The Development of Smart Sensors for Aquatic Water Quality Monitoring

270 Pages·2014·5.06 MB·English

by  Craig Alexander

The Development of Smart Sensors for
Aquatic Water Quality Monitoring

A thesis submitted to the University of Manchester for the degree of
Doctor of Philosophy in the Faculty of Engineering and Physical
Sciences

2014
CRAIG ALEXANDER

SCHOOL OF CHEMICAL ENGINEERING AND ANALYTICAL
SCIENCE
Craig Alexander
Contents
List of Figures ..........................................................................................................................................9
List of Tables..........................................................................................................................................16
Abstract ..................................................................................................................................................18
Declaration .............................................................................................................................................19
Copyright Statement ...............................................................................................................................19
Acknowledgements ................................................................................................................................20
List of Abbreviations ..............................................................................................................................21
Project Overview .................................................................................................................................. 24
1 Introduction ................................................................................................................................. 25
1.1 Aquarium Chemistry ................................................................................................................... 25
1.1.1 Analytes from the Nitrogen Cycle ................................................................................................ 26
1.1.1.1. Ammonia .................................................................................................................... 26
1.1.1.2. Nitrite .......................................................................................................................... 28
1.1.1.3. Nitrate ......................................................................................................................... 28
1.1.2 Aquarium pH ............................................................................................................................... 30
1.1.3 Chlorine .................................................................................................................................... 30
1.1.4 Dissolved Oxygen ....................................................................................................................... 31
1.1.5 Phosphate .................................................................................................................................... 32
1.1.6 Water Hardness ........................................................................................................................... 32
1.1.6.1. General Hardness ........................................................................................................ 32
1.1.6.2. Carbonate Hardness ..................................................................................................... 33
1.1.7 Summary of Parameters ............................................................................................................... 34
1.2 Current Methods of Analysis ....................................................................................................... 35
1.2.1 Test Kits .................................................................................................................................... 35
1.2.1.1. pH ............................................................................................................................... 36
1.2.1.2. Ammonia .................................................................................................................... 37
1.2.1.2.1. Nessler’s Reagent Method ........................................................................................... 37
1.2.1.2.2. Salicylate Method ........................................................................................................ 37
1.2.1.3. Nitrite .......................................................................................................................... 38
2
Craig Alexander
1.2.1.4. Nitrate ......................................................................................................................... 39
1.2.2 Commercial Sensors .................................................................................................................... 40
1.2.3 Benefits of the Proposed Device .................................................................................................. 40
1.3 Introduction to Chemical Sensors ................................................................................................ 42
1.3.1 Electrochemical Sensors .............................................................................................................. 43
1.3.1.1. Potentiometry .............................................................................................................. 43
1.3.1.2. Reference Electrodes ................................................................................................... 45
1.4 Ion-Selective Electrodes .............................................................................................................. 48
1.4.1 Selective Polymeric Membranes .................................................................................................. 48
1.4.2 Selectivity of ISEs ....................................................................................................................... 50
1.4.3 Polymer Membrane Electrodes .................................................................................................... 55
1.4.4 Miniaturisation of ISEs ................................................................................................................ 56
1.4.4.1. Coated-Wire Electrodes ............................................................................................... 56
1.4.4.2. Screen-Printed ISEs ..................................................................................................... 57
1.4.5 Sol-gels .................................................................................................................................... 59
1.4.5.1. Sol-gel Chemistry ........................................................................................................ 59
