Browsing by Author "Koch, Klaus R"
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- ItemOpen AccessAnalysis of platinum, palladium and rhodium at trace concentrations in lead using the time resolved spark emission technique called SAFT(2000) Sundquist, L. P; Koch, Klaus RThe fire assay technique may be used to extract noble metals from platinum bearing ores. It allows for the use of relatively large quantities of ore sample from which trace quantities of noble metals are concentrated. The fire assay with lead as the collector is one such procedure, where preconcentration of the noble metals allows for direct analysis of the noble metals in lead The samples may be prepared by pyrochemically treating the ore sample with a litharge-based flux. These lead buttons require an homogenising remelt and rapid cast before direct determination of the noble metals can be made using a time resolved form of spectroscopy called SAFf, or Spark Analysis for Traces. The unique characteristics of this technique is that inunediately after the electrical spark discharge has taken place radiation from atomic species continues and is termed after-glow. Special electronic techniques are required to observe this phenomenon as it takes place in microseconds. By studying the emission characteristics of various spectral wavelengths it is possible to determine the time at which the photomultiplier measures the atomic radiation. and not the background radiation. The atomic emission line to background ratio is thus improved and hence precision and limits of detection. Initial investigations into the SAFf analysis of platinum. palladium and rhodium using synthetic standards prepared from pure noble metals and lead revealed an analytical method of great promise. However the method failed when applied to real ore samples for several reasons. The SAFf analysis is particularly sensitive to the effects due to changes of the matrix of the lead depending on the type of sample used to prepare the lead buttons. Corrections for these effects could not be applied as preparation of matrix matched standards also failedAnother serious problem experienced with the SAFf technique was the inherent insensitivity of the selected platinum wavelengths together with high background emissions. The platinum atomic emission to background ratio was thus poor, and hence scientifically inappropriate practice to measure platinum in lead under these circumstances. The most sensitive platinum emission wavelength could not be used because corrections for a spectral interference from nickel could not be applied. A certain portion of base metals are collected in the lead buttons along with the noble metals during the fusion process, and since nickel is present in all ore samples associated with platinum group metals the presence of nickel and platinum together in lead after collection is inevitable. Because of the nature of the ore samples used in the investigations, the concentration range of platinum, palladium and rhodium in lead even after preconcentration using fire assay, was very limited, and attempts to create calibrations using only these samples proved unsuccessful. Additional standards prepared from different ore samples were used to extend the concentration ranges of the calibrations, however this also proved to be of no use as the different matrices of these samples detracted from any possibility of defining an accurate calibration curve.
- ItemOpen AccessThe chromatographic determination of fusarium toxins in maize associated with human oesophageal cancer(1989) Sydenham, Eric William; Koch, Klaus RThe necessity to obtain accurate and reliable data pertaining to the range and/or levels of mycotoxin contamination in a variety of food and feed substrates, intended for human or animal consumption, has therefore, become important. An integral part of this study will be the provision of the most suitable analytical methods for the determination of selected Fusarium mycotoxins, in maize. The culmination will be the application of those selected methodologies to a series of Transkeian maize samples associated with human oesophageal cancer-risk.
- ItemOpen AccessDevelopment of selective pre-concentration methodology of some of the platinum-group metals in acidic solutions, followed by their direct determination by ICP-OES(1999) Handforth, Darren Richard; Koch, Klaus RThe trace analysis of the platinum-group metals in complex, severely interfering matrices, such as industrial effluent, has been the focus of much research in_the past forty years. However, despite the greater availability of much improved instrumentation, such as ICP-OES, NAA and XRF, most analytical techniques currently employed for the determination of the platinum-group metals require selective sample preparation that ensures enrichment of the individual platinum-group metals at the trace and ultra trace level, along with simultaneous matrix removal, prior to determination. N-benzoyl-N', N'-dialkylthioureas act as selective complexing agents for the enrichment of platinum-group metals from strongly interfering matrices. This study describes the development of selective pre-concentration methodology for some of the platinum-group metals in post- processing effiuents (using this class of ligands) followed by their direct determination by ICP- OES, in an effort to recover the residual platinum-group metals present in real waste effiuents that are currently unable to be recovered, representing a substantial loss of income to the South African platinum-group metal producers.
