the influence of lateral flake size in …(hcng and g250) paste electrodes. scan rate: 50 mv s-1...
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Electronic Supporting Information (ESI):
The influence of lateral flake size in Graphene/Graphite
paste electrodes: an electroanalytical investigation
Alejandro García-Miranda Ferraria, Hadil M. Elbardisya,b, Valentine Silvaa, Tarek S. Belalc,
Wael Talaatb, Hoda G. Daabeesd, Craig E. Banksa and Dale A. C. Brownsona*
a: Faculty of Science and Engineering, Manchester Metropolitan University, Chester Street,
Manchester M1 5GD, UK.
b:Pharmaceutical Analysis Department, Faculty of Pharmacy, Damanhour University,
Damanhour, 22511, Egypt.
c: Department of Pharmaceutical Analytical Chemistry, Faculty of Pharmacy, Alexandria
University, Alexandria, 21521, Egypt.
d: Pharmaceutical Chemistry Department, Faculty of Pharmacy, Damanhour University,
Damanhour, 22511, Egypt.
*To whom correspondence should be addressed.
Email: [email protected]; Tel: ++(0)1612476561
Electronic Supplementary Material (ESI) for Analytical Methods.This journal is © The Royal Society of Chemistry 2020
Figure S1. (A) A schematic showing that the graphite/graphene pastes are mixed with Nujol
(60-40 % ratio respectively) before then being inserted into a polymeric-composite electrode
shell with an inner diameter of 4.5 mm. The electrode material is in contact with copper foil
as electrode connector. After polishing, the working electrode (WE) is ready to be used in
conjunction with reference (RE) and counter (CE) electrodes in a three-electrode cell
configuration. (B) Depicts the different working electrodes used in this manuscript.
(C) Shows the different graphene (AO1, AO3, AO4, AO2 and C1) and graphite (HCNG and G250)
powders used as electrode materials in this manuscript.
Figure S2. Voltammetric profiles for 72.36 μg mL-1 of COC (A) and MDMA (B) in B-R pH 9 and
PBS pH 7.4 respectively, using the range of graphene (AO1, AO4, AO2 and C1) and graphite
(HCNG and G250) paste electrodes. Scan rate: 50 mV s-1 (vs. Ag/AgCl). Solid lines represent
the largest (HCNG) and the smallest (G250) flakes used; dotted lines represent the
intermediate flake sizes (AO1, AO3, AO4, AO2 and C1). Data recorded using the AO3 electrode
has not been included due to a very high capacitive background current that does not allow
one to distinguish a redox peak.
Figure S3. Calibration plots of COC (A) and MDMA (B) in B-R pH 9 and PBS pH 7.4 respectively,
using the graphene (AO1, AO4, AO2 and C1) and graphite (HCNG and G250) paste electrodes.
Analytical sensitivities of these calibration plots are shown in Table S3. Scan rate: 50 mV s-1
(vs. Ag/AgCl). Solid lines represent the largest (HCNG) and the smallest (G250) flakes used;
dotted lines represent the intermediate flake sizes (AO1, AO3, AO4, AO2 and C1).
Data recorded using the AO3 electrode has not been included due to a very high capacitive
background current that does not allow one to distinguish a redox peak.
Table S1. Percentage Relative Standard Deviation (%RSD) values obtained at the various
electrode materials towards the detection of DA, UA, AA, NADH and MA. Values relative to
the calibration plots depicted in Figure 3. Scan rate: 50 mV s-1 (vs. Ag/AgCl) (N = 3).
Table S2. Comparison of the peak position (Ep, in V) obtained at the various electrode
materials towards the detection of 100 μg mL-1 COC (in B-R pH 9) and MDMA (in PBS pH 7.4).
Scan rate: 50 mV s-1 (vs. Ag/AgCl) (N = 3).
RSD DA
/ % RSD UA
/ % RSD AA
/ % RSD NADH
/ % RSD MA
/ %
GRAPHITE HCNG 8.0 13.0 5.3 9.1 10.2
GRAPHENE
AO1 5.5 5.5 10.2 7.3 7.5 AO3 5.3 2.5 9.9 5.5 4.3 AO4 9.2 3.7 7.3 6.8 17.3 AO2 5.7 10.8 9.0 7.5 8.9 C1 3.5 7.2 8.2 5.9 11.1
GRAPHITE G250 5.1 9.5 4.4 7.0 13.5
COC / V MDMA / V
GRAPHITE HCNG 0.925 1.096
GRAPHENE
AO1 0.922 1.099 AO3 0.960 1.096 AO4 0.926 1.101 AO2 0.908 1.153 C1 0.939 1.085
GRAPHITE G250 0.955 1.070
Table S3. Comparison of the analytical sensitivities (in A μg-1 mL) obtained at the various
electrode materials towards the detection of COC (in B-R pH 9) and MDMA (in PBS pH 7.4).
Scan rate: 50 mV s-1 (vs. Ag/AgCl) (calculated from gradient of calibration plots depicted in
Figure S3 between 11.86–72.36 μg mL-1 for COC and 5.96–72.36 μg mL-1 for MDMA) (N = 3).
Table S4. Comparison of the electrochemical limit of detection (LOD; LOD = 3*σ / slope)
obtained at the various electrode materials towards the detection of COC (in B-R pH 9) and
MDMA (in PBS pH 7.4). Scan rate: 50 mV s-1 (vs. Ag/AgCl) (calculated from gradient of
calibration plots depicted in Figure S3 between 11.86–72.36 μg mL-1 for COC and 5.96–72.36
μg mL-1 for MDMA) (N = 3).
COC / A μg-1 mL MDMA / A μg-1 mL
GRAPHITE HCNG 0.107 0.108
GRAPHENE
AO1 0.052 0.082 AO3 0.031 0.156 AO4 0.043 0.099 AO2 0.024 0.103 C1 0.046 0.109
GRAPHITE G250 0.160 0.124
COC / μg mL-1 MDMA / μg mL-1
GRAPHITE HCNG 1.04 3.12
GRAPHENE
AO1 1.45 0.28 AO3 13.02 18.65 AO4 0.25 0.84 AO2 1.63 0.27 C1 0.87 0.46
GRAPHITE G250 0.51 1.27
Figure S4. Scanning Electron Microscopy (SEM) images of the various powders utilised to
fabricate the electrodes studied herein. HCNG (A), AO1 (B), AO3 (C), AO4 (D), AO2 (E), C1 (F)
and G250 (G). Note that these are representative images obtained from ‘batch
characterisation’ of the samples that have been reported previously in Ref. [54].
Figure S5. Raman spectroscopy characterisation of the various graphitic powders: HCNG (A);
AO1 (B); AO3 (C); AO4 (D); AO2 (E); C1 (F); and G250 (G). Note that these are representative
spectra obtained from ‘batch characterisation’ of the samples and have been reported
previously in Ref. [54].