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A New Composite Electrode using Molecular Wires as the Binder and its Application to Simultaneous Determination of Dopamine and Serotonin

تعداد101 صفحه در فایل word

M.S. Thesis in

Analytical Chemistry

A New Composite Electrode using Molecular Wires as the Binder and its Application to Simultaneous Determination of Dopamine and Serotonin

Abstract

A new composite electrode based on the graphite and carbon nanotubes as a conductive phase and molecular wire as binder was proposed. An optimization of various components of the electrode was performed. Also, the conditions for preparation and pasting of the proposed electrode were optimized. The electrochemical characteristics of the electrode were performed via the study of redox behavior of various electrochemical probes via some electrochemical tests such as cyclic voltammetry and electrochemical impedance spectroscopy. The structural characteristics of electrode were studied via scanning electron microscopy. The suggested electrode showed favorable features which make it suitable for many electrochemical applications such as sensor.

In the second part of this thesis, the proposed electrode was used for the simultaneous determination of dopamine and serotonin. The electrode has shown high sensitivity, low detection limit, high repeatability and reproducibility. The electrode was used successfully in the analysis of the real sample. The individual calibration linear range was determined to be 1.0×10^-8to 4.5×10^-5M for dopamine and 5.0×10^-8to 4.0×10^-5M for serotonin; while for their simultaneous determination the calibration range was 7.0 to 750.0 µM for dopamine and 2.0 to 500 µM for serotonin. The effects of possible interferences were examined and the method was applied to the simultaneous determination of dopamine and serotonin in human blood serum samples.

Key Words: Carbon Electrode, Molecular Wires, Carbon Nanotube

دسته: زبان شناسی, علوم انسانی برچسب: Carbon Nanotube, Key Words: Carbon Electrode, Molecular Wires

توضیحات

Content Page

Chapter One: Introduction

1.1.Carbon Paste Electrodes. 2

1.1.1. Carbon as the Electrode Material 2

1.1.2 Binder (Pasting Liquid). 6

1.1.3 Physicochemical Properties of Carbon Pastes. 11

1.1.4 Typical Properties and Specifics of Carbon Paste Electrodes in Electrochemical and Electroanalytical Measurements. 13

1.2 Simultaneous Determination of Dopamine and Serotonin. 15

1.2.2 Dopamine. 15

1.2.3 Serotonin. 16

1.2.4 Methods of Simultaneous Determination of Dopamine and Serotonin 17

Chapter Two: Literature review

2.1 Carbon based MW as Potentiometric and Voltametric Sensor. 21

2.2 Simultaneous Determination of Dopamine and Serotonin. 22

2.3 Objective of the present work. 25

Chapter Three: Experimental

3.1 Design of a New Composite Electrode based on using Molecular Wires as the Binder 27

3.1.1 Materials. 27

Content Page

3.1.2 Synthesis of n-octylpyridinium hexafluorophosphate ionic liquid 28

3.1.2 Electrode preparation. 28

3.1.3 Apparatus. 30

3.2 Simultaneous determination of serotonin and dopamine. 30

3.2.1 Chemicals. 30

3.2.2 Apparatus. 31

Chapter Four: Results and Discussion

4.1 Design of a New Composite Electrode Based on Using Molecular Wires as the Binder 33

4.1.1 Physical Characteristics of Carbon Molecular Wire Electrode. 34

4.1.2 Electrochemical characteristics of carbon molecular wire electrode (CMWE) 37

4.2 Simultaneous Electrochemical Determination of Serotonin and Dopamine at Carbon Molecular Wire Electrode. 58

4.2.1 Cyclic Voltammetry of DA and 5-HT at CMWE.. 58

4.2.2 Effect of Scan Rate. 59

4.2.3 Effect of pH.. 63

4.2.4 Effect of Temperature. 66

4.2.5 Fouling Study. 66

4.2.6 Voltammetric Response of DA and 5-HT.. 68

4.2.7 Simultaneous Determination of DA and 5-HT Using Differential Pulse Voltammetry 70

4.2. 8 Interference Study. 72

4.2.9 Analysis of Real Samples. 74

4.2.10 Conclusion. 76

References………………………………………………………………………………………………. 77

List of Tables

Table Page

Table 2- 1 A Summary of the use of different non-electrochemical methods used for the determination of DA, 5-HT or their simultaneous determination. 23

Table 2-2 Different electrochemical methods for the determination of DA, 5-HT or their simultaneous determination. 24

Table 4-1 Comparison wetting angles of different electrodes. 37

Table 4-2 Comparison different electrochemical properties of CMWE with different percentages of MW. ( for 5th cyclic voltammograms of Fe^3+/2+ in H₂SO₄ 0.1 M). 46

