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SOLID BASED TITRAMETRY AS A STRAIGHTFORWARD METHOD FOR SPECIATION OF HYDROXYL AND CARBOXYLIC GROUPS IN ACTIVATED CARBON NANOSTRUCTURES AND DESIGN OF A NEW FLAME-CONTAINING MOLECULAR EMISSION CAVITY FOR SPECIATION OF S2-, SO32-, SO42-, SCN- AND S2O32- IN WASTEWATER

Name: SOLID BASED TITRAMETRY AS A STRAIGHTFORWARD METHOD FOR SPECIATION OF HYDROXYL AND CARBOXYLIC GROUPS IN ACTIVATED CARBON NANOSTRUCTURES AND DESIGN OF A NEW FLAME-CONTAINING MOLECULAR EMISSION CAVITY FOR SPECIATION OF S2-, SO32-, SO42-, SCN- AND S2O32- IN WASTEWATER
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تعداد110صفحه در فایل word

M.S. Thesis in Analytical Chemistry

SOLID BASED TITRAMETRY AS A STRAIGHTFORWARD METHOD FOR SPECIATION OF HYDROXYL AND CARBOXYLIC GROUPS IN ACTIVATED CARBON NANOSTRUCTURES

AND

DESIGN OF A NEW FLAME-CONTAINING MOLECULAR EMISSION CAVITY FOR SPECIATION OF S^2-, SO₃^2-, SO₄^2-, SCN^– AND S₂O₃^2- IN WASTEWATER

A novel method is proposed based on solid based titrametry for the speciation of –COOH and –OH functional groups in nanocarbons. In this technique, a known amount of carbon nanostructures is homogeneously mixed with NaCl powder as solid media. Then the mixture is put on a vibrating spatula for addition to a NaOH standard solution, resulting to have two distinct end points (EPs) in the titration curve for carbon nanostructures. The first EP is related to the simultaneous neutralization of –COOH and –OH with known equivalent of a standard basic solution. Whereas, the other EP is related to the reaction between added MWCNT-COOH and MWCNT-O^–, generated during the first EP.

A new flame-containing molecular emission cavity analysis (MECA) system was designed for speciation of sulfur compounds in wastewater. For this purpose, sulfur compounds were introduced to the MECA system through two injection ports and the blue S₂^* emission was monitored using a camera. For speciation of sulfur, SO₃^2- and S₂O₃^2- which were detected via formation of SO₂ during direct introduction to an air-bubbling, through the first injection port. Total quantity of SO₃^2-, S^2-, SO₄^2-, and SCN^– was also determined via introduction of the real sample to a vessel containing Ar-bubbling HClO₄ through the second injection port using a sonicator. For determination of sulfate, S^2-, SO₃^2-, and SCN^– were masked using a Ag(I), followed by introduction of the filtered solution through the second injection port. SCN^– was also detected based on its oxidation with I₃^– via evaluation of the enhancement in the molecular emission of generated SO₄^2-. In addition, S^2- was evaluated via difference between the molecular emissions of sulfur compounds.

دسته: زبان خارجه, زبان خارجه برچسب: DESIGN OF A NEW FLAME-CONTAINING MOLECULAR EMISSION CAVITY FOR SPECIATION OF S2-, SCN- AND S2O32- IN WASTEWATER, SO32-, SO42-, SOLID BASED TITRAMETRY AS A STRAIGHTFORWARD METHOD FOR SPECIATION OF HYDROXYL AND CARBOXYLIC GROUPS IN ACTIVATED CARBON NANOSTRUCTURES

توضیحات

sulfur compounds.

