Zinc, cobalt and iron phenylthio substituted phthalocyanines have been synthesized and characterized. Cyclic and square wave voltammetry in dimethylformamide containing tetrabutylammonium perchlorate revealed five and six redox processes respectively for the cobalt and iron phenylthio substituted phthalocyanines. These complexes are easier to reduce compared to the corresponding unsubstituted MPc and to butylthio substituted derivatives. Spectroelectrochemistry (in dimethylformamide containing tetrabutylammonium perchlorate) was employed to assign the cyclic voltammetry peaks, and gave spectra characteristic of Fe(I)Pc for reduction of iron phenylthio substituted phthalocyanine and Co(I)Pc for the reduction of cobalt phenylthio substituted phthalocyanine. The spectrum of the former is particularly of importance since such species have not received much attention in literature. Cobalt and iron phenylthio substituted phthalocyanines have been deposited on Au electrode surfaces through the self assembled monolayer (SAM) technique. The so formed layers were studied using voltammetric techniques. These SAMs blocked a number of Faradic processes and electrocatalyzed the oxidation of L-cysteine. Amine substituted cobalt phthalocyanine (CoTAPc) was deposited on gold surfaces by using an interconnecting SAM of mercaptopropionic acid or dithiobis(N-succinimidyl propionate) through the creation of an amide. Reductive and oxidative desorption of the SAMs limit the useful potential window. The SAM-CoTAPc layers show electrocatalytic activities towards oxygen reduction through the Co(I) central metal ion. Both SAMs were highly stable and hence will be interesting tools for further research in surface modification and sensor development.

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Ligand-isotope labelling studies were performed on Zeise’s salt derivatives with pyridine N-oxide and quinoline N-oxide, their perdeuterated and O-18 isotopomers, C₂D₄ and ¹³CO, and the results of the vibrational analyses are reported. The isotopomers are modelled utilizing DFT calculations at the B3LYP level with the 6-31 G** basis set, and a pseudopotential level for the Pt atom. The calculated and observed structure and vibrational spectra correlate well. The crystal structures of [Pt(C₂2H₄)(pyO)Cl₂] and [Pt(CO)(quinO)Br₂] are reported. The frequency for the νPt-O vibration, ambiguously assigned in the literature, is here assigned unequivocally at 400 cm⁻¹. Previously observed, but inadequately described phenomena are addressed: the νN-O vibration in substituted quinoline N-oxides has been assigned previously at significantly different frequencies, depending on the nature of the substituent. This suggests that there is no specific mid-ir band associated with a high N-O character. A suitable explanation is presented for this phenomenon, showing that in low symmetry systems (eg. quinO) the N-O stretch is dispersed among several modes, whereas in high symmetry systems (eg. pyO) only a few limited modes have a high N-O character. A theoretical study of Cu(I) carbonyl compounds with macrocyclic ligands is presented. Local and global HSAB parameters applied to the donor and Cu atoms are used to explain the observed reactivities and the available spectroscopic data. Extended to [Cu(CO){H₂N(CH₂)[subscript n]NH(CH₂)[subscript m] NH₂}] BPh₄ (where n = 2, m = 2, 3 and n =3, m = 3, 4) and their -d₅ and ¹³CO isotopomers, subtle differences obtained experimentally for the CO stretching frequency in this series have been reproduced in the DFT calculations at the B3LYP level, using the 6-31 G* and 6-31 G** basis sets. Several properties (ligand pK[subscript a] values, νCO frequencies, etc.) correlate with some HSAB descriptors. Vibrational analyses are presented of Cu(I) carbonyl Schiff-base derivatives of N-Benzylidene-N’-[2-(benzyilidene-amino)-ethyl]-ethane-1,2-diamine, {2,2N3(C₆H₄R)₂}, and their -d₅ and ¹³CO isotopomers. The crystal structure of [Cu(CO){2,2N3(C₆H₅)₂}]BPh₄ is reported. From geometry optimizations and the HSAB descriptors, spectroscopic trends ([n]Cu-N and [nu]CO) are related to calculated global hardness and the Hammett substituent parameters, and are discussed in terms of σ-donation and π-backbonding of Cu- CO.