Table 4- 3 Comparison of different electrochemical properties of CMWE with different percentage of CNT. ( for 5th scans of cyclic voltammograms of Fe^3+/2+ in H₂SO₄ 0.1 M). 46

Table 4- 4 Results of interference study for the determination of 100.0 µM DA 73

Table 4- 5 Results of interference study for the determination of 100.0 µM 5-HT 73

Table 4- 6 Determination of DA in human serum.. 74

Table 4- 7 Determination of 5-HT in human serum.. 75

List of Figures

Figure Page

Fig.1- 1 Crystal faces of a highly ordered crystal of graphite and the formation of an edge-plane step defect ¹². 4

Fig.1- 2 Three morphological variations of MWCNTs, and high-resolution transmission electron micrograph images of (a) bamboo-like and (b) hollow-tube MWCNTs. 5

Fig.1- 3 Examples of ionic liquids used for electrode modification ¹. 9

Fig.1- 4 Molecular structure of phenylene acetylene and schematic structures of the planar and alternating geometries, respectively ⁵⁷. 11

Fig.1- 5 Microstructure of carbon paste (left) made of glassy carbon powder with spherical particles and the respective cross section (right). a) Carbon paste bulk revealing graphite particles coated with pasting liquid, b) the respective outer layer, c) graphite particles alone, d) thin film of liquid binder ². 12

Fig. 3- 1 The system used for temperature control. 29

Fig. 4- 1 Comparison of the electrochemical response of different electrodes in 5 mM Fe^3+/2+, 0.1 M H₂SO₄. The inset shows comparison of CILE and CPE. Scan rate 50 mV s^-1. 34

Fig. 4- 2 SEM image of a) CPE, b) CILE and c) CMWE with graphite/CNT/MW (30/40/30). 35

Fig. 4-3 Photographs of 2.0 µl drop of water on a) CPE, b) CILE and c) CMWE surface 36

Figure Page

Fig. 4- 4 Effect of heating time with hair drier for 5.0 mM Fe^3+/2+in 0.1 M H₂SO₄. Scan rate 50 mV s^-1. 38

Fig. 4-5 Different time for heating with heater for 5.0 mM Fe^3+/2+in 0.1 M H₂SO₄. Scan rate 50 mV s^-1. 38

Fig. 4- 6 Cyclic voltammograms of 5.0 mM Fe^3+/2+in H₂SO₄ 0.1 M for electrodes with different method of heating. Scan rate 50 mV s^-1. 39

Fig. 4- 7 SEM images of a) CMWE before heating, b) CMWE after first step of heating and c) after second step of heating. 40

Fig. 4- 8 Successive (1-5) cyclic voltammograms of background (0.1 M HClO₄) at CMWE that was prepared by two-step heating. Scan rate 50 mV s^-1. 41

Fig. 4- 9 Successive (1-5) cyclic voltammograms of background (0.1 M HClO₄) at CMWE that was prepared by one-step heating. Scan rate 50 mV s^-1. 41

Fig. 4- 10 Background currents of CMWE in PBS (pH 7.0), 0.1 M KCl and 0.1 M HClO₄, after two step of heating. Scan rate 50 mV s^-1. 42

Fig. 4- 11 Successive (1-15) cyclic voltammograms of 5.0 mM Fe^3+/2+ at CMWE with 10/70/20 (CNT/graphite/MW). Scan rate 50 mV s^-1. 44

Fig. 4- 12 Successive (1-15)cyclic voltammogramsof 5.0 mM Fe^3+/2+ at CMWE with 10/80/10 (CNT/graphite/MW). Scan rate50 mVs^-1. 44

Fig. 4- 13 Successive (1-15) cyclic voltammograms of 5.0 mM Fe^3+/2+ at CMWE with 10/60/30 (CNT/graphite/MW). Scan rate 50 mV s^-1. 45

Fig. 4- 14 Successive (1-15) cyclic voltammograms of 5.0 mM Fe^3+/2+ at CMWE with 10/50/40 (CNT/graphite/MW). Scan rate 50 mV s^-1. 45

Fig. 4- 15 5th scans of cyclic voltammograms for 5.0 mM Fe^3+/2+using CNT/graphite/MW composite with different ratio of CNT and 30% MW. Supporting electrolyte 0.1 M H₂SO₄. Scan rate 50 mV s^-1. 47

Figure Page

Fig. 4- 16 Successive (1-15) cyclic voltammograms of 5.0 mM Fe^3+/2+ at CMWE with 10/60/30 (CNT/graphite/MW). Scan rate 50 mVs^-1. 49

Fig. 4- 17 Cyclic voltamograms of 5 mM Fe^3+/2+ in 0.1 M H₂SO₄ at CMWE after different anodizing time. 49

