Article pubs.acs.org/JAFC
Electrochemical Determination of Chlorpyrifos on a Nano-TiO2/ Cellulose Acetate Composite Modified Glassy Carbon Electrode Ammasai Kumaravel§ and Maruthai Chandrasekaran*,† †
CSIR−Central Electrochemical Research Institute (CECRI), Karaikudi 630006, Tamil Nadu, India PSG Institute of Technology and Applied Research, Coimbatore 641062, Tamil Nadu, India
§
ABSTRACT: A rapid and simple method of determination of chlorpyrifos is important in environmental monitoring and quality control. Electrochemical methods for the determination of pesticides are fast, sensitive, reproducible, and cost-effective. The key factor in electrochemical methods is the choice of suitable electrode materials. The electrode materials should have good stability, reproducibility, more sensitivity, and easy method of preparation. Mercury-based electrodes have been widely used for the determination of chlorpyrifos. From an environmental point of view mercury cannot be used. In this study a biocompatible nanoTiO2/cellulose acetate modified glassy carbon electrode was prepared by a simple method and used for the electrochemical sensing of chlorpyrifos in aqueous methanolic solution. Electroanalytical techniques such as cyclic voltammetry, differential pulse voltammetry, and amperometry were used in this work. This electrode showed very good stability, reproducibility, and sensitivity. A well-defined peak was obtained for the reduction of chlorpyrifos in cyclic voltammetry and differential pulse voltammetry. A smooth noise-free current response was obtained in amperometric analysis. The peak current obtained was proportional to the concentration of chlorpyrifos and was used to determine the unknown concentration of chlorpyrifos in the samples. Analytical parameters such as LOD, LOQ, and linear range were estimated. Analysis of real samples was also carried out. The results were validated through HPLC. This composite electrode can be used as an alternative to mercury electrodes reported in the literature. KEYWORDS: chlorpyrifos, biocompatible modified electrode, electroanalytical sensor, detection limits, real sample analysis
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INTRODUCTION Chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridinyl)phosphorothioate] is an organophosphate insecticide. It possesses low water solubility (1.39 mg/L) and a high soil sorption coefficient. Chlorpyrifos, like other organophosphate compounds, is known to produce toxic effects by inhibiting the acetylcholinesterase enzyme activity, which is responsible for the hydrolysis of acetylcholine, which is the key molecule in the control of cholinergic transmission in the central and peripheral nervous system. It is used to control mosquitoes, flies, various insects, and pests in domestic and agricultural fields. It is also used on sheep and cattle to control ectoparasites.1 The agricultural, residential, and commercial use of chlorpyrifos could lead to the accumulation of high concentrations in the environment.2 Chlorpyrifos persists in soil for 60−120 days and produces toxic effects to human beings and animals.3 Chlorpyrifos is a moderately toxic pesticide when compared to many other pesticides.4However, long-term health effects associated with human exposure to chlorpyrifos are the subject of increasing concern in recent years.5,6 Many analytical methods such as gas chromatography,7,8 negative ion chemical ionization gas chromatography, mass spectrometry,9 and high-performance liquid chromatography were developed for the determination of organophosphorus pesticides.10 However, these analytical methods are timeconsuming and costly, and also the availability of these highcost instruments in laboratories is limited. Therefore, there is a need to develop a sensitive, economically viable, portable instrument for the analysis of this pesticide. Electroanalytical techniques are more suitable because of their various advantages such as low cost, selective and sensitive responses © 2015 American Chemical Society
