Novel composite electrodes:Preparation and application to the electroanalytical study of two pharmaceutically active molecules, viz. mangiferin and quercetin

by TCHIENO MELATAGUIA Francis Merlin
POSTGRADUATE SCHOOL
DEPARTMENT OF CHEMISTRY
UNIVERSITY OF DSCHANG
DSCHANG SCHOOL OF
SCIENCES AND TECHNOLOGY
LABORATORY OF NOXIOUS CHEMISTRY AND ENVIRONMENTAL ENGINEERING
Doctorat/PhD Defence in Chemistry
The President
Emmanuel NGAMENI Professor Univ. of Dschang
The Rapporteur
Ignas TONLE KENFACK Ass. Professor Univ. of Dschang
The Examiners
Achille NASSI Ass. Professor Univ. of Douala
Emmanuel DJOUFAC W. Ass. Professor Univ. of Yaoundé I
ANAGHO Solomon G. Ass. Professor Univ. of Dschang

Novel composite electrodes: Preparation
and application to the electroanalytical
study of two pharmaceutically activestudy of two pharmaceutically active
molecules, viz. mangiferin and quercetin
francistchieno@gmail.com

Presentation outline
1. Introduction
Motivations and objectives
 Xanthones and mangiferin
2. Brief literature review
1
3. Experimental procedures
4. Results and discussion
Conclusion and perspectives
 Flavonoids and quercetin
 Composite electrodes

1. Introduction : motivations
 African drug market fast growing;
 Rapid population growth;
People in dire need of medicationsPeople in dire need of medications
especially from their immediate
environment;
 Much criticism has been laid on
indigenous drugs;
2

Lack of knowledge on their therapeutic
and toxic effects;
Quantification of bioactive molecules canQuantification of bioactive molecules can
improve pharmacotherapy;
Necessity to investigate the ingredients
of indigenous drugs.
3

 For such investigations, a number of
techniques are available
 Electrochemical methods and sensors
are the most attractive and suitable for
electroactive species:electroactive species:
 Simplicity,
 Low cost,
 Rapid response time,
 High sensitivity,
 Selectivity. 4

1. Introduction : objectives
Our work therefore had as objectives to:
elaborate and characterise new composite
materials using electrochemical and physico-
chemical techniques;
use these materials as electrode modifiers to
build amperometric sensors;
5
apply the obtained electrodes to the
electroanalytical study of some pharmaceutically
active molecules.

MG and its therapeutic activities
O
O
O
OH
HO
HO
OH
OH
OH
HO
1
2
3
4 5
6
7
8
1'
2'
3'
4' 5'6'
 Xanthones and mangiferin (MG): description
Scheme 1: Molecular structure of MG
HO
3'
 antioxidant
 anti-inflammatory
 anti-diabetic
activities have been reported for MG
(Wauthoz et al. Inter. J. Biomed. Pharm. Sci. 1(2) (2007) 112-119) 6
 anti-allergic,
 anti-tumor,
 antimicrobial

 Flavonoids and quercetin (QCT): description
QCT and its therapeutic activities
O
OH
OH
HO
OH
A
B
C
1'
2'
3'
4'
5'
6'
1
2
3
45
6
7
8
OOH
45
Scheme 2: The molecular structure of QCT
anti-inflammatory,
anti-bacterial,
anti-gastric ulcer,
7
 anti-cancer,
 anti-diabetic,
 anti-tumor.
(Havsteen (1983) Biochemical Pharmacology, 32(7), 1141-1148.
Izzo (1994) Phytotherapy Research, 8, 179-185)

 Composite electrodes: types
Type 1: Carbon paste electrodes (CPEs)Type 1: Carbon paste electrodes (CPEs)
(Carbonaceous material + Binder + Modifier)
Advantages:
Advantages:
 Ease of renewal
 Chemical inertness
 Low cost
 Wide potential window
 Flexible (electrodes of desired composition)
8

Drawbacks:
Type 1: Carbon paste electrodes (CPEs)Type 1: Carbon paste electrodes (CPEs)
(Carbonaceous material + Binder + Modifier)
Drawbacks:
 Experience of the user determines success,
 Regular removal of the electrode’s surface layer,
 Poor diffusion of analyte (organic binder).
9

Deposited or fixed chemical species with specific
properties on solid electrodes (Pt, GC, SnO2).
Type 2: Film modified electrodes (FMEs)Type 2: Film modified electrodes (FMEs)
• Drop-coating,
• Spin-coating,
• Electrodeposition,
10
• Self-assemble layers.

