An electrochemical sensor highly selective for lindane determination: A comparative study using three different α-MnO2 nanostructures

Article abstract of DOI:10.1039/c5ra26771d

Here we describe a simple, highly reproducible ultra-sensitive electrochemical sensor for lindane based on α-MnO₂ nanostructures. The results showed that the α-MnO₂ nanostructures effectively catalyzed the electrochemical reduction of lindane. A good linearity was obtained in the range of 1.1 to 510 μM with a detection limit of 114 nM. The proposed lindane sensor was successfully employed for the determination of lindane in tap water samples with good recoveries. Negligible amperometric currents are observed in the control experiments using triclosan (T), chlorobenzene (CB), benzene (B), 1,3,5-trichlorobenzene (1,3,5-TCB), and 4-chlorobenzaldehyde (4-CBA), suggesting a sensing specificity to lindane. The proposed sensor also exhibited good stability and reproducibility for lindane determination.

Full text of DOI:10.1039/c5ra26771d

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PAPER
Electrochemical sensor highly selective for lindane determination:
A comparative study using three different α-MnO nanostructures
2
Received 00th January 20xx,
Accepted 00th January 20xx
M.U. Anu Prathap, Shengnan Sun, and Zhichuan J. Xu*
DOI: 10.1039/x0xx00000x
Here we describe a simple, highly reproducible ultra‐sensitive electrochemical sensor for lindane based on α‐MnO
2
www.rsc.org/
nanostructures. The results showed that the α‐MnO nanostructures effectively catalyzed the electrochemical reduction of
2
lindane. A good linearity was obtained in the range of 1.1 to 510 µM with a detection limit of 114 nM. The proposed
lindane sensor was successfully employed for determining lindane in tap water samples with good recoveries. Negligible
amperometric currents are observed in the control experiments using triclosan (T), chlorobenzene (CB), benzene (B), 1,3,5‐
trichlorobenzene (1,3,5‐TCB), and 4‐chlorobenzaldehyde (4‐CBA), suggesting sensing specificity to lindane. The proposed
sensor also exhibited good stability and reproducibility for lindane determination.
bulwark. New methods, for lindane detection includes more
sophisticated
chromatography,
chromatographic-massspectrometry.
chromatographic methods are accurate, they are expensive and
time consuming.
available to date, electrochemical sensors are emerging to be a
technology of choice due to the rapid and sensitive response,
low fabrication cost and operational convenience.
excellent study discusses the reductive dechlorination of
analytical
liquid
approaches,
such
as
gas
gas
Introduction
Lindane (gamma isomer of hexachlorocyclohexane) is an
organochlorine insecticide named after Dutch chemist Teunis
van der Linden who was the first to isolate α-, β-, and γ-isomers
chromatography
or
6,7
Although
6-8
Among the various biosensing approaches,
1
,2
of hexachlorocyclohexane in 1912.
The insecticidal
properties of lindane were first demonstrated by Ulmann,
7,8
1,2
An
1
972.
Lindane has been used to treat food crops and to
forestry products, as a seed treatment, a soil treatment, and to
9
1-3
lindane catalyzed by bioreceptor probe. It was found that the
specificity of dechlorination depended on the enzyme stability,
pH and temperature, which is the major limitation. Lindane
treat livestock and pets. Lindane is reported to be a central
nervous system stimulant. Symptoms of acute exposure include
mental and motor retardation, central nervous system
excitation, tonic-clonic convulsions, respiratory failure,
7
has very low aqueous solubility and has a very high
overpotential for reduction, as a result the direct reduction of
lindane using the aqueous medium is a challenging task. Recent
publications discuss on dechlorination of lindane in
ethanol/water and lindane gave only one reduction wave and
benzene as the reduction product with 100 % yield.
results of other researchers show chloride ion was liberated
from lindane structure more rapidly than hydrogen or carbon
2,3
pulmonary edema and dermatitis. Lindane enters animal
tissues through food chain, respiration or dermal
2,3
contact. After being under review for nearly 30 years, the
pesticide lindane was finally withdrawn by the Environmental
1
0-15
3,4
The
Protection Agency (EPA) for use in agriculture. Lindane is
recognized by EPA as one of the most toxic, persistent, bio-
accumulative pesticides ever registered. Despite a recent
global ban on its agricultural use, the pesticide is still used and
approved by the Food and Drug Administration (FDA) as a
second-line therapy for topical treatment of pediculosis capitis
5
10-15
atom fragments.
non-enzymatic sensing of lindane using metal oxide, and it
appears to be more effective.
