<p>The transport of ammonia by various tissues throughout the body is of fundamental importance for nitrogen excretion in invertebrates, yet sites and mechanisms of ammonia transport are not presently well understood. In this thesis a novel ammonium-selective microelectrode was developed using the ionophore TD19C6, which is approximately 3800-fold more selective for NH₄⁺ than Na⁺ compared with the 100-fold difference of nonactin used in previous microelectrodes. We investigated the accuracy of the ammonium microelectrode in solutions simulating <em>Drosophila</em> haemolymph (25 mM K⁺) and secreted fluid (120 mM K⁺). In haemolymph-like solutions, ammonium could be measured down to about 1 mM, with an error of 0.5 mM, while in secreted fluid-like conditions ammonium could be determined to within 0.3 mM down to a level of 1 mM NH₄⁺ in the presence of 100 to 140 mM K⁺. These results suggested that the ammonium microelectrode could be used to measure ammonium in the presence of physiological levels of potassium, unlike previous studies. We also quantified ammonium secretion by the Malpighian (renal) tubules of larvae. Ammonium concentrations of secreted fluid were consistently equivalent to or above ammonium concentrations of bathing salines. With a lumen-positive transepithelial potential, these results suggested an active secretory mechanism for ammonia transport. Under conditions of low K⁺ concentrations, the ability of the tubules to concentrate ammonium in secreted fluid was significantly enhanced, indicating some level of competition between NH₄⁺ and K⁺ for common transporters. The new ammonium-selective microelectrode is sufficiently sensitive to detect ammonium at the picomol level.</p> / Master of Science (MSc)

This research conducted equilibrium experiments to determine ion exchange equilibria data for the inorganic cations Ca2+, Na+, and NH4+ for binary cation exchange involving sulfonic acid, polystyrene gel resins saturated with Na+ or NH4+. A linear least-square fitting was developed to find representative ion exchange capacity (IEC) and selectivity coefficient (K) values. Equilibrium experiments were utilized to test the developed new linearization method for binary systems: Ca-NH4; Ca-Na; and Na-NH4 using three commercial strong acid cation (SAC) exchange resins. It was determined that SAC exchange resins saturated with NH4+ were more selective towards Ca2+ than resins saturated with Na+. The valency and the size of the hydrated radius of the counterion influenced the selectivity of binary systems. A higher valence and a smaller hydrated radius resulted in an increased affinity of the resin for ions. Results can be used to estimate the technical and economic feasibility of a design process along with the estimation of the effect of a change in operating conditions. In addition, the removal of toxic heavy metals was also investigated with an initial metal concentration of 0.1 mg/L. Results showed that the maximum percent removal of toxic heavy metal ions, Cr3+, Pb2+, Ba2+, and Cd2+ ranged from ~ 95-99% when present in a solution containing a high molar concentration of Ca2+, Na+, and NH4+. It was observed that SAC exchange resins can effectively remove toxic heavy metals at very low concentrations. The high selectivity that SAC exchange resins possess towards heavy metals proves that they can be used as a pretreatment method for the removal of toxic heavy metals from municipal and industrial wastewaters. Moreover, the performance of SAC exchange resins for the removal of Ca2+ from waste solutions was investigated through computer modelling. Results showed that ion exchange is an efficient method for the removal of Ca2+. A sensitivity analysis showed that the variation in K and IEC greatly influenced the breakthrough time as an increase in both parameters resulted in greater Ca2+ uptake. Modelling results can be used to optimize the design of ion exchange systems for the pretreatment of inorganic cations which can reduce membrane scaling. / Thesis / Master of Applied Science (MASc)

