Electrochemical Determination of Chlorpyrifos on a Nano-TiO2

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Electrochemical Determination of Chlorpyrifos on a nano-TiO2/ C ellulose acetate Composite Modified Glassy Carbon Electrode Ammasai Kumaravel, and Maruthai Chandrasekaran J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b02057 • Publication Date (Web): 15 Jun 2015 Downloaded from http://pubs.acs.org on June 24, 2015

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Electrochemical Determination of Chlorpyrifos on a nano-TiO2/C ellulose acetate

2

Composite Modified Glassy Carbon Electrode

3

Ammasai Kumaravel1, and Maruthai Chandrasekaran*

4 5 6 7

CSIR-Central Electrochemical Research Institute (CECRI), Karaikudi-630006, Tamil Nadu, India 1PSG Institute of Technology and Applied Research, Coimbatore-641062, Tamil Nadu, India

8 9

A B S T R A C T: Rapid and simple method of determination of chlorpyrifos is important in

10

environmental monitoring and quality control. Electrochemical methods for the determination

11

of pesticides are fast, sensitive, reproducible and cost effective. The key factor in the

12

electrochemical methods is the choice of suitable electrode materials. The electrode materials

13

should have good stability, reproducibility, more sensitivity and easy method of preparation.

14

Mercury based electrodes have been widely used for the determination of chlorpyrifos. From

15

the environmental point of view mercury cannot be used. In this study a biocompatible nano

16

TiO2/cellulose acetate modified glassy carbon electrode was prepared by simple method and

17

used for the electrochemical sensing of chlorpyrifos in aqueous methanolic solution. Electro

18

analytical techniques such as Cyclic voltammetry, Differential Pulse voltammetry and

19

Amperometry were used in this work. This electrode showed very good stability,

20

reproducibility and sensitivity. A well defined peak was obtained for the reduction of

21

chlorpyrifos in Cyclic voltammetry and Differential pulse voltammetry.A smooth noise free

22

current response was obtained in Amperometric analysis.The peak current obtained was

23

proportional to the concentration of chlorpyrifos and was used to determine the unknown

24

concentration of chlorpyrifos in the samples. The analytical parameters such as LOD, LOQ

25

and Linear range were estimated. Analysis of real samples was also carried out. The results

26

were validated with the HPLC method. This composite electrode can be used as an

27

alternative to mercury electrodes reported in the literature. 1 ACS Paragon Plus Environment


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KEYWORDS: Chlorpyrifos, Biocompatible modified electrode, Electroanalytical sensor,

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Detection limits, Real sample analysis

30 31

INTRODUCTION

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Chlorpyrifos [o, o diethyl-o-(3, 5, 6-trichloro-2-pyridinyl) phosphorothioate] is an

33

organophosphate insecticide. It possesses low water solubility (1.39 mg / l) and high soil

34

sorption coefficient.

35

produce toxic effects by inhibiting the acetylcholinesterase enzyme activity, which is

36

responsible for the hydrolysis of acetylcholine, which is the key molecule in the control of

37

cholinergic transmission in the central and peripheral nervous system. It is used to control the

38

mosquitoes, flies, various insects and pests in the domestic and agricultural fields. It is also

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used on sheep and cattle to control ectoparasites1.The agricultural, residential and commercial

40

use of chlorpyrifos could lead to the accumulation of high concentration in the environment2.

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Chlorpyrifos persists in soil for 60-120 days and produces toxic effects to human beings and

42

animals3.Chlorpyrifos is a moderately toxic pesticide when compared to many other

43

pesticides4.However, long term health effects associated with human exposure to chlorpyrifos

44

is the subject of increasing concern in the recent years 5, 6. Many analytical methods such as

45

gas chromatography7,8, negative ion – chemical

46

spectrometry9and high performance liquid chromatography were developed for the

47

determination of organophosphorus pesticides 10.However, these analytical methods are time

48

consuming; high cost for making analysis and also the availability of these high cost

49

instruments in the laboratories are limited. So there is a need to develop a sensitive,

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economically viable, portable instrument for the analysis of this pesticide. Electro analytical

51

techniques are more suitable because of its various advantages like low cost, selective and

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sensitive responses within quick adsorption time, compact nature, easy handling and

Chlorpyrifos, like other organophosphate compounds, is known to

ionization gas chromatography, mass

2 ACS Paragon Plus Environment

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deployment in field trials. Even though electroanalytical techniques are more suitable for

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monitoring of toxic level of pesticides, unfortunately, less attention is paid for the

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development of electroanalytical sensor for the pesticides like chlorpyrifos.Very few on the

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electrochemical determination of chlorpyrifos works were reported. Indirect determination of

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chlorpyrifos using hanging mercury drop electrode (HMDE) by cathodic adsorptive stripping

58

voltammetry11,differential pulse polarographic analysis12, and adsorptive catalytic stripping

59

voltammetric determination using HMDE13 were reported. It is not advisable to use mercury

60

electrode due to its toxicity. Differential pulse adsorptive stripping voltammetric

61

determination of chlorpyrifos at a sepiolite modified carbon paste electrode was reported14.

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Electrochemical studies and square wave stripping voltammetry of chlorpyrifos on poly 3, 4-

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ethylenedioxythiophene modified wall – jet electrode were reported. The hydrodynamics of

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the wall jet electrode is complex15. Poly (3-hexylthiophene)/TiO2 based photoelectrochemical

65

sensing of chlorpyrifos16, surface molecular self-assembly strategy for molecular imprinting

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in electropolymerized polyaminothiophenol membranes at the surface of gold nanoparticles

67

modified glassy carbon electrode for the electrochemical detection of pesticide chlorpyrifos

68

were reported17. Anodic oxidation of chlorpyrifos using lead dioxide was also reported 18.

