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SIMULTANEOUS VOLTAMMETRIC DETERMINATION OF CAPTOPRIL AND HYDROCHLOROTHIAZIDE AS WELL AS MELAMINE ON A COPPER HYDROXIDE NANOPARTICLE-CARBON IONIC LIQUID COMPOSITE ELECTRODE

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M.Sc. THESIS IN

ANALYTICAL CHEMISTRY

AbstractSIMULTANEOUS VOLTAMMETRIC DETERMINATION OF CAPTOPRIL AND HYDROCHLOROTHIAZIDE AS WELL AS MELAMINE ON A COPPER HYDROXIDE NANOPARTICLE-CARBON IONIC LIQUID COMPOSITE ELECTRODE

A carbon ionic liquid electrode (CILE) modified with Cu(OH)₂ nanoparticles has been employed for simultaneous determination of captopril (CPT) and hydrochlorothiazide (HCT) by square wave voltammetry. Electrocatalytic oxidations of CPT and HCT were investigated with this electrode in phosphate buffer solution at pH 8.0. After optimizing the operational conditions, linear ranges concentration of 0.7-10 µM and 10-70 µM for CPT and 3-100 µM and 100-600 µM for HCT were obtained. Detection limits of 12.5 nM and 59.7 nM were obtained for CPT and HCT, respectively. The method was successfully applied for analysis of CPT and HCT in pharmaceutical preparations. The electrode showed good reproducibility, repeatability and storage stability. Also the electrode was employed for anodic stripping voltammetric determination of Melamine (MEL) by differential pulse voltammetry. Electrocatalytic oxidation of MEL was investigated by using this electrode in borate buffer solution at pH 10.0. After optimizing the operational conditions, linear ranges of 6-30 µM and 30-200 µM with a detection limit of 0.63 µM were obtained for MEL. The method was successfully applied for analysis of MEL in cow milk. This electrode showed good reproducibility, repeatability and storage stability.

Key words: Captopril, Hydrochlorothiazide, Melamine, Carbon Ionic Liquid, Copper Hydroxide Nanoparticle

دسته: زبان خارجه, زبان خارجه برچسب: Carbon Ionic Liquid, Copper Hydroxide Nanoparticle, Hydrochlorothiazide, Key words: Captopril, Melamine

توضیحات

Table of Contents

Content Page

CHAPTER ONE: INTRODUCTION

1.1 Electrochemical Techniques ……………………………………………………………. 2

1.2 Electrochemical Sensors………………………………………………………………….. 2

1.2.1 Voltammetric Sensors………………………………………………………………. 3

1.2.2 Amperometric Sensors……………………………………………………………… 3

1.2.3 Potentiometric Sensors…………………………………………………………….. 3

1.3 Carbon Electrodes…………………………………………………………………………… 3

1.3.1 Composite Electrodes and Carbon Composite Electrodes………… 4

1.4 Ionic Liquids……………………………………………………………………………………. 5

1.4.1 Application of IL as a Binder in Electrochemical Sensors………… 6

1.5 Nanoparticles………………………………………………………………………………….. 7

1.6 Captopril…………………………………………………………………………………………. 8

1.7 Hydrochlorothiazide……………………………………………………………………….. 9

1.8 Melamine………………………………………………………………………………………… 10

CHAPTER TWO: LITERATURE REVIEW

2.1 Electrochemical Oxidation of Captopril ………………………………………….. 12

2.2 Electrochemical Oxidation of Hydrochlorothiazide………………………… 14

2.3 Simultaneous Electrochemical Determination of Captopril and Hydrochlorothiazide 14

2.4 Electrooxidation of Melamine…………………………………………………………. 15

2.5 Application of Nanoscale Copper Hydroxide Composite Carbon Ionic Liquid Electrode 16

2.6 Objective of this stady…………………………………………………………………….. 17

Content Page

CHAPTER THREE: EXPERIMENTAL

3.1 Apparatus………………………………………………………………………………………… 19

3.2 Materials…………………………………………………………………………………………. 19

3.3 Synthesis of Cu(OH)₂ Nanoparticles……………………………………………….. 20

3.4 Synthesis of N-Octylpyridinum Hexafluorophosphate……………………. 20

3.5 Preparation of the Working Electrode……………………………………………… 21

3.5.1 Carbon Paste Electrode…………………………………………………………….. 21

3.5.2 Carbon Ionic Liquid Electrode (CILE)……………………………………… 21

3.5.3 Cu(OH)₂NPs/CPE .. 21

3.5.4 Cu(OH)₂NPs/CILE.. 22

CHAPTER FOUR: RESULTS AND DISCUSSION

4.1 Simultaneous Determination of Captopril and Hydrochlorothiazide on a Copper Hydroxide Nanoparticle Composite Carbon Ionic Liquid Electrode by Voltammetric Method 24