Fig. 4- 18 Measured Nyquist plots of CPE, CILE and CMWE in a solution of 0.5 mM K₄Fe(CN)₆ + K₃Fe(CN)₆ in 0.5 M KCl. The applied perturbation was 0.24 V (versus OCP) and the frequencies were swept from 10⁵to 10^-2Hz. 51

Fig. 4- 19 Backgrounds of a) CILE and b) CMWE in PBS (pH 7.0). 53

Fig. 4- 20 Cyclic voltammograms of 1.0 mM AA in PBS (pH 7.0) at a) CMWE, b) CILE and c) CPE. Scan rate 50 mVs^-1. 54

Fig. 4- 21 Cyclic voltammograms of 1.0 mM AA in PBS (pH 7.0) for repetitive consecutive scans (curves a-c). Curve d after stirring the solution for a few seconds at CMWE, scan rate 50 mV s^-1. 54

Fig. 4- 22 Cyclic voltammograms of 1.0 mM DA in PBS (pH 7.0). a) CMWE , b) CILE and c) CPE. Scan rate 50 mV s^-1. 55

Fig. 4- 23 Cyclic voltammograms of 1.0 mM DA in PBS (pH 7.0) for repetitive consecutive scans (curves a-c). Curve d after stirring the solution for a few seconds at CMWE, scan rate 50 mV s^-1. 55

Fig. 4- 24 Cyclic voltammograms of 1.2 mM NADH in PBS (pH 7.0) at a) CILE, b) CMWE and c) CPE. Scan rate 50 mVs^-1 . 57

Fig. 4- 25 Cyclic voltammograms of 1.2 mM NADH in PBS (pH 7.0) for repetitive consecutive scans (curves a-c). Curve d after stirring the solution for a few seconds at CMWE, scan rate 50 mV s^-1. 57

Fig. 4- 26 Cyclic voltammograms of a) PBS (pH 8.0) as electrolyte solution, b) 100.0 µM DA c) 100.0 µM 5-HT and d) a mixture containing 100 µM DA and 100 µM 5-HT.. 59

Figure Page

Fig. 4- 27 Cyclic voltammograms of (A) 100.0 µM DA and (B) 100.0 µM 5-HT in 0.1 M PBS (pH 8.0) at CMWE at different scan rates of: (a) 5, (b) 10, (c) 20, (d) 50, (e) 100, (f) 150, (g) 200, (h) 300 and (i) 400 mV s^-1. 61

Fig. 4- 28 The relationship between the oxidation peak current and (A) the square root of scan rate and (B) the scan rate for 100.0 µM DA.. 62

Fig. 4- 29 The relationship between the oxidation peak current and (A) the square root of scan rate and (B) the scan rate for 100.0 µM 5-HT. 63

Fig. 4- 30 Differential pulse voltammograms of 100.0 µM DA and 100.0 µM 5-HT in PBS at different pH value from 5.0 to 9.0. scan rate 50 mV s^-1. 65

Fig. 4- 31 Plot of the oxidation peak current of (A) DA and (B) 5-HT against pH in the solution containing 100.0 µM DA and 100 µM 5-HT at CMWE. The peak currents were measured using differential pulse voltammetry recorded in a PBS solution. Scan rate 50 mV s^-1. 65

Fig. 4- 32 Differential pulse voltammograms of 100.0 µM DA and 100.0 µM 5-HT in PBS pH 8.0 with different temperature for pretreatment of the electrode. Scan rate 50 mV s^-1. 66

Fig. 4- 33 Cyclic voltammograms of (A) 100.0 µM solution of DA and (B) 100.0 µM solution of 5-HT in PBS (pH 8.0) for repetitive scans (curves 1–3). Curve 4 after stirring the solution for a few seconds at CMWE. Scan rate 50 mV s^-1. 67

Fig. 4- 34 Differential pulse voltammograms of (A) DA in PBS (pH 8.0) (DA concentration: 0.01-600 µM) and (B) 5-HT at CMWE in in PBS (pH 8.0) (5-HT concentration: 0.5-550 µM). 68

Fig. 4- 35 Calibration curves for (A) oxidation peaks of (B) 5-HT. The error bars indicate mean ± SD (n=3). 69

Figure Page

Fig. 4- 36 Differential pulse voltammograms of (A) DA in the presence of 100 µM 5-HT in PBS (pH 8.0) (DA concentration: 5.0-750 µM) and (B) 5-HT in the presence of 100 µM DA in PBS (pH 8.0) (5-HT concentration: 2.0-500 µM) at CMWE. 71

Fig. 4- 37 Calibration curves for (A) oxidation peaks of DA in the presence of 100.0 µM 5-HT and (B) 5-HT in the presence of 100.0 µM DA at low and high concentration ranges. The error bars indicate mean ± SD (n=3). 72

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