Cette étude a fait l'objet de deux parties. L'une porte sur l'effet de différents types d'activation (chimique, thermique, mécanique) de kaolins (géo-matériaux riches en kaolinite) sur leurs propriétés de décoloration vis-à-vis de l'huile de riz. L'autre traite de l'effet de la taille et de la morphologie de kaolinites de synthèse sur leurs propriétés d'adsorption.Cette étude a montré que lorsque le kaolin était chauffé à plus de 100°C avant de subir une activation acide en milieu sulfurique, citrique ou oxalique, la capacité de décoloration vis-à-vis de l'huile de riz était fortement réduite. Cet effet a été directement mis en relation avec la destruction partielle ou totale de la structure de la kaolinite, associée à une forte lixiviation de l'aluminium de l'échantillon et à la précipitation de silice amorphe. Il s'est donc avéré que la préservation des sites aluminols présents sur les surfaces externes des particules de kaolinites semblait être un critère primordial à conserver en vue d'obtenir de bonne capacité de décoloration. Dans ce contexte, les meilleures capacités de décoloration (82% environ) ont été obtenues en utilisant conjointement un traitement thermique modéré (<100°C), un broyage mécanique de l'échantillon avant l'étape d'activation acide, une concentration en acide de l'ordre de 0.3 à 0.5 mol/L et un rapport (argile)/(solution acide) de l'ordre de 1/50. Notons que les plus fortes valeurs de surfaces spécifiques n'ont pas forcément été associées aux échantillons présentant les meilleures capacités de décoloration en raison de la présence de silice amorphe et de la non-préservation des sites aluminols de la kaolinite ; sites responsables de l'adsorption des pigments de molécules de chlorophylle-a.Par ailleurs, aucune étude à notre connaissance ne reliait directement les morphologies de particules de phyllosilicates à leurs propriétés d'adsorption vis-à-vis de deux cations inorganiques. Dans le cas des kaolinites naturelles, une charge permanente souvent significative et attribuable à des impuretés minéralogiques empêche toute tentative de relier directement la forme des particules à un coefficient de sélectivité entre deux cations pour des sites latéraux donnés. Des kaolinites ont donc été synthétisées par voie hydrothermale en considérant différentes conditions physico-chimiques, afin d'obtenir des morphologies variées (hexagones plus ou moins anisotropes). Pour ces échantillons synthétiques pour lesquels aucune impureté minéralogique et charge permanente n'a été détectée, des isothermes expérimentales d'adsorption entre Na+ et H+ ont été mesurées. Ces cations ont été choisis étant donné leur présence ubiquiste dans les eaux naturelles et leur fort pouvoir compétiteur par rapport aux cations traces métalliques. Grâce aux surfaces spécifiques des sites latéraux et des densités de site issues de la cristallographie des différentes faces présentes dans nos échantillons ((010), (110), (1-10)), un coefficient de sélectivité entre Na+ et H+ sur l'ensemble des sites latéraux d'une morphologie donnée a pu être estimé à l'aide d'un modèle de complexation de surface. Les résultats ont montré que le coefficient de sélectivité Na+/H+ dépendait très fortement de la morphologie de la particule, et que par conséquent les propriétés d'adsorption des kaolinites ne pouvaient pas être obtenues avec précision sans une connaissance fine de la morphologie des particules. / The dissertation consists of two main parts; the first part is devoted to the effect of physical/thermal and chemical activation of kaolin on bleaching of rice bran oil. In this study, samples were prepared from natural Ranong kaolin. This study focused on the effects of both thermal treatment (from 100 to 900°C) and chemical activation (sulfuric acid, hydrochloric acid, citric acid and oxalic acid using different acid concentrations or different clay/acid ratio) on the capacity of kaolins to bleach rice bran oil. When kaolin was treated with high temperature (>100°C) prior to reflux and with a high acid concentration during reflux, the kaolinite structure was partially or completely destroyed associated to a dramatic leaching of alumina, and amorphous silica dominated the samples. The