4.1.1 Characterization of Copper Hydroxide Nanoparticles……………… 25

4.1.2 Characterization of n- Octylpyridinum Hexafluorophosphate…. 26

4.1.3 Electrochemical Characterization of Cu(OH)₂NPs/CILE………….. 26

4.1.4 Electrocatalytic Oxidation of Captopril and
Hydrochlorothiazide on Different Electrodes…………………………. 30

4.1.5 Optimization of the Experimental Conditions………………………….. 34

4.1.7 Calibration Curves……………………………………………………………………. 46

4.1.8 Interference Study……………………………………………………………………. 51

4.1.9 Fouling Test……………………………………………………………………………… 52

4.1.10 Repeatability and Reproducibility of the Electrode
Response………………………………………………………………………………… 53

4.1.11 Simultaneous Determination of Captopril and Hydrochlorothiazide in Pharmaceutical Preparations……………………………………………………………………………. 54

Content Page

4.1.12 Conclusion……………………………………………………………………………… 55

4.2 Determination of Melamine on a Copper Hydroxide
Nanoparticle Composite Carbon Ionic Liquid Electrode
By Differential Pulse Anodic Stripping Voltammetric. 56

4.2.1 Electrocatalytic Oxidation of Melamine on Different
Electrodes………………………………………………………………………………………… 57

4.2.2 Optimization of the Experimental Conditions………………………….. 58

4.2.3 Effect of Scan Rate…………………………………………………………………… 63

4.2.4 Calibration Curve…………………………………………………………………….. 65

4.2.5 Interference Study……………………………………………………………………. 66

4.2.6 Repeatability and Reproducibility of the Electrode Response….. 67

4.2.7 Determination of Melamine in Milk Samples…………………………… 67

4.2.8 Conclusion……………………………………………………………………………………. 68

References………………………………………………………………………………………………… 69

Abstract and Title Page in Persian

List of Tables

Table Page

Table 1.1. Structure and nomenclature of cations and anions commonly employed in the synthesis of ILs …………………………………………………………………………………….. . 5

Table 4.1 Results of interference study for determination
of 50.0 µM CPT. 51

Table 4.2 Results of interference study for determination
of 50.0 µM HCT. 51

Table 4.3 Simultaneous Determination of Captopril and Hydrochlorothiazide in Tablets Sample. 54

Table 4.4 Comparison of different sensors for electrochemical determination of CPT and HCT. 55

Table 4.5 Results of interference study for determination
of 50.0 µM MEL.. 66

Table 4.6 Determination of Melamine in milk sample. 67

Table 4.7 Comparison of different sensors for electrochemical determination of MEL. 68

List of Figures

Figure Page

Figure 4.1 The XRD pattern of Cu(OH)₂ nanoparticles. 25

Figure 4.2 The NMR spectrum of OPFP……………………………………………………… 26

Figure 4.3 Cyclic voltammograms of: (a), CILE; and (b), Cu(OH)₂NPs/CILE in a solution containing 1.0 mM K₃[Fe(CN)₆] and 0.1 M KCl with a scan rate of 100 mV s^-1 27

Figure 4.4 Cyclic voltammograms of a solution containing 1.0 mM K₃[Fe(CN)₆] and 0.1 M KCl at the CILE with the scan rate range of 5-200 mV s^-1…………………. 28

Figure 4.5 Linear relationship between the redox peak current and
square root of the scan rate in the range of 5-200 mV s^-1………… 28

Figure 4.6 Cyclic voltammograms of a solution containing 1.0 mM K₃[Fe(CN)₆] and 0.1 M KCl at the Cu(OH)₂NPs/CILE
with scan rate range of 5-200 mV s^-1. 29

Figure 4.7 Linear relationship between the redox peak current and
square root of the scan rate in the range of 5-200 mV s^-1……….. 29

Figure 4.8 Cyclic voltammograms of 100 µM CPT in 0.2 M PBS
(pH 8.0) at bare CPE, (a); CILE, (b); Cu(OH)₂NPs/CPE,
(c); Cu(OH)₂NPs/CILE, (d); when the scan rate was
100 mV s^-1 and accumulation time was 5 min………………………… 31

