Electroanalytical determination of carbendazim and fenamiphos in natural waters using a diamond electrode

Diamond & Related Materials 27–28 (2012) 54–59

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Electroanalytical determination of carbendazim and fenamiphos in natural waters using a diamond electrode Rafaela F. França a, Hueder Paulo M. de Oliveira b, Valber A. Pedrosa c, Lucia Codognoto d,⁎ a

Universidade Camilo Castelo Branco, São José dos Campos — SP, Brazil Centro de Ciências Químicas, Farmacêuticas e de Alimentos, Campus Capão do Leão, Universidade Federal de Pelotas, RS, Brazil Institute of Bioscience, Department of Chemistry and Biochemistry, UNESP, Botucatu, SP, Brazil d Instituto de Ciências Ambientais, Químicas e Farmacêuticas, Departamento de Ciências Exatas e da Terra, Universidade Federal de São Paulo, Rua Prof. Artur Riedel, 275 — Bairro Eldorado, Diadema CEP: 09972-270, SP, Brazil b c

a r t i c l e

i n f o

Article history: Received 17 February 2012 Received in revised form 16 May 2012 Accepted 21 May 2012 Available online 26 May 2012 Keywords: Pesticide Diamond electrode Carbendazim Fenamiphos Water analysis

a b s t r a c t In this study, a method for electroanalytical determination of carbendazim (CBZ) and fenamiphos (FNP) in natural and spiked water was developed using square wave voltammetry in Na2HPO4 0.1 mol L− 1 as supporting electrolyte. The calibration curve for carbendazim detection presented good linearity in the concentration range of 0.50 to 15.0 μM, with a sensitivity of 0.080 A/mol L− 1 and a linearity of 0.998. The oxidation of fenamiphos on BDD electrode shows a dynamic range of concentration of 0.5 to 25.0 μM and sensibility of 0.14 A/mol L− 1. The recovery experiments showed values between 70 and 100% for spiked samples thus indicating the feasibility of the electroanalytical methodology to quantify CBZ and FNP in pure or natural waters. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Brazil is one of the world leaders in pesticide consumption and exposed workers are numerous and diversified. Acute poisonings are just the most visible aspect of pesticide impact on human health and few studies are available on acute pesticide exposure in poisoned subjects [1,2]. Recently, the FDA had detected low levels of carbendazim in some orange juice products [3]. Due to the high toxicity of carbendazim rapid detection of those toxic agents has become increasingly important for homeland security and health protection in the entire world [4]. New analytical tools for pesticide detection are needed to provide an easy, simple and cheap alternative by local agencies to protect and enhance environmental assets. Over the past years, carbendazim has been used for the control of a wide range of fungal diseases such as mold, spot, mildew, scorch, rot and blight in a variety of crops [5–7]. It is frequently sold in combination with other fungicides such as fenamiphos. Both pesticides are widely used in agriculture to control soil pests. Recently toxicology studies suggesting that both pesticides have potential for acute and chronic effects on human health, for groundwater contamination and for hazards to worker safety [8]. However, as far as we know, there are no methods reported in the literature for the simultaneous determination of

⁎ Corresponding author. Tel.: + 55 11 3319 3300; fax: + 55 11 4043 6428. E-mail address: [email protected] (L. Codognoto). 0925-9635/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2012.05.010

carbendazim and fenamiphos in natural water without a previous separation and preconcentration step. The most common approach has used chromatographic techniques to quantify both pesticides [9–11]. However, these methods require expensive instrumentation, using exhaustive pretreatment procedure and professional operators, which limit their application for real-time detection of these compounds. Moreover, they usually involve the manipulation of a large amount of organic solvents, with the use of hundreds of milliliters of solvent being common for the treatment of just one sample. The recovery and disposal of these solvents are sometimes difficult and incomplete. In this way, pesticide residues can easily enter the atmosphere with hazardous effect to the environment and/or to the laboratory/industry staff [12,13]. Electrochemical methods for detection and quantification of pesticides have attracted a crescent amount of attention so far. This is mainly due to the low cost and fast analysis time that can be achieved using these techniques, as well as the possibility to perform the analysis in environmental matrices, without requirements of separations and clean-up procedures. Thin films of boron-doped diamond (BDD) have emerged as excellent electrode materials for several electrochemical applications, especially electroanalytical ones, mainly due to properties such as a wide potential window in aqueous solutions (up to 3 V), low background currents, low adsorption, and low sensitivity to dissolved oxygen [14–17]. Studies of electroanalysis, particularly for quantitative detection of trace amounts of harmful compounds in polluted water, have been performed by using BDD electrodes on the basis of their