- ItemOpen AccessThe extraction of trichlorostannato-rhodium complexes by polyurethane foam(1990) Hall, Iris; Koch, Klaus RPolyurethane foam (polyether based) has been found to efficiently extract rhodium from hydrochloric acid solutions containing stannous chloride. The amount of rhodium extracted is significantly influenced by inter alia temperature, acid concentration, the Sn(II):Rh mol ratio and the presence of alkali metal cations. The extraction efficiency is promoted by increased acid concentration and high Sn(II):Rh ratios. The presence of K⁺ inhibits the extraction of rhodium, while the effect of Li⁺ and Na⁺ is small. A series of model urethane compounds (diurethane podands and linear polyurethanes) have been synthesized and characterized. These model compounds allowed the direct determination of the extracted trichlorostannato·rhodium complex anions by ¹¹⁹Sn nmr spectroscopy. Conditions favouring the formation of [Rh(SnCl₃)₅]⁴⁻ were found to result in the extraction of increased amounts of rhodium. The predominant species in the urethane phase was identified as the hydrido complex, [RhH(SnCl₃)₅]³⁻, which is formed by protonation of [Rh(SnCl₃)₅]⁴⁻. The protonation reaction has been shown to be reversible. The ¹¹⁹Sn nmr study showed the formation of a new rhodium-hydrido complex formulated to be [RhH(SnCl₃)₄Cl]³⁻. In the presence of low tin(II) concentrations {Sn(II):Rh = 4:1}, [Rh(SnCl₃)₃Cl₃]³⁻ is predominantly extracted by the foam phase. Analysis of the acid-decomposed polyurethane foam phase by atomic absorption spectroscopy and of the model urethane compound phase by ⁷Li nmr spectroscopy, confirmed the extraction of alkali metal cations from aqueous solutions containing alkali metal salts. Our studies indicate that the polyether chains of polyuretha foam playa major role in the extraction process, and that the flexibility of the chains influences the efficiency of polyurethane foam as an extractant. The creation of cationic sites within the foam matrix, which facilitate the extraction of the rhodium-tin complex anions, is postulated to occur by protonation of the donor oxygen atoms as well as by chelation of cations such as H₃O⁺, Li⁺, Na⁺ and K⁺ by the polyether chains. A working model for the extraction of the trichlorostannato-rhodium complexes by polyurethane foam is proposed.
- ItemOpen AccessFlow-injection analysis of the platinum-group metals(1995) Auer, Derek; Koch, Klaus RTo date the principle methods for the determination of the platinum-group metals (PGMs) use an "off-line" assay with flame-atomic absorption spectrometry and visible spectrometry. Both suffer numerous interferences and involve time-consuming and arduous laboratory separation methods prior to analysis. An "on-line" method for the rapid assay of the PGMs is indeed a lacking component in the analysts' repertoire of methods. This study describes the development of spectrophotometric methods for the determination of the PGMs using flow-injection analysis (FIA). The principle of exploiting the remarkably specific and selective reaction of stannous halides with the PGMs to yield a series of intensely coloured complexes in acidic solutions forms the basis of these methods. The reaction is subject to relatively few interferences from other transition metals. A high speed scanning spectrophotometer is employed to obtain second order data. The successful manipulation of the data enables the determination of PGMs as single components and also simultaneously in mixtures. Attention is focused on the establishment of principles for successful multi-component analysis of PGMs. The development of a software program for multi-wavelength data manipulation was mandatory and is described. Criteria for successful selection of analytical wavelengths are discussed. The usefulness of multi-dimensional graphical data representation is demonstrated in a stop-flow study of the palladium reaction with tin (II) chloride. Qualitative information is provided regarding the nature of complexes and their interactions. Correlation of spectrophotometric data with complex solution colour changes is made. The requirements for future progress in multi-component FIA determinations as well as the direction for future research conclude the study.