within quick adsorption times, compact nature, and easy handling and deployment in field trials. Even though electroanalytical techniques are more suitable for monitoring the toxic level of pesticides, unfortunately, less attention is paid to the development of electroanalytical sensors for pesticides such as chlorpyrifos. Very few works on the electrochemical determination of chlorpyrifos have been reported. Indirect determination of chlorpyrifos using a hanging mercury drop electrode (HMDE) by cathodic adsorptive stripping voltammetry,11 differential pulse polarographic analysis,12 and adsorptive catalytic stripping voltammetric determination using HMDE13 was reported. It is not advisable to use mercury electrodes due to their toxicity. Differential pulse adsorptive stripping voltammetric determination of chlorpyrifos at a sepiolite modified carbon paste electrode was reported.14 Electrochemical studies and square wave stripping voltammetry of chlorpyrifos on a poly(3,4-ethylenedioxythiophene)-modified wall-jet electrode were reported. The hydrodynamics of the wall-jet electrode is complex.15 Poly(3-hexylthiophene)/TiO2based photoelectrochemical sensing of chlorpyrifos16 and a surface molecular self-assembly strategy for molecular imprinting in electropolymerized polyaminothiophenol membranes at the surface of a gold nanoparticle-modified glassy carbon electrode for the electrochemical detection of pesticide chlorpyrifos were reported.17 Anodic oxidation of chlorpyrifos using lead dioxide was also reported.18 Received: Revised: Accepted: Published: 6150
April 30, 2015 June 9, 2015 June 15, 2015 June 15, 2015 DOI: 10.1021/acs.jafc.5b02057 J. Agric. Food Chem. 2015, 63, 6150−6156
Article
Journal of Agricultural and Food Chemistry
Preparation of n-TiO2 /CA/GCE. The GC electrode was hand polished with fine emery papers (1/0, 2/0, 3/0, 4/0), rinsed thoroughly with Millipore water, cleaned successively in 10% NaOH solution, 1:1 HNO3/water (v/v), and MeOH, each for 2 min, and dried in air.25 Before modification of the GC electrode, the reproducibility of the bare GC electrode was checked with the recording of cyclic voltammetric responses of a potassium ferrocyanide/ferricyanide redox system in 0.1 M KCl as reported in the literature.26 Cellulose acetate solution was prepared by following the procedure available in the literature.27,28 Cellulose acetate (0.2 g) was dissolved in solvents containing 12.7 mL of acetone and 10.6 mL of cyclohexanone and stirred for 3 h to get a homogeneous solution. The modifier solution n-TiO2/CA was prepared by mixing 4 mg of nano-TiO2 powder into 4 mL of the above prepared cellulose acetate solution and stirred for 1 h. This solution was used for modification of the GC electrode. The GC electrode was coated with 8 μL of n-TiO2/ CA solution by the drop−dry method. This 8 μL modifier solution contains 4.36 μL of acetone, 3.64 μL of cyclohexanone, 8 ng of TiO2 powder, and 0.05264 ng of cellulose acetate. The coated GC electrode was dried in air for 3 h. A very thin film was seen on the GC surface. This modified n-TiO2/CA/GCE was used for electrochemical measurements.
The solubility of chlorpyrifos in water is very low, and the analysis has to be carried out in toxic solvents such as DMF. The reduction potential of chlorpyrifos on mercury-based electrodes is almost close to the hydrogen evolution potential, which complicates the estimation of sensing currents (peak currents). In this work we tried to overcome these disadvantages by developing a newer modified electrode for the sensing of chlorpyrifos. Due to the high affinity of nano-TiO2 on phosphate groups, it was used as a sensor probe along with nafion for the electrochemical sensing of the organophosphate pesticide fenitrothion.19 Cellulose acetate (CA) is a porous material that is used to immobilize the enzymes, bacteria, and metal nanoparticles. The advantages of CA membrane are good stability in alcohol-based electrolyte, biocompatibility, easy filmforming properties, and low cost.20,21 Titanium dioxide immobilized on a cellulose acetate membrane, a hybrid material, shows a very attractive electrocatalytic property and stability in sensor applications.22,23 Nano-TiO2/cellulose acetate is a complex material with no chemical interaction between TiO2 particles and cellulose acetate, which are only physically mixed. However, very few studies were available in the literature using this composite modified electrode in sensor applications. Studies on the analysis of pesticides on this composite modified electrode were not reported in the literature. In this paper, we report the preparation, characterization, and application of a nano-TiO2/cellulose acetate modified glassy carbon electrode (n-TiO2/CA/GCE) for the electrochemical sensing of chlorpyrifos. SEM was used for surface characterization. Cyclic voltammetry, differential pulse voltammetry, and amperometry were used as sensing techniques.