R.F. França et al. / Diamond & Related Materials 27–28 (2012) 54–59

unique electrochemical properties [18–21]. Furthermore, determinations of pesticides have been extensively investigated by our group using BDD electrodes [22–27]. Our results show the development of a methodology to determine carbaryl, without any previous step of extraction, clean-up or pre-concentration step, with a detection limit of 0.2 μg L − 1 in natural water using BDD electrodes [22]. Another article reported a new strategy to detect parathion in spiked, pure and natural water [23]. The electrochemical reduction responses of parathion were analyzed and compared with those previously obtained using a hanging mercury drop electrode (HMDE). The detection and quantification limits were calculated from the analytical curves both for BDD and HMDE in pure water (2.4 and 7.9 μg L − 1 and 3.9 and 12.8 mg L− 1 respectively) showing only a slight improvement when BDD was used. However, if the application involves polluted natural waters the improvement is accentuated due to the very low adsorption characteristics of BDD, which prevent the fouling of electrode surface by organic pollutants. Recent works in the literature reported carbendazim detection by electroanalytical methodology. Ribeiro et al. [28] reported a stripping analysis of carbendazim using carbon nanotube modified glassy carbon electrode. The results have shown a highly sensitive and reliable method with an experimental work ranging from 0.25 to 3.11 μmol L − 1 with a detection limit of 10.5 ppb for a short (60 s) accumulation period. The accuracy of the method for real sample analysis was assessed by estimating the apparent recovery (93 ± 2.9% and 86 ± 4.1% for 4.3 × 10− 7 mol L− 1) for a carbendazim spiked river water sample. Del Pozo et al. [29] studied the electrochemical behavior of the supramolecular complex formed between the macrocyclic receptor cucurbituril [7] and carbendazim. Moreover, this host molecule is used to develop a selective and sensitive differential pulse voltammetric method for the determination of carbendazim through its cucurbituril [7] inclusion complex, allowing the detection of the analyte at 4.25 × 10 − 9 M. The method was applied to the determination of the fungicide in untreated apple peel samples after a matrix solid-phase dispersion sample preparation procedure. The detection limit calculated for this real sample was 0.17 mg kg− 1, which is below the legally allowed limit of 0.20 mg kg− 1. Abirama et al. [30] developed a new methodology to detect carbendazim using a modified glassy carbon electrode with multiwalled carbon electrode. An electroanalytical procedure for the determination of carbendazim was carried out by differential pulse stripping voltammetry over the range 0.01–5.0 × 10− 4 μg L − 1. The present study is an attempt to develop an accurate, simple and sensitive method for simultaneous determination of carbendazim (CBZ) and fenamiphos (FNP) in natural waters, without a previous separation or preconcentration step.

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conditioning [31]. An electrochemical analyzer Autolab® PGSTAT128N (Eco Chemie, Netherlands) was used for all voltammetric measurements with GPES software. In all cases, the experimental SWV parameters such as square wave frequency (f), amplitude (a) and scan increment (ΔEs) were optimized before the measurements and these results were also used for the characterization of the electrode process via the SWV diagnostic criteria. 2.2. Water samples Natural water samples were collected at Paraiba Valley River, near agricultural regions. The water samples were collected in glass bottles, during June (2010), and stored at 4 °C, for no longer than one week. Analytical curves were obtained by the standard addition method. The electrolytes were prepared by dissolving the salts necessary for the 0.1 mol L − 1 Na2HPO4 in either pure or natural waters and the measurements were performed without pre-treatment of the solutions but the pH was adjusted appropriately to the desired value in each case. Before each experiment, a stream of N2 was passed through the solution for ca. 10 min. For the determination of the detection (DL) and the quantification limit (QL), the standard deviation of the response (SB) was determined as the standard deviation of the mean value for ten voltammograms of the blank, obtained from the currents measured in the same peak potential voltammetric oxidation of CBZ and FNP, the slope of the straight line in the analytical curve (b) and Eqs. (1) and (2) shown below were used. DL ¼

