No description available.

This thesis describes the development and application of stripping potentiometric methods for reliable determination of some trace metals in natural waters on a glassy carbon mercury film electrode (GCMFE). The development of these methods involved investigation of factors influencing the stripping potentiometric measurement, such as selection of adequate supporting electrolyte, choice of pH and/or concentration of supporting electrolyte, oxidant concentration, deposition potential, deposition time, stirring or sample rotation rate and equilibrium period. Moreover, the influence of complexing agents and the magnitude of constant current were carefully investigated for adsorptive cathodic stripping potentiometric methods. In addition, linear concentration range and detection limits were considered. The analytical application of the method to some natural waters was also demonstrated. It is concluded that the stripping potentiometric methods developed in this study are adequate for ultra-trace determination of copper, lead, cadmium, zinc, nickel and molybdenum. The methods provide very simple procedures, excellent precision and accuracy for the reliable determination of the six metals in natural water samples. / Master of Science (Hons)

Two objectives are achieved in this thesis: (1) to develop a new method to measure the pH-dependent net surface charge of soils and (2) to determine if, by a combination of the surface charge evaluated by potentiometric titration and ion adsorption, we can separate the permanent charge, generated by the isomorphous substitution, from the variable charge. First, a laboratory procedure, using backtitration, was developed for the measurement of the pH-dependent net surface charge. This method was tested on ten soil horizons from Gleysols and Podzols. It appears that the pH-dependent net surface charge, measured by this technique, shows good agreement with that measured by ion adsorption. It is also possible, with this method, to identify some plateaus and inflection points in the backtitration curve associated with protonation/deprotonation reactions of specific soil components. Secondly, it was demonstrated that it is possible to increase the surface charge of montmorillonite with Al-oxide coatings under specific conditions.

Thesis (PhD)--University of South Australia, 1995

No description available.

No description available.

The experimental work described in this thesis is aimed at the elucidation of the speciation of the zinc and germanium 8-hydroxyquinoline systems. A knowledge of this speciation could aid in modelling the kinetics of solvent extraction of zinc and germanium with 7alkyl derivatives of 8-hydroxyquinoline. In this study the stability constants of the ligand 8hydroxyquinoline with the ions H+, Zn2+ and Ge4+ have been investigated by potentiometry at 25°C in a partially aqueous medium. A titration technique was used in which the hydrogen ion concentration was monitored using a glass indicating electrode. The partially aqueous medium comprised of O. 1 mol dm- 3 NaCl04 in 60% (v/v) dioxane and the concentration levels of the reagents were at least millimolar. The analysis of the potentiometric data was carried out with the aid of the computer programs HALTAFALL, ESTA and STATGRAPHICS. The results obtained for the systems involving the H+ and Zn2+ ions compare with those reported in the literature. The stability constant of a protonated species in the zinc-8-hydroxyquinoline system (ZnLH) was established for the first time. Precipitates obtained from the Zn2+ titrations were identified as zinc 8-hydroxyquinolate dihydrate. The germanium 8-hydroxyquinoline system has not been studied previously via potentiometry techniques. The complex hydrolysed species of germanium in aqueous solutions and the unusual features displayed in the formation curves increased the complexity of species selection. Although a suitable model of the species present could not be determined some evidence suggests the presence of protonated species. Hence, a prerequisite for resolving the germanium-8hydroxyquinoline system could be a more complete understanding of the hydrolysis of germanium in the partially aqueous medium used. / Thesis (M.Sc.)-University of Natal, Durban, 1991.

O presente estudo procura dar continuidade a um dos ramos de pesquisa desenvolvidos na área de Analítica do Instituto de Química da USP, onde se procura estudar a química de complexos formados entre diferentes metais e o ânion azoteto, N-3. O cátion índio(III), à semelhança do que ocorre com o ferro (III), complexa com o ânion azoteto em meio aquoso. Este poder de complexação foi constatado em estudos polarográficos do sistema In N3+ / N-3 ora em desenvolvimento. A obtenção das constantes de estabilidade dos complexos formados entre o In3+ e o ligante azoteto, por via potenciométrica, baseia-se na alteração do pH do tampão formado por N-3 e o ácido fraco HN3, quando se adicionam íons In3+. O acompanhamento da variação da concentração hidrogeniônica foi f.eito com o auxílio do eletrodo de vidro combinado. A concentração de N-3 de equilíbrio variou de valores próximos de zero a 90 mM, para que se obtivessem dados na mais larga faixa de concentraç6es de ligante. Manteve-se a força iônica das soluções em 2,00OM (NaCI04) e trabalhou-se a 25,0οC. A análise dos dados experimentais e tratamento matemático dos mesmos, evidenciaram a formação de complexos mononucleares e os valores das constantes globais encontrados foram: β1 = (2,0 ± 0,1) x 103M-1 β2 = (7 ± 3) x 105M-2 β3 = (5 ± 1) x 107M-3 β4 = (7 ± 3) x 108M-4 / The present study is a branch of the main work concerned with the complex formation between several metal cations and azide anion in aqueous media. Indium (III) was selected, in analogy to iron (III), because forms complexes with azide in aqueous media. Polarographic studies in development showed the tendency of these complexation. To determine the stability constants of complexes was used potentiometric method using glass e1ectrode. The main advantage is based on pH modification of the buffer solution constituted by azide and hidrazoic acid (N-3;/HN3) when indium (III) cations are added in the buffer. The azide concentration was a1tered from near zero to 90 mM, the ionic strenght he1d at 2,000 M with sodium perchlorate and the temperature kept constant at 25,0°C. The evaluation of experimental data shawed mononuclear species and the global constants found were: β1 = (2,0 ± 0,1) x 103M-1 β2 = (7 ± 3) x 105M-2 β3 = (5 ± 1) x 107M-3 β4 = (7 ± 3) x 108M-4

Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2016. / Boron concentration analysis is an important and critical analysis performed by the Analytical Chemistry Laboratory at Koeberg Nuclear Power Station (KNPS), because boron controls reactivity and the concentration determination is a Technical Specification Parameter (safety parameter). Hence accurate, precise results for boron concentration produced by laboratories and on-line analysers are important because of their operational implications associated with reactivity control and also for nuclear safety. The project focused on comparing the quality of chemical analysis results of boron produced by analysis techniques/ methods used at Koeberg Nuclear Power Station namely; Potentiometric Titration, Atomic Absorption Spectrophotometry (Flame) and UV-VIS Azomethine-H method. The methods were described, optimised, evaluated and compared in terms of uncertainty of measurement, accuracy, precision, analysis range, limitations, appropriateness and applicability for boron analysis in 2500 mg B/kg concentration range. For Potentiometric Titration method, the measurement uncertainty = 2500 ±16 mg B/kg, accuracy= 0.2%, precision= 0.08% the range of analysis= 5-800 mg B/kg. For Atomic Absorption Spectrophotometry (Flame) the measurement uncertainty= 2500 ±51 mg B/kg, accuracy= 0.12%, precision= 0.44% the range of analysis= 0 -500 mg B/kg. For UV-VIS Azomethine-H the measurement uncertainty= 2500 ±72 mg B/kg, accuracy= 0.08%, precision= 0.44% the range of analysis= 0 -10 mg B/kg. The INPOs 95% accuracy and precision criteria for boron is ± 1%. So these techniques could be used for boron analysis in PWR. Based on the evaluation and assessments mentioned above; the Potentiometric Titration was found to be the most preferred method for boron analysis for Pressurised Water Reactors followed by Atomic Absorption Spectrophotometry (Flame) that can be of good use in determining boron especially in waste samples and samples with complex matrices. The UV-VIS Azomethine-H methods can only be used when it is really necessary to determine very low levels of boron between 0- 10mg B/kg of which it was never required before. Since it is specifically the B-10 isotope that is responsible for the ability to control reactivity, the implementation of isotopic boron analysis (by Inductively Coupled Plasma – Mass Spectrometry) at KNPS is explained and the advantage of the programme is illustrated. Although the current state of instrumental capabilities is adequate for 10B isotope determination, further work of optimising the methodology for even better results is recommended.

No presente trabalho comprova-se o efeito prejudicial do oxalato, utilizado para a separação prévia de cálcio e magnésio, na determinação complexométrica deste último com EDTA em águas, usando-se em titulação visual o indicador Negro de Eriocromo T e, em titulação potenciométrica, o sistema indicador Hg/Hg-EDTA. Comprovou-se, também, a viabilidade de se usar como titulante uma solução de EDTA \"tetraneutralizado\", em titulações potenciométricas com medidas de pH através de eletrodo de vidro combinado. Neste caso o ponto final é obtido através da hidrólise da espécie Y4-, após o ponto de equivalência. Assim evidenciou-se a viabilidade de um novo método para a determinação da mistura de cálcio e magnésio, pelo uso EDTA \"tetraneutralizado\" e separação prévia dos dois cátions através da adição de oxalato. A detecção do ponto final nestas titulações com EDTA \"tetraneutralizado\" pode também ser feita visualmente com fenolftaleína. O efeito de volume em titulações potenciométricas em geral, num certo nível de concentração, foi objeto de análises diversas inclusive por cálculo computacional de curvas derivativas. Comprovou-se que quanto menor o volume do titulado maior é o salto potenciométrico obtido, caracterizando-se o que se denominou de \"paradoxo potenciométrico\", pois uma menor massa de substância pode ser titulada com, teoricamente, o mesmo erro relativo que para uma massa maior de substância. / Alternative method for the complexometric determination of magnesium. Influence of volume on potentiometric titrations. Keywords: Potentiometry, Magnesium, EDTA. Present paper has been found the negative effect of oxalate, used to the previous separation of calcium and magnesium in a complexometric determination of this last with EDTA in waters, using at visual titration Eriochrome black T as indicator and at potentiometric titration the indicator system Hg/Hg-EDTA. It has been found, also, the viability in the use as titrant a \"tetraneutralized\" EDTA solution, in potentiometric titration with measurements of pH with the glass electrode. In this case the end point is obtained on basis of hydrolysis of Y4- species, after the equivalent point. So it has been displayed the viability of a new method to the determination of the mixture calcium and magnesium by the use of \"tetraneutralized\" EDTA and previous separation of both cations by addition of oxalate. The end point detection can be visually found, in these titrations with \"tetraneutralized\" EDTA, by using of phenolphthalein. The effect of volume in potentiometric titration in general, at a defined concentration level, was subject of several analysis incluse using the compute calculation of derivative curves. It has been found that as smaller volume of titrated performes a higher potentiometric jump, this effect was called for us \"potentiometric paradox\", since an smaller weight of substance can be titrated, with theoretically, the same relative error that to a greater weight of substance.