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The solubility of chlorpyrifos in water is very low and the analysis has to be carried out

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in toxic solvents like DMF. The reduction potential of chlorpyrifos on mercury based

71

electrodes is almost close to the hydrogen evolution potential which complicates the

72

estimation of sensing currents (peak currents).In this work we tried to overcome these

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disadvantages by developing a newer modified electrode for the sensing of chlorpyrifos.

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Due to the high affinity of nano TiO2 on phosphate groups, it was used as a sensor probe

75

along with nafion for the electrochemical sensing of organophosphate pesticide –

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fenitrothion1. Cellulose acetate (CA) is a porous material which is used to immobilize the

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enzymes, bacteria and metal nanoparticles. The advantages of cellulose acetate membrane are


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good stability in alcohol based electrolyte, biocompatibility, easy film forming properties and

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low cost

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material shows very attractive electro catalytic property and stability in sensor

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applications22,23.The nano TiO2/cellulose acetate is a complex material with no chemical

82

interaction between TiO2 particles and cellulose acetate and only physically mixed.However,

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very few reports were available in the literature using this composite modified electrode in

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sensor applications. Studies on the analysis of pesticides on this composite modified

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electrode were not reported in the literature.

20,21

.Titanium dioxide immobilised on a cellulose acetate membrane - a hybrid

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In this paper, we report the preparation, the characterisation and application of nano -

87

TiO2/cellulose acetate modified glassy carbon electrode (n-TiO2/CA/GCE) for the

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electrochemical sensing of chlorpyrifos. SEM was used for surface characterization. Cyclic

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voltammetry, differential pulse voltammetry and amperometry were used as sensing

90

techniques.

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EXPERIMENTAL PROCEDURES

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Apparatus.Cyclic

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Amperometry were performed with the computer controlled Autolab PGSTAT 30 (Eco

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Chemie, The Netherlands) electrochemical system. DPV was recorded with the following

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optimized instrumental settings: modulation amplitude 40 mV, modulation step 4 mV and the

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set scan rate is 8 mVs-1. For electrochemical experiments, a 10 ml glass cell with a

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TiO2/cellulose acetate coated glassy carbon electrode (GCE Alfa Aesar 3 mm dia) as the

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working electrode, platinum foil as the counter electrode and saturated calomel electrode

99

(SCE) as the reference electrode was used. SEM analysis was done with a Hitachi Model S-

100

3000H with 20 kV (acceleration voltage). HPLC analysis was carried out with an LC-10AT

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pump and SPD-10A detector (Shimadzu, Japan) at 254 nm with a Shimpack CLC ODS-18

votammetry

(CV),

Differential

pulse


votammetry

(DPV)

and

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column. Prior to electrochemical measurements, the solution was deareated by purging with

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pure nitrogen for 15 min. All electrochemical experiments were carried out at 30 +1oC.

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Reagents and Chemicals. Chlorpyrifos was purchased from AccuStandard, USA. A stock

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solution of chlorpyrifos (2424 µM) was prepared in methanol. Tetra-n-butyl ammonium

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bromide was purchased from Alfa Aesar and its 0.05 M solution was prepared in 60:40

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methanol /water (v/v). It was used as the solvent–supporting electrolyte system. The nano

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TiO2

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Titanium (IV) butoxide(10 gms) was dissolved in cyclohexanol solvent. To this solution,

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premixed solution containing water, cyclohexanol and hexadecyltrimethyl ammonium

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bromide was

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precipitate TiO2 powder.The TiO2 powder was separated, washed with acetone and dried in

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air at 353 K for 2 hrs.The dried powder was calcined at 773 K to give nano TiO2

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powder.Other reagents used were analytical reagent grade.

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Preparation of n-TiO2 /CA/GCE. The GC electrode was hand polished with the fine emery

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papers (1/0, 2/0, 3/0, 4/0), rinsed throughouly with Millipore water, cleaned successively in

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10% NaOH solution,1:1HNO3-water (v/v) and MeOH each for 2 min and dried in air25.

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Before modification of the GC electrode, the reproducibility of the bare GC electrode was

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checked with the recording of Cyclic voltammetric responses of Potassium ferrocyanide

120

/ferricyanide redox system in 0.1M KCl as reported in the literature26.

powder was prepared as follows and the details are available in the literature24 .

added

at

room temperature. After 12 hrs triethylamine was added to

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Cellulose acetate solution was prepared by following the procedure available in the

122

literature27,28.0.2 g of cellulose acetate was dissolved in solvents containing 12.7 ml of

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acetone, and 10.6 ml of cyclohexanone and stirred for 3 h to get homogenous solution.

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The modifier solution nTiO2/CA was prepared by mixing 4 mg of nano TiO2 powder

125

into the 4 ml of the above prepared cellulose acetate solution and stirred for 1 h.This solution

126

was used for modification of GC electrode. The GC electrode was coated with 8 micro litre



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of nTiO2/CA solution by drop–dry method. This 8 micro litre modifier solution contains 4.36

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micro litre acetone, 3.64 micro litre cyclohexanone, 8 nanogram TiO2 powder and 0.05264

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nanogram cellulose acetate. The coated GC electrode was dried in air for 3 h.A very thin film

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was seen on the GC surface. This modified nTiO2/CA/GCE was used for electrochemical

131

measurements.