Sequential injection analysis (SIA) that was developed in 1990 is a simple, versatile and automated technique based on precise aspiration of small volumes of reagents and samples into a single channel. It is economical in terms of reagent consumption and waste generation. SIA is applied to food, environmental and pharmaceutical samples. SIA parameters and the chemical variables are optimized and figures of merit are reported. Spectrophotometer has been used as a detector in the analysis of formaldehyde (HCHO), ascorbic acid and ferric iron (Fe (III)). A stopped flow method was adapted to SIA spectrophometric technique. Enhanced sensitivity was obtained using a stopped flow method as compared to a non-stopped flow method. The SIA spectrophotometric determination of Fe (III) through complex formation with the thiocyanate and the Tiron reagents has been studied in chapter 3. The two methods were compared based on convenience, sensitivity, simplicity, reliability and on general application. Both methods are simple, employ readily available reagents and have lower detection limits and shorter analysis time of 72 samples per hour. The thiocyanate method enabled the determination of Fe (III) in the linear range of 2 to 50 mg/ℓ with a detection limit of 0,2 mg/ℓ whereas the Tiron method provided a linear range of 1 to 50 mg/ℓ with a detection limit of 0,1 mg/ℓ. Chapter 4 presents the application of SIA spectrophotometric method for the determination of formaldehyde in wastewater. The method is based on the inhibition of brilliant green-sulfite reaction by formaldehyde. The kinetic method was implemented by stopping the flow when the complex reaches the detector and the measurements were taken as the reaction proceeds. The SIA method was compared with the chromotropic acid method and the paired t-test was used to determine whether the results obtained by the two methods differ significantly. Good sensitivity with a detection limit of 0,06 mg/ℓ and a wider linear range of 1-3 mg/ℓ was achieved. Chapter 5 describes the indirect determination of ascorbic acid in pharmaceutical samples, sweets and beverage (orange juice). This method is based on reduction of Fe (III) to ferrous iron (Fe (II)) by ascorbic acid under UV-light irradiation and the reaction of generated Fe (II) with 1,10-phenanthroline. The flow was stopped in the holding coil for a defined time to ensure that complete reduction process take place under irradiation. Photochemical reaction methods improved the sensitivity with detection limit of 0,06 mg/ℓ. Good precision was obtained with relative standard deviation of 1,3 %. The method compared well with the N-bromosuccinimide titration method. The versatility and simplicity of SIA technique makes it suitable to different requirements of various analytical problems. / Dissertation (MSc (Chemistry))--University of Pretoria, 2007. / Chemistry / MSc / unrestricted

Mass spectrometry is a widely used technique for the performance of elemental analysis: not only does it provides excellent limits of detection for a large number of elements, but it is also able to provide information about the isotopic distribution of the analyte. The radio-frequency quadrupole ion trap is a relatively new design of mass spectrometer, which offers the ability to confine charged particles for extended periods of time in a well defined volume by applying a radio-frequency oscillating voltage to an arrangement of three electrodes. A mass analysis of the trapped ions can be obtained by selectively extracting the ions from the cavity of the trap, where they can be detected by an electron multiplier. Despite its unique capabilities, to date the applications of the ion trap mass spectrometer have mostly been restricted to gas chromatography detection. Until recently, there have been very few attempts to use it for any other types of routine analysis. Our interest lies in the development of an instrument capable of performing a complete mass spectrometric elemental analysis of small volume liquid samples (a few (μL) at trace or ultra-trace concentration levels. The ability of the ion trap to accumulate ions in its cavity and to provide an entire mass spectrum of these ions in a single scan of the radio-frequency oscillating voltage applied between the electrodes, makes it a very interesting candidate for the ultra-trace analysis of small size samples. However, to perform an analysis on a sample with the ion trap the sample must first be vaporized; and if an elemental analysis is required, the sample will also have to be atomized. The graphite furnace atomizer used in atomic absorption spectroscopy offers a number of advantages which make it potentially useful for this purpose: it has a high transport efficiency of the analyte from liquid or solid state to the vapour phase, the ionization of the analyte in the furnace is very low (as required by the