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Hindawi Journal of Analytical Methods in Chemistry Volume 2020, Article ID 8068137, 10 pages https://doi.org/10.1155/2020/8068137 Research Article A Low-Cost Layered Double Hydroxide (LDH) Based Amperometric Sensor for the Detection of Isoproturon in Water Using Carbon Paste Modified Electrode 1,2 1 1,3 Herve Leclerc Tcheumi , Aude Peggy Kameni Wendji, Ignas Kenfack Tonle, and Emmanuel Ngameni Laboratoire de Chimie Analytique, D´epartement de Chimie Inorganique, Faculte´ de Sciences, Universite´ de Yaounde´ I, ´ ´ BP 812 Yaounde, Yaounde, Cameroon Laboratoire de Chimie de l’Environnement, Departement des Sciences Environnementales, Ecole Nationale Sup´erieure Polytechnique de Maroua, Universit´e de Maroua, BP 46 Maroua, Maroua, Cameroon Laboratoire de Chimie Min´erale, D´epartement de Chimie, Facult´e des Sciences, Universit´e de Dschang, BP 67 Dschang, Dschang, Cameroon Correspondence should be addressed to Herve Leclerc Tcheumi; firstname.lastname@example.org Received 18 February 2020; Revised 4 July 2020; Accepted 30 July 2020; Published 21 August 2020 Academic Editor: Jose Vicente Ros Lis Copyright © 2020 Herve Leclerc Tcheumi et al. *is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In this work, a Layered Double Hydroxide (NiAl-LDH) was obtained by coprecipitation method and used to elaborate an elec- trochemical sensor for the determination of isoproturon, which is a hazardous pollutant, widely used in agriculture, and its residue is distributed into aqueous environment through run-oﬀ and leaching from the soil. Various physicochemical techniques such as FT-IR spectroscopy, X-ray diﬀraction, and thermal analysis were used to characterize this material. *e anionic exchange capacity of NiAl- 3- LDH on carbon paste modiﬁed electrode was investigated toward [Fe(CN) ] using cyclic voltammetry. Used as electrode modiﬁer of carbon paste electrode for isoproturon detection, a remarkable increase in isoproturon signal on modiﬁed carbon paste electrode by LDH was observed. *e peak current obtained after 3 min of preconcentration in 25 μM ISO on NiAl-LDH/CPE was 2.6 times higher than that exhibited by the same analyte on the unmodiﬁed CPE, thereby opening the way to the development of a sensitive method for the detection of ISO. Other parameters that can aﬀect the stripping response (preconcentration time, pH of detection medium, and LDH loading within the paste) were investigated to optimize the proposed sensor. After optimization, a linear calibration curve was −8 −7 −9 obtained in the concentration range from 2 × 10 to 1.8 × 10 M, leading to a detection limit of 1 × 10 M (S/N � 3). *e relative standard deviation for 5 identical measurements was 2.7%. *e interfering eﬀect of some compounds and ions was examined on the stripping response of ISO. *e applicability of the method was veriﬁed by the determination of ISO in spiked water sample. by means of contaminated water . Its residues can cause 1.Introduction severe health eﬀects in both human and animals upon its Isoproturon [3-(4 isopropylphenyl)-1,1-dimethylurea, referred absorption , due to its chronic toxicity, carcinogenicity, and to as ISO hereafter] is a phenylurea herbicide widely used for genotoxicity . *erefore, sensitive determination of ISO is pre- and postemergence control of annual grasses and broad- highly important. Up to now, several techniques have been leaved weeds in spring and water cereals . Progressive in- reported for phenylurea herbicides determination; they include crease in the production and application of ISO for plant ultraviolet spectroscopy , capillary electrophoresis [3,6], and protection induces the problem of water quality due to the long mainly gas or liquid chromatography [7,8]. Nevertheless, these time taken by this class of compounds to degrade . *e methods are not