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RESULTS AND DISCUSSION Surface Morphology of n-TiO2/CA/GCE. An SEM image of the composite modified GCE is shown in Figure 1. From the
EXPERIMENTAL PROCEDURES
Apparatus. Cyclic votammetry (CV), differential pulse votammetry (DPV), and amperometry were performed with the computercontrolled Autolab PGSTAT 30 (Eco Chemie, Utrecht, The Netherlands) electrochemical system. DPV was recorded with the following optimized instrumental settings: modulation amplitude, 40 mV; modulation step, 4 mV; and set scan rate, 8 mV s−1. For electrochemical experiments, a 10 mL glass cell with a TiO2/cellulose acetate coated glassy carbon electrode (GCE Alfa Aesar, 3 mm diameter) as the working electrode, platinum foil as the counter electrode, and saturated calomel electrode (SCE) as the reference electrode was used. SEM analysis was done with a Hitachi model S3000H with 20 kV acceleration voltage. HPLC analysis was carried out with an LC-10AT pump and an SPD-10A detector (Shimadzu, Kyoto, Japan) at 254 nm with a Shimpack CLC ODS-18 column. Prior to electrochemical measurements, the solution was deareated by purging with pure nitrogen for 15 min. All electrochemical experiments were carried out at 30 ± 1 °C. Reagents and Chemicals. Chlorpyrifos was purchased from AccuStandard, New Haven, CT, USA. A stock solution of chlorpyrifos (2424 μM) was prepared in methanol. Tetra-n-butyl ammonium bromide was purchased from Alfa Aesar, and its 0.05 M solution was prepared in 60:40 methanol/water (v/v). It was used as the solvent− supporting electrolyte system. The nano-TiO2 powder was prepared as follows, and the details are available in the literature.24 Titanium(IV) butoxide (10 g) was dissolved in cyclohexanol solvent. To this solution a premixed solution containing water, cyclohexanol, and hexadecyltrimethylammonium bromide was added at room temperature. After 12 h, triethylamine was added to precipitate TiO2 powder. The TiO2 powder was separated, washed with acetone, and dried in air at 353 K for 2 h. The dried powder was calcined at 773 K to give nano-TiO2 powder. Other reagents used were of analytical reagent grade.
Figure 1. SEM image of n-TiO2/CA/GCE.
figure, it can be seen that the composite film uniformly covered the surface of the GCE with pores and shrinking of the film. The nano-titania particles are spread on the surface. Optimization of Modified Electrode Preparation. The volume of nano-TiO2/cellulose acetate solution used for modification of the GCE surface was optimized by recording cyclic voltammetry of 50 μM chlorpyrifos in 0.05 M on nTiO2/CA/GCE in TBAB 60:40 methanol/water (Figure 2). The peak current increases with the increase in the volume of nano-TiO2/cellulose acetate solution up to 8 μL. A further increase in the volume of nano-TiO2/cellulose composite solution on GCE results in a decrease in the peak current value. This may be due to the formation of thicker films, which may render the mass transport difficult, so the optimum volume of 8 μL was used to modify the electrode surface. Cyclic Voltammetric Analysis. Figure 3 shows the cyclic voltammetric response of 50 μM chlorpyrifos at n-TiO2/CA/ 6151
DOI: 10.1021/acs.jafc.5b02057 J. Agric. Food Chem. 2015, 63, 6150−6156
Article
Journal of Agricultural and Food Chemistry
root of the scan rates reveals that the reduction process is diffusion controlled. The reduction of CN of the pyridine ring is difficult and occurs very close to the hydrogen evolution region and sometimes completely overlaps with the background reduction, that is, hydrogen evolution. However, the attachment of three chlorine atoms in the pyridine ring delocalizes the electrons at the −CN− bond and, consequently, enhances the reduction of the −CN− bond of the pyridine ring at lesser negative potentials.11 However, studies on the direct reduction of chlorpyrifos are limited. The reduction of chlorpyrifos was carried out on the bare glassy carbon electrode (Figure 3a), cellulose acetate modified GCE (Figure 3b), and nTiO2/CA/GCE (Figure 3c). The n-TiO2/CA/GCE gives a high sensing current when compared to the CA/GCE and bare GCE. The presence of TiO2 nanoparticles in the cellulose acetate matrix leads to the shift of hydrogen evolution nearly by 200 mV more cathodic region, which improves the measurement of true sensing current of chlorpyrifos. The peak observed on bare GCE is close to the hydrogen evolution potential. Cellulose acetate is a negatively charged membrane, which is a good matrix for the incorporation of TiO2 nanoparticles due to the physical interaction of TiO2 nanoparticles with cellulose acetate,29 which was confirmed by FT-IR analysis. Figure 4
Figure 2. Effect of volume of nano-TiO2/cellulose acetate composite solution on the peak current of 50 μM chlorpyrifos in 60:40 (v/v) methanol/water containing 0.05 M TBAB at 100 mV s−1.