3SB b

ð1Þ

QL ¼

10SB b

ð2Þ

The recovery experiments were carried out by adding a known amount of specific pesticide to the supporting electrolyte followed by standard additions from the pesticide stock solution and plotting the resulting analytical curve. All measurements were performed in triplicate. The recovery efficiencies (R%) for the different systems under investigation were calculated using Eq. (3) where the value [pesticide] found refers to the concentration obtained by extrapolation of the analytical curve in the corresponding spiked water samples: R% ¼ 100

½pesticide found : ½pesticide added

ð3Þ

2. Experimental 3. Results and discussion 2.1. Reagents and apparatus 3.1. Electrochemical response of CBZ and FNP All chemicals were of analytical reagent grade and the aqueous solutions were prepared with ultra-purified water from Milli-Q system (Millipore Corporation). 1.0 × 10− 3 mol L − 1 stock solution of the pesticides (carbendazim and fenamiphos, Sigma-Aldrich 98.0%), was prepared in acetonitrile. The supporting electrolyte was 0.1 mol L− 1 Na2HPO4. The influence of pH was evaluated for each pesticide using the DDB electrode in a 0.1 mol L − 1 BR buffer varying the pH in the interval 2.0–8.0. A conventional three-electrode cell with the Ag/AgCl system and a Pt wire as the reference and auxiliary electrodes were used, respectively. The working electrode was a BDD (8000 ppm boron) film, 0.5 cm2 surface area from the Centre Suisse de Electronique et de Microtechnique SA (CSEM), Neuchatel, Switzerland. Prior to the experiments, BDD electrode was once submitted to anodic treatment (+3.0 V vs. Ag/AgCl for 10 min) to remove hydrophobic film. After that, a cathodic treatment was realized (−3.0 V vs. Ag/AgCl for 10 min) to surface

First, cyclic voltammograms of CBZ and FNP on the BDD electrode in the aqueous solution were obtained. The electrochemical oxidation of carbendazim exhibited an irreversible oxidation peak at 1.1 V vs. Ag/Cl in pH 3.5 (Fig. 1A). Our results indicate an irreversible process controlled by diffusion. The electrochemical response of FNP exhibited one oxidation peak at 1.2 V vs. Ag/AgCl (pH 2.0), with irreversible process features (instead there is no peak in the reserve scan, Fig. 1B). In addition, scan rate variation analysis demonstrated that oxidation process of FNP at BDD electrodes is controlled by diffusion, as current peak increases linearly with scan rate square root (results not shown). The influence of pH was evaluated for each pesticide using the BDD electrode in a 0.1 mol L − 1 BR buffer varying the pH in the interval 2.0–8.0. Fig. 2A shows the effect of the peak current versus pH for carbendazim analysis. The Ip vs. pH plot revealed a maximum current

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R.F. França et al. / Diamond & Related Materials 27–28 (2012) 54–59

A

A

2.4

1.3

3 2.0

I / µA

2

1.1

1.2

1.0

0.8

1

0

0.9

0.4

CBZ Blank

0.0 0.8

1.0

1.2

0.8 1

1.4

2

3

4

5

6

7

8

pH

E/V

B

Ep / V

Ip / µA

1.2 1.6

B

8

3.0

1.3

2.5 6

Ip / µA

I / µA

4

2

FNP Blank

0 0.8

1.0

1.2

1.4

1.5 1.1

1.0 0.5

3.2. Analytical curves Optimization of the square-wave parameters aiming the maximum analytical signal led to the following values to be used in the analytical determinations: (a) frequency of 100 s− 1, (b) amplitude of 50 mV, and (c) scan increment of 2 mV. Here the parameters were considered in relation to both the maximum peak current (sensitivity) and the minimum halfpeak width (selectivity). The dependence of the peak current with concentration resulted in the linear plot shown in the inset of Fig. 4A. The corresponding linear equation was Ip =−0.01 μA+0.08 A/mol×[CBZ], with r=0.998 while the DL was 1.2×10− 7 mol L− 1 (22.0 μg L− 1) and QL was 4.0×10− 7 mol L− 1 (75.0 μg L− 1) and is included in Table 1. Both values obtained are lower than the maximum contamination level in waters allowed by the local environmental authorities for domestic consumption, i.e., 80 μg L− 1 [32]. After the electrochemical measurements, the electrode was removed from the electrolyte, washed thoroughly with water, reintroduced into the blank buffer solution and conditioned by potential sweeping until the original background current was restored. The results for 10 successive CBZ determinations (fixed