Attapulgite clayAttapulgite clay
Natural crystalline hydrated magnesium aluminium silicate
Zeolite-like channels with cross-sectional dimensions 3.7 Å x 6.0 Å
(Frost & Ding, 2003, Thermochimica Acta, 397, 119-128)
Scheme 3: Ideal structure of attapulgite (Bradley, 1940, American Mineralogist, 25, 405-410).
11

low cost,
high chemical stability,
Attapulgite clayAttapulgite clay
high adsorption and penetrability due to formation of
well-ordered coatings with large surface area on electrode
surfaces (Chen et al., 2011, Talanta, 86, 266-270)
ion-exchange properties,
12

3. Experimental setup and procedures
Preparation of organoattapulgite clay
Purification of the attapulgite sample
Fine attapulgite fractions obtained by sedimentation
based on Stokes’ law
13
≤ 10 µm attapulgite particles were siphoned at x = 20
cm after 33 min
 2
p fgd - x
V
18 t
 

 

Preparation of organoattapulgite clay
Grafting procedure
2 g
Attapulgite
15 mL
Toluene
+
4 mL
[3-(2-aminoethylamino)propyl]
trimethoxysilane
+
trimethoxysilane
N2 atm 3 h reflux
Washing with Toluene and Isopropanol
Drying at 100 °C for 14 h
AttaNHAttaNH22 14

Characterisation of the grafted clay
Scanning electron microscopy (SEM)
Elemental analysis (EA)
X-ray diffraction (XRD) analysis
Fourier transform infrared (FTIR) spectroscopy
15

Preparation of working electrodes
Organoattapulgite film modified GCE
10 mg AttaNH2 1 mL H2O+
Ultrasonication
10 mg AttaNH2 1 mL HCl (pH1)+
Ultrasonication
AttaNH2 suspension
5 min drying (110 °C)
GCE/AttaNH2
Deposition on GCE
6 µL
16
5 min drying (110 °C)
GCE/ AttaNH3
+
Deposition on GCE
6 µL
AttaNH3
+ suspension

Activated chitosan CPE
Silicone oil
(pasting liquid)
Graphite
powder
Chitosan
powder
+ +
Activated CPE-CHI
Final paste filled into Teflon tube
Homogenisation
Activation 5 cyclic voltametric
scans in 0.5 M HCl
17

Why chitosan?
 Film forming ability,
 Biocompatibility,
 Good adhesion,
 Susceptibility to chemical modification.
 Biocompatibility,
(Martinez-Huitle et al., 2010, Portugaliae Electrochimica Acta, 28(1), 39-49)
18

1-ethylpyridinium bromide/CPE
Silicone oil
(pasting liquid)
Graphite
powder
1-Ethylpyridinium
bromide
+ +
Final paste filled into Teflon tube
Homogenisation
CPE-EPB 19

Why an ionic liquid as modifier?
 Creation of a variety of interactions
(hydrogen bonds, dipole-dipole, electrostatic),
20
(hydrogen bonds, dipole-dipole, electrostatic),
 Presence increase rate of electron transfer
by decreasing the overpotential
(Maleki et al., 2007, Analytical Biochemistry, 369(2), 149-153.
Safavi et al., 2008, Electrochemistry Communications, 10, 420-423)

Electroanalytical techniques used
 Electrochemical impedance spectroscopy (EIS)
 Cyclic voltammetry (CV)
 Cyclic voltammetry (CV)
 Differential pulse voltammetry (DPV)
 Chronocoulometry
21

4. Results and discussion: findings
CV analysis
1
(a)
2 µA
Current
(b)
2 A
Current
Electrochemical study of MG at the activated CPE-CHI
-0.2 0.0 0.2 0.4 0.6 0.8 1.0
4
3
2
1
Current
Potential (V) vs Ag/AgCl
-0.2 0.0 0.2 0.4 0.6 0.8 1.0
(i)
(ii)
Current
Figure 1: (a) CV response of 20.4 µM MG in PB (pH 5) at CPE-CHI (3%): (1)
scan 1, (2) scan 2, (3) scan 3 and (4) blank. (b) Comparison of CV responses
at (i) bare CPE and (ii) activated CPE-CHI (3%). v = 75 mV/s. 22