Figure 3. Cyclic voltammograms of 50 μM chlorpyrifos at (a) bare GCE, (b) cellulose acetate modified GCE, and (c) n-TiO2/CA/GCE in 0.05 M TBAB 60:40 (v/v) methanol/water containing 0.05 M TBAB at 100 mV s−1.
Figure 4. FTIR spectra of (a) cellulose acetate, (b) nano-TiO2, and (c) nano-TiO2/cellulose acetate composite.
GCE. The reduction peak is observed at around −1.55 V. This peak is due to the electroreduction of −CN of the pyridine ring of the chlorpyrifos via a 2e− transfer step as reported earlier.11−13
shows the FTIR spectra of the CA, nano-TiO2, and n-TiO2/CA composites. The peaks are identified as follows: The broad peak at 3430 cm−1 is due to the −OH stretching frequencies. The broad peak around 2900 cm−1 is due to the −C−H stretching frequencies. The absorption peak around 1700 cm−1 is due to the CO stretching frequencies.30,31 The −C−H bending vibration peak around 904 cm−1 and the −OH out-of-plane bending peak around 600 cm−1 are of low intensity in the composite film (Figure 4c). The IR absorption peaks above 2000 cm−1 are intense and are composition dependent. All three IR spectra show similar characteristics, which demonstrates that the interaction between titania particles and cellulose acetate film matrix is through physical adsorption and not chemical bonding. The presence of TiO2 in the cellulose acetate increases the sensing current of chlorpyrifos, which is due to the electrocatalytic activity of TiO2 nanoparticles. The pores in the film may also contribute to the increase in the peak currents. Figure
No peaks are observed on the reverse scan, which means that the reduction process is irreversible. The peak current increases with the increase in the scan rates and the concentrations. A linear relationship between the peak currents and the square 6152
DOI: 10.1021/acs.jafc.5b02057 J. Agric. Food Chem. 2015, 63, 6150−6156
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Journal of Agricultural and Food Chemistry
concentration of chlorpyrifos. The peak current varies linearly with an increase in the concentration of chlorpyrifos from 20 to 110 μM (inset in Figure 6). The LOD and the LOQ values are 3.5 and 11.7 μM, respectively. The analytical parameters obtained on various electrodes reported in the literature are presented in Table 1. Although the reduction potential of chlorpyrifos on nano-TiO2/cellulose acetate modified GCE is higher than the values reported on mercury-based electrodes, from an environmental point of view, mercury is not a suitable material for sensing. The reduction potentials are comparable with the PEDOT modified and carbon paste modified electrodes. The nano-TiO2/cellulose acetate modified GCE presented in this work is stable, reproducible, and biocompatible and, moreover, the preparation of the modified electrode is simple. Amperometric Analysis. Figure 7 shows the amperometric response of chlorpyrifos at nano-TiO2/cellulose acetate modified GCE. It was recorded at a constant potential of −1.5 V. The reduction current increases for each addition of chlorpyrifos, and the steady state current was measured. The peak current varies linearly with the increase in concentration of chlorpyrifos from 20 to 340 μM (inset in Figure 7). The LOD and the LOQ values are 11.8 and 39.2 μM, respectively. Reproducibility and Stability of n-TiO2/CA/GCE. The electrochemical responses are affected by the surface chemistry of carbon−oxygen functionalities present on the GC electrode and cleanliness, that is, the absence of adsorbed impurities.33−36 In the present work GC was hand polished with finer emery papers to remove the oxide layers and adsorbed impurities on the electrode surface. Then the GC electrode was throughouly washed with Millipore water to remove the loosely adsorbed particles on the GC surface. The GC electrode was further chemically cleaned with NaOH, HNO3, and MeOH. The electron