4

2

6

8

pH Fig. 2. Influence of pH on the peak potential (●) and peak current (■) for the oxidation of CBZ (A) and FNP (B), on BDD electrode, pesticide concentrations of the 7.5 × 10− 5 mol L− 1 in 0.1 mol L− 1 BR buffer.

concentration of 5.0×10− 6 mol L− 1) in the same conditions showed an RSD of only 2.0%. The DL of CBZ reported here was comparable with other techniques such as fluorescence method [33], liquid chromatography [34], and adsorptive stripping voltammetry using multiwalled carbon nanotubes as modified electrode [35]. Also, in comparison with the results obtained by Ribeiro et al. [28], del Pozo [29], and Abirama [30] it is clearly seen that the limit of detection of the proposed method is comparable with their results, however modified electrode can suffer fouling layer, which may occur after prolonged use. One advantage of using the DDB electrode is the unmodified surface creating a cost‐effective robust sensor, which is suitable for routine analysis as the analytical frequency is very high. Also, the detection in the proposed amperometric method is direct, whereas some of the reported procedures are based on indirect reactions involving the formation of species with some appropriate chemical characteristic for monitoring. The same electroanalytical methodology described above was applied to quantify FNP in pure water. The peaks for increasing levels of

6

A

B

1.2

1.4

4

I / µA

at approximately pH 2.0 decreasing with increasing of pH. The graph shows the linear relationship between the anodic peak potential and pH with the slope value 65 mV suggesting that equal number of protons and electrons is involved in the electrochemical oxidation of CBZ at BDD electrode. Fenamiphos experiments were carried out in the same conditions and reveals that the peak current has a maximum value in pH 3.0 decreasing sharply in higher pH (Fig. 2B). However, the simultaneous quantification of this couple is possible at pH 2.0 where FNP has a well-defined oxidation peak at 1.2 V, while CBZ shows a potential peak at 1.36 vs. Ag/AgCl (Fig. 3). Also, pH 2.0 provided better overall separation and peak resolution than pH 3.0 for simultaneous determination without pre-steps or mathematical treatment. For this reason, all subsequent experiments were carried out at pH 2.0.

1.0 10

0.0

E/V Fig. 1. Cyclic voltammogram for CBZ (A) and FNP (B) on BDD electrode (7.5× 10− 5 mol L− 1) in Na2HPO4 0.1 mol L− 1, pH 3.5 (CBZ) and pH 2.0 (FNP), scan rate 100 mV s− 1.

Ep / V

1.2

2.0

2

0 0.6

0.8

1.0

E/V Fig. 3. Cyclic voltammograms for mixture of (A) CBZ (5.0 × 10− 5 mol L− 1) and (B) FNP (7.5 × 10− 5 mol L− 1) in 0.1 mol L− 1 Na2HPO4, pH = 2.0. The sweep rate is 100 mV s− 1.

R.F. França et al. / Diamond & Related Materials 27–28 (2012) 54–59

A 1.2

3.3. Application in natural water

k

I / µA

0.8

0.4

a 0.0 0.8

1.0

1.2

1.4

E/V

B

4

j 3

I / µA

57

2 1

a 0 0.6

0.8

1.0

1.2

1.4

E/V Fig. 4. (A) SWV responses for the oxidation of different CBZ concentrations: 0.5 (a), 2.5 (b), 3.7 (c), 5.0 (d), 6.2 (e), 7.5 (f), 8.7 (g), 10.0 (h), 11.2 (i), 12.5 (j), 15.0× 10− 6 mol L− 1 (k) in BR buffer pH 3.5. Inset: linear dependence of Ip with CBZ concentration. (B) SWV responses for the oxidation of different FNP concentrations: 0.5 (a), 2.5 (b), 5.0 (c), 7.5 (d), 10.0 (e), 12.5 (f), 15.0 (g), 17.5 (h), 20.0 (i), 25.0× 10− 6 mol L− 1 (j) in Na2HPO4 0.1 mol L− 1 pH= 2.0. Inset: linear dependence of Ip with FNP concentration. (f = 150 s− 1, a = 40 mV, ΔEs = 2 mV.)