Few studies have been dedicated to the
1
2,15
Thus, it is important to pursue
a suitable modified electrode for the efficient reduction of
lindane.
In recent years, the application of nanoscaled metal oxides
has received great attention in biotechnology and bio-analytical
(
head lice), pediculosis pubis (pubic lice), or scabies in patients
greater than two years of age who cannot tolerate or have failed
first-line treatment. Therefore, quantitative analysis of lindane
is a paramount area in the context of the environmental
5
1
6-20
chemistry.
as a variety of stable oxides (MnO, Mn
crystallize in various types of crystal structures. Among them,
α-MnO has been widely investigated and extensively used in
Transition metal element; manganese can exist
3
O
4
, Mn , MnO ) and
2
O
3
2
School of Materials Science and Engineering, Nanyang Technological University,
5
†
0 Nanyang Avenue, Singapore 639798, Singapore. E-mail: xuzc@ntu.edu.sg
Electronic Supplementary Information (ESI) available: [Experimental details,
2
supplementary figures]. See DOI: 10.1039/x0xx00000x
adsorption, catalysis, sensors, rechargeable lithium batteries
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Nanoscale
and ion exchanges owing to the existing unique layers or Synthesis of α‐MnO
2
hollow nanotube (α‐MnO
2
‐NT)
2
1-23
tunnels in crystal lattices.
physicochemical properties of MnO
crystallographic structure, morphology, and surface area.
In this work, we report three synthetic pathways for the addition of 5 mL hydrochloric acid (11.65 M, 35% (w/w)),
preparation of α-MnO nanostructures, (e.g., NW (nanowire), forming a solution. The resulting mixture was stirred for 0.5 hr;
NT (nanotube), and MS (microsphere); designated as: α-MnO the solution was transferred to a Teflon-lined autoclave (50 mL
NW, α-MnO -NT, and α-MnO -MS). We further demonstrated capacity). The hydrothermal process was conducted at 383 K
α-MnO nanostructures exhibit excellent electrocatalytic for 15 hr. Product was filtered, washed with water and ethanol,
It is generally accepted that the α-MnO
2
-NT was synthesized by a hydrothermal approach by
25
2
are greatly affected by the modifying the recipe. 15 mmol (2.37 g) of KMnO
4
was
dissolved in 200 mL of deionized water (DW), followed by the
2
1
2
2
-
2
2
2
activity for lindane reduction. The prepared sensor was dried in an oven at 353 K for 8 h.
characterized by electrochemical impedance spectroscopy
(
EIS), differential pulse voltammetry (DPV), cyclic Materials characterizations
voltammetry (CV), pulsed amperometry (PA) and The as-prepared materials were characterized with X-ray
chronoamperometry. Under the optimized conditions, the powder diffractometer (XRD; Shimadzu XRD-6000, Cu Kα
−
1
prepared sensor exhibited selective recognition and a highly radiation) at a scan rate of 1° min . Scanning Electron
sensitive detection toward lindane.
Microscopy (FESEM, JSM-7600F) and transmission electron
microscopy (TEM; JEOL, JEM-2100F) operated at 200 kV was
used to observe the morphological features. Nitrogen
adsorption measurement at 77 K was performed by Tristar-
Experimental
Materials
All chemicals were analytical grade and used without further 3000 surface area analyzer. Samples were out-gassed at 423 K
purification. KMnO
, urea, γ-HCCH (Lindane), cyclohexane, for 4 h in the degas port of the adsorption apparatus. The
chlorobenzene, 4-chlorobenzaldehyde, triclosan, benzene and specific surface area was determined by Brunauer–Emmett–
4
tetra-n-butyl ammonium bromide (TBAB) were obtained from Teller (BET) method using the data points of P/P
0
in the range
Sigma-Aldrich. Deionized water from Millipore Milli-Q system of about 0.05–0.3.