1.4.5.2. Sol-gel Ion-Selective Membranes ................................................................................ 61
1.4.6 ISEs for Aquarium-Significant Analytes ...................................................................................... 63
1.4.6.1. pH ............................................................................................................................... 63
1.4.6.2. Ammonia/Ammonium ................................................................................................. 65
1.4.6.3. Nitrite .......................................................................................................................... 67
1.4.6.4. Nitrate ......................................................................................................................... 69
1.5 Impedimetric Interdigitated Electrode Chemical Sensors ............................................................. 72
1.5.1 Electrical Impedance ................................................................................................................... 72
1.5.2 Interdigitated Electrodes .............................................................................................................. 74
1.5.3 IDEs for Chemical Sensing Applications ..................................................................................... 75
1.5.3.1. Ion-Selective Conductometric Microsensors ................................................................ 75
1.5.4 IDE Fabrication Techniques ........................................................................................................ 76
1.5.4.1. Photolithography ......................................................................................................... 77
1.5.4.2. Screen-Printing............................................................................................................ 79
3
Craig Alexander
1.5.5 Membrane Coating Techniques.................................................................................................... 80
1.5.5.1. Spin-Coating ............................................................................................................... 80
1.5.5.2. Dip-Coating ................................................................................................................ 81
1.5.5.3. Drop-Coating .............................................................................................................. 81
1.5.5.4. Screen-Printing............................................................................................................ 81
1.6 Aims and Objectives .................................................................................................................... 82
2 Materials and Methods................................................................................................................. 83
2.1 Preparation of Ion-Selective Membranes...................................................................................... 83
2.1.1 Materials .................................................................................................................................... 83
2.1.2 Polyvinyl Chloride Membranes.................................................................................................... 84
2.1.3 Sol-Gel Membranes ..................................................................................................................... 85
2.1.3.1. MTES ......................................................................................................................... 85
2.1.3.2. DEDMS/TEOS............................................................................................................ 85
2.1.4 Dielectric Screen-Printing Paste Membrane ................................................................................. 86
2.2 Construction of Ion-Selective Electrodes ..................................................................................... 87
2.2.1 Materials .................................................................................................................................... 87
2.2.2 Polymer Membrane Electrodes .................................................................................................... 87
2.2.3 Coated-Wire Electrodes ............................................................................................................... 88
2.3 Potentiometric Measurements ...................................................................................................... 89
2.3.1 Measurement Instrumentation ...................................................................................................... 89
2.3.2 Sensor Testing ............................................................................................................................. 89
2.3.2.1. Materials ..................................................................................................................... 89
2.3.2.2. Nitrate ISEs ................................................................................................................. 90
2.3.2.2.1. Stock Solutions ........................................................................................................... 90
2.3.2.2.2. Calibrations ................................................................................................................. 90
2.3.2.2.3. Selectivity Determination ............................................................................................ 91
2.3.2.3. Ammonium ISEs ......................................................................................................... 92
2.3.2.3.1. Stock Solutions ........................................................................................................... 92
2.3.2.3.2. Calibrations ................................................................................................................. 92
2.3.2.3.3. Selectivity Determination ............................................................................................ 93
4
Craig Alexander
2.3.2.4. pH ISEs ....................................................................................................................... 94
2.3.2.4.1. Stock Solutions ........................................................................................................... 94
2.3.2.4.2. Calibrations ................................................................................................................. 94
2.3.2.4.3. Selectivity Determination ............................................................................................ 95
2.3.2.5. Nitrite ISEs ................................................................................................................. 95
2.4 Fabrication of Interdigitated Electrodes ....................................................................................... 96