Aiming to evaluate the behavior of BDD electrodes in complex matrices, the same electroanalytical methodology described above was applied to determine both pesticides in natural water samples. Here, the samples collected from the Paraiba Valley River were used to prepare the supporting electrolyte and then spiked with the minimum detectable amount of CBZ and FNP. The electroanalytical procedure applied here has no previous extraction, clean-up or pre-concentration step, which is a key factor in improving sample throughput and providing a robust analysis. In Fig. 5A and B the calibration curves obtained for natural water are shown for CBZ and FNP, respectively. There was a significant change (t-test, p b 0.05) at quantification limit values obtained for CBZ (75.0 μg L − 1), which represents sensitivity decrease, probably due to organic compounds in sample. Such behavior could be associated with the interactions existing between diamond surfaces and organic molecules that lead to inhibition of the pesticide oxidation by blockage of the electrode surface. Such behavior was not found in the FNP studies, which indicates that oxidation mechanism is also an important step. Moreover, recovery studies were carried out for quantification of CBZ and FNP in natural waters. When analyzing real-life samples such as groundwater samples, matrix interference must be taken into consideration in order to define a reproducible method. The values obtained for the samples at points 1 and 2 are shown in Tables 1 and 2. There was no significant change at quantification limit values (t-test, p > 0.05), which means that in this case the potential matrix effect has a small influence in the pesticide determination. The results obtained with the BDD demonstrate that the electroanalytical procedure used here is suitable for CBZ and FNP quantification in the complex matrices without any prestep. This behavior is associated with the very low interactions existing between diamond surfaces and organic molecules thus minimizing the inhibition of the pesticide reduction by blockage of the electrode surface [30]. 3.4. Simultaneous determination of CBZ and FNP

FNP (0.50 to 25.0 × 10 − 6 mol L − 1) are clearly noticeable (Fig. 4B). The response increases linearly with the concentration, as indicated from the corresponding calibration plot (shown as the inset figure; the corresponding linear equation Ip = −0.03 μA + 0.14 A/mol L − 1 [FNP] with r = 0.989). The detection limit can be estimated as 1.0 × 10− 7 mol L− 1 (30.0 μg L − 1) and QL as 3.0 × 10− 7 mol L − 1 (91.0 μg L − 1). The results of ten replicate measurements showed an RSD of 3.1%. All the analytical value obtained for FNP at BDD was included in Table 2.

The methodology was applied to the simultaneous quantification of CBZ and FNP in contaminated waters. Square wave voltammograms for CBZ and FNP mixture are presented at Fig. 6. The peak potential values for each process were 1.2 for CBZ and 1.4 vs. Ag/AgCl for FNP. The inset shows all the points of the corresponding analytical curve and the linear region, that is, from 0.50 to 15.0 × 10− 6 mol L− 1. On the other hand, the calculated value of DL for the BDD electrode was 9.2 μg L− 1. The new calculated QL for CBZ was 125.0 μg L − 1. The values of QL are slightly

Table 1 Analytical parameters for carbendazim determinations on BDD electrodes in pure and contaminated water samples. Water sample

r

b/ (A/mol L− 1)

SB/ (nA)

Added (10− 6 mol L− 1)

Recovered (10− 6 mol L− 1)

% of recovery ±RSD (n = 3)

Milli-Q Sample 1

0.998 0.997

0.080 0.040

3.2 2.7

Sample 2

0.988

0.038

2

– 10.0 20.0 10.0 20.0

– 9.4 18.8 9.6 10.2

– 90.0 ± 3.5 94.0 ± 2.8 2.0 ± 3.2 96.0 ± 2.5

Table 2 Analytical parameters for fenamiphos determinations on BDD electrodes in pure and contaminated water samples. Water sample

r

b/ (A/mol L− 1)

SB/ (nA)

Added (10− 6 mol L− 1)

Recovered (10− 6 mol L− 1)

% of recovery ±RSD (n = 3)

Milli-Q Sample 1

0.989 0.988

0.12 0.12

3.6 3.7

Sample 2

0.997

0.13

3.8

– 0.5 4.0 0.5 4.0

– 0.49 4.30 0.48 4.10

– 98.0 ± 2.1 107.5 ± 1.5 96.0 ± 2.5 102.5 ± 1.8

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R.F. França et al. / Diamond & Related Materials 27–28 (2012) 54–59

A

as calculated by Eq. (2), was also included in Tables 1 and 2. They clearly demonstrate that the BDD electrode shows excellent recovery rates even in highly polluted water samples thus offering the possibility of analytical determinations in environmental matrices.

