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An atmospheric pressure radio frequency capacitively coupled plasma (CCP) has been developed and characterized for applications in atomic emission spectrometry (AES), atomic absorption spectrometry (AAS) and gas chromatography (GC). The CCP torch was initially designed as an atom reservoir for carrying out elemental analysis using atomic absorption. Functionally, the device consists of two parts, the CCP discharge tube and the tantalum strip electrothermal vaporization sample introduction system. The torch design provides for very effective energy transfer from the power supply to the plasma by capacitive coupling. Therefore, the plasma can be generated at atmospheric pressure with a flexible geometry. The plasma can be operated at very low rf input powers (30-600 W) enabling optimal conditions for atom resonance line absorption measurements. Absorption by the analyte takes place within the plasma discharge which is characterized by a long path length (20 cm) and low support gas flow rate (0.2 L/Min). Both of these characteristics ensure a relatively long residence time. The device exhibits linear calibration plots and provides sensitivities in the range of 3.5-40 pg. A preliminary measurement gave a Fe I excitation temperature of approximately 4000 K for the discharge. At this temperature, potential chemical interferences are likely to be minimal. Chemical interferences for Fe, Al, As, Ca, Co, Cd, Li, Mo and Sr were negligible in the determination of silver. Chloride interference, which is prevalent in GF-AAS, was not found. The amount of Ag found in a SMR#1643b (NIST) water sample was 9.5 ± 0.5 ng/g which fell in the certified range of 9.8 ± 0.8 ng/g. Spikes of 30 ng/g and 60 ng/g of silver were added to the SRM and recoveries were found to be in a range from 105 % to 96.2 %. The RSD obtained for 7 replicates of 270 pg silver was 4.6 %. The results for the CCP AES are even more promising. The interferences of thirteen elements are negligible in the determination of silver. The chloride interference was not found. The detection limits for Ag, Cd, Li, Sb and B are 0.7, 0.7, 2, 80 and 400 pg respectively. The amount of silver found in a SRM#1643b (NIST) water sample was 9.3 ± 0.5 ng/g which also fell in the certified range of 9.8 ±0.8 ng/g. Spikes of 30 ng/g and 60 ng/g of silver were added into the SRM#1643b (NIST) samples; the recoveries were found to range from 97 % to 104 %. The RSD obtained for 7 analyses of 270 pg silver were 1.5 % for CCP-AES. It was also found that the signal to noise ratios (S/N) are higher in the AES mode than those in the AAS mode in the same CCP atomizer. In order to exploit advantages inherent in both GF-AAS and I CP-AES, an atmospheric pressure capacitively coupled plasma sustained inside a graphite furnace was developed. This source combines the high efficiency of atomization in furnaces and the high efficiency of the excitation in atmospheric pressure plasmas. In general, plasma sources are able to effectively excite high-lying excited states for most metals and non-metals and can also ionize vaporized elements. Therefore the possibility exists of using non-resonance lines to avoid the effects of self-absorption at high analyte concentrations. Ion lines may also be used in cases where they provide better sensitivity or freedom from spectral interferences. This source also offers the ability to independently optimize vaporization and excitation. However, the most important aspect of this new source is that it can be used for simultaneous, multielement determinations of small sized samples in a graphite furnace atomizer, a design which has been proven to be effective over many years of use. Preliminary quantitative characteristics of this new atmospheric pressure plasma emission source have been studied. The detection limit for Ag of 0.3 pg is lower than the value of 0.4 pg reported for GF-AAS. Variants of the CCP, including a gas chromatography (GC) detector, combinations of laser ablation - CCP, rf sputtering - CCP direct solid analysis, and its application as an intense spectral lamp have been developed and are reported in this dissertation. / Science, Faculty of / Chemistry, Department of / Graduate

M.Sc. (Chemistry) / The determination of 17 trace elements (As. Ba. Co. Cr. Cu. Mo. Nb. Ni. Pb. Rb. Sr. Th. U. V. Y. Zn and Zr) in uranium ores by X-ray fluorescence spectrometry was investigated in this study. The determination of major elements. however. was also necessary for the calculation of mass absorption coefficients. Major elements were determined on borate melts and trace elements on powder briquettes pressed at 7 t with a binder in liquid form. Initially a method was developed for the determination of the elements of interest in unmineralised rocks The rhodium tube was used for the Group 1 elements (As. Mo. Nb. Pb, Bb, Sr. Th, U. Y and Zr) and the gold tube for the Group 2 elements [Ba, Co. Cr. Cu. Ni. V and Zn). Background and peak overlap corrections were made by means of background and interference factors. Corrections for absorption of radiation by the sample were made by means of mass absorption coefficients. which were calculated from the major element composition or obtained from the relation between the inverse of the mass absorption coefficient and the intensity of the Compton scattering peak. Due to various problems. only the latter method was suitable for uranium ores. The high uranium content in uranium ores mainly affected the Group 1 elements. Because of the high intensity of various UL lines. large overlap corrections were necessary. while only a few completely interference-free background positions were available. Consequently. the Feather and Willis method was used for determining the background intensity at the peak positions as well as for mass absorption coefficients. As a result of the presence of the UL absorption edges both primarx and secondary mass absorption coefficients had to be used for matrix corrections. Furthermore. it was observed that the background intensity in the region of the uranium lines increases with increasing uranium content of the sample instead of the expected decrease due to the increasing mass absorption coefficient. This effect was greater for the LiF(11 0) crystal than for the LiF(100) and was attributed to the scattering of uranium lines in the spectrometer chamber. especially from the crystal. A method was developed to correct the measured intensities for this scattering effect. Calibration lines of the contribution from the scattering of uranium lines to the measured intensity at the different 28 positions versus the uranium peak intensity were plotted by using samples with various uranium concentrations (<2 %) and for which the mass absorption coefficients and concentrations of the various elements were known. The precision of the method was less than 2.5 % at concentrations greater than 50 ppm. With the exception of barium. detection limits varied between 1 and 5 ppm. Accurate results were obtained over large concentration ranges for various unmineralised samples and for uranium ores. The results of the analysis of a number of Karoo uranium ores are given.