2.4.1 Lift-off Photolithography ............................................................................................................. 96
2.4.1.1. Materials ..................................................................................................................... 96
2.4.1.2. Sensor Design ............................................................................................................. 97
2.4.1.3. Fabrication Process ..................................................................................................... 98
2.4.1.4. Reduced Geometry IDEs ........................................................................................... 100
2.4.2 Screen-Printing .......................................................................................................................... 101
2.4.2.1. Materials ................................................................................................................... 101
2.4.2.2. Sensor Design ........................................................................................................... 102
2.4.2.3. Fabrication Process ................................................................................................... 104
2.4.2.3.1. Attempt One .............................................................................................................. 104
2.4.2.3.2. SP IDE Design 1 ....................................................................................................... 104
2.5 Construction of Ion-Selective Impedimetric Microsensors ......................................................... 106
2.5.1 Photolithographically-prepared IDE Sensors .............................................................................. 106
2.5.1.1. IDE Design 1............................................................................................................. 106
2.5.1.2. IDE Design 2............................................................................................................. 107
2.5.2 Screen-Printed IDEs .................................................................................................................. 107
2.5.2.1. SP IDE Design 1 ....................................................................................................... 107
2.6 Impedance Measurements .......................................................................................................... 108
2.6.1 Measurement Instrumentation .................................................................................................... 108
2.6.2 Sensor Testing ........................................................................................................................... 109
2.7 Ion-Selective Impedimetric Microsensors Methodology ............................................................ 110
2.7.1 Materials .................................................................................................................................. 110
2.7.2 Nitrate Sensors .......................................................................................................................... 110
2.7.2.1. Stock Solutions ......................................................................................................... 110
5
Craig Alexander
2.7.2.2. Pure Water Calibrations............................................................................................. 111
2.7.2.3. Background Effects ................................................................................................... 112
2.7.2.4. Selectivity ................................................................................................................. 112
2.7.2.5. Reproducibility.......................................................................................................... 114
Ammonium Sensors............................................................................................................................ 114
2.7.2.6. Stock Solutions ......................................................................................................... 114
2.7.2.7. Measurements in Water ............................................................................................. 114
2.7.2.8. Selectivity ................................................................................................................. 114
2.7.3 pH Sensors ................................................................................................................................ 115
2.7.3.1. Stock Solutions ......................................................................................................... 115
2.7.3.2. Calibrations ............................................................................................................... 116
2.7.4 Nitrite Sensors ........................................................................................................................... 117
2.7.4.1. Stock Solutions ......................................................................................................... 117
2.7.4.2. Measurements in Water ............................................................................................. 117
2.7.4.3. Selectivity ................................................................................................................. 117
3 Potentiometric Characterisation of Ionophores ........................................................................... 119
3.1 Nitrate-Selective Electrodes ....................................................................................................... 119
3.1.1 Nitrate PMEs ............................................................................................................................. 119
3.1.2 Nitrate CWEs ............................................................................................................................ 124
3.2 Ammonium-Selective Electrodes ............................................................................................... 129
3.3 Hydrogen Ion-Selective Electrodes ............................................................................................ 133
3.4 Conclusions for Chapter 3.......................................................................................................... 136
4 Nitrate Sensing using IDE Design 1 .......................................................................................... 140
4.1 Sensor Calibration ..................................................................................................................... 140
4.2 PVC Membrane Sensors ............................................................................................................ 147
4.2.1 Calibrations ............................................................................................................................... 147