measured maximum bleaching capacity obtained was not consistent with the highest specific surface area and pore volume; rather, it depended on the alumina contents in the samples. Thus, the partial preservation of the kaolinite structure is crucial to obtain an appropriate bleaching capacity of kaolin. This is directly related to the preservation of the aluminol sites present at the kaolinite surface. XRF analysis showed that the alumina contents of 28-34% were values to reach in order to obtain optimum bleaching capacities of kaolin, independently of the different acid used. Finally, optimum bleaching of ~83%, ~82% and ~81% were achieved by grinding the kaolin prior to reflux with low acid concentration of hydrochloric acid (0.5 M), sulfuric acid (0.3 M) and citric acid (0.5 M), respectively with clay/acid ratio of 1:50.The second part of the thesis aims to elucidate the influence of morphology of kaolinites on their sorption properties. For that, Na+/H+ sorption isotherms in water saturated conditions of synthetic kaolinites and natural well crystallized kaolinite, called KGa--1b commercialized by the Clay Mineral Society, were performed and interpreted. Kaolinites used in this study were hydrothermally synthesized from partially crystallized kaolinite as a function of different final pH (pHF) ranging from 0.8 to 8.3. Results obtained for KGa--1b were compared with data obtained in literature for this mineral, in order to fully validate this approach. This study found that cation exchange capacity, due to both isomorphic substitutions in the crystals (permanent charge), and silanol and aluminol edge sites were highly variable. Typically, CEC at pH=9 varied from ~0.8 cmolc/kg for well crystallized kaolinite (pHF 0.8) to ~33 cmolc/kg for disordered lath-shaped kaolinite (pHF 8.3). Na+/H+ sorption isotherms were obtained for all synthetic kaolinites as a function of pH ranging from pH 3 to 11. Results showed that sorption of Na+ increases dramatically with pH. Typically for all kaolinite samples except for the one synthesized at pHF=8.3, Na+ sorption is rigorously equal to zero when pH<7, indicating no permanent charge in the samples (in contrast to natural KGa--1b kaolinite), and increases when pH>7 due to sorption on edge sites. The amount of dissolved silica measured during Na+/H+ isotherm is higher for experiments performed with kaolinites synthesized in basic conditions (for pHF 7.4 and pHF 8.3) than for kaolinites synthesized in acid conditions (for pHF 0.8 and pHF 3.3). These latter results lead to conclude that sorption site density can be considered constant when pH is between 4 and 10, independently of the morphologies of particles. In this context, a thermodynamic modeling procedure using a complexation model was applied to interpret the data obtained with hexagonal- and lath-shaped particles. During this procedure, selectivity coefficient between Na+ and H+ cations were obtained considering the total edge site densities calculated from lateral specific surfaces estimated for synthetic kaolinites and crystallography data.

Highly selective and sensitive phosphate sensors have been fabricated by constructing a solid membrane disk consisting of variable mixtures of aluminium powder (Al), aluminium phosphate (AlPO4) and powdered copper (Cu). Both binary and ternary electrode systems are produced depending on their composition. The ternary membranes exhibit greater selectivity over a wide range of concentrations. The ternary electrode with the composition 25% AlPO4, 25% Cu and 50% Al was selected as our preferred electrode. The newly fabricated ternary membrane phosphate selective electrodes exhibited linear potential response in the concentration range of 1.0 × 10−6 to 1.0 × 10−1 mol L−1. The electrodes also exhibit a fast response time of <60 s. Their detection limit is 1.0 × 10−6 mol L−1. The unique feature of the described electrodes is their ability to maintain a steady and reproducible response in the absence of an ionic strength control. The electrodes have a long lifetime and can be stored in air when not in use. The selectivity of the new phosphate selective electrodes with respect to other common ions is excellent. The results obtained provide further insight into the working principles of the newly fabricated phosphate selective electrodes. Dephosphorylation and phosphorylation reactions were monitored using the preferred phosphate selective electrode. The following reactions were studied and inferences drawn; (a) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[OH(PO2O)]2- for 1:1, 2:1 and 3:1 *[{CoN4(OH)(OH2)}]2+ to *[OH(PO2O)]2- ratios.