ion trap) and it handles small volume samples very well. A graphite furnace ion trap mass spectrometer was designed to fulfil the need of having instrumentation capable of multielemental mass spectrometric analysis of small volume samples containing traces of the analytes of interest. This document contains a description of the principles of operation of the ion trap as well as a detailed description of the instrument actually built. Data are presented in order to assess the capabilities of the instrument, as well as some of the problems encountered with it. The results obtained with the graphite furnace ion trap mass spectrometer allow us to conclude that the proposed design is not appropriate for the performance of elemental analysis, but is appropriate for mass spectrometric study of low boiling point compounds which can interfere with atomic absorption analysis: it is calculated that these compounds could be analysed at the ppm level. Promising results obtained with a set up in which the analyte is vaporized directly into the cavity of the ion trap through laser ablation are also presented. These limited results show the potential of this methodology for direct elemental analysis of solid samples. / Science, Faculty of / Chemistry, Department of / Graduate

Spectroscopic ellipsometry is a nondestructive, ambient surface analysis technique for studying surfaces, interfaces and thin films. To take advantage of this method an automatic spectroscopic ellipsometer was designed and constructed for the microstructural characterization of thin films. This high precision instrument is capable of measuring in real-time the optical properties of bulk or thin film materials over the visible-UV region (1.5 - 6.0 eV). The microstructure of thin films can be determined from an effective medium theory analysis of the spectroellipsometric data to investigate how the film morphology evolves with varying preparation conditions and to determine the optimum deposition parameters. In this thesis the pseudodielectric function of palladium films prepared by dc planar magnetron sputtering was measured while the substrate temperature, argon partial pressure and rf-induced substrate bias were varied independently during deposition. The film data are in excellent agreement with the effective medium theory of Sen, Scala, and Cohen, relevant for a random coated-particle microstructure where the grains are optically isolated from each other. With increasing substrate temperature, the Pd volume fraction in the bulk was found to decrease slightly, while the rms microroughness of the film surface increased in magnitude. At 190° C, the rms microroughness was 80 ± 3 Awith the Pd volume fraction in the bulk region falling slightly to 97 ± 1% relative to the film deposited at 22° C. For argon partial pressures below a transition pressure, Pt≃15 mTorr, the films consisted of densely packed grains, corresponding to the zone T in Thornton's structure zone model. Above this transition pressure, the films developed into a more voided columnar structure, characteristic of the zone 1 region. A microstructural analysis indicated a general trend towards increased porosity and microroughness of the films with higher argon pressures. The zone 1 region was best described optically by a random coated-particle microstructure and the electron microscopy confirmed that for thin films prepared at argon pressures higher than Pt, the grains became isolated by void boundaries. The optical data could not distinguish whether or not the films were 2- or 3-dimensionally isotropic. With increasing rf-induced substrate biasing, the Pd film microstructure was modified in a manner similar to that obtained by varying the substrate temperature alone. Significant resputtering of the Pd films occurred, varying from 2 to 11 A/sec for bias voltages of -550 V to -1375 V, respectively. The measured deposition rate while bias sputtering was significantly higher than that expected upon the measured resputtering rate and several mechanisms were proposed to account for the enhancement in the deposition rate. The films were best characterized by a 2-dimensional isotropy which was supported by the columnar nature of the films observed by electron microscopy. Finally, the dielectric function of the "best" palladium film is compared to optical constants of Pd previously reported in the literature for bulk and thin film specimens. While all the authors quote essentially the same values for the real part of the dielectric function, regardless of the preparation or measurement technique, the imaginary part differs up to a factor of two. Surface microroughness, bulk porosity and oxide layers are unable to account for the difference. A possible grain boundary scattering mechanism is suggested. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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