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Applications of Capillary Electrophoresis and Mass APPLICATIONS OF CAPILLARY ELECTROPHORESIS AND MASS SPECTROMETRY FOR THE ANALYSIS OF THIOSALTS by © Michael Pappoe A Thesis submitted to the School of Graduate Studies in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Chemistry, Faculty of Science Memorial University of Newfoundland November, 2014 St. John’s Newfoundland ABSTRACT Thiosalt species are unstable, partially oxidized sulfur oxyanions formed in sulfur-rich environments but also during the flotation and milling of sulfidic minerals especially those containing pyrite (FeS2) and pyrrhotite (Fe(1-x)S, x = 0 to 0.2). Detecting and 2- 2- quantifying the major thiosalt species such as sulfate (SO4 ), thiosulfate (S2O3 ), 2- 2- 2- trithionate (S3O6 ), tetrathionate (S4O6 ) and higher polythionates (SxO6 , where 3 ≤ x ≤ 10) in the milling process and in the treated tailings is important to understand how thiosalts are generated and provides insight into potential treatment. As these species are unstable, a fast and reliable analytical technique is required for their analysis. Three capillary zone electrophoresis (CZE) methods using indirect UV-vis detection were developed for the simultaneous separation and determination of five thiosalt anions: 2- 2- 2- 2- 2- SO4 , S2O3 , S3O6 , S4O6 and S5O6 . Both univariate and multivariate experimental design approaches were used to optimize the most critical factors (background electrolyte (BGE) and instrumental conditions) to achieve fast separation and quantitative analysis of the thiosalt species. The mathematically predicted responses for the multivariate experiments were in good agreement with the experimental results. Limits of detection (LODs) (S/N = 3) for the methods were between 0.09 and 0.34 μg/mL without a sample stacking technique and nearly four-fold increase in LODs with the application of field- amplified sample stacking. As direct analysis of thiosalts by mass spectrometry (MS) is limited by their low m/z values and detection in negative mode electrospray ionization (ESI), which is typically less sensitive than positive ESI, imidazolium-based (IP-L-Imid ii and IP-T-Imid) and phosphonium-based (IP-T-Phos) tricationic ion-pairing reagents were used to form stable high mass ions non-covalent +1 ion-pairs with these species for ESI- MS analysis and the association constants (Kassoc) determined for these ion-pairs. Kassoc values were between 6.85 × 102 M-1 and 3.56 × 105 M-1 with the linear IP-L-Imid; 1.89 ×103 M-1 and 1.05 × 105 M-1 with the trigonal IP-T-Imid ion-pairs; and 7.51×102 M-1 and 4.91× 104 M-1 with the trigonal IP-T-Phos ion-pairs. The highest formation constants 2- were obtained for S3O6 and the imidazolium-based linear ion-pairing reagent (IP-L- 2- Imid), whereas the lowest were for IP-L-Imid: SO4 ion-pair. iii ACKNOWLEDGMENTS I thank my supervisor Dr. Christina S. Bottaro and my supervisory committee members Dr. Fran Kerton and Dr. Bob Davis for their direction and guidance in helping me successfully complete my work. I am grateful to my office colleagues Ali Modir and Dr. Geert van Biesen of for their help and especially for their suggestions in troubleshooting the capillary electrophoresis (CE) and CE-ESI-MS instrumentation. My appreciation also goes to Linda Windsor and Dr. Celine Schneider in C-CART for training me to use the various instruments in C-CART and Dr. Louise Dawe for analyzing my synthesized single crystals. I also appreciate the help and encouragement from my office colleagues. I would not have come this far in this research without everyone’s help. Finally, I thank my wife Michaelina for her love and overwhelming support without which I would not have come this far. iv Table of Contents ABSTRACT......................................................................................................................... ii ACKNOWLEDGMENTS .................................................................................................. iv Table of Contents .................................................................................................................v List of Tables .......................................................................................................................x List of Figures .................................................................................................................... xii List of Abbreviations ....................................................................................................... xvii List of Appendices ............................................................................................................ xxi Chapter 1. Introduction and Overview................................................................................ 1 1.1 General introduction ................................................................................................. 2 1.2 The generation and chemistry of thiosalts from sulfidic minerals............................ 4 1.2.1 Chemical oxidation of sulfidic ores ................................................................... 6 1.2.2 Enzymatic Oxidation of sulfidic ores in aqueous systems................................. 8 1.3 Thermodynamic and Kinetic Properties of Thiosalts in Aqueous Systems.............. 9 1.3.1 Reactions involving the thiosulfate ion.............................................................. 9 1.3.2 Reactions involving the trithionate ion ............................................................ 11 1.3.3 Reactions involving the tetrathionate ion ........................................................ 14 1.3.4 Reactions involving the pentathionate and hexathionate ions ......................... 15 1.4 An overview of analytical techniques for detecting and quantifying thiosalts ....... 20 1.4.1 Chromatographic techniques............................................................................ 20 1.4.2 Capillary electrophoresis.................................................................................. 24 1.4.2.1 CE Separation techniques for inorganic ions ............................................. 29 1.4.2.2 Detection of inorganic ions in CE.............................................................. 33 1.4.2.2.1 CE with direct UV-vis detection ......................................................... 34 1.4.2.2.2 CE with indirect UV-vis detection ...................................................... 35 v 1.4.2.2.3 Selected applications of CE with direct UV-vis detection .................. 37 1.4.2.2.4 Selected applications of CE with both direct and indirect UV-vis detection ............................................................................................................. 41 1.4.2.2.5 Selected applications of CE with indirect UV-vis detection............... 43 1.4.2.2.6 CE with Electrochemical detection ..................................................... 44 1.4.3 Use of ion-pairing reagents for CE-MS analysis ............................................. 46 1.5 Research objectives and organization of thesis ...................................................... 51 1.6 Co-authorship Statement......................................................................................... 53 1.7 References ............................................................................................................... 55 Chapter 2. Systematic Optimization of a Pyromellitic Acid Background Electrolyte for Capillary Zone Electrophoresis With Indirect UV-Vis Detection and Online Pre- concentration Analysis of Thiosalt Anions in the Treated Mine Tailings ........................ 72 2.1 Introduction ............................................................................................................. 73 2.2. Experimental .......................................................................................................... 77 2.2.1 Chemicals......................................................................................................... 77 2.2.2 Instrumentation ................................................................................................ 77 2.2.3 Overview of factors studied ............................................................................. 79 2.3. Results and discussions .......................................................................................... 79 2.3.1 UV-vis analysis of thiosalts ............................................................................. 79 2.3.2 Influence of EOF modifier concentration ........................................................ 80 2.3.3 Influence of PMA chromophoric probe concentration .................................... 84 2.3.4 Influence of pH and applied field on the electrophoretic mobilities of thiosalts ................................................................................................................................... 85 2.3.5 Optimization of sensitivity............................................................................... 85 2.3.6 Linearity of method, sensitivity and LOD determination ................................ 86 vi 2.3.7 Comparison to commercially available PMA BGE for inorganic anions........ 90 2.3.8 Application of method to thiosalt standard mixture and tailings pond samples ................................................................................................................................... 90 2.4. Conclusions and future work ................................................................................. 93 2.5. References .............................................................................................................
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