transfer rates of redox reactions and reproducibility on the GC electrode are controlled by the distribution of surface oxides. The distribution of surface oxides was modified by exposing the GC electrode to NaOH and HNO3. The surface of GC contains COH and CO functional groups. The relative density of these species varies with the chemical treatments with NaOH and HNO3. Treatment with NaOH increases the surface coverage of COH and with HNO3 increases the surface coverage of CO. Methanol is a less aggressive cleaning agent, which desorbs the solution impurities.37,38 Bare GC electrodes pretreated by the above methods gave reproducible voltammetric responses for the ferrocyanide/ferricyanide redox system in 0.1 M KCl. Hence, the above pretreatment procedures were adopted in the present work. First, the reproducibility of the bare GC electrode pretreated with emery papers and chemical agents such as NaOH, HNO3, and MeOH was established by recording the cyclic voltammetric responses of ferricyanide/ferrocyanide in 0.1 M KCl.26 The pretreatment procedures used in this work were sufficient to give reproducible CV responses. The pretreated GC electrode was used for modification with n-TiO2/CA composite film. The modified GC electrode was potentiostatically cycled from the rest potential to the hydrogen evolution potential at slow sweep rates, for example, 10 mV s−1 in supporting electrolyte solution. After a few cycles, the background current was stable and reproducible. Then cyclic voltammograms were recorded for the reduction of chlorpyrifos on n-TiO2/CA/GCE.
5 shows the effect of various concentrations of chlorpyrifos on the peak current of chlorpyrifos. The peak current increases
Figure 5. Influence of various concentrations of chlorpyrifos on the peak current, (a) 10, (b) 30, (c) 50, (d) 70, (e) 90, (f) 110, (g) 130 μM, at nano-TiO2/cellulose acetate modified GCE in 60:40 (v/v) methanol/water containing 0.05 M TBAB at 100 mV s−1. (Inset) Calibration graph.
with the increase in the concentrations of chlorpyrifos ranging from 10 to 130 μM (inset graph in Figure 5). The limit of detection (LOD) and limit of quantitation (LOQ) were calculated from the calibration graph constructed with concentration of chlorpyrifos on the x-axis and reduction current on the y-axis using the relationships LOD = 3s/m and LOQ = 10s/m, where s is the standard deviation of the intercept and m is the slope of the calibration curve.32 The LOD is 4.4 μM, and the LOQ is 14.7 μM. Differential Pulse Voltammetric Analysis. Typical DPV curves at various concentrations of chlorpyrifos are shown in Figure 6. The peak current obtained after subtracting the background current increases with the increase in the
Figure 6. Differential pulse voltammetric response of concentrations of chlorpyrifos, (a) 20, (b) 30, (c) 40, (d) 80, and (f) 110 μM, at nano-TiO2/cellulose acetate modified 60:40 (v/v) methanol/water containing 0.05 M TBAB. Calibration graph.
various 50, (e) GCE in (Inset) 6153
DOI: 10.1021/acs.jafc.5b02057 J. Agric. Food Chem. 2015, 63, 6150−6156
Article
Journal of Agricultural and Food Chemistry Table 1. Comparison of Analytical Parameters on Various Modified Electrodes
a
method
electrodea
linear range
DPASV DPV cyclic voltammetry DPP DPAdSV cyclic voltammetry DPV amperometry
HMDE (−1.2 V) HMDE (−1.2 V) PEDOT/GCE (−1.6 V) DME (−1.2 V) CMCPE (−1.2 V) TiO2/CA/GCE (−1.5 V) TiO2/CA/GCE (−1.5 V) TiO2/CA/GCE
9.9 × 10−8−5.96 × 10−7 M (5.7−28.5) × 10−8 M 10 × 10−10−7 × 10−7 M 9.7 × 10−7−6.9 × 10−6 M 2.8 × 10−10−5.7 × 10−6 M (10.0− 30) × 10−6 M (20.0−110) × 10−6 M (20.0−340) × 10−6 M
LOD 9.9 × 10−8 4.0 × 10−10 8 × 10−10 8.7 × 10−7 2.2 × 10−10 4.4 × 10−6 3.5 × 10−6 11.8 × 10−6
LOQ M M M M M M M M
1.2 × 10−9 M
14.7 × 10−6 M 11.7 × 10−6 M 39.2 × 10−6 M
ref 11 13 15 12 14 present work present work present work
The value given in parentheses is the reduction potential.