(
Resistivity 18.2 M cm) was used in the electrochemical
studies. Solutions for all electrochemical experiments were Electrochemical measurements
deoxygenated with zero-grade argon.
Cyclic voltammetry (CV), Differential pulse voltammetry
DPV), Pulsed amperometry (PA) and Continuous
amperometric studies were performed by using a computer-
(
Preparation of solution
Stock solution of lindane was prepared in methanol. 0.05 M controlled Pine Instrument. A three electrode electrochemical
tetra-n-butyl ammonium bromide (TBAB) solution was cell was employed with Ag/AgCl as the reference electrode
prepared in 60:40 (v/v) methanol–water. It was used as the (3M KCl), metal oxide mounted glassy carbon electrode (GCE)
2
supporting electrolyte.
(0.196 cm ) as the working electrode, and Pt foil as the counter
electrode. Before modification of GCE, the polished electrode
was ultrasonicated in ethanol and deionized water for 5
Synthesis of α‐MnO
α-MnO
a modified procedure first reported by our group. 1.5 mmol follows: 10 µL aliquot of MnO
0.237 g) of KMnO
was dissolved in 100 mL of deionized sonicated solution of 10 mg of MnO
2
2 2
microspheres (α‐MnO ‐MS)
-MS was synthesized by a hydrothermal approach with minutes, respectively. The working electrodes were prepared as
2
1
5
2
suspension (a homogenous
(
4
and a mixture of 0.1 mL
water (DW), followed by the addition of 5 mL hydrochloric of Nafion and 0.9 mL of water) was placed onto the electrode
acid (11.65 M, 35% (w/w)), forming a solution. The resulting surface, the electrode was dried in air leaving the material
mixture was stirred for 0.5 hr; the solution was transferred to a mounted onto the GCE surface.
Teflon-lined autoclave (50 mL capacity). The hydrothermal
process was conducted at 353 K for 12 hr. Product was filtered, Results and discussion
washed with water and ethanol, dried in an oven at 353 K for 8 XRD analysis was primarily used to determine the structure of
h.
the α-MnO
indexed to a tetragonal α-MnO
Similar XRD observation was also noticed for α-MnO
-MS prepared in this study (Figure not shown). Fig. 1b-
increased temperature for higher purity samples. In a typical h shows the SEM and HRTEM images with different
procedure, 10 mmol (0.6 gram) of urea was dissolved in 35 mL magnifications of α-MnO -MS, α-MnO -NT, and α-MnO -NW.
deionized water, followed by the addition of 10 mmol (1.58 g) The SEM morphology of α-MnO -MS is spherical with a
KMnO
, forming a solution. The resulting mixture was stirred flower-like morphology (Fig. 1b,c). The higher magnification
2
-NW (Fig. 1a). All the diffraction peaks can be
(JCPDS, file No.: 44-0141).
-NT and
2
Synthesis of α‐MnO
2
nanowires (α‐MnO
2
‐NW)
2
α-MnO
2
-NW was prepared by reported procedure with α-MnO
2
2
4
2
2
2
2
4
for 30 min; the solution was transferred to a Teflon-lined image shows that the petal structure of microspheres is
autoclave (50 mL capacity). The hydrothermal process was assembled by many nanosheets (Fig. 1c). Figs. 1(d-f) is the
conducted at 433 K for 20 hours. The products was filtered, representative SEM and HRTEM images of the as-prepared α-
washed with DW and dried at 353 K overnight.
2 2
MnO -NT. Evidently, each MnO nanotubes are of high
quality; they are open-ended and have a length of hundreds of
2
| J. Name., 2012, 00, 1‐3
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Paper
3
−/4−
nanometer Figs. 1(e,f). Fig. 1g shows the low magnification corresponding to Fe(CN)
SEM image of the α-MnO
product consists of nanowires. The MnO
investigated by HRTEM (Fig. 1h). The diameters of the of various electrodes was calculated according to the Randles-Sevčik
6
redox couple (Fig. 2b). Among the
2
-NW; it can be found that the various modified electrodes investigated in this study, α-MnO
2
-NW
2
nanowires are further exhibited the highest current response. The electroactive surface area
23
presented MnO
sorption isotherm of the α-MnO
curve with a sharp capillary condensation step in the relative
pressure range of 0.6–1 and H hysteresis loop, indicative of
uniform cylindrical mesopores (Fig. 2a).
nanostructures synthesized in this study exhibited type IV electrons participating in the redox reaction, A is the electroactive
2
nanowire are within 50 nm (Fig. 1h). The N
2
equation (Eq. 1).