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RESULTS AND DISCUSSION

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Surface Morphology of n-TiO2 /CA/GCE.SEM image of the composite modified GCE is

134

shown in Fig.1.From the figure, it can be seen that the composite film is uniformly covered

135

the surface of the GCE with pores and shrinking of the film. The nano Titania particles are

136

spread on the surface.

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Optimization of Modified Electrode Preparation.The volume of nano TiO2/cellulose

138

acetate solution used for modification of GCE surface was optimized by recording cyclic

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voltammetry of 50 µM chlorpyrifos in 0.05M on n-TiO2 /CA/GCE in TBAB 60:40 methanol/

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water (Fig.2).The peak current increases with the increase in the volume of nano

141

TiO2/cellulose acetate solution up to 8 µL. A further increase in the volume of nano

142

TiO2/cellulose composite solution on GCE, results decrease in the peak current value. This

143

may be due to the formation of thicker films, which may render the mass transport difficult.

144

So the optimum volume of 8 µL was used to modify the electrode surface.

145

Cyclic Voltammetric Analysis.Fig.3 shows the cyclic voltammetric response of 50 µM

146

chlorpyrifos at n-TiO2 /CA/GCE. The reduction peak is observed at around –1.55 V. This

147

peak is due to the electroreduction of - C=N of the pyridine ring of the chlorpyrifos via 2e-

148

transfer step as reported earlier11-13.

149 150 151

Cl Cl S C 2H 5 O

P

N

+

Cl

O

2e - +

2H +

C 2H 5 O C 2H 5 O

C 2H 5O

S P

HN Cl

O H Cl

Cl


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No peaks are observed on the reverse scan, which means that the reduction process is

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irreversible. The peak current increases with the increase in the scan rates and the

154

concentrations. A linear relationship between the peak currents and the square root of the

155

scan rates reveals that the reduction process is diffusion controlled. The reduction of C=N of

156

the pyridine ring is difficult and occurs very close to the hydrogen evolution region and

157

sometimes completely overlap with the background reduction i.e. hydrogen evolution.

158

However, the attachment of three chlorine atoms in the pyridine ring makes the delocalization

159

of electrons at the -C=N- bond and consequently, enhances the reduction of the -C=N- bond

160

of the pyridine ring at lesser negative potentials11.However, the studies on the direct

161

reduction of chlorpyrifos are limited. The reduction of chlorpyrifos was carried out on the

162

bare glassy carbon electrode (Fig.3a), cellulose acetate modified GCE (Fig.3b) and n-TiO2

163

/CA/GCE (Fig.3c). The n-TiO2 /CA/GCE gives high sensing current when compared to the

164

CA/ GCE and bare GCE. The presence of TiO2 nanoparticles in the cellulose acetate matrix

165

leads to the shift of hydrogen evolution nearly by 200 mV more cathodic region which

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improves the measurement of true sensing current of chlorpyrifos. The peak observed on bare

167

GCE is intimate to the hydrogen evolution potential. Cellulose acetate is a negatively charged

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membrane, which is a good matrix for the incorporation of TiO2 nanoparticles due to the

169

physical interaction of TiO2 nanoparticles with cellulose acetate29 which was confirmed by

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FT-IR analysis. Fig.4 shows the FTIR spectra of the CA, nano TiO2 and n-TiO2/CA

171

composites. The peaks are identified as follows: The broad peak at 3430 cm-1 is due to the -

172

OH stretching frequencies. The broad peak around 2900 cm-1 is due to the -C-H stretching

173

frequencies. The absorption peak around 1700 cm-1 is due to the C=O stretching

174

frequencies30,31.The -C-H bending vibration peak around 904 cm-1 and the -OH out plane

175

bending peak around 600 cm-1 with low intensity in the composite film (Fig. 4c). The IR

176

absorption peaks above 2000 cm-1 are intense and are composition dependent. All the three



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IR spectrum shows similar characteristics which demonstrate that the interaction between

178

titania particles and cellulose acetate film matrix is through physical adsorption and no

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chemical bonding.

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The presence of TiO2 in the cellulose acetate increases the sensing current of

181

chlorpyrifos, which is due to the electrocatalytic activity of TiO2 nanoparticles.The pores in

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the film may also contribute to the increase in the peak currents. Fig. 5 shows the effect of

183

various concentrations of chlorpyrifos on the peak current of chlorpyrifos. The peak current

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increases with the increase in the concentrations of chlorpyrifos range from 10 to 130 µM

185

(inset graph in Fig. 5). Limit of Detection (LOD) and Limit of Quntitation (LOQ) were

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calculated from the calibration graph constructed with concentration of chlorpyrifos in the x-

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axis and reduction current in the y-axis using the relation, LOD=3s/m; LOQ=10s/m where s

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is the standard deviation of the intercept and m is the slope of the calibration curve

189

limit of detection (LOD) is 4.4 µM and the limit of quantitation (LOQ) is 14.7 µM.

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Differential Pulse Voltammetric (DPV) Analysis. Typical differential pulse voltammetric

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curves at various concentrations of chlorpyrifos are shown in Fig.6.The peak current obtained

192

after subtracting the background current increases with the increase in the concentration of

193

chlorpyrifos. The peak current varies linearly with an increase in the concentration of

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chlorpyrifos ranges from 20 to 110 µM (inset graph in Fig. 6). The LOD and the LOQ values

195

are 3.5 µM and 11.7 µM respectively. The analytical parameters obtained on various

196

electrodes reported in the literature are presented in Table 1. Though the reduction potential

197

of chlorpyrifos on nano TiO2/cellulose acetate modified GCE is higher than the values

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reported on mercury based electrodes, from the environmental point view, mercury is not a

199

suitable material for sensing. The reduction potentials are comparable with the PEDOT

200

modified and carbon paste modified electrodes. The nano TiO2/cellulose acetate modified


32

.The

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GCE presented in this work is stable, reproducible and biocompatible and moreover the

202

preparation of the modified electrode is simple.

