorded from seven genera, seven species and four strains of bacteria. Some of the spectra were considered to be too low in intensity to be included in statistical analysis. Data points from three specific windows of the remaining spectra were used to determine spectral distances between spectra. These spectral distances were used to perform cluster analysis using Ward's method, the Complete Linkage method and the Centroid method. The statistical analysis created successful clusters for several of the species used but was inconclusive overall in being able to distinguish between spectra at the genus, species and strain level. This may be due to inconsistent growth of bacteria and insufficient manipulation of the data. This study has shown the potential for FT-IR spectroscopy to be used to identify bacteria with significance for food but further development is needed to reproduce the consistent results demonstrated in current literature.

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