Content Page

CHAPTER ONE: INTRODUCTION

1.1 Introduction to titration…………………………………………………………………… 2

1.1.1 Different methods of titrimetric analysis…………………………………. 2

1.1.1.1 Volumetric titration………………………………………………………….. 2

1.1.1.2 Gravimetric titration…………………………………………………………. 3

1.1.1.3 Coulometric titration………………………………………………………… 3

1.1.2 Dilution error…………………………………………………………………………… 3

1.1.3 Types of titrations……………………………………………………………………. 4

1.1.4 Endpoint and equivalence point………………………………………………. 5

1.1.5 Measuring the endpoint of a titration………………………………………. 6

1.1.6 Back titration…………………………………………………………………………… 7

1.2 Introduction to Carbon Nanotubes (CNT)………………………………………. 7

1.2.1 Synthesis of CNTs……………………………………………………………………. 8

1.2.2 Properties of CNTs…………………………………………………………………… 9

1.2.2.1 Strength of CNTs……………………………………………………………… 9

1.2.2.2 Hardness of CNTs……………………………………………………………. 9

1.2.2.3 Kinetic properties of CNTs………………………………………………. 9

1.2.2.4 Electrical properties of CNTs………………………………………….. 10

1.2.2.5 Optical properties of CNTs……………………………………………… 10

1.2.2.6 Electromagnetic Wave absorption of CNTs…………………….. 10

1.2.2.7 Thermal properties of CNTs……………………………………………. 10

1.2.3 Defects of CNTs……………………………………………………………………… 10

Content Page

1.2.4 Toxicity of CNTs…………………………………………………………………….. 11

1.2.5 Introduction to functionalize CNTs………………………………………… 11

1.3 Luminescence……………………………………………………………………………….. 13

1.3.1 General principles………………………………………………………………….. 14

1.3.2 Main CL systems for analytical purposes………………………………. 17

1.3.2.1 Gas-phase CL reactions…………………………………………………… 17

1.3.2.2 Liquid-phase CL reactions………………………………………………. 19

1.3.2.2.1 Acyl hydrazides……………………………………………………….. 19

1.3.3 Applications……………………………………………………………………………. 19

1.4 Molecular emission cavity analysis……………………………………………….. 20

1.4.1 Principles and applications…………………………………………………….. 20

1.4.1.1 Hydrogen diffusion flame……………………………………………….. 20

1.4.1.2 Cavity……………………………………………………………………………… 22

1.4.2 Conventional MECA………………………………………………………………. 22

1.4.3 Gas generation MECA detection…………………………………………….. 23

1.5 The importance of measuring Sulfite, sulfide, thiocyanate,

thiosulfate and sulfate……………………………………………………………………….. 24

CHAPTER TWO: LITERATURE REVIEW

2.1 Solid based titrametry as a straightforward method for

speciation of hydroxyl and carboxylic groups in activated

carbon nanostructures………………………………………………………………………… 27

2.2 Design of a new flame-containing molecular emission

cavity for speciation of S^2-, SO₃^2-, SO₄^2-, SCN^– and S₂O₃^2-

in wastewater………………………………………………………………………………………. 30

2.3 Objective of this work…………………………………………………………………… 39

Content Page

CHAPTER THREE: EXPERIMENTAL

3.1 Solid based titrametry as a straightforward method for speciation

of hydroxyl and carboxylic groups in activated carbon nanostructures 41

3.1.1 Materials……………………………………………………………………………….. 41

3.1.2 Instrumentation …………………………………………………………………….. 41

3.1.3 General procedure…………………………………………………………………. 42

3.2 Design of a new flame-containing molecular emission cavity

for speciation of S^2-, SO₃^2-, SO₄^2-, SCN^– and S₂O₃^2- in wastewater ……… 43

3.2.1 Reagents and Solutions………………………………………………………….. 43

3.2.2 Apparatus………………………………………………………………………………. 44

3.2.2.1 Molecular emission cavity analysis instrumentation……….. 44

3.2.3 Procedure for sulfur speciation ……………………………………………… 46

CHAPTER FOUR: RESULTS AND DISCUSSION

4.1 Solid based titrametry as a straightforward method for speciation

of hydroxyl and carboxylic groups in nanocarbons …………………………… 50

4.1.1 Solid based titrametry…………………………………………………………….. 53

4.1.2 Proposed Mechanism……………………………………………………………… 58

