Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Multiwalled carbon nanotube modified with 5-Br-PADAP for stripping voltammetric
determination of Pb(II)
Ashraf Salmanipour, 1 Mohammad Ali Taher 1 and Alireza Mohadesi 2*
1
Department of Chemistry, Shahid Bahonar University of Kerman, P.O. Box 76175-133, Kerman, Iran
2
Department of Chemistry, Payame Noor University (PNU), P.O. Box 76175-559, Kerman, Iran
Abstract— In this work, we have demonstrated that glassy carbon electrode (GCE) modified with multiwalled carbon
nanotube (MWNT) functionalized with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) as a ligand can be
used for the stripping voltammetry of lead(II). The ability of the 5-Br-PADAP to extract Pb(II) into the electrode surface leads
to an electrochemical sensor that is precise and accurate for determination of lead(II) in water samples.
Adsorptive stripping voltammetry generally applies an
accumulation step prior to the voltammetric scan in order to
develop analysis methods with higher levels of sensitivity. In
this step, analyte (metal ion) is adsorbed from sample solution
to electrode surface based on complexation between metal ion
and ligand immobilized on the electrode surface. In this sense,
owing to the strong sorption properties of carbon nanotubes
and their advantages in electrochemical measurements, this
nanostructured material has allowed some novel methods of
stripping analysis to be developed [1-4].
In this work, the MWNT functionalized with a complex
reagent (5-Br-PADAP) was prepared and coated on a GCE.
This modified electrode was used successfully for anodic
stripping determination of lead(II) in some real samples.
Before use, the MWNTs were purified and pretreated to
remove graphitic nanoparticles, amorphous carbon, and
catalyst impurities, and then functionalized with carboxylic
acid groups according to the literature [5]. After these
procedures, the carboxylic acid groups were introduced onto
the cross sections of the MWNTs. For preparation of 5-Br-
PADAP-functionalized MWNT, the 5-Br-PADAP dissolved
in ethanol was added to 1 g of pretreated MWNT, step by step
and the solution was stirred for 24 hour till the solution
became colorless. Then the modified MWNTs were filtered
and washed with doubly distilled water and got dried at room
temperature. Then ultrasonication agitation for 20 min was
applied to disperse 0.5 mg 5-Br-PADAP/MWNT into 1 ml of
double distilled water to give 0.5 mg/ml suspension. Before
coating, the GCE was polished with a nano-Al 2 O 3 powder on a
polishing pad rinsed thoroughly with doubly distilled water,
then sonicated in aceton for 2 min. Finally, the GCE was
coated with 10 μL of 0.5 mg/ml 5-Br-PADAP/MWNT
suspension and the water allowed evaporating at room
temperature in the air. The bare electrode was prepared by the
same procedure just with unfunctionalized MWNTs.
For differential pulse anodic (DPA) or cyclic stripping
voltammetric experiments, the 5-Br-PADAP/MWNT/GCE
was immersed in a 25 ml of sample solution (0.1 M acetate
buffer pH 5.58) containing a known amount of Pb(II) and the
solution was stirred for 15 min. This was followed by medium
exchange to a 0.1 M stripping solution (0.1 M KNO 3 , 0.1 M
acetate buffer pH 4.23), where the DPA or cyclic
voltammograms were recorded from -1.0 to -0.2 V.
Figure 1a shows typical cyclic voltammogram for the
detection of Pb 2+ following open-circuit accumulation onto 5-
Br-PADAP/MWNT film. An anodic peak at -0.55 V can be
observed, which is related to the oxidation of accumulated
lead(II). To prove further the importance of 5-Br-PADAP as a
chelator reagent in the electrode surface, GC electrode
modified with MWNT without 5-Br-PADAP were prepared,
and used for the accumulation and stripping of Pb 2+ . Figure 1c
shows no significant peak, as expected, in the case of
unmodified MWNT. These results show the importance of
modification of MWNT with 5-Br-PADAP for the
preconcentration of Pb 2+ .
From the above observations, under the conditions of the
experiments, the possible pathways for the analysis cycle,
from modification of MWNT to stripping voltammetry, are
postulated below ("sol", or "surf" subscript means compound
is in solution or electrode surface):
Modification of pretreated-MWNT with 5-Br-PADAP:
reflux
MWNT + 5 − Br − PADAP( sol )
⎯⎯⎯
→ 5 − Br − PADAP / MWNT
Accumulation of Pb 2+ from acetate buffer solution:
Pb
2+
(
sol
)
+
open circuit 2+
[ 5 − Br − PADAP / MWNT ](
surf )
⎯⎯ ⎯⎯→
[ Pb / 5 − Br − PADAP / MWNT ](
surf
Reduction of accumulated Pb 2+ in clean acetate buffer:
2+
in more negative than −0.7V
0
[ Pb / 5 − Br − PADAP / MWNT]
( surf )
+ 2e
⎯⎯⎯⎯⎯⎯⎯⎯→
Pb(
surf )
+ [5 − Br − PADAP / MWNT]
( surf
Stripping of reduced lead in clean acetate buffer:
Pb
⎯⎯⎯⎯⎯⎯⎯→Pb
0 Scan from −1.0
to −0.2V
2+
( surf )
( surf )
Figure 1. Cyclic (50 mV/s) voltammograms in acetate buffer pH 4.23 after
open circuit accumulation (15 min) in acetate buffer pH 5.58: (a) 5-Br-
PADAP/MWNT/GCE, with 100 μg L -1 Pb(II) in accumulation medium, (b) 5-
Br-PADAP/MWNT/GCE, no Pb(II) in accumulation medium, (c)
MWNT/GCE, with 100 μg L -1 Pb(II) in accumulation medium and (d)
MWNT/GCE, no Pb(II) in accumulation medium.
*Corresponding author: mohadesi_a@yahoo.com
[1] G.H. Hwang et al., Talanta 76 301–308 (2008)
[2] K. Wu et al., Anal. Chim. Acta 489 215–221 (2003)
[3] H. Xu et al., Electroanalysis 20 2655 – 2662 (2008)
[4] L. Zhu et al., Electroanalysis 20 527 – 533 (2008)
[5] X. Tan et al., Anal. Biochem. 337 111 (2005)
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6th Nanoscience and Nanotechnology Conference, zmir, 2010 365