(b) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[O2NC6H4PO2(O)(OH)]- for 1:1, 2:1 and 3:1 *[{CoN4(OH)(OH2)}]2+ to *[O2NC6H4PO2(O)(OH)]- ratios. (c) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[(OH)2(PO2)2O]2- for 1:1, 2:1 and 3:1 [{CoN4(OH)(OH2)}]2+ to *[(OH)2(PO2)2O]2- ratios, and (d) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[(OH)2(PO2)3O2]3- for the 1:1, 2:1 and 3:1 [{CoN4(OH)(OH2)}]2+ to *[(OH)2(PO2)3O2]3- ratios. Further insight into dephosphorylation and phosphorylation reactions is unravelled by the novel phosphate selective electrode monitoring. *For clarity of the complexes utilized, see chapter 4, table 4.1. KEY WORDS; Dephosphorylation, phosphorylation, ion selective electrodes, phosphate ion selective electrode, decontamination, electromotive force, potential difference, activity, concentration, selectivity coefficient, calibration, ionic strength, hydrolysis, inorganic phosphates, nitrophenylphosphate, pyrophosphate, tripolyphosphate, organophosphate esters. / Chemistry / D.Phil (Chemistry)

Highly selective and sensitive phosphate sensors have been fabricated by constructing a solid membrane disk consisting of variable mixtures of aluminium powder (Al), aluminium phosphate (AlPO4) and powdered copper (Cu). Both binary and ternary electrode systems are produced depending on their composition. The ternary membranes exhibit greater selectivity over a wide range of concentrations. The ternary electrode with the composition 25% AlPO4, 25% Cu and 50% Al was selected as our preferred electrode. The newly fabricated ternary membrane phosphate selective electrodes exhibited linear potential response in the concentration range of 1.0 × 10−6 to 1.0 × 10−1 mol L−1. The electrodes also exhibit a fast response time of <60 s. Their detection limit is 1.0 × 10−6 mol L−1. The unique feature of the described electrodes is their ability to maintain a steady and reproducible response in the absence of an ionic strength control. The electrodes have a long lifetime and can be stored in air when not in use. The selectivity of the new phosphate selective electrodes with respect to other common ions is excellent. The results obtained provide further insight into the working principles of the newly fabricated phosphate selective electrodes. Dephosphorylation and phosphorylation reactions were monitored using the preferred phosphate selective electrode. The following reactions were studied and inferences drawn; (a) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[OH(PO2O)]2- for 1:1, 2:1 and 3:1 *[{CoN4(OH)(OH2)}]2+ to *[OH(PO2O)]2- ratios.(b) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[O2NC6H4PO2(O)(OH)]- for 1:1, 2:1 and 3:1 *[{CoN4(OH)(OH2)}]2+ to *[O2NC6H4PO2(O)(OH)]- ratios. (c) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[(OH)2(PO2)2O]2- for 1:1, 2:1 and 3:1 [{CoN4(OH)(OH2)}]2+ to *[(OH)2(PO2)2O]2- ratios, and (d) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[(OH)2(PO2)3O2]3- for the 1:1, 2:1 and 3:1 [{CoN4(OH)(OH2)}]2+ to *[(OH)2(PO2)3O2]3- ratios. Further insight into dephosphorylation and phosphorylation reactions is unravelled by the novel phosphate selective electrode monitoring. *For clarity of the complexes utilized, see chapter 4, table 4.1. KEY WORDS; Dephosphorylation, phosphorylation, ion selective electrodes, phosphate ion selective electrode, decontamination, electromotive force, potential difference, activity, concentration, selectivity coefficient, calibration, ionic strength, hydrolysis, inorganic phosphates, nitrophenylphosphate, pyrophosphate, tripolyphosphate, organophosphate esters. / Chemistry / D. Phil (Chemistry)