easy to carry out because they often necessitate intensive use of phenylurea herbicides as ISO in agriculture long analysis times and require several preprocessing steps and results in a high risk of these herbicides entering the food chain expensive equipment. Additionally, these methods are not 2 Journal of Analytical Methods in Chemistry sensitive. *erefore, the development of simple, low cost, and *is study designed and developed an electrochemical sensitive methodologies for monitoring of pesticides remains a sensor for ISO detection using CPE modiﬁer electrode with daily concern. Following these lines, electrochemical analysis NiAl-LDH. *e ISO retention by NiAl-LDH was through has signiﬁcant advantages such as speediness and less expensive H-bonding between the hydroxyl group NiAl-LDH and instrumentation. However, the unmodiﬁed electrodes suﬀer amide group of ISO. *is type of interaction can contribute from drawbacks such as high overpotential and electrodes to the enhancement of the sensitivity of ISO during the surfaces fouling issues. As such, ﬁnding suitable electrode detection step. NiAl-LDH synthetized was fully character- modiﬁed for determination of organic pollutants is an inter- ized (FT-IR, XRD, and TGA) prior to their application as esting research. In that context, Sundari and Manisankar  electrode material and used for the development of a sen- elaborated a modiﬁed electrode by coating multiwalled carbon sitive sensor dedicated to the electrochemical determination nanotube ﬁlm on a glassy electrode for electrochemical de- of ISO in water samples. termination of ISO; Noyrod et al.  reported a simultaneous determination of ISO and carbendazim by single drop analysis 2.Experimental Methods using a graphene-based electrochemical sensor. Promising research results have been obtained with electrodes modiﬁed 2.1. Chemicals and Reagents. All chemicals and reagents with Layered Double Hydroxides (LDHs) for electroanalysis of used in this work were of analytical grade and used as re- −2 organic and inorganic pollutants as have also been explored ceived. ISO was purchased from Supelco, France, and 10 M [11–14], because of their ability to accumulate various chemical stock solutions were prepared in methanol. K Fe(CN) 3 6 species in their interlayer region. In fact, LDHs are the class of (>99%, Prolabo) was reagent grade and used as received. An host-guest type layered material consisting of positively acetate buﬀer solution was used as supporting electrolyte −1 charged metal hydroxide layers acting with free hydrated and was prepared by mixing 0.1 mol L CH COONa and anions located in the interlayer space. A general formula for the CH COOH (Riedel-de-Haen). *e pH of solution was ad- II III x+ n− most widely studied LDHs is [M M (OH) ] .[(A ) . 1−x x 2 x/n justed using molar NaOH and HNO solutions prepared II 2+ 2+ 2+ III mH O] where M can be Mg , Mn , Ni , etc., while M 2 from analytical reagents purchased, respectively, from BDH 3+ 3+ 3+ n− may be Al , Mn , Cr , etc. A represents an intercalable and Prolabo. All the aqueous solutions were prepared using anion, and x is the molar ration. Recently, considerable interest deionized water. has been diverted to the study of the adsorption of environ- mental contaminant by LDH materials ; however, most of them were focused on the adsorption of anion pollutants. As a 2.2. Synthesis of NiAl-LDH and 3eir Characterization. result, it is necessary to design and synthesize adsorbents based *e synthesis of NiAl-LDH by a conventional coprecipi- on LDH materials for adsorption of neutral pollutants. tation method was adapted to the method previously re- Several approaches have been used to synthetize LDH; these ported . In practice, an aqueous solution of nickel nitrate include coprecipitation hydrothermal method, urea hydrolysis, and aluminum nitrate in the