Figure 4.9 Cyclic voltammograms of 100.0 µM HCT in 0.2 M PBS
(pH 8.0) at bare CPE, (a); CILE, (b); Cu(OH)₂NPs/CPE,
(c); Cu(OH)₂NPs/CILE, (d); when the scan rate was
100 mV s^-1 and accumulation time was 5 min…………………………. 32

Figure Page

Figure 4.10 Cyclic voltammograms of 100 µM CPT and 100 µM HCT
in 0.2 M PBS (pH 8.0) at bare CPE, (a); CILE, (b); Cu(OH)₂NPs/CPE, (c); Cu(OH)₂NPs/CILE, (d); when the
scan rate was 100 mVs^-1 and accumulation time was 5 min…… 33

Figure 4.11 Effect of SW step potential on oxidation peak current
of 50.0 µM (A) CPT and (B) HCT in 0.2 M PBS at pH 8.0.
The error bars correspond to standard deviations (n=3)…………. 35

Figure 4.12 Effect of SW amplitude on oxidation peak current
of 50.0 µM (A) CPT and (B) HCT in 0.2 M PBS at pH 8.0.
The error bars correspond to standard deviations (n=3). 36

Figure 4.13 Effect of SW frequency on oxidation peak current
of 50.0 µM (A) CPT and (B) HCT in 0.2 M PBS
at pH 8.0. The error bars correspond to standard
deviations (n=3)……………………………………………………………………… 37

Figure 4.14 Effect of weight percentage of Cu(OH)₂NPs on oxidation
peak current of 50.0 µM (A) CPT and (B) HCT in 0.2 M
PBS at pH 8.0. The error bars correspond to standard deviations (n=3). 38

Figure 4.15 Effect of pH on oxidation peak current of 50.0 µM (A)
CPT and (B) HCT in 0.2 M PBS at pH 5.0 to 10.0.
The error bars correspond to standard deviations (n=3)…………. 40

Figure 4.16 Effect of supporting electrolytes on oxidation peak
current of (A) 50.0 µM (A) CPT and (B) HCT
(0.2 M buffer, pH 8.0). The error bars correspond to
standard deviations (n=3)……………………………………………………… 41

Figure Page

Figure 4.17 Effect of concentration of supporting electrolytes on
oxidation peak current of 50.0 µM (A) CPT and
(B) HCT in various concentration of PBS at pH 8.0.
The error bars correspond to standard deviations (n=3). 42

Figure 4.18 Effect of adsorption time on oxidation peak current
of 50.0 µM (A) CPT and (B) HCT in 0.2 M PBS at
pH 8.0. The error bars correspond to standard deviations
(n=3)……………………………………………………………………………………… 43

Figure 4.19 Cyclic voltammograms of 50.0 µM CPT solution in
0.2 M PBS at pH 8.0 on Cu(OH)₂NPs/CILE with different
scan rate from 5 to 200 mV s^-1. 44

Figure 4.20 Plot of peak current versus scan rate in the range of 5
to 200 mV s^-1 for 50.0 µM CPT solution…………………………………. 45

Figure 4.21 Cyclic voltammograms of 50.0 µM HCT solution
in 0.2M PBS at pH 8.0 on Cu(OH)₂NPs/CILE with
different scan rate from 5 to 200 mV s^-1…………………………………. 45

Figure 4.22 Plot of peak current versus scan rate in the range of 5
to 200 mV s^-1 for 50.0 µM HCT solution……………………………….. 46

Figure 4.23 Square wave voltammograms of CPT at Cu(OH)₂NPs/CILE
in the presence of 50 µM HCT in 0.2 M PBS at pH 8.0.
CPT concentration: 0.70, 0.90, 1.0, 3.0, 5.0, 6.0, 7.0, 8.0,
9.0, 10.0, 20.0, 30.0, 50.0, 70.0 µM………………………………………… 47

Figure 4.24 Calibration curve for the determination of CPT at Cu(OH)₂NPs/CILE in 0.2 M PBS at pH 8.0. The error
bars correspond to standard deviations (n=3)……………………….. 47

Figure Page

Figure 4.25 Square wave voltammograms of HCT at Cu(OH)₂NPs/CILE
in the presence of 50 µM CPT in 0.2 M PBS at pH 8.0.
HCT concentration: 3.0, 5.0, 7.0, 10.0, 30.0, 50.0, 70.0,
80.0, 100.0, 200.0, 300.0, 400.0, 500.0, 600.0 µM………………….. 48