Optimisation of experimental parameters by DPV
Effect of accumulation time and electrolysis potential
4.0
4.5 (a)
6
7
(b)
Peakcurrent(µA)
23
0 50 100 150 200 250 300
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Peakcurrent(µA)
Accumulation time (s)
-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0
3
4
5
6
Peakcurrent(µA)
Electrolysis potential (V)
Figure 2: Dependence of current response at CPE-CHI (3%) for 10.3 µM MG
in 0.1 M PB (pH 5) on (a) accumulation time and (b) electrolysis potential.
240 s - 0.1 V

Effect of pH of supporting electrolyte
(a)
Current
5 A
1.0
0.6
0.7 (b)
Peakpotential(V)
Optimisation of experimental parameters by DPV
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Potential(V) vs Ag/AgCl
Current
6.0
3.1 2.0
4.2
5.1
1 2 3 4 5 6
0.3
0.4
0.5
Peakpotential(V) pH of supporting electrolyte
Figure 3: (a) Effect of detection medium pH on the anodic peak
current of MG, at CPE-CHI (3%). (b) Variation of the peak
Potential as a function of pH of the detection medium. 24

Calibration Curve and limit of detection
(a)
20 µA
Current
30
40
50
(b)
Peakcurrent(µA)
0.4 0.5 0.6 0.7 0.8 0.9
p
a
Current
0 10 20 30 40 50 60 70
0
10
20
Peakcurrent(µA)
[Mangiferin] (µM)
Figure 4: (a) DPV curves obtained under optimised conditions in HCl/KCl buffer
(pH 1) at CPE-CHI (3%) for various concentrations of MG (a-p): 0 - 67.4 µM MG.
(b) Corresponding calibration graph of MG. 25
LOD: 1.84 µM

Calibration Curve and limit of detection in human urine
(a)
6 µA
Current
20
25 (b)
Peakcurrent(µA)
0.48 0.54 0.60 0.66 0.72 0.78
h
a
Current
0 10 20 30 40 50 60
5
10
15
Peakcurrent(µA)
[Mangiferin] (µM)
Figure 5: (a) DPV curves obtained under optimised conditions in HCl/KCl buffer
(pH 1)/human urine mixture at CPE-CHI (3%) for various concentrations of MG
(a-h): 0 - 59.5 μM MG. (b) Corresponding calibration graph of MG. 26
LOD: 2.98 µM

Interference of some organic molecules
Table 1: Influence of some organic compounds on the determination of
10.1 µM MG
Interfering organic
species
Concentration
(µM)
Increase in peak
current of MG
species (µM) current of MG
Ascorbic acid 51.1 ≈ 19 %
Uric acid 51.1 ≈ 30 %
Dopamine 51.1 ≈ 63 %
L-Aspartic acid 51.1 ≈ -2 %
Citric acid 51.1 ≈ 1 %
D-(+)-Glucose 51.1 ≈ 18 % 27

SEM micrographs of attapulgite and AttaNH2
Physico-chemical characterisation of amine-grafted attapulgite
Figure 6: SEM micrographs of Attapulgite (a and b) and AttaNH2 (c and d). 28

Elemental analysis
Elemental analysis: 13.40% C, 3.60% H and 5.55% N
Theoretical content: C (13.71%), H (4.40%) and N (4.57%)
OH
OH
Si N
H
NH2
OCH3
OCH3
H3CO+ 2
Attapulgite
Reflux
Toluene
Si N
H
NH2
OCH3
OCH3
O
Attapulgite
Si N
H
NH2
OCH3
OCH3
O
+ 2 CH3OH
Scheme 4: Aminoattapulgite grafting process.
Si8O20Mg5(OH2)4•4H2O[OSi(OCH3)2(CH2)3NH(CH2)2NH2]2
29