molar ratio 3/1 was prepared by and electrodeposition . Nevertheless, coprecipitation is a dissolving, respectively, 0.0045 mol and 0.015 mol of these technique that is widely used to make batches materials due to its compounds in 100 ml of deionized water, the ph being relative simplicity and ease of use of the resulting material for maintained constant at 10.1± 0.5 by the addition of a sodium adsorption of pollutant in batch adsorption mode . *e hydroxide solution (2 m). *e synthesis was carried out development of electrochemical sensors for ISO at trace level has using boiling water and under nitrogen atmosphere in order attracted an increasing interest in the last decade. Diﬀerent to minimize the contamination with atmospheric CO . *e methods have been proposed to modify electrode surface with resulting suspension was then stirred for 16 h and ﬁltered LDH ﬁlm [12, 13]; the most common one consists of depositing and the solid obtained was collected, washed, and dried in an a ﬁxed amount of a colloidal solution of the LDH, previously oven at 70 c for 24 h. synthesized in bulk by the coprecipitation method , onto the NiAl-LDH was subsequently characterized by X-ray support. *is method suﬀers a drawback of poor adhesion of the powder diﬀraction (XRD), Fourier Transform Infrared (FT- ﬁlm to the support material, thus lacking the reproducibility of IR), and thermal analysis. the results obtained. To overcome of this weakness of ﬁlm XRD patterns were recorded at room temperature using modiﬁer electrode, Carbon Pate Electrode (CPE) presents in- a classical powder diﬀractometer (X’PERT PRO, Philips) teresting alternative. In fact, carbon paste electrode possesses equipped with a Cu anode (quartz monochromator, kα many advantages which include low background current, rapid radiation, λ � 1.54056 A). and confortable renewal of the active surface of the electrode, Diﬀuse reﬂectance infrared spectra were recorded be- −1 and easy fabrication and modiﬁcation with a wide range of tween 4000 and 500 cm , using a FT-IR Perkin Elmer 2000 compounds. Investigations dealing with the use of LDH as spectrometer equipped with a DTGS detector. *e sample modiﬁer of CPE for sensing of pollutant are not widespread. To was analyzed at room temperature using KBr pellets. *e overcome these, numerous attempts have been made. For ex- diﬀuse reﬂectance R of the sample and R of KBr used as s r ample, Fuerte et al.  investigated the electrochemical oxi- nonabsorbing reference powder were measured in the same −1 dation of 4-chlorophenol using CPE modiﬁed with ZnAl-LDH conditions. *e spectrum resolution was 4 cm and the and Isa et al.  used multiwalled carbon nanotube modiﬁed accumulation time was 5 min. with ZnAl-LDH to prepare chemically modiﬁed carbon for *ermal Gravimetric Analysis (TGA) was performed on 2+ Hg determination. a SDT simultaneous DSC-TGA instrument under N ﬂow 2 Journal of Analytical Methods in Chemistry 3 −1 ° ° (100 mL.min ). Approximately 20 mg of the NiAl-LDH was 15% in the temperature range between 20 C and 190 C, placed on the thermobalance of analyzer, which was purged which is attributed to the loss of water molecules adsorbed with helium gas. on the external surface of NiAl-LDH or in the interlayer ° ° surfaces. From 250 C to 450 C, signiﬁcant mass losses (25%) in two stages were observed, corresponding to the dehy- 2.3. Working Electrode Preparation, Electrochemical Equip- droxylation and the loss of nitrate ions [27, 28]. *e ﬁrst ment and Procedures. *e preparation of CPE modiﬁed by event is fast and characterized by a well-deﬁned DTG with a LDH (namely, NiAl-LDH/CPE) was similar to the proce- peak at 327 C, while the second is much slower with a broad dures previously described . Brieﬂy, CPE was obtained and poorly deﬁned peak centered at 400 C. by intimately mixing a carbon powder from Alfa (particle size< 325 