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  • Unive

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    LINEAR LIBRARY c 1 0088 3930

    Ill II~ Ill ~ I Flow-Injection Analysis of the Platinum-Group Metals

    A Thesis Presented for the Degree of

    DOCTOR OF PHILOSOPHY

    in the Department of CHEMISTRY

    UNIVERSITY OF CAPE TOWN

    February 1995

    by

    DEREKAUER

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    The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non-commercial research purposes only.

    Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author.

  • Flow-Injection Analysis of the Platinum-Group Metals

    / I

    DerekAuer

    /

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    1 0 AUG i.u1i.

  • Flow-Injection Analysis of the Platinum-Group Metals

    by

    Derek Auer

    Supervisor: Associate Professor Klaus R. Koch,

    Department of Chemistry, University of Cape Town,

    South Africa.

  • Flow-Injection Analysis of the Platinum-Group Metals

    by

    DerekAuer

    Process Analytical Science Group, Analytical Science Division,

    Council for Mineral Technology, Randburg, Republic of South Africa

    February 1995

    ABSTRACT

    To 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.

  • Flow-Injection Analysis of the Platinum-Group Metals

    Table of Contents

    Abstract

    Table of Contents

    List of Figures

    List of Tables

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ ......................... .

    Acknow Iedgements

    1 Introduction

    ii

    Vlll

    XIV

    XVl

    1

    1.1 Determination of the Platinum-Group Metals . . . . . . . . . . . . . . . . . . . . 5

    1.2

    1.3

    1.4

    1.5

    1.6

    1.7

    1.8

    The Platinum-Tin(II) Chloride Complex

    The Palladium-Tin(II) Chloride Complex

    The Rhodium-Tin(II) Chloride Complex

    Tin(II) Bromide Complexes

    Flow-Injection Analysis

    Objectives of Research

    References

    10

    14

    17

    20

    22

    31

    33

    2 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

    2.1 Analytical Visible Spectrophotometry . . . . . . . . . . . . . . . . . . . . . 39

    2.1.1 Absorption of Radiation

    2.1.2 Absorption Laws

    2.1.3

    2.1.4

    Deviations from Beer's Law ......................... .

    Spectrophotometric Detectors

    ll

    40

    43

    46

    48

  • 2.2

    Flow-Injection Analysis of the Platinum-Group Metals

    Quantitation of Spectrophotometry 52

    2.2.1 Single Component Analysis (SCA) ... ; . . . . . . . . . . . . . . . . . . 54

    2.2.2 Multi-Component Analysis (MCA) . . . . . . . . . . . . . . . . . . . . . . . 57

    2.2.3 Multi-Wavelength Linear Regression Analysis (MLRA) . . . . . . 65

    2.2.4 Wavelength Selection 69

    2.3 Principles of Flow-Injection Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 70

    2.4

    2.3.1 Dispersion and Mixing Processes ...................... .

    2.3.1.1

    2.3.1.2

    2.3.1.3

    2.3.1.4

    Convection (Laminar flow)

    Secondary Flow

    Molecular Diffusion

    Turbulent (chaotic) Flow

    2.3.2 The Dispersion Coefficient

    2.3.3 A Novel Non-equilibrium Environment ................... .

    2.3.4 Manifold Design Criteria

    References

    71

    71

    72

    73

    74

    75

    78

    78

    80

    3 Data Acquisition and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

    3.1

    3.2

    Automation and Control

    3.1.1 Objectives of Automation

    3.1.2 Computer-Aided Flow Analysis

    Microcomputer Software Development

    3.2.1 Microcomputers and Accessories

    3.2.2 Meeting the Challenge of the Graphical User Interface ....... .

    3.2.3 Program Structure and Design

    82

    82

    83

    86

    87

    87

    .90

    3.2.4 Data Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

    lll

  • 3.3

    3.4

    3.5

    3.6

    Flow-Injection Analysis of the Platinum-Group Metals

    3.2.5 Software Performance and Validation

    Experimental Procedure

    Programming Language Remarks

    Conclusions

    References

    98

    . 98

    100

    101

    102

    4 Flow-Injection Analyis Manifold Design and Optimisation . . . . . . . . 103

    4.1 Preliminary Manifold Design Investigations . . . . . . . . . . . . . . . . . . . . . 104

    4.1.1 Spectrophotometer Flowcell . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

    4.1.2 Manifold Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

    4.2

    4.3

    4.4

    4.1.3 Ultra-Violet Spectrophotometric Detection

    4.1.4 Peak Height or Peak Area Measurement?

    4.1.5 Spectra FOCUSTM Data Acquisition

    Optimisation of the FIA Manifold

    4.2.1 Sample Injection Volume

    4.2.2 Reaction Coil Length

    ............................

    4.2.3 Reagent and Carrier Flow Rate

    4.2.4 Reagent and Carrier Concentrations

    4.2.5 Sample Acid Concentration

    Conclusions

    References ........................................... ~ ..

    IV

    107

    108

    108

    110

    112

    114

    116

    119

    126

    126

    128

  • Flow~lnjection Analysis of the Platinum-Group Metals

    5 Single Component Analysis of the Platinum-Group Metals . . . . . . . . 129

    5.1 The Determination of Platinum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

    5.2

    5.3

    5.4

    5.5

    5.6

    5.1.1 The Effect of the Platinum Oxidation State 130

    5.1.2 Visible Spectra of the Platinum-Tin(II) Chloride Complexes . . . 131

    5.1.3 Calibration

    5.1.4 Analysis of Synthetic Solutions

    5.1.5 Analytical Features and Performance

    The Determination of Palladium

    134

    135

    138

    139

    5.2.1 Stopped-Flow Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . 139

    5.2.2 Visible Spectra of the Palladium-Tin(II) Chloride Complexes . . . 148

    5.2.3 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

    5.2.4 Analysis of Synthetic Solutions

    5.2.5 Analytical Features and Performance

    The Determination of Rhodium

    151

    152

    153

    5.3.1 Visible Spectra of the Rhodium-Tin(II) Bromide Complexes . . . 153

    5.3.2 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

    5.3.3 Analysis of Synthetic Solutions

    5.3.4 Analytical Features and Performance

    Preliminary Interference Study

    5.4.1 Base Metal Interferences

    157

    157

    158

    159

    5.4.2 Interferences from other Platinum-Group Metals . . . . . . . . . . . 161

    Conclusions

    References

    v

    162

    163

  • 6

    Flow-Injection Analysis of the Platinum-Group Metals

    Multi-Component Analysis of the Platinum-Group Metals 164

    6.1 The Determination of Platinum and Palladium in HCl......... . . . . . . 165

    6.1.1 Wavelength Selection

    6.1.2 Multi-Component Analysis

    Classical Simultaneous Linear Equations

    Sequential Analyte Determination

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