X-ray diffractograms of attapulgite and AttaNH2
AttaNH2
(b)
Intensity(a.u.)
4 8 12 16 20 24
(a)
Intensity(a.u.)
2 (°)
Attapulgite
Figure 7: X-ray powder diffraction patterns of (a) pristine
attapulgite and (b) amine-grafted attapulgite. 30

FTIR spectra of attapulgite and AttaNH2
Assignment
Wavenumber (cm-1)
Attapulgite AttaNH2
ν (Mg)3-OH 3613 3615
νas physisorbed
H2O
3545 3535
νas C-H - 2929
νs C-H or ν O-CH3 - 2851
(b)425
469
974
1361
1472
2851 2929
Absorbance(a.u)
Figure 8: FTIR spectra of (a) pristine attapulgite
and (b) amine-grafted attapulgite.
δ physisorbed H2O 1650 1651
δas C-H - 1472
δs C-H - 1361
ν Si-O-Si
1193
1030
974
1190
1125
978
δ (Mg)3-OH 911 905
δ Si-O 507
469
503
438
ν Si-O-Mg 425 423
31
500 1000 1500 2000 2500 3000 3500 4000
Wavenumber (cm
-1
)
(a)
507
911
1030
1193 1650 3545 3613
Absorbance(a.u)

Electrochemical characterisation by EIS
8
10
12
14
16
(a)
)
0 5 10 15 20 25 30 35 40
0
2
4
6
8
(c)
(b)
-Z''()
Z' ()
Figure 9: Nyquist plot of the EIS data obtained at (a) bare GCE, (b) GCE/AttaNH2
and (c) GCE/AttaNH3
+ in 0.2 M KCl containing 0.1 mM [Fe(CN)6]3-/4-.
32

EIS data fitting
Z' (Ω)
-Z"(Ω)
(a)
bare GCE
(b)
Z' (Ω)
-Z"(Ω)
Z' (Ω)
Z' (Ω)
-Z"(Ω)
(c)
GCE/AttaNH2 GCE/AttaNH3
+
33Figure 10: Experimental ( ) and fitted ( ) EIS spectra for
(a) bare GCE, (b) GCE/AttaNH2 and (c) GCE/AttaNH3
+.

EIS data fitting
Rct W
RΩ
Cdl
EIS characterisation of amine-grafted attapulgite
Electrode RΩ (Ω) Rct (Ω) Cdl (µF)
Bare GCE 537 14063 0.27
GCE/AttaNH2 183 4892 2.06
GCE/AttaNH3
+ 272 3785 5.32
Table 2: Circuit parameter values from the EIS experimental data
recorded at bare GCE, GCE/AttaNH2 and GCE/AttaNH3
+.
Scheme 5: Randles equivalent electrical circuit of an electrochemical cell for a simple electrode process.
34

Electrochemical characterisation by permeation studies
(a)
1 µA
Current
(b)
30
1
2 µA
Current
Electrochemical characterisation of amine-grafted attapulgite
Figure 11: Multisweep cyclic voltammograms recorded in 0.2 M KCl containing
0.1 mM [Fe(CN)6]3- on GCE coated with (a) AttaNH2. Inset shows response at
pristine attapulgite. (b) AttaNH3
+. 35
0.0 0.2 0.4 0.6
Current
-0.2 0.0 0.2 0.4 0.6
1 µA
Current
0.0 0.1 0.2 0.3 0.4 0.5 0.6
1
Current Potential (V) vs Ag/AgCl

CV response
(iii)
4 µA
Current
Electrochemical quantification of MG at the grafted attapulgite film modified GCE
 
 
 
aα n F
logI = constant + E
2.3RT
Tafel equation
Tafel region
-0.4 0.0 0.4 0.8 1.2
(ii)
(iii)
(i)
Current
Figure 12: (a) Cyclic voltammograms recorded at
(i) blank , (ii) bare GCE and (iii) GCE/AttaNH3
+ with
78.1 µM MG added. Potential scan rate was 75 mV/s. 36
 2.3RT
GCE/AttaNH3
+ αanα = 0.56
bare GCE αanα = 0.37
αa = 0.56
Tafel region