4.2.2 Selectivity.................................................................................................................................. 155
4.3 Sol-gel Membrane Sensors ........................................................................................................ 157
4.3.1.1. DEDMS/TEOS Membrane ........................................................................................ 157
4.3.1.1.1. Calibrations ............................................................................................................... 157
6
Craig Alexander
4.3.1.1.2. Selectivity ................................................................................................................. 167
4.4 Conclusions for Chapter 4.......................................................................................................... 170
5 Nitrate Sensing using IDE Design 2 ........................................................................................... 174
5.1 Sensor Calibration ..................................................................................................................... 174
5.2 PVC Membrane Sensors ............................................................................................................ 177
5.2.1.1. Spin-coated Membranes ............................................................................................ 177
5.2.1.1.1. Calibrations ............................................................................................................... 177
5.2.1.1.2. Selectivity ................................................................................................................. 182
5.2.1.2. Drop-coated Membranes ........................................................................................... 183
5.2.1.2.1. Calibrations ............................................................................................................... 184
5.2.1.2.2. Selectivity ................................................................................................................. 202
5.3 Conclusions for Chapter 5.......................................................................................................... 207
6 Nitrate Sensing using SP IDE Design 1...................................................................................... 211
6.1 Issues Experienced with Initial Sensor Designs .......................................................................... 211
6.2 SP IDE Design 1 Calibration ..................................................................................................... 212
6.3 SP IDE Design 1 Selectivity ...................................................................................................... 224
6.4 Conclusions for Chapter 6.......................................................................................................... 227
7 pH, Ammonium and Nitrite Sensing using IDE Design 2 ........................................................... 230
7.1 Ammonium Sensors .................................................................................................................. 230
7.2 Nitrite Sensors ........................................................................................................................... 234
7.3 pH Sensors ................................................................................................................................ 238
7.4 Conclusions for Chapter 7.......................................................................................................... 244
8 Conclusions and Suggestions for Further Work ......................................................................... 246
8.1 Conclusions ............................................................................................................................... 246
8.2 Future Work .............................................................................................................................. 250
8.2.1 Individual Sensor Testing .......................................................................................................... 250
8.2.2 Membrane Characterisation ....................................................................................................... 252
8.2.3 Membrane Materials .................................................................................................................. 252
8.2.4 IDE Geometry ........................................................................................................................... 253
8.2.5 Screen-Printed Sensors .............................................................................................................. 254
7
Craig Alexander
8.2.6 Considerations for a Prototype Device ....................................................................................... 254
8.2.7 Sensor Longevity ....................................................................................................................... 255
8.2.8 Data Display .............................................................................................................................. 256
9 References ................................................................................................................................. 257
10 Appendices ................................................................................................................................ 265
10.1 Molar Equivalent Concentrations of Ions ................................................................................... 265
10.2 Details of Commercial Ionophores Used .................................................................................... 266
10.3 Potentiometric Data Acquisition System .................................................................................... 267

Final word count: 56,647
8
Craig Alexander
List of Figures
1.1 Algae accumulation caused by high levels of nitrate in an aquarium ........................................... 29
1.2 Structure of the two forms of phenol red which result in the observed colour change ................. .36
1.3 Structure of three forms of bromothymol blue which result in a colour change at varying pH
values…... ................................................................................................................................... 36
1.4 Structure of indosalicylate. .......................................................................................................... 38
1.5 Schematic representation of a double-junction Ag/AgCl reference electrode with
1 M LiCH COO as outer filling solution. ..................................................................................... 47
3
1.6 (A) Potassium tetrakis-[3,5,-bis-(trifluoromethyl)phenyl]borate – used as an ionic additive in
cation-selective membranes; (B) tridodecylmethyl ammonium chloride (TDMACl)– used as an