- ItemOpen AccessFumonisins : chromatographic methodology and their role in human and animal health(1994) Sydenham, Eric William; Koch, Klaus R; Thiel, Pieter GThe fumonisins consist of a group of 7 structurally related mycotoxins originally isolated from Fusarium moniliforme, a fungal contaminant of maize worldwide. The incidence of F. moniliforme in home-grown maize, has been associated with human oesophageal cancer (OC) risk in the Transkei and China. Fumonisin B₁ (FB₁), the major fumonisin analogue, exhibits both cancer-initiating and -promoting activities, and has been shown to induce a number of disease syndromes in different animal species. Two other fumonisin analogues, fumonisins B₂ (FB₂) and B₃ (FB₃) also exhibit cancer-initiating potentials, similar to those observed for FB₁. A method, developed at PROMEC, for the analytical determination of FB₁ and FB₂ in maize, based on ion-exchange purification of crude extracts, derivatisation, reversed-phase liquid chromatography separation and fluorescence detection, was subjected to an international collaborative study involving 11 laboratories from 6 countries. Although the results established that the method was highly reproducible, alterations were made in order to reduce analysis time, identify and eliminate potential sources of error and include the co-determination of FB₃. Both methods were used, in conjunction with confirmatory techniques, to determine the extent of animal and human exposure to the fumonisins. Naturally occurring fumonisin levels in animal feeds, were used in conjunction with hazard assessment data, to establish fumonisin tolerance guidelines for selected animal species. The results indicated that combined fumonisin concentrations in feeds of 10 and 100 μg/g (ppm) should be regarded as potentially harmful to horses and swine, respectively. Human exposure assessment was based on data from various sources, including the 1989 and 1990 South African maize crops, maize imported into South Africa, retail maize-based foods from 14 countries, and home-grown maize from the Transkei. The data indicated that fumonisin contamination occurs worldwide, while the levels to which populations are exposed differ considerably. A statistical association was established between fumonisin contamination of home-grown maize, and the prevalence of human OC in the Transkei, where humans can be exposed to fumonisin levels that would be deemed harmful to both horses and swine.
- ItemOpen AccessGas-solid chromatographic studies of two well-known catalysts(1983) Mason, Robert Peter; Irving, H M N H; Koch, Klaus RThis work was initiated to explore the scope and feasibility of using a gas chromatograph to study catalytic reactions. Various methods have been proposed in the literature and it was decided to investigate various possible systems. Two catalysts were chosen for study. The dehydration of alcohols over alumina catalysts has been extensively studied and found to be ideally suited to studies by gas chromatography. The effect of modification of the catalyst by inorganic ions and by water was investigated. The dehydration of ethanol and pentanol were studied. Results indicated that alumina has two types of active sites responsible for the dehydration of alcohols. Zeolite catalysts are well-known and in this work the catalytic cracking of alkanes over zeolite Y was studied. The reaction mechanism was found to be complex and catalyst deactivation due to build-up of highly carbonaceous deposits occurred. All components of the reaction products were produced at similar rates to the overall reaction rate indicating that desorption of alkane product species was not the rate determining step. Between 150° and 300°C propane was the smallest product formed. Only alkanes were found in the product spectrum which was temperature dependent. Addition of hydrogen gas greatly increased the amount of detectable products. Heptane was found to react significantly above 200 °C, hexane about above 225°C and pentane above 250°C. Hexane and cyclohexane reacted at similar temperatures.
- ItemOpen AccessHeavy metal interactions with nucleic acid derivatives : a nuclear magnetic resonance study(1979) Koch, Klaus R; Fazakerley, G VThe aqueous solution conformation of SAH and SAM has been investigated using lanthanide probes. SAH at pH 7.0 interacts normally with lanthanide aquo ions and lanthanide-EDTA complexes via coordination at the carboxyl group. The conformation of the homocysteine fragment is found to, be extended but bent back towards the adenine base. SAM does not interact with lanthanide aquo ions in the pH region 2-7. It does form complexes with lanthanide-EDTA species via an ion-pairing mechanism rather than direct coordination. In addition to lanthanide probes, 250 MHz 1H n.m.r. spectra yielded vicinal JHH coupling constants from which the ribose conformation in both SAM and SAH could be more accurately determined.