CV response: successive scans
5 A
Current
-0.4 0.0 0.4 0.8 1.2
3
2
1
Current
Figure 13: CV response of 40 µM MG in HCl/KCl (pH 1) at GC/AttaNH3
+:
(1) scan 1, (2) scan 2 and (3) scan 3. Potential scan rate 75 mV/s. 37

m
a
15 µA
Current
CV response: variation of scan rate
0.0 0.3 0.6 0.9 1.2 1.5
Current
Figure 14: Cyclic voltammograms of 200 µM
MG at different scan rates (a-m):15 - 300 mV/s. 38

Laviron equation
0.84
0.88
Ag/AgCl
Figure 15: The plot of Epa against Inѵ.
αa = 0.58
a a a  
   
   
   
0 s
pa
RT RTk RT
= + ln + lnE E
α n F α n F α n F

39
Average αa = 0.573.0 3.6 4.2 4.8 5.4 6.0
0.72
0.76
0.80
Epa
(V)vsAg/AgCl
In (v/mVs
-1
)

8
10
12
Randles-Sevcik equation
0.1 0.2 0.3 0.4 0.5 0.6
2
4
6
Ip
(µA)

1/2
((V/s)
1/2
)
Figure 16: The plot of Ip against ѵ1/2. 40
n = 2.11 ≈ 2
)paI
1/25 1/2
α n= )n( ACD(2.99x10 a  1/2

Electrochemical oxidation mechanism of MG
O OHHO O OHO
O
Glu OH
OH O
Glu O
OH
- 2e-
- 2H+
Scheme 6: Proposed electrochemical oxidation mechanism of MG.
41

DPV response
0.3 A
Current
(a)
0.8
1.0
1.2
1.4
Peakcurrent(µA)
(b)
0.5 0.6 0.7 0.8 0.9
a
h
Current
0 2 4 6 8 10 12
0.2
0.4
0.6
0.8
Peakcurrent(µA)
[Mangiferin] (µM)
Figure 17: (a) DPV curves obtained in HCl/KCl buffer (pH 1) using GCE/AttaNH3
+
(a-h): 0 - 10.57 µM MG. (b) The corresponding calibration curve obtained .
LOD: 0.275 µM MG
42

Chronocoulometric studies
Effective surface areas of GCE and GCE/AttaNH3
+
bare GCE: 0.125 cm2
GCE/AttaNH + : 0.223 cm2
1/2 1/2
c ads1/2
2nFAD Ct
Q = + +Q Q
π
GCE/AttaNH3
+ : 0.223 cm2
Anson equation
π
43
D = 2.18 x 10-5 cm2/sDiffusion coefficient of MG
Monolayer adsorption (Inzelt (2010)
Chronocoulometry. In: Scholz F. (Ed.),
Electroanalytical methods: Guide to
experiments and applications, 2nd
edition, Springer-Verlag, Berlin,
Germany)
Γ = 1.81 x 10-11 mol/cm2
Γ = 1.09 x 1013 MG molecules/cm2
adsQ
Γ =
nFA
Amount of adsorbed MG

Interference study
0.3
0.4
0.5
0.6
Selectivitycoefficient(Kamp
)
C
itricacidU
ricacidD
opam
ine
A
scorbicacid
L-A
sparticacid
D
-(+)-G
lucose
0.0
0.1
0.2
0.3
Selectivitycoefficient(K
Figure 18: Selectivity coefficients for some potential interferents in the presence of MG. 44

Application to a real sample
Table 3: Determination of MG in human urine samples.
Sample Urine dilution MG added (µM) MG found (µM) Mean recovery (%)
Sample Urine dilution MG added (µM) MG found (µM) Mean recovery (%)
1 x 100 5.70 6.72 117.9
2 x 200 5.70 5.98 104.9
3 x 300 5.70 5.84 102.5
4 x 300 8.49 8.55 100.7
45

EIS characterisation
1.2
1.5
1.8 (a)
0.5
0.6
0.7
(b)
Electrocatalytic sensing of QCT at the 1-ethylpyridinium bromide CPE
0.0 0.5 1.0 1.5 2.0 2.5
0.3
0.6
0.9
1.2
-Z
''
(k)
Z
'
(k)
0.9 1.0 1.1 1.2 1.3 1.4 1.5
0.1
0.2
0.3
0.4
-Z
''
(k)
Z
'
(k)
Figure 19: Nyquist plot of the EIS data obtained at (a) bare CPE and
(b) CPE-EPB (10%) in 0.2 M KCl containing 0.1 mM [Fe(CN)6]3-/4-. 46