Figure 4.26 Calibration curve for the determination of CPT at Cu(OH)₂NPs/CILE in 0.2 M PBS at pH 8.0. The error bars correspond to standard deviations (n=3)….. 48

Figure 4.27 Square wave voltammograms of various concentrations
of CPT and HCT in 0.2 M PBS at pH 8.0. CPT
concentration: 1.0, 2.0, 4.0, 5.0, 8.0, 10.0, 20.0, 50.0,
60.0 µM and HCT concentration: 7.0, 20.0, 50.0, 80.0,
100.0, 200.0, 300.0, 400.0, 500.0 µM……………………………………… 49

Figure 4.28 Calibration curve for the determination of (A) CPT in the presence of various concentration of HCT and (B) HCT in presence of various concentration of CPT at Cu(OH)₂NPs/CILE. The error bars correspond to standard deviations (n=3). 50

Figure 4.29 Cyclic voltammogramms of 100.0 µM CPT in 0.2 M PBS
at pH 8.0 for consecutive scan (a) first scan (b) second scan, scan rate of 100 mV s^-1. 52

Figure 4.30 Cyclic voltammogramms of 100.0 µM HCT in 0.2 M PBS
at pH 8.0 for consecutive scan (a) first scan (b) second scan, scan rate of 100 mV s^-1. 53

Figure Page

Figure 4.31 Cyclic voltammograms of 50.0 µM MEL in 0.25 M
borate buffer solution (pH 10.0) at bare CPE, (a); CILE,
(b); Cu(OH)₂NPs/CPE, (c); and Cu(OH)₂NPs/CILE,
(d); when the scan rate was 100 mV s^-1 and the
accumulation potential was -0.3 V and accumulation
time was 10 min. The inset show the base line of Cu(OH)₂NPs/CILE in borate buffer solution at pH 10.0 ………………………………………………………………… 58

Figure 4.32 Effect of weight percentage of Cu(OH)₂NPs on
oxidation peak current of 50.0 µM MEL in 0.25 M
borate buffer at pH 10.0. The error bars correspond
to standard deviations (n=3)…………………………………………………… 59

Figure 4.33 Effect of accumulation potential on oxidation peak
current of 50.0 µM MEL in 0.25 M borate buffer solution
at pH 10.0. The error bars correspond to standard
deviations (n=3). 60

Figure 4.34 Effect of accumulation time on oxidation peak current
of 50.0 µM MEL, in 0.25 M borate buffer solution at
pH 10.0. The error bars correspond to standard
deviations (n=3)……………………………………………………………………… 60

Figure 4.35 Effect of pH on oxidation peak current of 50.0 µM
MEL in 0.25 M borate buffer solution at pH 8.5-11.0.
The error bars correspond to standard deviations (n=3)…………. 61

Figure 4.36 Effect of supporting electrolytes (buffer) on oxidation
peak current of 50.0 µM MEL. (0.25 M buffer pH 10.0).
The error bars correspond to standard deviations (n=3). 62

Figure Page

Figure 4.37 Effect of concentration of supporting electrolyte on
oxidation peak current of 50.0 µM MEL in borate buffer solution at pH 10.0. The error bars correspond to standard deviations (n=3). ……………………….. 63

Figure 4.38 Linear sweep voltammograms of 50.0 µM MEL solution
in 0.25 M borate buffer at pH 10.0 on Cu(OH)₂NPs/CILE
with different scan rate from 5 to 200 mV s^-1. ………………………… 64

Figure 4.39 Plot of peak current versus scan rate of 50.0 µM MEL
solution in 0.25 M borate buffer at pH 10.0 on Cu(OH)₂NPs/CILE with different scan rate from 5
to 200 mV s^-1. 64

Figure 4.40 Differential pulse voltammograms of MEL at Cu(OH)₂NPs/CILE in 0.25 M borate buffer solution at
pH10.0. The MEL concentration: 6.0, 7.0, 9.0, 10.0, 15.0,
20.0, 25.0, 30.0, 40.0, 50.0, 60.0, 80.0, 100.0, 150.0,
200.0 µM. ……………………………………………………………………………….. 65

Figure 4.41 Calibration curve for the determination of MEL at Cu(OH)₂NPs/CILE in 0.25 M borate buffer solution at
pH 10.0. The error bars correspond to standard
deviations (n=3). ……………………………………………………………………. 66

List of Schemes

Figure Page

Scheme 1. Chemical structures of (a) CPT and (b) HCT. 9

Scheme 2 Chemical structures of melamine………………………………………………. 10

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