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The Fabrication and Study of Metal Chelating Stationary Phases for the High Performance Separation of Metal Ions

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The Fabrication and Study of Metal Chelating Stationary Phases for the High Performance Separation of Metal Ions University of Plymouth PEARL https://pearl.plymouth.ac.uk 04 University of Plymouth Research Theses 01 Research Theses Main Collection 2000 THE FABRICATION AND STUDY OF METAL CHELATING STATIONARY PHASES FOR THE HIGH PERFORMANCE SEPARATION OF METAL IONS Shaw, Matthew James http://hdl.handle.net/10026.1/1938 University of Plymouth All content in PEARL is protected by copyright law. Author manuscripts are made available in accordance with publisher policies. Please cite only the published version using the details provided on the item record or document. In the absence of an open licence (e.g. Creative Commons), permissions for further reuse of content should be sought from the publisher or author. THE FABRICATION AND STUDY OF METAL CHELATING STATIONARY PHASES FOR THE HIGH PERFORMANCE SEPARATION OF METAL IONS by Matthew James Shaw A thesis submitted to the University of Plymouth in partial fulfilment for the degree of DOCTOR OF PHILOSOPHY Department of Environmental Sciences Faculty of Science March 2000 mno. i 8 mv ClassNo. Contl.No. 900426331 9 REFERENCE OISL/ LIBRARY STORE: ABSTRACT THE FABRICATION AND STUDY OF METAL CHELATING STATIONARY PHASES FOR THE HIGH PERFORMANCE SEPARATION OF METAL IONS By Matthew J. Shaw The preparation and characterisation of chelating sorbents suitable for the high efficiency separation of trace metals in complex samples, using a single column and isocratic elution, is described. Hydrophobic, neutral polystyrene divinylbenzene resins were either impregnated with chelating dyes or dynamically modified with heterocyclic organic acids, using physical adsorption and chemisorption processes respectively. A hydrophilic silica substrate was covalently bonded with a chelating aminomethylphosphonic acid group, to assess the chelating potential of this molecule. These substrates were characterised in terms of metal retention capability (selectivity coefficients and capacity factors), separation performance, column efficiency and suitability for analytical applications. Chelating molecules with different ligand groups were found to have unique selectivity patterns dependant upon the conditional stability constants of the chelate. Other factors, including mobile phase constituents - complexing agents, ionic strength and pH, column length and column capacity were additionally investigated to examine their effect upon the separation profiles achieved. The promising metal separation abilities illustrated by a number of these chelating columns were exploited for the determination of trace toxic metals in complex sample matrices using High Performance Chelation Ion Chromatography (HPCIC). This included the determination of beryllium in a certified stream sediment, uranium in seawater and a certified stream sediment, and cadmium, lead and copper in a certified rice flour. The results for each analysis fell within the certified limits, and reproducibility was good. The optimisation of post column detection systems using chromogenic ligands additionally gave good detection limits for the metals in each separation system. in LIST OF CONTENTS Copyright statement i Title Page ii Abstract iii List of Contents iv List of Tables x List of Figures xii Acknowledgements xxiii Author's Declaration xxiv CHAPTER 1. Introduction 1.1 Trace metal analysis 1 1.2 Principles of the liquid chromatographic process 3 1.3 Ion chromatography 6 1.3.1 Simple ion - exchange 7 1.3.2 Chelating ion exchange 12 1.3.2.1 Principles of chelation 14 1.4 Chelating substrates 24 1.5 Ion chromatographic analysis of metal ions - a review 26 1.5.1 Polystyrene Resins 28 1.5.2 Silica Substrates 31 1.5.3 Chelation Ion Chromatography (CIC) 32 1.5.4 High Performance Chelation Ion Chromatography (HPCIC) 33 1.6 Detection of metal ions 37 1.7 Aims and objectives of this work 40 IV CEIAPTER 2. A Comparison of Chelating Dyes Impregnated onto Polystyrene resins for Trace Metal Separations 2.1 Introduction 43 2.1.1 Dye immobilised low efficiency supports 43 2.1.2 High performance dye impregnated supports 47 2.1.3 Dyes added to the mobile phase for high efficiency separations 49 2.1.4 Aims of this study 51 2.2 Experimental 54 2.2.1 Instrumentation 54 2.2.2 Reagents 54 2.2.3 Dye types studied 56 2.2.4 Procedures 57 2.2.4.1 Column Preparation 57 2.2.4.2 Column Capacity Measurement 57 2.2.4.3 Capacity Factor Determination 58 2.3 Results and Discussion ^ 61 2.3.1 Aurin Tricarboxylic Acid (ATA) Column 61 2.3.2 Pyrocatechol Violet (PCV) Column 69 2.3.3 0-Cresolphthalein Complexone (CPC) Column 73 2.3.4 Calmagite (CAL) Column 78 2.3.5 4-(2-pyridyla2o)resorcinol (PAR) Column 82 2.3.6 2-(3-sulphobenzoyl)pyridine 2-pyridylhydrazone (SPP) Column 88 2.3.7 Effect of System Parameters on Metal Ion Separations 94 2.3.7.1 Column Length 94 2.3.7.2 Column Capacity 98 2.3.7.3 Mobile phase ionic strength 104 2.3.7.4 Complexing eluent effects 107 2.3.7.5 Bare resin characteristics 108 2.4 Summary 109 CHAPTER 3. Chelating Exchange Separation Properties of Aminophosphonate Functionalised Silica. 