2
-NW sample shows a type IV
5
3/2
1/2
1/2
I
p
= (2.69 x 10 ) n AD C ν
(1)
1
2
6
2 p
α-MnO -NT Where, I is the peak current of redox couple, n is the number of
2
isotherm with H
mesoporous materials. High uptake of N
relative pressure (~ 0.4) reveal abundant micropores located in bulk solution (mol/cm ), and ν is the scan rate (V/s). The effective
the α-MnO -NT (Fig. 2a). Textural properties for various surface area of different modified electrodes was calculated as 0.403,
materials obtained from the N
Table S1, ESI†. The specific BET surface area for α-MnO
NW, α-MnO -NT, and α-MnO
3
hysteresis, which is characteristic of the surface area (cm ), D is the diffusion coefficient of K
3
[Fe(CN)
6
] in
2
2
adsorption at a low the solution (cm /s), C is the concentration of K
3
[Fe(CN) ] in the
6
3
2
2
2
-adsorption study is provided in 0.305, and 0.259 cm for α-MnO
MS, respectively. The high electroactive surface area of α-MnO
2
-NW, α-MnO
2
-NT, and α-MnO
2
-
-
2
-
2
2
2
2
-MS were found to be 124.2 NW significantly eases the electron transfer rate at the electrode-
2
2
27
m /g, 79.3 m /g and 12.2 m /g, respectively. From the SEM electrolyte interface. Fig. 2c displays typical Faradaic impedance
images it can be seen that α-MnO -NW has short fiber lengths spectra (presented as Nyquist plot) of the α-MnO -NW electrode
and diameters ~ 50 nm, while α-MnO -NT has a diameter of ~ before and after additions of different concentrations of the lindane.
10 nm and α-MnO -MS has higher diameter (sub-micrometer Electrochemical impedance spectra were recorded in the frequency
2
2
2
1
2
size), the decrease of the lateral dimensions (diameter) to the range from 1 MHz to 10 mHz with the AC signal amplitude of 10
nanoscale offers a high specific surface area and a high surface mV. It can be clearly observed that the electron-transfer resistance
2
6
site density to α-MnO
2
-NW (Fig. 1).
(semicircle diameter) decreases as the lindane concentration is
elevated. In EIS, the diameter of the semicircle portion at higher
frequencies corresponds to the electron-transfer resistance (Ret). The
change of Ret value at high frequencies was associated with the
2
8
blocking behavior of the modified layer at the electrode surface.
The collected data show that the Ret values are significantly smaller
after the addition of lindane, e.g., decreasing from 7.02 kΩ to 3.12
kΩ, upon increasing the lindane concentration from 0 to 180 μM.
The smaller semi-circle diameter (i.e. lower value of Ret) indicates
faster electron-transfer kinetics of lindane (reduction) at the α-
2
8
MnO
2
-NW modified electrode.
-NW modified electrode was constructed to obtain
α-MnO
2
the optimized analysis parameter for lindane reduction. The
electrochemical behaviour of lindane was first investigated
using cyclic voltammetry in the absence and presence of 300
µM lindane. In the absence of lindane, no peak was observed.
When lindane was added, a distinct peak at –1.45 V (versus
Ag/AgCl) was appeared, which is completely irreversible (Fig.
1
0-15
-1
S1, ESI†).
The effect of scan rate (range of 20–200 mV s )
was investigated to predict the reaction kinetics process using
cyclic voltammetry as shown in Fig. 2d. The results reveal that
the reduction peak current of lindane was directly proportional
-
1
to the square root of scan rate up to 200 mV s , the negative
intercept suggests that the electrode reaction is not a pure
1
0-15
Fig.1 XRD pattern (a) of α‐MnO
SEM images (d,e) and TEM image (f) of the α‐MnO
and TEM images (h) of the α‐MnO ‐NW. The inset of (h) is a close view of α‐
MnO ‐NW.