EIS data fitting
(a) (b)
Figure 20: Experimental ( ) and fitted ( ) EIS spectra
for (a) bare CPE and (b) CPE-EPB (10%).
Z' (Ω)
-Z"(Ω)
Z' (Ω)
-Z"(Ω)
47

EIS data fitting
Rct W
RΩ
Cdl
Scheme 7: Randles equivalent electrical circuit of an electrochemical cell for a simple electrode process.
Table 4: Circuit parameter values from the EIS experimental data recorded at bare CPE and CPE-EPB (10%).
Electrode RΩ (Ω) Rct (Ω) Cdl (µF)
Bare CPE 120 1729 0.16
CPE-EPB (10%) 90 885 1.01
48

Electrochemical oxidation of QCT
30 µA
(b)
2
1
OH
(a)
15 µA
-0.2 0.0 0.2 0.4 0.6 0.8 1.0
(i)
(ii)3
Current
Figure 21: (a) Cyclic voltammetric response in HCl/KCl (pH 1) on bare CPE.
(b) DPV at (i) bare CPE and (ii) CPE-EPB (10%) in 40.6 μM QCT. 49
O
O
OH
OH
HO
OH
A
B
C
1'
2'
3'
4'
5'
6'
1
2
3
45
6
7
8
0.0 0.2 0.4 0.6 0.8 1.0 1.2
(ii)
(i) 3
1 2
Current

Variation of scan rate
(a) 2
1
100 µA
Current
0.70
0.77
0.84
(b) 2
(V)vsAg/AgCl
-0.2 0.0 0.2 0.4 0.6 0.8 1.0
Current
Figure 22: Cyclic voltammograms of 100 µM QCT at CPE-EPB (10%) in PB pH 3
at different scan rates (a-g): 50 - 500 mV/s. (b) Corresponding Ep against lnv plots.
n1 = 2.6 ≈ 3 and n2 = 1.3 ≈ 1
50
3.5 4.0 4.5 5.0 5.5 6.0 6.5
0.49
0.56
0.63
0.70
1
Epa
(V)vsAg/AgCl
ln(v/mVs
-1
)

Optimisation of experimental conditions by DPV
Optimisation of the modified CPE composition
30
35Peakcurrent(µA)
10% EPB
0 5 10 15 20
5
10
15
20
25
Peakcurrent(µA)
Mass of EPB (mg)
Figure 23: Variation of peak currents of 20.7 μM QCT with mass of EPB
in 100 mg paste. The DPV curves were recorded in 0.1 M PB (pH 3). 51

Effect of pH
50 µA 2.11
1.08(a)
50
60
0.4
0.5
0.6
Peakcurrent(µA)
(c)
Peakpotential(V)
pH 3.08
-0.30 -0.15 0.00 0.15 0.30 0.45 0.60
8.00
6.98
6.00
5.03
3.08
4.05
9.04
Current
0 2 4 6 8 10
10
20
30
40
0.0
0.1
0.2
0.3
0.4
Peakcurrent(µA)
pH of supporting electrolyte
(b)
Peakpotential(V)
Figure 24: (a) Effect of detection medium pH (1.08 - 9.04) on the anodic peak position of QCT,
at CPE-EPB (10%) in 20.7 μM QCT. (b) Variation of the peak current as a function of pH of
the detection medium. (c) Peak potential as a function of the pH of the detection medium. 52

Effect of preconcentration time and electrolysis potential
65
70
75
(a)
Peakcurrent(µA)
50
60 (b)
Peakcurrent(µA)
0 30 60 90 120 150 180
45
50
55
60
65
Peakcurrent(µA)
Preconcentration time (s)
-0.6 -0.5 -0.4 -0.3 -0.2
20
30
40
Peakcurrent(µA)
Electrolysis potential (V)
Figure 25: Dependence of current response at CPE-EPB (10%) in 0.1 M PB (pH 3) on
(a) preconcentration time in 0.248 μM QCT and (b) electrolysis potential in 20.7 μM QCT. 53
- 0.3 V130 s