mesh), a pasting liquid (silicone oil, Prolabo), and 3.2. Electrochemical Characterization of NiAl-LDH. In order LDH particles (60-30-10% w/w). *e mixture was homog- to explore the possible use of the NiAl-LDH material as enized in a mortar for 40 min and placed in a cylindrical modiﬁer of CPE, some preliminary experiments were per- Teﬂon tube (6 mm internal diameter), equipped with a 3− formed using [Fe(CN) ] ions as electroactive probe. *e stainless steel screw and piston acting as the electrical reactivity of a material at a given modiﬁed electrode strongly contact. *e active surface of the electrode was then polished depends on the properties of that material. *us to get on a sheet of clean paper. precise information about this material ion exchange vol- *e electrochemical measurements were performed on a tammetry was used. *is was done by examining the elec- μ-Autolab potentiostat controlled by the GPES software. 3− trochemical behavior of [Fe(CN) ] ions at modiﬁed and Cyclic voltammetry was used to examine the electrochemical unmodiﬁed carbon paste electrode, by recording a series of behavior of ISO, while square wave voltammetry was cyclic voltammograms. Figure 2 displays multisweep cyclic employed to optimize the sensitivity of sensor. Electro- voltammograms recorded at bare CPE (Figure 2(a)) and chemical procedure for sensing ISO was as follow: the NiAl-LDH/CPE (Figure 2(b)). At bare CPE, well-deﬁned modiﬁed electrode was dipped in a beaker containing 25 μM 3- diﬀusion controlled redox behaviors with [Fe(CN) ] with a of aqueous solution of ISO (50 mL) and maintained under constant steady state were recorded upon repetitive scan- mild stirring for 5 min for accumulation at open circuit. ning. *e cyclic voltammogram recorded at bare CPE were After this step, the electrode was removed, rinsed with centered at E � ½(E + E ) � 0.245 V with peak to peak pc pa distilled water, and then transferred to the electrochemical separation values of ΔEp � (E E ) � 0.09 V at scan 50 mV/ pa− pc cell containing the detection solution. Prior to the SWV s and the magnitude of i /i is equal to 1.09; this value pa pc experiment, the detection medium was deaerated with ni- suggests a reversible electrochemical system as a result of trogen for 3 min. *e regeneration of sensor was made by 3− monoelectronic transformation involving [Fe(CN) ] and transferring the modiﬁed electrode (after detection) to a 4− [Fe(CN) ] . When the electrode was modiﬁed by NiAl- blank acetate solution under mild stirring. *e trace LDH, the multisweep cyclic voltammetry performed on the amounts of ISO were totally desorbed after 1 min, shown by same probe solution led to a diﬀerent behavior as shown in a ﬂat voltammogram recorded after transferring the elec- Figure 2(b). During the ﬁrst scan, a poor signal was observed trode from the detection medium. due to the eﬀect caused by nonconductive NiAl-LDH ma- terial. Since this material is an excellent anionic exchanger, 3.Results and Discussions gradual increase in the intensities of the signals with the number of scan is observed. *e peak current reaches its 3.1. Physicochemical Characterization of the NiAl-LDH. maximum value after 40 cycles and the current was 49 times Figure 1(a) shows the FT-IR spectra of NiAl-LDH. A large higher than that recorded for the unmodiﬁed CPE. *e peak −1 absorption band which is centered at 3427 cm corresponds to peak separation recorded at NiAl-LDH/CPE was 0.045 V. to the stretching vibrations mode of hydrogen bonded *is value was lower for about 45 mV compared with that physisorbed and intercalated water molecules . Similarly, obtained at bare CPE, suggesting that the diﬀusion of the −1 the band close to 1640 cm corresponds to the O–H probe is easy at modiﬁed electrode. *is result is a proof that bending vibration of the interlayer water . *e intense 3− NiAl-LDH accumulates [Fe(CN) ] ions by anion exchange −1 band at 1383 cm is due to theѴ vibration mode of nitrate mechanism [29, 30]. ion in D symmetry present in the interlayer space . *e 3h *e active area of electrodes was studied using Rand- band characteristic to metal-oxygen bond stretching appears les–Sevcik equation. *e cyclic voltammetry at varying sweep −1 −1 at 644 cm and 540 cm is caused by various lattice vi- −3 rates was recorded using K [Fe(CN) ] solution 10 M in KCl 3 6 brations associated with metal hydroxide sheets . solution 0.1 M. From the slope of the plot of Ip vs. ]1/2 (Figure *e XDR pattern of NiAl-LDH is presented in S1), the A value was calculated using the following equation: ° ° Figure 1(b). *e peaks at 11.03 and 22.7 2θ are assigned to 5 (3/2) the 003 and 006 reﬂections, respectively . *e ﬁrst peak (1) i � 2.69.10 D n C A. p 0 0 corresponds to a d value of 8.2Ǻ. Also noted is the presence 3− −3 −6 2 of well-deﬁned reﬂections—012, 110, and 113—that are Here, for [Fe(CN) ] �10 M, D � 7.6.10 cm /s, and 6 o frequently used to conﬁrm the good crystallinity of LDH . n � 1, the calculated eﬀective surface areas were found to be 2 2 *e result of thermal analysis of material is presented in 0.047 cm and 0.055 cm for bare CPE and with NiAl-LDH/ Figure 1(c). NiAl-LDH displayed a progressive mass loss of CPE, respectively. 4 Journal of Analytical Methods in Chemistry (003) (012) (113) (006) (110) 4000 3500 3000 2500 2000 1500 1000 500 0 15 30 45 60 75 90 –1 Wavenumber (cm ) 2θ (degrees) (a) (b) 327°C 4 15 % 80 2 25% 0 200 400 600 800 1000 1200 Temperature (°C) (c) −1 Figure 1: (a) Infrared spectra (4000-500 cm region); (b) X-ray diﬀraction; (c) TG and DTG patterns of NiAl-LDH. 10 µA 0.2 µA –0.2 0.0 0.2 0.4 0.6 0.8 –0.2 0.0 0.2 0.4 0.6 0.8 Potential (V) vs. SCE Potential (V) vs. SCE (a) (b) −1 −4 3- Figure 2: Multisweep cyclic voltammograms recorded at 50 mV s in NaCl 0.1 M + 10 M of [Fe(CN) ] : (a) CPE; (b) NiAl-LDH/CPE. Scan rate 50 mV/s. Transmittance (a.u) Weight loss (%) Intensity (a.u) –1 Deriv.weight (mg°C ) Journal of Analytical Methods in Chemistry 5 3.3. Electrochemical Behavior of Isoproturon on NiAl-LDH/ fenuron [3, 31]. *e equation of this transformation was CPE. Cyclic voltammogram of 50 μM of ISO in acetate illustrated by (2) . From this cyclic voltammogram, it is buﬀer at CPE and NiAl-LDH/CPE was recorded as shown in obvious that oxidation peak current is greater for NiAl- Figure 3(a). *e blank cyclic voltammogram obtained at LDH/CPE than EPC. *e peak current on NiAl-LDH/CPE NiAl-LDH/CPE in acetate buﬀer is included (dotted line). In was 3.25 times higher than that recorder on CPE, indicating both cases, the electrochemical response shows one main an eﬀective preconcentration ability of ISO by NiAl-LDH/ anodic peak centered on 0.9 V. Such electrochemical be- CPE. *e increase in peak current may be due to adsorptive havior of ISO was similar to previous work described in the ability of NiAl-LDH through hydrogen bonding between literature with phenylurea compound such as diuron and hydroxyl group of NiAl-LDH and amide group of ISO. 2H (2) (H C) HC NH C N(CH ) (H C) HC NH + CO + NH(CH ) 3 2 3 2 3 2 2 3 2 -2e In order to yield more insights in the electrochemical Afterwards, the peak current increased much slightly as with behavior of ISO, further experiments were performed; these further increase in the accumulation time. *is phenomenon include the studying of the eﬀect of increasing the potential could be attributed to the saturated adsorption of ISO on scan rate. From Figure 3(b), it appears that the peak current NiAl-LDH/CPE. Considering sensitivity, the optimal accu- increases with the potential scan rate. A plot of the anodic mulation time of 150 s was employed in further experiments. 1/2 peak current versus V exhibits a linear dependence as indicated by the graph in Figure 3(b), indicating that elec- 3.4.2. 