2
‐NW. FE‐SEM images (b,c) of α‐MnO
2
‐MS, FE‐ diffusion-controlled process (Fig. 2d, inset).
Randles-
2
‐NT, and FE‐SEM image (g)
Sevčik equation for a reduction process with a zero intercept
suggests a complete diffusion control process, thus, the
negative intercept from the plot of peak current versus square
root of scan rate can be explained as an adsorption of the
lindane molecule after diffusion to the electrode surface. The
results of the voltammetric analyses are collected in Table S2.
α was calculated from the peak
width ( ). For all scan rates, a very low value of
is obtained less than 0.5, showing that the rate-determining
2
2
The electrochemical behavior of different modified electrodes
was investigated using potassium ferricyanide as the electrochemical
probe by CV. Study was performed in 0.2 M KCl solution
15
containing 50 mM K
mV/s at different modified electrodes. The CV of various modified
electrodes exhibited pair of well-defined redox peaks
3 6 4 6
[Fe(CN) ]/K [Fe(CN) ] at a scan rate of 20
The electron transfer coefficient
∆Ep/2 = Ep/2 –E
p
a
α
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Nanoscale
step of the electrode process is dissociative electron transfer reported that the elimination of a chlorine atom by the reduction
(
ET), which is concerted with the cleavage of the carbon– of polychlorinated benzenes always leads to a product that is
2
9,30
30,31
halogen bond.
Dechlorination or displacement of chlorine more difficult to be reduced.
In contrast, breaking of
of polychlorinated cyclohexanes is different from the carbon-chlorine bonds in lindane occur very fast and readily
3
1,32
31,32
dechlorination of polychlorinated benzenes.
Earlier workers form fully reduced benzene.
(
a) 500
(b)2000
0
0
0
.12
.08
.04

MnO - NW
2
400
300
200
100
MnO - NT
1000
0
2
MnO - MS
2
0.00
-1000
-2000
-3000
0
50
100
150
-MnO -NW
2
Pore diameter (nm)
-MnO - NT
2

-MnO - MS
2
0
0
.00
0.25
0.50
0.75
1.00
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (P/P0)
Potential (V vs. Ag/AgCl)
(
c) 4000
(d)
0
0
4
1
1
1
M
0 M
00 M
40 M
80 M
20 mV/s
-5
200 mV/s
3
2
1
000
000
000
0
-
10
-10
-20
-30
-15
-
-
-
20
25
30
4
8
12
16
s
1
/2
1/2 -1/2
Scan rate (mV
)
-35
0
2000
4000
6000
8000
-1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6
Re(Z) (Ohm)
Potential (V vs. Ag/AgCl)
Fig. 2 (a) N
electrodes in 0.2 M KCl electrolyte containing 50 mM of [Fe(CN)
electrode in the presence of increasing concentrations of lindane, using 0.05 M TBAB solution in 60:40 methanol–water (20 mL) over the frequency range from 1 MHz
2
adsorption–desorption isotherms of materials synthesized in this study. The inset shows pore size distribution. (b) CV responses of various modified
3
‐
/
4
‐
‐
1
6
]
2
at a scan rate of 20 mVs . (c) Typical EIS response recorded at the α‐MnO ‐NW modified
‐
1
to 10 mHz a bias potential of ‐1.45 V. (d) CVs of lindane (200 μM) at various scan rates (20‐200 mVs ) at α‐MnO
peak currents vs. square root of scan rates. All scans are applied between ‐0.6 V and ‐1.8 V.