M.Sc. (Chemistry) / The usefulness of vibrational spectroscopy in identifying surface species, determining adsorbate structures and studying surface reactions has been widely demonstrated. Most of the infrared work on surface species is currently performed using the transmission technique with very thin pressed discs of self supported catalysts. This technique has several disadvantages of which the limited transmission of many catalysts and the loss of available surface area during sample preparation, are but a few. Because of these limitations, information obtained from conventional transmission studies has limited application in terms of understanding and/or improving commercial catalysts. An alternative method which does not suffer from these limitations is Diffuse Reflectance Infrared Fourier Transform Spectroscopy or DRIFTS as it is commonly known. This spectroscopic technique has only recently been extended into the infrared region because of the progress in FTIR instrumentation. Because this is a reflectance technique, the sample is most appropriately a powder, so a high surface area catalyst in its normal powder form can be examined directly without altering its state. A spectroscopic facility which is capable of obtaining DRIFT spectra of adsorbed species at high sensitivity and in situ operating conditions has been established. This facility consists of an FTIR instrument fitted with a diffuse reflectance unit, a heatable high pressure cell and the necessary attachments for gas flow, pressure and temperature control. The project work consisted of an investigation into CO-adsorption on supported rhodium catalysts. By using different combinations of the three parameters: reduction temperature, metal loading and support material, several different species of surface bonded CO have been identified. The three rnein species being: geminal dicarbonyl, linear and bridging CO. As each of these species is associated with a specific Rh-site, conclusions concerning the oxidation state and dispersion of the Rh on the surface could be made. The thermal stability of the different CO-species was studied by increasing the catalyst temperature in a linear fashion. It was found that the geminal dicarbonyl species was the most stable in an oxidising atmosphere. The interconversion of chemisorbed . CO-species at higher temperatures has been spectroscopically verified. A mechanism for CO-dissociation on Rh-catalysts was proposed. In additional experiments the sensitivity of DRIFTS for adsorbed hydrocarbons has been demonstrated. It is concluded that this spectroscopic technique has been proven to be of great significance in the study of surface species on heterogeneous catalysts.

No description available.

One- and two-dimensional NMR spectroscopy, including 13C{6Li}{1H} triple resonance techniques, were used to characterize a series of mixed alkyllithium aggregates and to study their exchange processes.

No description available.

A unique Raman spectroscopic investigation combining a number of different techniques has been conducted in situ on the composition of the passive film on iron, both during its growth in 0.05 M NaOH by potentiodynamic polarization and during localized breakdown by pitting after addition of 0.05 M NaCl. There are differing theories for the mechanism of pit initiation and formation in the passive film on iron, and while these are in part due to different environmental factors, they are also influenced by differing theories for the nature of the passive film. The detailed information obtained in this study corroborate the two layer model for the passive film on iron, with γ-Fe2O3 forming the inner layer and the outer layer consisting of δ-FeOOH, α-FeOOH, γ-FeOOH, other components such as Fe(OH)2 and other intermediates. In the passive region of anodic polarization the film became increasingly hydrated with increasing anodic potential and with increased cycles became amorphous, comparing well with the Hydrated Polymeric Oxide model. Pre-resonance enhancement of the Raman bands of iron oxides and particularly iron oxy-hydroxides was afforded by excitation at 636.4 nm, and particularly at low wavenumbers. The use of Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) enabled determination of the relative amounts of the iron oxide and oxy-hydroxide components from the complex spectra recorded during potentiodynamic polarization. The amount of water incorporated in the passive film under the same conditions was also monitored in situ at similar potentials using excitation at 514.5 nm. Addition of chloride ions resulted in an increase in hydration and a change of the composition of the passive film to comprise mainly β-FeOOH and Green complex with some γ-Fe2O3 and γ-FeOOH. At the pitting potential significant changes in the composition occurred along with reduction in hydration, so that re-passivation could no longer be maintained at the same rate as dissolution by the chloride ions, enabling stable pitting. These observations indicate that water plays a protective role in the passive film and reinforce the mechanisms for pit initiation based on the De-passivation–Re-passivation theory and Chemical Dissolution theory.

Elevated concentrations of mercury in soils are quite hazardous to flora and fauna and water bodies near these soils. This makes continuous monitoring of mercury very essential. This work compares two potential spectroscopic methods LIBS and SIBS at their optimum experimental conditions for mercury monitoring. The experimental conditions for Hg measurements with LIBS and SIBS were determined and calibration was developed. The limits of detection (LODs) of Hg in soil were calculated from the Hg calibration curves. The LOD for mercury (Hg) in soil calculated using LIBS and SIBS are 483 parts-per-million and 20 parts-per-million, respectively. The present study indicates that SIBS is more efficient with powder samples in a low concentration region for quantification of mercury in soils while LIBS is efficient in the region of higher concentrations using pellet samples. Both these techniques can be further investigated and improved for in-situ analysis of soils.