- ItemOpen AccessPotential platinum DNA-Metallointercalators : synthesis, characterisation and 1H NMR studies on [Pt(diimine)(N,N-di(n-butyl)-N'-acylthioureato)]+PF6 complexes in solution(1997) Lawrence, Claire Joanna; Koch, Klaus RA series of mixed-ligand [Pt(diimine)(N,N-di(n-butyl)-N'-acylthioureato)fPF6- complexes has been synthesised and fully characterised (where diimine is: 1,10 phenanthroline; 4,7-diphenyl-1,10- phenanthroline; 2,2'-bipyridyl; 4,4'-dimethyl-2,2'-bipyridyl and 4,4'-di-tert-butyl-2,2'-bipyridyl and acyl is: benzoyl or naphthoyl).
- ItemOpen AccessReactions of halogens with Pt(II) complexes of N-alkyl- and N,N-dialkyl-Nʹ -benzoylthioureas: oxidative addition and formation of an I₂ inclusion compound(2005) Westra, Arjan N; Bourne, Susan A; Esterhuysen, Catharine; Koch, Klaus RThe treatment of cis-[PtII(L1a/b-S,O)2] complexes of N,N-diethyl- (HL1a) and N,N-di(n-butyl)-N'-benzoylthiourea (HL1b) with I2 or Br2 in chloroform, leads to rapid oxidative addition to yield several geometric isomers of [PtIV(L-S,O)2X2] (X = I, Br); the reactions can be monitored by 195Pt NMR and UV-visible spectrophotometry. The products cis-[PtIV(L1a-S,O)2I2] 6 and cis-[PtIV(L1a-S,O)2Br2] 7, which have been isolated and structurally characterized, are the first-reported crystal structures of complexes of Pt(IV) with this class of ligand. Molecules of 6 pack such that the I–Pt–I axes are essentially aligned, with unusually close nearest-neighbour iodide contacts (3.553(1) A˚ ). These short I···I intermolecular interactions lead to infinite chains of weakly connected molecules in crystals of the compound. No such interactions are evident in the corresponding crystals of 7. Reaction of the Pt(II) complex of N-propyl-N'-benzoylthiourea (H2L2a) cis-/trans-[PtII(H2L2a-S)2Br2] with Br2 also results in oxidative addition, to yield trans-PtIV(H2L2a-S)2Br4 9. By contrast, treatment of cis-/trans-[PtII(H2L2a-S)2I2] with I2 does not lead to an oxidative addition product, yielding instead an interesting iodine inclusion compound of PtII, trans-[PtII(H2L2a-S)2I2]·I2 8. In 8, short intermolecular I···I distances of 3.453(1) A˚ between I2 and coordinated iodide ions in trans-[PtII(H2L2a-S)2I2] molecules, result in infinite chains of weakly linked trans-[PtII(H2L2a-S)2I2] ···I2 groups in the lattice. However, the empirically estimated bond order of 0.75 for the included I2 molecules does not support the possible existence of discrete tetraiodide ions (I42−) in the lattice of compound 8.
- ItemOpen AccessStudies with dithizone : the extraction of thallium (III)(1985) Sacht, Cheryl; Irving, H M N H; Koch, Klaus RThallium(III) reacts with dithizone(I) in a complicated way through a number of intermediate products which depend on the relative proportions of reactants, the pH of the aqueous phase, the order of mixing of reactants, the time of phase equilibrium and the nature of the organic solvent used. The reaction between thallium(III) and dithizone is essentially oxidative in character. In the present work the complete reaction scheme is proposed: Thallium(III) reacts with dithizone to give a thallic-dithizonate complex, [TlIII(HDz)₃], which spontaneously and oxidatively disproportionates to the disulphide (III) and a thallium(I)-dithizonate complex, [Tl(HDz)]. The disulphide(III) decomposes by first-order heterolytic fission to give equimolar amounts of dithizone and the mesoionic compound (IV) . The Tl(HDz) complex undergoes reversion to give Tl+ in the aqueous phase and dithizone in the organic phase. In the presence of excess thallium(III) the regenerated dithizone is oxidized to the mesoionic compound (IV): the mesoionic compound (IV), partitions between the two phases and appears to react with excess thallium(III) to give possibly a mesoionic compound (IV)-thallium(III) complex and an unspecified oxidation product. The molecular structure of the 1 : 1 adduct formed between diphenylthallium( III) and dithizone has been shown by single crystal X-ray diffraction, to be a five co-ordinate diphenylthallium(III) complex: the dithizone acts as a bidentate chelating ligand co-ordinating through the nitrogen and sulphur atoms. Ethanol (solvent of recrystallisation) co-ordinates in the fifth position.