Variation of QCT Concentration and Calibration Graph
Current
(a)
25 A
80
100
120
140
(b)
Current(µA)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
h
a
Current
0 1 2 3 4 5 6 7 8
0
20
40
60
80
Current(µA) [Quercetin] (µM)
Figure 26: (a) DPV curves obtained under optimised conditions in 0.1 M PB pH 3 at CPE-EPB (10%)
for various concentrations of QCT (a-h): 0 - 7.434 µM QCT. (b) The corresponding calibration graph.
LOD: 0.0448 µM QCT
54

Chronocoulometry
bare CPE: 0.1984 cm2
CPE-EPB (10%): 3.962 cm2
Electrochemical effective surface area
1/2 1/2
c ads1/2
2nFAD Ct
Q = + +Q Q
π
CPE-EPB (10%): 3.962 cm2
Anson equation
π
55
Diffusion coefficient of QCT D = 4.52 x 10-5 cm2/s
Molecular surface coverage
adsQ
Γ =
nFA
Γ = 6.95 x 10-11 mol/cm2
Γ = 4.18 x 1013 QCT molecules/cm2
Monolayer adsorption

Interferences
Table 5: Effect of some interfering organic species on the signal of 20.7 µM QCT.
Interfering organic
species
Concentration
(µM)
Increase in peak current
of QCT
Ascorbic acid 21.0 ≈ 6 %
Uric acid 21.0 ≈ 9 %
Dopamine 21.0 ≈ 13 %
L-Aspartic acid 21.0 ≈ –4 %
Citric acid 21.0 ≈ –4 %
D-(+)-Glucose 21.0 ≈ 6 %
56

Real sample analyses
Table 6: Quantification of QCT in human urine samples.
Sample Urine dilution QCT added (µM) QCT found (µM) Mean recovery (%)
1 x 100 4.06 3.65 89.9
2 x 200 4.06 3.89 95.8
3 x 300 4.06 3.93 96.8
4 x 300 6.10 6.38 104.6
57

Linear range Detection limit
In HCl/KCl pH 1 2.06 µM to 67.4 µM 1.84 μM
In human urine 2.04 µM to 59.5 µM 2.98 µM
Activated chitosan modified CPE for MG determination
Amine-grafted Attapulgite modified GCE for MG determination
In HCl/KCl pH 1 0.61 µM to 10.57 µM 0.275 µM
Characterised by SEM, EA, FTIR, XRD and EIS
In PB pH 3 0.248 µM to 7.43 µM 0.0448 µM
1-Ethylpyridinium bromide modified CPE for QCT determination
58

 Successful application to real sample analysis,
 Successful determination of MG and QCT in the
presence of interferents,
 Envisage amperometric sensor with mediators for
simultaneous determination of molecules of
medicinal importance,
 Determination of such molecules in plants extracts.
59

Résumé
De nouvelles électrodes composites ont été mises au point,
puis appliquées à l’électroanalyse de deux composés d’intérêt
médical de la famille des xanthones et des flavonoïdes:
 une EPC modifiée par une poudre de chitosane activée pour
l’électroanalyse de la mangiférine,
 une EF d’attapulgite modifié par greffage covalente du [3-(2-
aminoéthylamino)propyl]triméthoxysilane pour l’électroana-
lyse de la mangiférine,
 une EPC modifiée par un liquide ionique pour l’électronalyse
de la quercétine.
60

Acknowledgements
Great support from the following is acknowledged:
The University of Dschang
The International Foundation for Science (IFS)
The Academy of Sciences for the Developing World (TWAS)
 Pr A. TAPONDJOU (DCH, FS, UDs),
 Pr B. T. NGUELEFACK (DAB, FS, UDs),
Pr W. SCHUHMANN (Ruhr-University, Bochum, Germany),
Drs F. DOUNGMENE and G. KENNE-DEDZO,
The Members of Jury. 61

Thank
you for
youryour
kind attention

Novel composite electrodes:Preparation and application to the electroanalytical study of two pharmaceutically active molecules, viz. mangiferin and quercetin

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Novel composite electrodes:Preparation and application to the electroanalytical study of two pharmaceutically active molecules, viz. mangiferin and quercetin