4.1.3 Speciation of -COOH and -OH in carbon nanostructures……….. 60

4.1.4. Modeling………………………………………………………………………………… 6

4.1.5 Conclusions……………………………………………………………………………. 61

4.2 Design of a new flame-containing molecular emission cavity

for speciation of S^2-, SO₃^2-, SO₄^2-, SCN^– and S₂O₃^2- in wastewater……….. 62

4.2.1 Selective determination of SO₃^2-……………………………………………. 62

4.2.2 Selective determination of S₂O₃²……………………………………………. 65

4.2.3 Simultaneous determination of S^2-, SO₄^2- and SCN^– ………………. 69

4.2.3.1 Catalytic role of H⁺ during sulfur determination…………….. 74

4.2.3.2 Selective determination of SO₄^2- ……………………………………. 76

Content Page

4.2.3.3 Selective determination of SCN^–…………………………………….. 78

4.2.3.4 Determination of S^2-……………………………………………………….. 80

4.2.4 Analytical figures of merit…………………………………………………….. 80

4.2.5 Interference …………………………………………………………………………… 82

4.2.6 Real sample analysis……………………………………………………………… 85

4.2.7 Conclusions…………………………………………………………………………… 85

References………………………………………………………………………………………………. 86

LIST OF TABLES

Table Page

Table 4.1 Comparison between the proposed method and

back titration Method………………………………………………………………………………. 60

Table 4.2. Figures of merit for sulfur speciation in the MECA system…….. 81

Table 4.3 Effect of foreign ions on sulfur speciation………………………………. 84

Table 4.4 Determination of sulfur species in a wastewater sample………….. 85

LIST OF FIGURES

FIGURE PAGE

Figure 1.1 Conventional MECA cavity introduction into flame

by manual rotation…………………………………………………………………………………… 23

Figure 1.2 Schematic of a gas generation MECA system f

or the determination of ammonium by generation of ammonia……………….. 24

Figure 3.1 Instrumentation system of solid based titrametry…………………. 42

Figure 3.2 Schematic of A) the stainless steel cavity, and B) the

assembly for MECA-VAP ………………………………………………………………………. 45

Figure 3.3 Schematic representing the procedure related to

the sulfur speciation ……………………………………………………………………………….. 48

Figure 4.1 TEM images of MWCNTs treated with A) strong acid and

B) ozone…………………………………………………………………………………………………. 51

Figure 4.2 Raman spectra of MWCNTs treated with A) ozone and

B) acid……………………………………………………………………………………………………. 51

Figure 4.3 FT-IR spectra of MWCNTs treated with

A) O₃, and HNO₃/H₂SO₄ for B) ~9 h and C) 24 h……………………………………… 52

Figure 4.4 Titration curves of KHP with 3.0 mL of 0.05 mol L^-1

NaOH solution…………………………………………………………………………………………. 54

Figure 4.5 Titration curves showing the effect of different concentrations

of NaOH solution…………………………………………………………………………………….. 55

Figure 4.6 Titration curves representing the effect of different kinds

of inert electrolytes mixed with MWCNTs titrated with 0.05 mol L^-1

NaOH ……………………………………………………………………………………………………… 56

FIGURE PAGE

Figure 4.7 Titration curves revealing the effect of the different ratios

of MWCNT/ NaCl, titrated with 0.05 mol L^-1 NaOH………………………………… 57

Figure 4.8 Titration curves related to the interaction

between MWCNTs/NaCl with a ratio equal to 1:8 (w/w) with water

as blank solution and B) suspension of CNT-COO^–/CNT-O^–……………………. 59

Figure 4.9 Titration curve of ozonized MWCNTs with 0.50 mL

of 0.05M NaOH solution…………………………………………………………………………. 60

Figure 4.10 Theoretical titration curve evaluated for titration

of activated MWCNTs with 0.05M NaOH ………………………………………………. 61

Figure 4.11 UV-Vis. Spectra of solution generated using a known

amount of sulfur powder and MECA-generated sulfur into THF/ethanol… 64

Figure 4.12 Histogram showing the effect of Cu(II) 100 µg mL^-1

as a masking agent for selective separation of 1.0 µg mL^-1 sulfide

from sulfite and sulfate …………………………………………………………………………… 65

Figure 4.13 Effect of pH values on the CL intensity of 60.0 µg mL^-1