203

Amperometric Analysis.Fig.7 shows the amperometric response of chlorpyrifos at nano

204

TiO2/cellulose acetate modified GCE. It was recorded at constant potential of -1.5 V. The

205

reduction current increases for each addition of chlorpyrifos and the steady state current was

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measured. The peak current varies linearly with the increase in the concentration of

207

chlorpyrifos ranges from 20 to 340 µM (inset graph in Fig.7). The LOD and the LOQ values

208

are 11.8 µM and 39.2 µM respectively.

209

Reproducibility and Stability of n-TiO2 /CA/GCE.The electrochemical responses are

210

affected by the surface chemistry of carbon-oxygen functionalities present on GC electrode

211

and cleanliness i.e. absence of adsorbed impurities

212

polished with finer emery papers to remove the oxide layers and adsorbed impurities on the

213

electrode surface. Then GC electrode was throughouly washed with Millipore water to

214

remove the loosely adsorbed particles on GC surface. The GC electrode was further

215

chemically cleaned with NaOH, HNO3 and MeOH.The electron transfer rates of redox

216

reactions and reproducibility on GC electrode are controlled by the distribution of surface

217

oxides. The distribution of surface oxides were modified by exposing the GC electrode to

218

NaOH and HNO3.The surface of GC contains C-OH and C=O functional groups. The relative

219

density of these species varies with the chemical treatments with NaOH and HNO3.Treatment

220

with NaOH increases the surface coverage of C-OH and with HNO3 increases the surface

221

coverage of C=O. Methanol is less aggressive cleaning agent which desorbs the solution

222

impurities37,38.Bare GC electrode pretreated by the above methods gave reproducible

223

voltammetric responses for ferrocyanide/ferricyanide redox system in 0.1M KCl.Hence the

224

above pretreatment procedures was adopted in the present work.

33-36

.In the present work GC was hand



225

Firstly the reproducibility of the bare GC electrode pre-treated with emery papers and

226

chemical agents such as NaOH, HNO3 and MeOH was established by recording the cyclic

227

voltammetric responses of ferricyanide/ferrocyanide in 0.1M KCl26.The pretreatment

228

procedures used in this work was sufficient to give reproducible CV responses.The the

229

pretreated GC electrode was used for modification with n-TiO2/CA composite film.The

230

modified GC electrode was potentiostatically cycled from the rest potential to the hydrogen

231

evolution potential at slow sweep rates say 10 milli volts per second in supporting electrolyte

232

solution.After few cycles, the background current was stable and reproducible.Then cyclic

233

voltammograms were recorded for the reduction of chlorpyrifos on nTiO2/Ca/GCE.

234

Reproducibility of the electrochemical response of this electrode was checked by

235

carrying out series of 7 repetitive experiments for the fixed concentration of 50 µM

236

chlorpyrifos. The peak currents are reproducible with the relative standard deviation of

237

2.54%. The reproducible response of the modified electrode with respect to time was checked

238

(Fig. 8). After the modification, the same electrode was used for the sensing of chlorpyrifos

239

for fifteen days successively. The peak currents are reproducible with the relative standard

240

deviation of 5.3%. Stability of the electrode was also checked. After 40 cycles of cyclic

241

voltammetric scans, the peak current variation from the initial current is 2.8 % only. This

242

shows that the nano TiO2 / cellulose acetate film is highly stable and reproducible.

243

Interference Study. The interference study of several inorganic species and pesticides on the

244

reduction signal of 50 µM chlorpyrifos was carried out using cyclic voltammetry. The

245

concentration of the pesticides and the interfering ions were taken in 1:1 ratio. The inorganic

246

ions such as Ca2+, Mg2+, Na+, NH4+ and K+, which do not interfere the chlorpyrifos reduction

247

signal.

248

parathion, fenitrothion were also checked. These pesticides are reduced at around -700 mV

249

on n-TiO2/CA/GCE where as chlorpyrifos is reduced at around -1.55 V. The wide variation in

Possible interferences with the other nitroaromatic pesticides such as methyl


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the reduction potential makes the possibility of the determination of chlorpyrifos even in the

251

presence of these nitro pesticides. The possible interference of chlorocompounds such as

252

chlorophenol, chloroaniline, and chlorobenzene were also analyzed. The reduction of these

253

chlorocompounds is not observed on this electrode under the present experimental conditions

254

and these chlorocompounds do not show any interference in the sensing signal of

255

chlorpyrifos (Fig. 9).

256

Real Sample Analysis

257

Chlorpyrifos Spiked Water Analysis. The analytical utility of the above methods was

258

checked with the water sample, which was collected at the Central Electrochemical Research

259

Institute (CECRI) premises. It was tested for the presence of chlorpyrifos. Chlorpyrifos was

260

absent in the water sample. So 100 µM concentration of chlorpyrifos was spiked into the

261

water sample and was thoroughly shaken for one hour. Then it was extracted by using

262

dichloromethane. The small amount of anhydrous sodium sulphate was added to the extracted

263

sample to remove the traces of water. The solvent was slowly evaporated to get the residue.