3

Ip / µA

2

4. Conclusions

1

0

0

10

20

30

40

[CBZ] / 10-6 mol L-1

B

1,5

Ip / µA

1,2 0,9 0,6

An alternative analytical procedure has been proposed in this paper, which allows easier monitoring of FNP and CBZ concentrations in natural waters, since it did not require separations, clean-up or pre-concentration steps, which are indispensable in several other analytical methodologies. The BDD is less sensitive to impurities and has a superior performance when dealing with contaminated samples. In both cases, the recovery experiments were totally satisfactory and the conclusion is that diamond electrodes are an interesting and desirable alternative for use in electroanalysis. Moreover, it was possible to simultaneously determine both pesticides. Considering official requirements the methodology provides satisfactory data. The advantage of the proposed method over some existing ones lies in its simplicity, low consumption of reagents, higher sample frequency and possibility of automation. The method has been satisfactorily applied to the determination of carbendazim and fenamiphos in natural water samples.

0,3 Acknowledgments

0,0 0

2

4

6

8

10

12

[FNP] / 10-6 mol L-1 Fig. 5. (A) Analytical curves for CBZ oxidation on the BDD electrode in solutions prepared with: Milli-Q water (■), point 1 (▲) and point 2 (●) water samples from the Paraiba Valley river. (B) Analytical curves for FNP oxidation on the BDD electrode in solutions prepared with: Milli-Q water (■), point 1 (▲) and point 2 (●) water samples from the Paraiba Valley river.

influenced by matrix since the highest value of QL, 130.0 μg L− 1, was found for water collected in point 1, a highly polluted sample. It can be observed that FNP determination does not show interaction with organic compound present at these samples, but our results obtained for CBZ show a small decrease of signal. We suggest that some organic compounds that are present in all samples can interact with the CBZ that is present in the mixture, thus reducing its effective concentration at the interface. This interaction decreases the sensitivity of the analytical procedure, but the methodology avoids a separation and clean-up procedure. In the sequence, several standard solutions were added, altering the concentration in the voltammetric cell up to 15.0× 10− 6 mol L − 1. Straightforward, a mixture containing a constant concentration of CBZ and FNP was analyzed by SWV and the resulting voltammograms are shown in Fig. 6. The percentage found for each recovery experiment,

g

0.7 0.6

I / µA

0.5 0.4 0.3 0.2

a

0.1 0.0 0.8

1.0

1.2

1.4

E / V vs Ag/AgCl Fig. 6. Square wave voltammograms for CBZ and FNP mixtures, in 0.1 mol L− 1 Na2HPO4, pH 2.0, f = 100 s− 1, a = 50 mV, and ΔEs = 2 mV. Inset: current peak vs. concentration of FNP (■) and CBZ (●). Linear interval CBZ (a) 1.0 × 10− 6 mol L− 1 to 15.0 × 10− 6 mol L− 1 and FNP (a) 0.5 × 10− 6 mol L− 1 to 7.0 × 10− 6 mol L− 1.