S₂O₃^2-, Experimental conditions: temperature of ~45^oC,

Al(III) concentration of 5.0×10^-4, H₂ and air flow rates equal to at 220

and 350 mL min^-1, respectively……………………………………………………………….. 67

Figure 4.14 Effect of reaction temperature on CL intensity

of 60.0 µg mL^-1S₂O₃^2-, Experimental conditions: pH 8.0,

Al(III) concentration of 5.0×10^-4, H₂ and air flow rates equal to

at 220 and 350 mL min^-1, respectively……………………………………………………. 67

Figure 4.15 Histogram showing the effect of different concentrations

of Al(III) on CL intensity of 60.0 µg mL^-1S₂O₃^2-, Experimental

conditions: pH 8.0, temperature of ~45^oC, H₂ and air flow rates equal

to at 220 and 350 mL min^-1, respectively………………………………………………… 68

FIGURE PAGE

Figure 4.16 Calibration carve of CL intensity versus S₂O₃^2-

concentration in the range of 20 µg mL^-1to 100 µg mL^-1,

Experimental conditions: pH 8.0, temperature of ~45^oC,

Al(III) concentration of 5.0×10^-4, H₂ and air flow rates equal to

at 220 and 350 mL min^-1, respectively…………………………………………………….. 68

Figure 4.17 Calibration carve of CL intensity versus total of S^2-,

SO₃^2-, SO₄^2-, S₂O₃^2-, and SCN^–concentration in the range

of 0.0 µg mL^-1to 2.0 µg mL^-1, Experimental conditions: 0.5 mol L^-1

HClO₄, temperature of ~25^oC, H₂, air and argon flow rates equal to

at 440, 710 mL min^-1 and 55 mL……………………………………………………………… 70

min^-1 respectivelyFigure 4.18 Histogram showing the effect of pH

on the CL intensity of 1.0 µg mL^-1sulfur component,

Experimental conditions: temperature of ~25^oC, H₂, air and argon

flow rates equal to at 440, 710 mL min^-1 and 55 mL min^-1 respectively…… 71

Figure 4.19 Comparison between the CL intensity of 1.0 µg mL^-1of

Sulfur component at pH 7.0, Experimental conditions: temperature

of ~25^oC, H₂, air and argon flow rates equal to at 440, 710 mL min^-1

and 55 mL min^-1 respectively………………………………………………………………….. 71

Figure 4.20 Comparison between the CL intensity of 1.0 µg mL^-1 of

sulfur component in acidic pH, Experimental conditions:

0.50 mol L^-1HClO₄, temperature of ~25^oC, H₂, air and argon

flow rates equal to at 440, 710 mL min^-1 and 55 mL min^-1 respectively…… 72

Figure 4.21 Diagram representing the effects of, hydrogen flow rate

on the CL intensity of 1.0 µg mL^-1 of each sulfide, sulfate and

thiocyanate, Experimental conditions: 0.50 mol L^-1HClO₄,

temperature of ~25^oC ……………………………………………………………………………… 73

FIGURE PAGE

Figure 4.22 Diagram representing the effects of air flow rate

on the CL intensity of 1.0 µg mL^-1of each sulfide, sulfate and

thiocyanate, Experimental conditions: 0.50 mol L^-1HClO₄,

temperature of ~25^oC……………………………………………………………………………… 73

Figure 4.23 Diagram representing the effects of argon flow rate

on the CL intensity of 1.0 µg mL^-1of each sulfide, sulfate and

thiocyanate, Experimental conditions: 0.5 mol L^-1HClO₄,

temperature of ~25^oC ……………………………………………………………………………… 74

Figure 4.24 Histogram showing the effect of different liquid media

0.50 mol L^-1 such as HNO₃, HCl, H₃PO₄, and HClO₄ for CL intensity

of 1.0 µg mL^-1sulfite, sulfide and sulfate, Experimental

conditions: temperature of ~25^oC, H₂, air and argon flow rates

equal to at 440, 710 mL min^-1 and 55 mL min^-1respectively……………………. 75

Figure 4.25 Effect of different concentrations of HClO₄ on CL

intensity of µg mL^-1thiocyanate, sulfide and sulfate, Experimental

conditions: temperature of ~25^oC, H₂, air and argon flow rates

equal to at 440, 710 mL min^-1 and 55 mL min^-1 respectively…………………… 76

Figure 4.26 Effect of different concentrations of Ag(I) on CL

intensity of 1µg mL^-1SO₃^2-, S^2- and SCN^–, Experimental conditions:

0.5 mol L^-1HClO₄, temperature of ~25^oC, H₂, air and argon

flow rates equal to at 440, 710 mL min^-1 and 55 mL min^-1 respectively…… 77

Figure 4.27 Calibration curve of CL intensity versus SO₄^2-

concentration in the range of 20.0 ng mL^-1to 90.0 µg mL^-1,

Experimental conditions: 0.5 mol L^-1 HClO₄, temperature of ~25^oC,

10.×10^-5 mol L^-1 Ag⁺, H₂, air and argon flow rates equal to at 440,

710 mL min^-1 and 55.0 mL min^-1 respectively………………………………………….. 78

FIGURE PAGE

Figure 4.28 Histogram showing effect of I₃^– on CL intensity o

f 10.0 µg mL^-1 SCN^–, Experimental conditions: 0.50 mol L^-1

HClO₄, temperature of ~25^oC, H₂, air and argon flow rates equal

to at 440, 710 mL min^-1 and 55 mL min^-1respectively……………………………. 79

Figure 4.29 Effect of different concentrations of I₃^– on CL intensity

of 10.0 µg mL^-1 SCN^–, Experimental conditions: 0.50 mol L^-1HClO₄,

temperature of ~25^oC, H₂, air and argon flow rates equal to at 440,

710 mL min^-1 and 55.0 mL min^-1 respectively…………………………………………. 79

Figure 4.30 Calibration curve of CL intensity versus SCN^–

concentration in the range of 0.0 µg mL^-1to 30.0 µg mL^-1,

Experimental conditions: 0.50 mol L^-1 HClO₄, 5.0×10^-4 mol L^-1

I₃^–temperature of ~25^oC, H₂, air and argon flow rates equal to at 440,

710 mL min^-1 and 55 mL min^-1respectively……………………………………………. 80

Figure 4.31 CCD images related to the introduction of various

sulfur species to the MECA system including A) thiocyanate,

B) sulfite, C) sulfide, and D) sulfate ……………………………………………………….. 81

Figure 4.32 CCD images related to the introduction of

various sulfur species to the MECA system with cation as an

interference including A) after 5 s, B) after 15 s …………………………………….. 83

SOLID BASED TITRAMETRY AS A STRAIGHTFORWARD METHOD FOR SPECIATION OF HYDROXYL AND CARBOXYLIC GROUPS IN ACTIVATED CARBON NANOSTRUCTURES AND DESIGN OF A NEW FLAME-CONTAINING MOLECULAR EMISSION CAVITY FOR SPECIATION OF S2-, SO32-, SO42-, SCN- AND S2O32- IN WASTEWATER

تعداد110صفحه در فایل word

M.S. Thesis in Analytical Chemistry

SOLID BASED TITRAMETRY AS A STRAIGHTFORWARD METHOD FOR SPECIATION OF HYDROXYL AND CARBOXYLIC GROUPS IN ACTIVATED CARBON NANOSTRUCTURES

AND

DESIGN OF A NEW FLAME-CONTAINING MOLECULAR EMISSION CAVITY FOR SPECIATION OF S2-, SO32-, SO42-, SCN– AND S2O32- IN WASTEWATER

sulfur compounds.