264

The chlorpyrifos residue was dissolved in solvent supporting electrolyte and was used as

265

analyte for electrochemical experiments. The recovery rates obtained in electrochemical

266

techniques are summarized in Table 2. The results are compared with the HPLC method.

267

Commercial Sample Analysis.The commercial chlorpyrifos sample was analysed using

268

nano TiO2/cellulose acetate modified GCE as a sensor probe. 100 ml of commercial

269

chlorpyrifos was purchased from the local market which contains approximately 20% (v/v)

270

chlorpyrifos. The actual concentration of the commercial samples was determined using

271

HPLC technique and was taken as reference value. It was diluted to 100 µM. Then it was

272

used as an analyte in cyclic voltammetry, differential pulse voltammetry and amperometry to

273

verify the concentrations specified by the manufacturer. The concentration obtained in



274

electroanalytical techniques is given in Table 3. The results obtained in electroanalytical

275

techniques are comparable with the results obtained in the HPLC method.

276

Soil Analysis. The 10 ml of chlorpyrifos was taken from the 100 ml commercial chlorpyrifos

277

pack which contains 20% (v/v) chlorpyrifos and it was diluted to 1000 ml. Then this

278

pesticide was sprayed on the pomegranate tree using air sprayer. After one week the 112.6g

279

of soil under the pomegranate plant was collected and thoroughly grinded. Then it was

280

extracted as per the procedure explained above. The extracted sample was analysed by electro

281

analytical techniques and HPLC measurements. The data obtained in HPLC measurements is

282

taken as reference value.

283

comparable with the HPLC techniques (Table 4). So the electrochemical sensor using this

284

nano TiO2-cellulose acetate modified electrode is promising for the analysis of environmental

285

samples.

286

In this study a stable, reproducible and biocompatible nano TiO2/cellulose acetate modified

287

electrode was developed and was used for the analysis of chlorpyrifos. The presence of TiO2

288

nanoparticles increases the sensing current of chlorpyrifos, which enhances the sensitivity of

289

the sensor. Moreover, the presence of TiO2 nanoparticles in the cellulose acetate matrix shifts

290

the hydrogen evolution markedly, which improves the measurement of true sensing current of

291

chlorpyrifos. The modified electrode is highly stable with respect to time so that the electrode

292

once modified that can be used many times for the sensing of chlorpyrifos. The electrode

293

modification procedure outlined in this work is also simple. The nano-TiO2/cellulose acetate

294

film on the glassy carbon electrode surface is highly stable in alcoholic medium which makes

295

this physically mixed composite material suitable for the determination of chlorpyrifos in

296

alcoholic medium. This modified electrode replaces the mercury sensing electrode in the

297

determination of chlorpyrifos. The materials used in the preparation of the modified electrode

298

are cheap. The modified electrode can easily be renewed for subsequent analysis. The

The results obtained in electrochemical techniques are well


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analytical utility of the proposed method was checked in the spiked water sample and the

300

commercial sample.

301

Acknowledgment. The authors thank Department of Science and Technology, New Delhi,

302

India for financial support. One of the authors A. Kumaravel thanks Council of Scientific and

303

Industrial Research (CSIR), New Delhi, India for awarding Senior Research Fellowship

304

(SRF).

305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323



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trichloro-2-pyridinol residues in peppermint hay and peppermint oil.

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J. Agric. Food Chem. 1981,29, 321-323. (8) Oliva,J;Navarro,J.S; Barba,A; Navarro,G. Determination of

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chlorpyrifos,penconazole,fenarimol, vinclozolin and metalaxyl in grapes, must and

348

wine by on-line microextraction and gas chromatography. J. Chromatogr. A ,1999,

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833, 43-51. 14 ACS Paragon Plus Environment

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(9)

Brzak,K.A; Harms,D.W; Bartels ,M.J; Nolan,R.J. Determination of chlorpyrifos,

351

chlorpyrifos oxon, and 3,5,6-trichloro-2-pyridinol in rat and human blood. J. Anal. Toxicol.

352

1998,22 , 203-210.

353 354

(10) Mauldin,R.E;Primus,T.M; Buettgenbach,T.A; Johnston,J.J.A simple HPLC method

355

for the determination of chlorpyrifos in black oil sunflower seeds.

356 357 358

J. Liq. Chromatogr. R. T.,2006,29 , 339-348. (11) El-Shahawi ,M.S; Kamal.M.M,.Determination of the pesticide Chlorpyrifos by

359

cathodic adsorptive stripping voltammetry.Fresenius J. Anal. Chem. 1998,362 ,

360

344-347.

361 362 363

(12) Al-Meqbali,A.S.R; El-Shahawi,M.S;Kamal,M.M. Differential pulse polarographic analysis of chlorpyrifos insecticide. Electroanalysis ,1998 ,1,784-786. (13) Pelit,F.O; Ertas,H; Ertas,F.N. Development of an adsorptive catalytic stripping

364

voltammetric method for the determination of an endocrine disruptor pesticide

365

chlorpyrifos and its application to the wine samples. J. Appl. Electrochem. 2011,41

366

1279-1285.

367

(14) Sirisha,K; Mallipattu,S; Reddy,S.R.J; Differential pulse adsorptive stripping

368

voltammetric determination of chlorpyrifos at a sepiolite modified carbon paste

369

electrode. Anal. Lett. 2007,40, 1939-1950.

370

(15) Manisankar,P;Viswanathan,S; Pushpalatha,A.M;Rani,C. Electrochemical studies and

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square wave stripping voltammetry of five common pesticides on poly 3,4-

372

ethylenedioxythiophene modified wall-jet electrode.Anal. Chim. Acta ,2005 , 528, 157-

373

163.