3.1 Introduction 113 3.2 Experimental 118 3.2.1 Instrumentation 118 3.2.2 Reagents 118 3.2.3 Sorbent Preparation 118 3.2.3.1. Silica Bound Aminophosphonic acid ( APAS ) 119 3.2.3.2 Silica Bound Phenylphosphonic Acid ( PPAS ) 119 3.3 Results and Discussion 120 3.3.1 Chelating Mechanism of Aminophosphonate Functional Groups 120 3.3.2 APAS Column Selectivity 122 3.3.3 Phenylphosphonic Acid Column Selectivity 140 3.4 Summary 144 CHAPTER 4. The Determination ofTrace Beryllium in a Stream Sediment. 4.1 Introduction 145 4.2 Experimental 148 4.2.1 Instrumentation 148 4.2.2. Reagents 148 4.2.3 Sample pre-treatment 148 4.3 Results and Discussion 149 4.3.1 Choice of Chelating Column 149 4.3.2 Retention Characteristics and Selectivity of Be(n) and Selected 150 Trivalent Metal Ions on APAS. 4.3.3 Method Development 155 4.3.3.1 Effect of Sample Ionic Strength on Metal Retention 155 Characteristics 4.3.3.2 Separation Conditions 155 4.3.3.3 Detection Conditions 159 4.3.4 Analytical Performance Characteristics 167 4.4 Summary 170 VI CHAPTER 5. Separation of Metal Ions using Neutral Substrates Dynamically Modified with Low Molecular Weight Chelating Molecules 5.1 Introduction 171 5.2 Experimental 173 5.2.1 Instrumentation 173 5.2.2 Reagents 174 5.2.3 4-Chlorodipicolinic acid synthesis 174 5.2.4 Preparation of the mobile phase 174 5.3 Results and Discussion 175 5.3.1 Measurement of the dynamic loading of each carboxylic acid 175 5.3.2 Effect of ionic strength on dynamic loading 177 5.3.3 Effect of particle size on dynamic loading 177 5.3.4 Reproducibility of dynamically modified substrates 178 5.3.5 Chelating exchange properties of the dynamically coated carboxylic 179 acids 5.3.5.1 Picolinic Acid 180 5.3.5.2 Quinaldic acid 182 5.3.5.3 Dipicolinic acid 188 5.3.5.4 4-Chlorodipicolinic acid 194 5.3.5.4.1 Preliminary 100mm PS-DVB column investigations 195 5.3.5.4.2 250mm PS-DVB column investigations 203 5.3.6 L -Tryptophan 209 5.3.7 2-hydroxyhexadecanoic acid 210 5.4 Summary 211 VII CHAPTER 6. Determination of Trace Metals in Environmental Samples using Dynamically Modified Substrates. Part 1. Determination of Uranium in a Stream Sediment and Complex Aqueous Matrices. 6.1 Introduction 213 6.2 Experimental 216 6.2.1 Instrumentation 216 6.2.2 Reagents 216 6.2.3 Sample Pre-treatment 217 6.3 Results and Discussion 219 6.3.1 Retention Characteristics of Uranium on the Dynamically Modified 219 Substrate 6.3.2 Method Development - Separation Conditions 221 6.3.3 Method Development - Detection Conditions 224 6.3.4 Analytical Characteristics for the Determination of Uranium 229 6.4 Summary 236 Part 2. The Determination of Pb(IO, Cd(II) and Cu(II) in Rice Flour 6.5 Introduction 237 6.6 Experimental 242 6.6.1 Instrumentation 242 6.6.2 Reagents 242 6.6.3 Sample Pre-treatment 242 6.7 Results and Discussion 244 6.7.1 Choice of Digestion Procedure 244 6.7.2 Method Development - Detection Conditions 245 6.7.3 Method Development - Separation conditions 247 6.7.4 Analytical Characteristics of the Analysis 257 6.8 Summary 258 vin CHAPTER 7. Conclusions and Suggestions for Further Work 7.1 Conclusions 260 7.2 Further Work 265 REFERENCES 269 LIST OF TABLES CHAPTER I. Table 1.1 Metal ions as hard or soft acids 15 Table 1.2 Ligands as hard or soft bases 16 Table 1.3 Stepwise formation constants of selected nitrogen complexes 20 CHAPTER 2. Table 2.1 Chelating dyes studied, and resins used 56 Table 2.2 Log stability constants of metal complexes with ATA 61 Table 2.3 Log stability constants of metal complexes with CPC 74 Table 2.4 Log stability constants of selected metal ions with CAL 78 Table 2.5 Log stability constants of metal ions with PAR 82 Table 2.6 Efficiency of analyte peak, Pb(II), with column length 95 Table 2.7 Change in the Selectivity factors with column capacity 98 Table 2.8 Effect of Acetate Concentration on Metal Retention 107 Table 2.9 Retention of selected transition metals on Dionex resins 108 Table 2.10 Dye immobilised resin characteristics 109 Table 2.11 Metal selectivity on each dye column 110 CHAPTER 3, Table 3.1 Log stability constants of selected metal complexes with 114 iminodiacetate Table 3.2 Log stability constants of selected metals with 116 aminoethylphosphonic acid Table 3.3 Column efficiency ( N ) on the APAS substrate at 0.5 and IM 134 KNO3 ( pH 2.3 ) CHAPTER 4.
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