ionic additive in anion-selective membranes ................................................................................ 49
1.7 Structures of three commonly-used plasticisers within ISEs (A) dioctyl sebacate (DOS),
(B) o-nitrophenyloctyl ether (NPOE), (C) dioctyl phthalate (DOP).. ............................................ 50
1.8 Example calibration curve for calculating the selectivity coefficent using the FIM ....................... 52
1.9 Schematic diagram of a typical PME set-up, showing the cell potential of an ISE being
measured against a SCE reference ............................................................................................... 55
1.10 Structures of three typical silicon alkoxide sol-gel precursors – (A) methyltriethoxysilane (MTES);
(B) tetraethoxysilane (TEOS); (C) diethoxydimethylsilane (DEDMS) ......................................... 60
1.11 Selection of the Hofmeister series showing the order of anion hydrophobicity ............................. 67
1.12 A typical AC sine wave voltage and current. ................................................................................ 72
1.13 Schematic diagram of a typical IDE design. ................................................................................. 74
1.14 Cross-section schematic representation of the electric field penetration depth from a
typical IDE when an AC voltage is applied. ................................................................................. 75
1.15 Schematic representation of an ISCOM ....................................................................................... 76
1.16 Photolithographic preparation of thin-film electrodes using (a) chemical etching and
(b) lift-off procedures .................................................................................................................. 78
1.17 Schematic diagram of screen-printing for the fabrication of thick-film electrochemical sensors. .. 79
2.1 Schematic representation of IDE Design 1 ................................................................................... 98
2.2 Microscope image (4x) of the digits of IDE Design 1, fabricated in-house using a mask-less,
lift-off photolithographic technique followed by e-beam deposition of gold metal ..................... 100
2.3 IDE Design 2 ............................................................................................................................. 101
2.4 Schematic representation of the screens used to produce 6 different IDE designs. ...................... 103
2.5 Schematic representation of SP IDE Design 1 ............................................................................ 104
2.6 Outline of the screen-printing fabrication process of SP IDE Design 1 ....................................... 105
2.7 Microscope image (4x) of the electrode digits of SP IDE Design 1 ............................................ 106
9
Craig Alexander

2.8 Front panel of the LabVIEW program used to control the Agilent E4980A LCR meter .............. 108
2.9 Schematic diagram of the experimental set-up for testing IDE ion sensors using the Agilent
E4980A LCR meter. .................................................................................................................. 110
3.1 Calibration graph of two nitrate-selective PMEs prepared using a PVC membrane containing
1% w/w TDAN as the ionophore. .............................................................................................. 119
3.2 Calibration graph of two nitrate-selective PMEs prepared using a PVC membrane containing
1% w/w NO3V as the ionophore ................................................................................................ 121
3.3 Selectivity determination of TDAN PME 1 using the FIM in 1000 ppm Cl- and
1000 ppm NO -. ........................................................................................................................ .122
2
3.4 Selectivity determination of NO3V PME 1 using the FIM in 1000 ppm Cl- and
1000 ppm NO -. ......................................................................................................................... 123
2
3.5 Calibration graph of two nitrate-selective CWEs prepared by dip-coating the electrode into a
PVC membrane ‘cocktail’ containing 1% w/w TDAN as the ionophore ..................................... 124
3.6 Calibration graph of four nitrate-selective sol-gel CWEs (two MTES and two DEDMS)
containing TDAN as the ionophore ............................................................................................ 125
3.7 Selectivity determination of TDAN PVC CWE 1 using the FIM in 1000 ppm Cl- and
1000 ppm NO - .......................................................................................................................... 126
2
3.8 Selectivity determination of TDAN MTES CWE 1 using the FIM in 1000 ppm Cl- and
1000 ppm NO - .......................................................................................................................... 127
2
3.9 Selectivity determination of TDAN DEDMS CWE 1 using the FIM in 1000 ppm Cl- and
1000 ppm NO -. ......................................................................................................................... 128
2
3.10 Calibration graph of two ammonium-selective PMEs prepared using a PVC membrane
containing 1% w/w NH4I as the ionophore ................................................................................ 129
3.11 Selectivity determination of NH4I PME 1 using the FIM in 1000 ppm of the interfering cations
sodium, potassium, magnesium and calcium .............................................................................. 130
3.12 Calibration graph of two ammonium-selective PMEs prepared using a PVC membrane
containing 1% w/w NH4I as the ionophore, with the ionic additive omitted ............................... 131
3.13 Selectivity determination of NH4I PME 1 (ionic additive omitted) using the FIM in 1000 ppm
of the interfering cations sodium, potassium, magnesium and calcium.. ..................................... 132
3.14 Calibration graph of two hydrogen ion-selective PMEs prepared using a PVC membrane
containing 1% w/w HIII as the ionophore.. ................................................................................ 133
3.15 Calibration graph of two hydrogen ion-selective PMEs prepared using a PVC membrane
containing 1% w/w HV as the ionophore. .................................................................................. 134
3.16 Selectivity determination of HIII PME 1 using the FIM in 0.1 M of the interfering cations
sodium, potassium and magnesium.. .......................................................................................... 135
3.17 Selectivity determination of HV PME 1 using the FIM in 0.1 M of the interfering cations
sodium, potassium and magnesium.. .......................................................................................... 136
10