2
‐NW modified electrode. Inset shows the plot of
Under the optimized conditions, pulsed amperometry and Where S is the standard deviation of the blank signal, and q is
differential pulse voltammetry were used to determine lindane the slope of the calibration curve. A comparison of the
concentration. The Fig. 3a shows the pulsed amperometric modified electrodes toward electrocatalytic reduction of lindane
response of α-MnO
constant potential -1.45 V (vs Ag/AgCl), the measured current can conclude that α-MnO
response is linear vs. the lindane concentration (Fig. 3a). α- superior sensing ability and current sensitivity compared to
MnO -NW modified electrode can detect lindane in the other modified electrodes investigated in this study. The high
concentrations range from 1.1 to 510 µM in the amperometric electrocatalytic response observed for the α-MnO -NW can be
mode with a linear regression equation of, (µA) = -4.64- correlated with the large surface area, excellent site
= 0.9989) with the sensitivity of 0.18 accessibility and a low mass-transfer resistance for lindane.
2
-NW modified electrode to lindane. At the is presented (Fig. 4a). Based on the experimental evidence, one
2
-NW modified electrode exhibited
2
2
I
−
1
2
0
.0346C (µmol L ) (R
−
1
-2
µA µM cm and a lower detection limit of 114 nM. The
intercept of the calibration curve was not found to be zero,
suggesting undesired non-Faradaic processes (Fig. 3a, inset).
(
a) 75
0
-5
33
60
45
30
15
0
-
-
10
15
DPV measurements were also carried out containing different
lindane concentrations to obtain an analytical curve. Fig. 3b
shows that the cathodic peak current was linearly dependent on
the lindane concentration in the range from 2 to 520 µM with a
-20
-25
0
150 300 450
Concentration (M)
0 V
0
V
0 M
linear regression equation of,
I
(µA) = -6.208-0.022
C (µmol
-
15
30
−
1
2
−1
-2
L ) (R
= 0.9983) with the sensitivity of 0.14 µA µM cm
-1.45 V
510 M
-
and a lower detection limit of 517 nM (Fig. 3b, inset).
Similarly, linear relationship between oxidation peak currents
and lindane concentrations was observed in the range of 4–500
0
5
10
15
20
Time (sec)
0
-5
(
b)
0
M
2 2
µM, and 15–350 µM for α-MnO -NT and α-MnO -MS
5
20 M
-
4
8
modified electrodes (Fig. S2 and Fig. S3, ESI†). To obtain the
limit of detection (LOD), we used an IUPAC (International
Union of Pure and Applied Chemistry) recommended
-
-
-
-
10
15
20
-
12
-16
-20
3
4
methodology, using the standard approach of alternative (SA).
0
150 300 450
Concentration (M)
LODSA = 3S/q
(2)
-1.8
-1.5
-1.2
-0.9 -0.6 -0.3
Potential (V vs. Ag/AgCl)
4
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Fig. 3 (a) Pulsed amperometric response of the α‐MnO
to different concentrations of lindane at the specified voltage values. The inset
shows the calibration plot. (b) DPVs of lindane at varying the concentrations at
2
‐NW modified electrode
mM), and cyclohexane (1 mM) as compared to the successive addition of
lindane.
the α‐MnO
2
‐NW modified electrode using 0.05 M TBAB solution in 60:40
Fig. 6a illustrates a pulse amperometric response for series
of injections of standard lindane solution at a fixed potential
(pulse sequence (n)=5). Fig. 6a shows that when a fixed
potential was applied (-1.45 V) the signal current increased
relatively fast and no decrease of the signal was observed
during the pulse length (relative standard deviation ~ 1.02%),
suggesting very high reproducibility. After each measurement,
the electrode was rinsed thoroughly with deionized water and
was stored at room temperature when not in use and reactivated
by dipping in the supporting electrolyte for 30 minutes before
methanol–water (20 mL). The inset shows the calibration plot. DPV parameters
were selected as: peak height = 50 mV; peak width = 200 ms; peak period = 400
ms; increment = 20 mV; pre and post‐pulse width = 3 ms.
The sensing ability of the prepared α-MnO
electrode towards lindane was compared with the reported
nanostructures (Table S3, ESI†).