Figure 8. Stability of the n-TiO2/CA/GCE electrode over time for the addition of 50 μM chlorpyrifos in 60:40 (v/v) methanol/water containing 0.05 M TBAB at 100 mV s−1.
Figure 7. Amperometric response of chlorpyrifos for the constant addition of 20 μM at nano-TiO2/cellulose acetate modified GCE in 60:40 (v/v) methanol/water containing 0.05 M TBAB. (Inset) Calibration graph.
nitropesticides. The possible interference of chlorocompounds such as chlorophenol, chloroaniline, and chlorobenzene was also analyzed. The reduction of these chlorocompounds is not observed on this electrode under the present experimental conditions, and these chlorocompounds do not show any interference in the sensing signal of chlorpyrifos (Figure 9). Real Sample Analysis. Chlorpyrifos-Spiked Water Analysis. The analytical utility of the above methods was checked with the water sample, which was collected at the Central Electrochemical Research Institute (CECRI) premises. It was tested for the presence of chlorpyrifos. Chlorpyrifos was absent in the water sample. Therefore, a 100 μM concentration of chlorpyrifos was spiked into the water sample and was thoroughly shaken for 1 h. Then it was extracted by using dichloromethane. A small amount of anhydrous sodium sulfate was added to the extracted sample to remove traces of water. The solvent was slowly evaporated to get the residue. The chlorpyrifos residue was dissolved in solvent supporting electrolyte and was used as analyte for electrochemical experiments. The recovery rates obtained in electrochemical techniques are summarized in Table 2. The results are compared with the HPLC method. Commercial Sample Analysis. The commercial chlorpyrifos sample was analyzed using nano-TiO2/cellulose acetate modified GCE as a sensor probe. One hundred milliliters of commercial chlorpyrifos was purchased from the local market, which contains approximately 20% (v/v) chlorpyrifos. The
Reproducibility of the electrochemical response of this electrode was checked by carrying out a series of seven repetitive experiments for the fixed concentration of 50 μM chlorpyrifos. The peak currents are reproducible with the relative standard deviation of 2.54%. The reproducible response of the modified electrode with respect to time was checked (Figure 8). After the modification, the same electrode was used for the sensing of chlorpyrifos for 15 days successively. The peak currents are reproducible with the relative standard deviation of 5.3%. The stability of the electrode was also checked. After 40 cycles of cyclic voltammetric scans, the peak current variation from the initial current was 2.8% only. This shows that the nano-TiO2/cellulose acetate film is highly stable and reproducible. Interference Study. The interference study of several inorganic species and pesticides on the reduction signal of 50 μM chlorpyrifos was carried out using cyclic voltammetry. The concentration of the pesticides and the interfering ions were taken in 1:1 ratio. The inorganic ions such as Ca2+, Mg2+, Na+, NH4+, and K+ do not interfere with the chlorpyrifos reduction signal. Possible interferences with the other nitroaromatic pesticides such as methyl parathion and fenitrothion were also checked. These pesticides are reduced at around −700 mV on n-TiO2/CA/GCE, whereas chlorpyrifos is reduced at around −1.55 V. The wide variation in the reduction potential makes it possible to determine chlorpyrifos even in the presence of these 6154
DOI: 10.1021/acs.jafc.5b02057 J. Agric. Food Chem. 2015, 63, 6150−6156
Article
Journal of Agricultural and Food Chemistry
sample was analyzed by electroanalytical techniques and HPLC measurements. The numer obtained in HPLC measurements is taken as reference value. The results obtained in electrochemical techniques are well comparable with the HPLC techniques (Table 4), so the electrochemical sensor using this nano-TiO2-cellulose acetate modified electrode is promising for the analysis of environmental samples. Table 4. Soil Sample Analysis electroanalytical technique cyclic voltammetry differential pulse voltammetry amperometry HPLC
concn (μM)a,b 91.62 91.64 102 99.6
± ± ± ±
0.31 0.23 0.12 0.08
a
Number of samples analyzed was 6. bTotal weight of the soil was 112.6 g.