The authors thank FAPESP (proc. no. 2008/50588-6) and CNPq, Brazil, for scholarships and financial support to this work. Dr. Pedrosa acknowledges support by FUNDUNESP (proc. no. 0049/11-DFP). References [1] N.M.X. Faria, A.G. Fassa, L.A. Facchini, Cien. Saude Colet. 12 (2007) 25–38. [2] W. Soares, S. Moro, R.M. Almeida, Appl. Health Econ. Health Policy 1 (2002) 157–164. [3] Food and Drug Administration, Department of Health & Human Services, Jan 09/12. [4] M. Sbai, H. Essis-Tome, U. Gombert, T. Breton, M. Pontié, Sens. Actuators B 124 (2007) 368–375. [5] M. del Pozo, L. Hernández, C. Quintana, Talanta 81 (2010) 1542–1546. [6] L.F. Lopez, A.G. Lopez, M.V. Riba, J. Agric, Food Chem. 37 (1989) 684–687. [7] EPA 738-R-02-004, Interim Reregistration Eligibility Decision (Fenamiphos), 2002. [8] A. Rico, A.V. Waichman, R. Geber-Corrêa, P.J. van den Brink, Ecotoxicology 20 (2011) 625–636. [9] C.C. Leandro, P. Hancock, R.J. Fussell, B.J. Keely, J. Chromatogr. A 1103 (2006) 94–101. [10] S.H. Tseng, Y.J. Lin, H.F. Lee, S.C. Su, S.S. Chou, D.F. Hwang, J. Food Drug Anal. 15 (2007) 316–324. [11] A.D. Strickland, C.A. Batt, Anal. Chem. 81 (2009) 2895–2903. [12] M. Guptaa, A. Jaina, K.K. Verma, Talanta 80 (2009) 526–531. [13] H. Liang, C. Li, Q. Yuan, F. Vriesekoop, J. Agric, Food Chem. 56 (2008) 7746–7749. [14] T.N. Rao, B.H. Loo, B.V. Sarada, C. Terashima, A. Fujishima, Anal. Chem. 74 (2002) 1578–1583. [15] M. Hupert, A. Muck, J. Wang, J. Stotter, Z. Cvackova, S. Haymond, Y. Show, G.M. Swain, Diamond Relat. Mater. 12 (2003) 1940–1949. [16] S. Ferro, A. De Battisti, I. Duo, C. Comminellis, W. Haenni, A. Perret, J. Electrochem. Soc. 147 (2000) 2614–2619. [17] M.C. Granger, G.M. Swain, J. Electrochem. Soc. 146 (1999) 4551–4558. [18] V.A. Pedrosa, A. Malagutti, L.H. Mazo, L.A. Avaca, Anal. Lett. 39 (2006) 2737–2748. [19] K. Peckova, J. Musilova, J. Barek, Anal. Chem. 39 (2009) 148. [20] K. Pecková, J. Barek, Curr. Org. Chem. 15 (2011) 3014–3028. [21] T.A. Ivandinia, R. Sato, Y. Makide, A. Fujishima, Y. Einaga, Diamond Relat. Mater. 13 (2004) 2003–2008. [22] L. Codognoto, S.T. Tanimoto, V.A. Pedrosa, H.B. Suffredini, S.A.S. Machado, L.A. Avaca, Electroanalysis 18 (2006) 253–258. [23] V.A. Pedrosa, D. Miwa, S.A.S. Machado, L.A. Avaca, Electroanalysis 18 (2006) 1590–1597. [24] L. Codognoto, S.A.S. Machado, L.A. Avaca, Diamond Relat. Mater. 11 (2002) 1670–1675. [25] V.A. Pedrosa, L. Codognoto, S.A.S. Machado, L.A. Avaca, J. Electroanal. Chem. 573 (2004) 11–18. [26] V.A. Pedrosa, S.A.S. Machado, L.A. Avaca, Anal. Lett. 39 (2006) 1955–1965. [27] V.A. Pedrosa, L. Codognoto, L.A. Avaca, Quím. Nova 26 (2003) 844–849. [28] W.F. Ribeiro, T.M.G. Selva, I.C. Lopes, E.C.S. Coelho, S.G. Lemos, F.C. Abreu, V.B. Nascimento, M.C.U. Araujo, Anal. Methods 3 (2011) 1202–1206. [29] M. del Pozo, M. Alonso, L. Hernández, C. Quintana, Electroanalysis 23 (2011) 189–195.

R.F. França et al. / Diamond & Related Materials 27–28 (2012) 54–59 [30] P.L. Abirama Sundari, S.P. Palaniappan, P. Manisankar, Anal. Lett. 43 (2010) 1457–1470. [31] H.B. Suffredini, V.A. Pedrosa, L. Codognoto, R.C. Rocha-Filho, S.A.S. Machado, L.A. Avaca, Electrochim. Acta 49 (2009) 4021–4027. [32] Available at www.anvisa.gov.br (accessed in 11/04/2011).

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[33] M. Galera, D.P. Zamora, J.L.M. Vidal, A.G. Frenich, A. Espinosa-Mansilla, A.M. de la Pena, F.S. Lopez, Talanta 59 (2003) 1107–1116. [34] M. Chiba, R.P. Singh, J. Agric, Food Chem. 34 (1986) 108–112. [35] M.J.G. Huebra, P.H.O. Nieto, Y. Ballesteros, L. Hernándes, L. Fresenius, J. Anal. Chem. 367 (2000) 474–478.