374

(16) Li,H; Li,L; Xu,Q;Hu,X. Poly(3-hexylthiophene)/TiO2 nanoparticle-functionalized

375

electrodes for visible light and low potential photoelectrochemical sensing of

376

organophosphorus pesticide chlorpyrifos. Anal. Chem. ,2011,83,9681-9686. 15 ACS Paragon Plus Environment


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(17) Xie,C;Li,H;Li,S;Wu,J;Zhang,Z. Surface molecular self-assembly for organophosphate

379

pesticide imprinting in electropolymerized poly(p-aminothiophenol) membranes on a

380

gold nanoparticle modified glassy carbon electrode. Anal. Chem.,2010, 82 , 241-249.

381 382 383

(18) Samet,Y, Agengui,L, Abdelhedi,R. Anodic oxidation of chlorpyrifos in aqueous solution at lead dioxide electrodes. J. Electroanal. Chem, 2010,650 , 152-158. (19) Kumaravel,A; Chandrasekaran, M.A biocompatible nano TiO2/nafion composite

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modified glassy carbon electrode for the detection of fenitrothion,

385 386 387

J. Electroanal. Chem. 2010,650 , 163-170. (20) Kumaravel,A; Vincent,S ;Chandrasekaran, M.Development of an electroanalytical

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sensor for γ-hexachlorocyclohexane based on a cellulose acetate modified glassy

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carbon electrode. Anal. Methods,2013, 5,931-938.

390

(21) Wu,S ;Liu,J; Bai,X ; Tan, W. Stability improvement of prussian blue by a protective

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cellulose acetate membrane for hydrogen peroxide sensing in neutral media.

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Electroanalysis .2010,22 ,1906-1910.

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(22) Hoffmann, A.A;Dias, S.L.P; Benvenutti, E.V;Lima,E.C; Paavan, F.A;Rodrigues, J.R; Scotti, R; Ribeiro,E.S; Gushikem.Y.Cationic dyes immobilized on cellulose acetate

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surface modified with titanium dioxide:Factorial design and an application as sensor for

396

NADH. J. Braz. Chem. Soc. 2007,18, 1462-1472.

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(23) Hoffmann,A.A; Dias, S.L.P;Rodrigues, J.R; Paavan,F.A; Benvenutti, E.V; Lima, E.C;

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Methylene blue immobilized on cellulose acetate with titanium dioxide: an application as

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sensor for ascorbic acid. J. Braz. Chem. Soc, 2008,19 , 943-949.

400

(24) Kamalan Kirubakaran,A.M; Selvaraj,M; Maruthan, K; Jeyakumar,D. Synthesis and

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characterization of nanosized titanium dioxide and silicon dioxide for corrosion

402

resistance applications. J. Coat. Technol. Res, 2012,9 , 163-170.


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(25) Xu,C;Wu,K;Hu,S; Cui,D.Electrochemical detection of parathion at a glassy carbon

404

electrode modified with hexadecane.Anal Bioanal.Chem,2002,373,284-288.

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(26) Noel,M;Anantharaman,P.N.Voltammetric studies on a glassy carbon electrode.Part

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K4[Fe(CN)6] system. Analyst,1985,110,1095-1103.

408

(27) Wang,J; Golden,T;Li,R.Cobalt/phthalocyanine/cellulose acetate chemically modified

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electrodes for electrochemical detection in flow streams.Multifunctional operation

410

based upon the coupling of electrocalalysis and permeability.

411

Anal.Chem,1988,60,1642-1645.

412

(28) Wu,S;Liu,J;Bai,X.W.Stability improvement of Prussian Blue by a protective cellulose

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acetate membrane for Hydrogen peroxide sensing in neutral media .

414

Elecroanalysis,2010,22,1906-1910.

415

(29) Jin,X;Xu,J;Wang,X;Xie,Z;Liu,Z;Liang,B;Chen,D;Shen,Gouzhen.

416

Flexible TiO2/cellulose acetate hybrid film as a recyclable photocatalyst.

417

RSC Adv,2014,4,12640-12648.

418 419 420 421 422 423 424 425 426 427 428

(30) Ilharco, L.M; Brito de Barros,R. Aggregation of pseudoisocyanine iodide in celluloseacetate films: Structural characterization by FTIR . Langmuir ,2000, 16, 93319337. (31) Ugur,S.S;Sariisik, M; Aktas,A.H. Nano-TiO2 based multilayer film deposition on cotton fabrics for UV-protection. Fiber. Polym,2011,12 , 190-196. (32) Skoog, D;Holler,K;Nieman, T.Principles of Instrumental Analysis 5th Ed,Harrcourt Brace College Publishers,Orlando Florida,1998,13,14.

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(33) Ray III,K.G;Mc Creery,R.L.Characterisation of the surface carbonyl and hydroxyl

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coverage on glassy carbon electrodes using Raman Spectroscopy.J.Electroanal.Chem,

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1999,469,150-158.

435

(34) Mc Creery,R.L.Electrochemical properties of carbon surfaces , Interfacial Chemistry,

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A. Wiechowski,Editor,Dekkar NY .1999, Chapter 35,631-643.

437

(35) Chen, P;Mc Creery,R.L. Control of electron transfer kinetics at Glassy carbon

438

electrodes by specific surface modifications.Anal.Chem,1996,68,3938-3965.