- ItemOpen AccessSynthesis characterisation and chemistry of N-alkyl-and N,N-dialkyl-N'-acylthiourea platinum(II) and palladium(II) complexes(1997) Wang, Yali; Koch, Klaus RN-(n-butyl)-N-methyl-N'-benzoylthiourea and N-(n-butyl)-N-methyl-N'-naphthoylthiourea (HL) have been synthesised and characterised. These ligands react with K2PtCl4 to yield neutral square planar cis- [Pt(L-O,S)2] complexes. These complexes exist as mixture of EE, EZ and ZZ isomers.
- ItemOpen AccessSynthesis, characterisation and coordination chemistry of novel N-alkyl- and N,N-dialkyl-N'-acylthioureas(1995) Grimmbacher, Tarron; Koch, Klaus RA series of N-alkyl- and N,N-dialkyl-N'-acylthioureas are synthesised and characterised. The crystal structure of N-butyl-N'-benzoylthiourea indicates that an intramolecular hydrogen bond locks the potentially bidentate chelate moiety into a planar six-membered ring with an overall rod-like molecular structure. The rod-like structure of the N-alkyl-N'-benzoylthioureas is exploited and the synthesis and characterisation of a novel series of liquid crystals based on N-(p-alkyl(oxy))aniline-N'-(p-alkyl(oxy))benzoylthiourea is discussed. The liquid-crystalline phases are identified with the aid of Polarising Optical Microscopy and confirmed by Differential Scanning Calorimetry studies. The compounds display nematic, smectic A or a combination of these liquid crystal phases. The X-ray crystal structure of N-(p-hexyloxy)aniline-N'-(pmethyloxy) benzoylthiourea shows co-planarity of the aromatic and hydrogen-bonded six-membered rings. Intennolecular hydrogen bond interactions between adjacent molecules allow for favourable molecular interaction for the formation of liquid crystal phases.
- ItemOpen AccessSynthesis, characterization and potential chromatographic separation of palladium and platinum complexes of N,N-Dialkyl-N'-Benzoylthioureas(1990) Matoetoe, Mangaka Clara; Koch, Klaus RA series of para-phenyl substituted N,N-dialkyl-N'-benzoylthioureas where para-phenyl substituents are H, Cl, Br, I, NO₂ and OCH₃ and alkyl chains are -CH₂CH₃, -(CH₂)₃CH₃ and and -CH₂C₆H₅ as well as their corresponding neutral bis complexes of type cis [ML₂] where M = Pd(II) and Pt(II) have been prepared and characterized. The structures of these compounds has been studied using high resolution nuclear magnetic resonance technique. Studies were also carried out to investigate possible use of these N,N-dialkyl-N-benzoylthioureas as ligands suitable for the chromatographic separation of Pt(II), Pd(II), Ni(II) and Cu(II). To this end the possible selective extraction of these complexes from acidic aqueous phases was examined. This layer normal phase chromatography has been mainly used, using a variety of organic phases as eluent. A preliminary investigation of the suitability of using normal phase HPLC for the separation of the platinum and palladium complexes was undertaken.