Figure 9. Interference study of various inorganic metal ions and pesticides on the reduction signal of 50 μM chlorpyrifos at n-TiO2/ CA/GCE in 60:40 (v/v) methanol/water containing 0.05 M TBAB at 100 mV s−1.
In this study a stable, reproducible, and biocompatible nanoTiO2/cellulose acetate modified electrode was developed and used for the analysis of chlorpyrifos. The presence of TiO2 nanoparticles increases the sensing current of chlorpyrifos, which enhances the sensitivity of the sensor. Moreover, the presence of TiO2 nanoparticles in the cellulose acetate matrix shifts the hydrogen evolution markedly, which improves the measurement of true sensing current of chlorpyrifos. The modified electrode is highly stable with respect to time so that the electrode once modified can be used many times for the sensing of chlorpyrifos. The electrode modification procedure outlined in this work is also simple. The nano-TiO2/cellulose acetate film on the glassy carbon electrode surface is highly stable in alcoholic medium, which makes this physically mixed composite material suitable for the determination of chlorpyrifos in alcoholic medium. This modified electrode replaces the mercury sensing electrode in the determination of chlorpyrifos. The materials used in the preparation of the modified electrode are cheap. The modified electrode can easily be renewed for subsequent analysis. The analytical utility of the proposed method was checked in the spiked water sample and the commercial sample.
Table 2. Recovery Study of Chlorpyrifos in Spiked Water Samples method
amount added (μM)
amount recovereda (μM) ± SD
recovery rate (%)
100 100
91.84 ± 0.18 96.28 ± 0.11
91.84 96.28
100 100
96.46 ± 0.01 98.80 ± 0.08
96.46 98.80
cyclic voltammetry differential pulse voltammetry amperometry HPLC a
Number of samples analyzed was 6.
actual concentration of the commercial samples was determined using an HPLC technique and was taken as reference value. It was diluted to 100 μM. Then it was used as an analyte in cyclic voltammetry, differential pulse voltammetry, and amperometry to verify the concentrations specified by the manufacturer. The concentration obtained in electroanalytical techniques is given in Table 3. The results obtained with electroanalytical techniques are comparable with the results obtained in the HPLC method.
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*(M.C.) Phone: +91 4565 241552. Fax: +91 4565 227779, 227713. E-mail:
[email protected].
Table 3. Commercial Sample Analysis method cyclic voltammetry differential pulse voltammetry amperometry HPLC
AUTHOR INFORMATION
Corresponding Author
concn (%)a,b (v/v) 17.5 18.00 16.5 18.61
± ± ± ±
Funding
We thank the Department of Science and Technology, New Delhi, India, for financial support. A.K. thanks the Council of Scientific and Industrial Research (CSIR), New Delhi, India, for awarding a Senior Research Fellowship (SRF).
0.50 0.09 0.08 0.10
a
Notes
Concentration specified by the manufacturer is approximately 20% (v/v). bNumber of samples assayed was 6.
The authors declare no competing financial interest.
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Soil Analysis. Ten milliliters of chlorpyrifos was taken from the 100 mL commercial chlorpyrifos pack, which contains 20% (v/v) chlorpyrifos, and it was diluted to 1000 mL. Then this pesticide was sprayed on a pomegranate tree using an air sprayer. After 1 week, 112.6 g of soil under the pomegranate plant was collected and thoroughly ground. Then it was extracted as per the procedure explained above. The extracted
REFERENCES
(1) Venkata Mohan, S.; Sirisha Ra, N. C.; Sarma, P. N.; Reddy, S. J. Degradation of chlorpyrifos contaminated soil by bioslurry reactor operated in sequencing batch mode: bioprocess monitoring. J. Hazard. Mater. 2004, 116, 39−48. (2) De Silva, P. M. C. S; Samayawardhena, L. A. Effects of chlorpyrifos on reproductive performances of guppy (Poecilia reticulata). Chemosphere 2005, 58, 1293−1299.
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Article
Journal of Agricultural and Food Chemistry
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DOI: 10.1021/acs.jafc.5b02057 J. Agric. Food Chem. 2015, 63, 6150−6156