439

(36) Ping,W.X;Lan,Z;Wen-Rong,L; Ping,D.J;QingC.H;Nan,C.G.Study on the interfacial

440 441

behavior of Melatonin with an activated electrode,Electroanalysis, 2012,14,1654-1660. (37) Braga,O.Comprestrini,C.I;Vieira,I.C;A.Spinelli,Sulfadiazine determination in

442

pharmaceuticals by electrochemical reduction on a glassy carbon electrode.

443

J.Braz.Chem Soc,2010,21,813-820.

444

(38)

Jain,R;Sharma,S. Glassy carbon electrode modification with multiwalled

445

carbon nanotubes sensor for the quantification of antihistamin drug phenaramine in

446

solubilised systems.J.Pharmaceutical Analysis,2012,1,56-61.

447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462


Page 18 of 35

Page 19 of 35


463

AUTHOR INFORMATION

464

Corresponding Author

465

Maruthai Chandrasekaran received his Ph.D degree in chemistry in 1989 from Madurai

466

Kamaraj University, Madurai, India. He is a Senior Principal Scientist at Central

467

Electrochemical Research Institute, Karaikudi-630006, India.His field of interests are

468

electrochemical sensors, electro organic synthesis and combinatorial electrochemistry.

469

Tel.: +91 4565 241552; fax: +91 4565 227779, 227713

470

E-mail address: [email protected].

471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487



Page 20 of 35

`

488

489

Table 1. Comparison of Analytical Parameters on Various Modified Electrodes

Method

Electrode a

Linear range

LOD

LOQ

Ref.

DPASV

HMDE (-1.2 V)

9.9x10-8 to 5.96x10-7 M

9.9x10-8 M

-

[11]

DPV

HMDE (-1.2 V)

5.7x10-8 to 28.5x10-8 M

4.0x10-10 M

1.2x10-9 M

[13]

Cyclic voltammetry

PEDOT/GCE (-1.6 V)

10x10-10 to 7x10-7 M

8x10-10 M

-

[15]

DPP

DME (-1.2V)

8.7x10-7 M

-

[12]

DPAdSV

CMCPE (-1.2V)

2.8x10−10 to 5.7x10−6 M

2.2x10−10 M

-

[14]

Cyclic voltammetry

TiO2/CA/GCE (-1.5V)

10.0x10−6 to 130x10−6 M

4.4x10−6 M

14.7 x10-6 M

Present work

DPV

TiO2/CA/GCE (-1.5V)

20.0x10−6 to 110x10−6 M

3.5x10−6 M

11.7x10-6 M

Present work

Amperometry

TiO2/CA/GCE

11.8 x10−6 M

39.2x10-6 M

Present work

a

9.7x10-7 to 6.9x10-6 M

20.0x10−6 to 340x10−6 M

The value given in the bracket is the reduction potential

490 491 492 493 494 495 496 20 ACS Paragon Plus Environment

Page 21 of 35


497

Table 2. Recovery Study of Chlorpyrifos in Spiked Water Samples a

498 (µM)

Amount recovered (µM) + SDa

Recovery rate (%)

Cyclic voltammetry

100

91.84±0.18

91.84

Differential pulse voltammetry

100

96.28± 0.11

96.28

Amperometry

100

96.46± 0.01

96.46

HPLC

100

98.80±0.08

98.80

Amount added

Method

499

number of sample analyzed is 6

500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 21 ACS Paragon Plus Environment


515 516

Table 3. Commercial Sample Analysis

517 518

Conc % a,b

Method

(V/V)

519

Cyclic voltammetry

17.5±0.50

Differential pulse

18.00±0.09

520 521

voltammetry

522 523 524 525 526 527 528

a b

Amperometry

16.5±0.08

HPLC

18.61±0.10

Conc. specified by the manufacturer is approximately 20 %(v/v) number of sample assayed is 6

529 530 531 532 533 534 535 536 537 538 539 540 541 22 ACS Paragon Plus Environment

Page 22 of 35

Page 23 of 35


542

Table 4. Soil Sample Analysis

543 544

Electroanalytical

Concentration

545

techniques

(µM)a,b

546

CV

91.62±0.31

547

DPV

91.64±0.23

548

Amp

102±0.12

549

HPLC

99.6±0.08

550 551 552 553

a b

number of sample analysed is 6 Total weight of the soil is 112.6 g

554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 23 ACS Paragon Plus Environment


Page 24 of 35

`

569

Figure captions

570 571 572

Fig. 1 SEM image of n-TiO2 /CA/GCE Fig. 2 Effect of volume of nano TiO2/cellulose acetate composite solution on the

573

peak current of 50 µM chlorpyrifos in 60:40(v/v) methanol/ water containing 0.05M

574

TBAB at 100 mVs-1.

575

Fig. 3 Cyclic voltammograms of 50 µM chlorpyrifos at (a) bare GCE, (b)

576

cellulose acetate modified GCE and (c) n-TiO2 /CA/GCE in

577

TBAB 60:40 (v/v) methanol /water containing 0.05M TBAB at 100 mVs-1.

578

Fig. 4 FTIR spectra of (a) cellulose acetate (b) nano TiO2, (c) nano TiO2/cellulose

579 580

0.05 M

acetate composite. Fig. 5 Influence of various concentrations of

chlorpyrifos on

the peak current:

581

a) 10 b) 30 c) 50 d) 70 e) 90 f) 110 g) 130 h) 150 i) 170 j) 190 k) 210 and l)

582

230 µM at nano TiO2/ cellulose acetate modified GCE in 60:40(v/v)

583

methanol / water containing 0.05M TBAB at 100 mVs-1. Inset shows the calibration

584

graph.