TABLE OF CONTENTS

Content Page

CHAPTER ONE: INTRODUCTION

1.1 Introduction to titration…………………………………………………………………… 2

1.1.1 Different methods of titrimetric analysis…………………………………. 2

1.1.1.1 Volumetric titration………………………………………………………….. 2

1.1.1.2 Gravimetric titration…………………………………………………………. 3

1.1.1.3 Coulometric titration………………………………………………………… 3

1.1.2 Dilution error…………………………………………………………………………… 3

1.1.3 Types of titrations……………………………………………………………………. 4

1.1.4 Endpoint and equivalence point………………………………………………. 5

1.1.5 Measuring the endpoint of a titration………………………………………. 6

1.1.6 Back titration…………………………………………………………………………… 7

1.2 Introduction to Carbon Nanotubes (CNT)………………………………………. 7

1.2.1 Synthesis of CNTs……………………………………………………………………. 8

1.2.2 Properties of CNTs…………………………………………………………………… 9

1.2.2.1 Strength of CNTs……………………………………………………………… 9

1.2.2.2 Hardness of CNTs……………………………………………………………. 9

1.2.2.3 Kinetic properties of CNTs………………………………………………. 9

1.2.2.4 Electrical properties of CNTs………………………………………….. 10

1.2.2.5 Optical properties of CNTs……………………………………………… 10

1.2.2.6 Electromagnetic Wave absorption of CNTs…………………….. 10

1.2.2.7 Thermal properties of CNTs……………………………………………. 10

1.2.3 Defects of CNTs……………………………………………………………………… 10

Content Page

1.2.4 Toxicity of CNTs…………………………………………………………………….. 11

1.2.5 Introduction to functionalize CNTs………………………………………… 11

1.3 Luminescence……………………………………………………………………………….. 13

1.3.1 General principles………………………………………………………………….. 14

1.3.2 Main CL systems for analytical purposes………………………………. 17

1.3.2.1 Gas-phase CL reactions…………………………………………………… 17

1.3.2.2 Liquid-phase CL reactions………………………………………………. 19

1.3.2.2.1 Acyl hydrazides……………………………………………………….. 19

1.3.3 Applications……………………………………………………………………………. 19

1.4 Molecular emission cavity analysis……………………………………………….. 20

1.4.1 Principles and applications…………………………………………………….. 20

1.4.1.1 Hydrogen diffusion flame……………………………………………….. 20

1.4.1.2 Cavity……………………………………………………………………………… 22

1.4.2 Conventional MECA………………………………………………………………. 22

1.4.3 Gas generation MECA detection…………………………………………….. 23

1.5 The importance of measuring Sulfite, sulfide, thiocyanate,

thiosulfate and sulfate……………………………………………………………………….. 24

CHAPTER TWO: LITERATURE REVIEW

2.1 Solid based titrametry as a straightforward method for

speciation of hydroxyl and carboxylic groups in activated

carbon nanostructures………………………………………………………………………… 27

2.2 Design of a new flame-containing molecular emission

cavity for speciation of S2-, SO32-, SO42-, SCN– and S2O32-

in wastewater………………………………………………………………………………………. 30

2.3 Objective of this work…………………………………………………………………… 39

Content Page

CHAPTER THREE: EXPERIMENTAL

3.1 Solid based titrametry as a straightforward method for speciation

of hydroxyl and carboxylic groups in activated carbon nanostructures 41

3.1.1 Materials……………………………………………………………………………….. 41

3.1.2 Instrumentation …………………………………………………………………….. 41

3.1.3 General procedure…………………………………………………………………. 42

3.2 Design of a new flame-containing molecular emission cavity

for speciation of S2-, SO32-, SO42-, SCN– and S2O32- in wastewater ……… 43

3.2.1 Reagents and Solutions………………………………………………………….. 43

3.2.2 Apparatus………………………………………………………………………………. 44

3.2.2.1 Molecular emission cavity analysis instrumentation……….. 44

3.2.3 Procedure for sulfur speciation ……………………………………………… 46

CHAPTER FOUR: RESULTS AND DISCUSSION

4.1 Solid based titrametry as a straightforward method for speciation

of hydroxyl and carboxylic groups in nanocarbons …………………………… 50

4.1.1 Solid based titrametry…………………………………………………………….. 53

4.1.2 Proposed Mechanism……………………………………………………………… 58

4.1.3 Speciation of -COOH and -OH in carbon nanostructures……….. 60

4.1.4. Modeling………………………………………………………………………………… 6

4.1.5 Conclusions……………………………………………………………………………. 61

4.2 Design of a new flame-containing molecular emission cavity

for speciation of S2-, SO32-, SO42-, SCN– and S2O32- in wastewater……….. 62

DESIGN OF A NEW FLAME-CONTAINING MOLECULAR EMISSION CAVITY FOR SPECIATION OF S^2-, SO₃^2-, SO₄^2-, SCN^– AND S₂O₃^2- IN WASTEWATER

cavity for speciation of S^2-, SO₃^2-, SO₄^2-, SCN^– and S₂O₃^2-

for speciation of S^2-, SO₃^2-, SO₄^2-, SCN^– and S₂O₃^2- in wastewater ……… 43

for speciation of S^2-, SO₃^2-, SO₄^2-, SCN^– and S₂O₃^2- in wastewater……….. 62

4.2.1 Selective determination of SO₃^2-……………………………………………. 62

4.2.2 Selective determination of S₂O₃²……………………………………………. 65

4.2.3 Simultaneous determination of S^2-, SO₄^2- and SCN^– ………………. 69

4.2.3.1 Catalytic role of H⁺ during sulfur determination…………….. 74

4.2.3.2 Selective determination of SO₄^2- ……………………………………. 76

4.2.3.3 Selective determination of SCN^–…………………………………….. 78

4.2.3.4 Determination of S^2-……………………………………………………….. 80