2
-NW modified
9,12,13,15,35-37
The performance of α-
MnO -NW nanostructures modified electrode is comparable if not
2
superior to those reported in the literature Table S3, ESI†. For the
practical use of non-enzymatic lindane sensors, specificity is another
important factor that needs attention. Under a rational design, the
designed lindane sensor should have minimal interferences from
water and soil samples from industrial areas and agricultural land. In
the present work, interfering compounds were picked based on
structural similarity and solubility in water and soil.
inorganic ions, electroactive organic compounds and organic
compounds containing chlorine groups were chosen which may
potentially interfere with determination of lindane.
amperometric response of the α-MnO -NW modified electrode to the
stepwise addition of lindane in the presence of 1 mM each of various
interfering species such as cyclohexane (CH), triclosan (T),
chlorobenzene (CB), and benzene (B) at an applied potential of -1.45
2
measurement. Furthermore, α-MnO -NW modified electrode
could be used more than 13 times after subsequent cycles of
washing and measuring operations. On the other hand, three
37-39
2
fresh fabricated α-MnO -NW modified electrodes were also
Therefore,
used for determining 50 µM lindane. The RSD was calculated
to be 2.71%. Therefore, our proposed lindane electrochemical
sensor has a satisfactory repeatability. We examined the current
37-39
The
2
stability for α-MnO -NW modified electrode by recording
2
amplitude of the pulse currents correspond to the addition of
lindane (200 µM) (Fig. 6b). The amplitude of the 40 pulse
currents display insignificant changes (<0.5%), indicating a
good stability of the α-MnO
storage stability was tested by storing the α-MnO
2
-NW modified electrode. The
-NW
V is shown in Fig. 4b. The α-MnO
excellent anti-interference behaviour towards interfering species
Fig. 4b). It may further be noted that when 150 times higher
2
-NW modified electrode shows
2
modified electrode for two weeks. The result showed that the
reduction peak potential of lindane had no shift and the current
response only showed 4.3% decrease compared with the
original test.
(
concentration of 4-CBA (0.5 M) and 1,3,5-TCB (0.5 M) interfere
with the determination of lindane (Fig. 5(a,b)). The results also
2+
2+
showed that 1 mM concentrations of inorganic ions (Ca , Co ,
2+
2+
2+
2+
Mg , Mn , Ni , and Zn ) did not interfere with the detection of
lindane (Fig. 5c).
(
a) 0
(b)
0
-2
0
.5 M
0.5 M
1,3,5-TCB
4
-CBA
-
-
-
2
5
7
(
a)0.25
-5

-MnO - NW
2
0
0
0
0
0
.20
.15
.10
.05
-7

-MnO - NT
-10
12
-10
-12
2

-MnO - MS
2
-
0
90
180
270
0
90 180 270 360
Time (s)
Time (s)
(
c) 30
.00
5
1
50 M Lindane
2+
Electrode
20
Ca
Co
Mn
Mg
(
b)
2+
5
0 M
CB B T CH
Lindane
10
0
2+
2+
1
50 M
0
Lindane
2+
Ni
2+
-
-
10
20
Zn
-5
-10
-30
0
5
10
15
20
-
15
Time (sec)
0
30
60
90 120 150 180
Time (s)
Fig. 5 Continuous amperometric response at the α‐MnO
2
‐NW modified electrode
in the presence of high concentration of interfering species, such as (a) 4‐
chlorobenzaldehyde (0.5 M), and (b) 1,3,5‐trichlorobenzene (0.5 M) as compared
to the addition of lindane (300 µM). (c) Pulsed amperometric response to 150
Fig. 4 (a) Comparison of the sensitivity for lindane at different modified
electrodes investigated in this study. (b) Continuous amperometric response at
the α‐MnO
2
‐NW modified electrode in the presence of high concentration of
µM lindane spiked with 1mM each of various metal ions at α‐MnO
2
‐NW modified
interfering species, such as chlorobenzene (1 mM), benzene (1 mM), triclosan (1
electrode (E = 0 V for 5 s; E = ‐1.45 V for 10 s and E = 0 V, for 5 s).
1
2
3
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Nanoscale
(
FACTS) in Nanyang Technological University for materials
characterizations.
To demonstrate the feasibility of sensor in practicable
application, the proposed sensor was applied to the
determination of lindane in tap water samples. No voltammetric
response corresponding to lindane was observed in tap water,
thus different quantity of lindane was added to the tap water
samples. Spiking method was adopted to evaluate the lindane
Notes and references
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2
2
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Paper
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