- ItemOpen AccessTowards the separation of linear α-olefins from industrial process streams using transition metal stationary phases(1994) Phaho, David Sekgweng; Koch, Klaus RThe use of silver modified stationary phases for the separation of olefins from hydrocarbon mixtures was investigated. Gas solid chromatography (GSC) was found to be a quick and efficient technique for screening ion exchange resins and zeolites as potential support materials in olefin separation. Using GSC, the efficiency of Ag⁺ exchanged resin in retaining olefins relative to alkanes in a given mixture was found to be dependent on the porosity of the resin used. The silver form of the porous, macroreticular type Amberlyst A-15 resin strongly retained olefins in the GC column as compared to the microporous Amberlite IR(120) resin. Olefins were so strongly retained on the Ag⁺exchanged Amberlyst A-15 resin that they could only be eluted efficiently from the GC column at elevated temperatures. The Ag⁺ exchanged resin was however found to undergo degradation at elevated temperatures (> 140⁰C) and hence the resin packed columns could not be re-used.
- ItemOpen AccessThe use of polyurethane foams for the extraction of platinum (II) from hydrochloric acid solutions in the presence of tin (II) chloride(1984) Brackenbury, Karim Francis Gavin; Koch, Klaus RA preliminary investigation prior to the study of the extraction of platinum, was conducted on the Co(NCS)₄²⁻ /foam system to, (a) develop a suitable experimental apparatus in order to study the loading of platinum foams and (b) obtain fundamental kinetic and thermodynamic data concerning the sorption process. The sorption of platinum(II) as complexes of [Pt(SnCl₃)nCl₄-n]²⁻ and [Pt(SnCl₃)₅]³⁻ from hydrochloric acid solutions by polyurethane foams was examined in detail. Our studies show that the capacity of the foam to extract platinum depends on the following solution conditions of, temperature, initial platinum concentration, hydrochloric acid and hydrogen ion concentrations, the Sn:Pt ratio and the presence of interfering cations and anions. The rate of platinum sorption is shown to be dependent on temperature, initial platinum concentration, the Sn:Pt ratio and the mass of the foam. The foam's ability to selectively extract platinum from solutions containing platinum and certain base metals is examined. Results obtained show that in all cases almost complete extraction of platinum was achieved. Of all the base metals investigated only Cu(II) co-extracts to a small extent with the noble metal. In this work a procedure has been developed in which we are able to quantitatively recover both platinum and tin from loaded foams, by dissolving the polyurethane in warm nitric acid. A simple distillation allows for the satisfactory separation of platinum from tin.
- ItemOpen AccessUse of water-soluble phosphine ligands in heterogeneous hydroformylation catalysis : application to long-chain 1-alkenes(1994) Du Toit, Judith G O; Koch, Klaus RThe two-phase rhodium-tri(m-sulfonatophenyl)phosphine (Rh-TPPTS) system for the hydroformylation of 1-octene, 1-decene, and 1-dodecene to the corresponding aldehydes, has been investigated. Due to the two distinct phases - the catalytic species in the aqueous phase and the products and reactants in the organic phase - the separation of the catalyst was easily facilitated. A comparison was made of the activity, selectivity towards linear aldehydes, and catalyst lifetime of two systems where i) the active catalytic species were generated in situ from rhodium trichloride (RhCl₃.3H₂O) and excess phosphine ligand (TPPTS) under mild hydroformylation conditions (5 MPa H₂/CO (1:1); 100 °C); and ii) where the rhodium(I) complex, RhH(CO)(TPPTS)₃ is used as the catalyst precursor. The former system was found to be superior in activity and selectivity to that of the latter, achieving fairly high conversions of ca. 60% for the hydroformylation of 1-octene, with n:iso ratios of up to 16:1 for a catalyst composition a Rh:P ratio of 1:30. Unfortunately low conversions of ca. 10% for the hydroformylation of 1-decene and ca. 4% for that of 1-dodecene resulted under the same conditions. While the reasons for the drastic decrease in conversion for C₁₀ and C₁₂ alkenes is not completely clear, this poor conversion is attributed to the extremely low solubility of the long-chain 1-alkenes in the aqueous phase. Under certain optimum conditions (Rh:P ≥ l :20), virtually no leeching of rhodium into the organic phase was detected. A ³¹P NMR spectroscopic study was undertaken in an attempt to ascertain the nature and distribution of rhodium tertiary-phosphine complexes in the aqueous phase before and after the mixture was subjected to standard hydroformylation conditions.