585 586 587 588 589

Fig. 6 Differential

pulse voltammetric response of

various concentrations

of chlorpyrifos a) 20 b) 30 c) 40 d) 50 e) 80 and f) 110 µM at nano TiO2 /cellulose acetate modified GCE in 60:40 (v/v) methanol /water containing 0.05M TBAB. Inset shows the calibration graph. Fig. 7 Amperometric response of chlorpyrifos for the constant addition of 20 µM at

590

nano TiO2 /cellulose acetate modified GCE in 60:40(v/v) methanol /water

591

containing 0.05M TBAB.Inset shows the calibration graph.

592

Fig. 8 Stablity of the n-TiO2 /CA/GCE electrode over time for the addition of 50 µM

593

chlorpyrifos in 60:40(v/v) methanol/water containing 0.05 M TBAB at 100

594

mVs-1.


Page 25 of 35


595

Fig. 9 Interference study of various inorganic metal ions and pesticides on the

596

reduction signal of 50 µM

chlorpyrifos at n-TiO2 /CA/GCE in

597

60:40(v/v) methanol/water containing 0.05M TBAB at 100 mVs-1.

598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619



620

Figure.1

621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643


Page 26 of 35

Page 27 of 35


644

Figure. 2

645 646

-8.0

647 -7.5

648 649

-7.0

651

i / µΑ

650 -6.5

652 653 654

-6.0

-5.5

655 656 657

-5.0 4

6

8

10

Volume of nano TiO2/cellulose acetate solution in µL

658 659 660 661 662 663 664 665 666 667 668


12


Page 28 of 35

`

669

Figure. 3

670 671 672 673

-16

674

-14

675

c

-12

676

b a

-10

677

i / µΑ

-8

678 -6

679 -4

680 681 682 683 684

-2 0 2 -1.0

-1.1

-1.2

-1.3

-1.4

-1.5

E/V

685 686 687 688 689 690 691 692 693


-1.6

Page 29 of 35


694

Figure. 4

695 696 697 698

c

699

700

transmittance(%)

b

701

-CH str

702 904

OH Str

-OH out plane bending peak

705

904

a

706

904

707 708

4000

3000

2000

1000 -1

709

wavenumber(cm )

710 711 712 713 714 715 716 717 718


703 704 604

604


Page 30 of 35

`

719

Figure. 5

720 721 722 723

-30

724

-14 -12

725 i / µA

-10

-20

726

-8 -6

g

-4

727

i / µΑ

-2 0

0

20

40

60

80

100

120

140

C / µΜ

-10

728 a

729 730 0

731 732

-1.1

-1.2

-1.3

-1.4

-1.5

-1.6

E/V

733 734 735 736 737 738 739 740 741 742 743


-1.7

Page 31 of 35


744

Figure. 6

745 746 747

-5

-7

-4

748

e

750

i / µΑ

-3

-6

749

i / µΑ

-5

-2

-1

0 0

20

40

-4

60

80

100

751

120

C / µΜ

752 -3

753

a -2

754 755

-1 -1.35

756

-1.40

-1.45

-1.50

-1.55

-1.60

E/V

757 758 759 760 761 762 763 764 765 766 767 768


-1.65


769

Figure. 7

770 771 772 773

0 20 µΜ

774 -3

775

-6

776

-9

777

-7

-6

-12

779

i / µΑ

i / µΑ

-8

778

-5

-4

780

-15

781

-18

-3

-2 0

100

200

300

400

500

600

700

t/s

782 200

783

400

600

800

t/s

784 785 786 787 788 789 790 791 792 793


Page 32 of 35

Page 33 of 35


794

Figure. 8

795 796 797

-50

798

-40

799

-30

800 i / µΑ

801

-20

-10

802 0

803 10

804 20

805 806

0

2

4

6

8

10

12

14

no. of days

807 808 809 810 811 812 813 814 815 816 817 818


16


Page 34 of 35

`

819

Figure. 9

820 -7

821 822

-6

823 -5

824 825

i / µΑ

-4

826 -3

827 828

-2

829

-1

830 +

Na

+

NH4

+

K

831

itr ot hi ch on lo ro ph en ch ol lo ro an ch ili ne lo ro be nz en e

2+

Mg

pa ra hi on fe n

2+

Ca

m et hy l

832

Ch lo r

py rif os

0

833 834 835 836 837 838 839 840 841 842 843


Page 35 of 35


844

TOC Graphic

845 Nano TiO2/Cellulose acetate

-1 6 -1 4 -1 2 -1 0

C l

i /µΑ µΑ µΑ µΑ

846

-8 -6 -4

C

847

H

2

C

O

5

H

2

S

-2

N

0 2 - 1 .0

P

- 1 .1

- 1 .2

- 1 .3

C l

O

- 1 .4

- 1 .5

-1 . 6

E / V

O

5

-7

-6

C l

-5


848

2e

-

Chlorpyrifos

-4

-3

-2

C l

-1 - 1 .3 5

- 1 .4 0

- 1 .4 5

- 1 .5 0

- 1 .5 5

- 1 .6 0

- 1 .6 5

E / V

2

H

5

O

P

H N -2

C l

O

-3 -4

C

2

H

5

O

-5

H


849

C

S

-6 -7 -8

C l

850

-9 -1 0 -1 1 2 0 0

4 00

6 0 0

t/ s

851 852 853 854 855


8 00

10 0 0

Electrochemical Determination of Chlorpyrifos on a Nano-TiO2

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