3e Eﬀect of NiAl-LDH Amount on the Paste trochemical oxidation takes place via adsorption with mass Composition. *e study of the eﬀect of NiAl-LDH propor- transfer . From the above cyclic voltammetry studied, it tion within the CPE was also expected to aﬀect the electrode appears that NiAl-LDH used as electrode modiﬁer can be response. Figure 6(b) presents the evolution of the SWV peak suitable for building an electrochemical sensor for ISO. current when the detection of ISO was performed with NiAl- Figure 4 presents the SWV curves of acetate buﬀer so- LDH/CPE prepared with various amounts of NiAl-LDH. *e lution at a CPE (Figure 4(a)) and 25 μM ISO in acetate so- peak current was shown to increase with the amount of NiAl- lution at a CPE (Figure 4(b)) or NiAl-LDH/CPE (Figure 4(c)). LDH incorporated in the paste, up to a maximum value of A well-deﬁned but rather low peak was obtained in the 10%. *is was followed by the decrease of the current for potential range of 0.5 to 1.1 V with CPE (Figure 4(b)) pointing higher amount of LDH within the paste. From 2.5% to 10%, out the weak sorption capacity of the carbon towards ISO. the increase on peak current was due to the number of ad- When the CPE was modiﬁed by NiAl-LDH, its sensitivity was sorption sites, which increases at the solution electrode in- signiﬁcantly improved (Figure 4(c)). *e peak current terface. *e reduction of peak current observed at 12% is due measured was found to be equal to 13 μA; this value is more to the fact that LDHs are weakly conductive material. *e than 2.6 times higher than that recorded at CPE (5 μA). high amount of this modiﬁer within the carbon paste reduced Some important physicochemical parameters involved in the conductivity of the electrode . *e optimum per- the stripping process were examined in order to optimize the centage of NiAl-LDH/CPE incorporated into the CPE was sensitivity of the modiﬁed electrode, in view of its possible use chosen to be 10% due to the best compromise between the as ISO sensor. Prior to this study, the stability and repro- number of sites and the conductivity of the paste. ducibility of the signal of ISO on the NiAl-LDH/CPE were evaluated before its application to the voltammetric detection of ISO. *us, a series of ﬁve successive SWV experiments of the 3.4.3. Inﬂuence of the pH of the Detection Medium. *e same electrode were performed in 25 μM of ISO solution acidity of the detection medium is a key parameter that can (Figure 5), and a coeﬃcient of variation of 2% was noticed, aﬀect the mass transport to the electrode surface, especially indicating that the modiﬁed electrode has good reproducibility. when the redox process involves some protons as in the *e stability of the electrode was also investigated by measuring present case. *e inﬂuence of the pH on the ISO response was the electrode response with 25 μM of ISO every day. Between ° studied at NiAl-LDH/CPE between pH 1 to 6, because ISO the measurements, the electrode was stored at 4 C in a re- can be partially hydrolyzed in alkaline medium . It is frigerator. *e current response decreases to 5% after 5 days. observed from Figure 6(c) that the peak current increased with an increase of pH of the detection medium to a max- imum value at pH 4.5. After this value, the decrease of 3.4. Optimization of Experimental Parameters for ISO sensibility with increase of pH value was observed. For higher Detection pH values, low current value was observed. *e low electrode 3.4.1. Inﬂuence of the Accumulation Time. *e eﬀect of response obtained for pH< 2 may be due to prior protonation accumulation time is shown in Figure 6(a). *e peak current of amino group in the substrate, which induces electrostatic increased gradually with the accumulation time up to 150 s. repulsion between the analyte and NiAl-LDH edges layer 6 Journal of Analytical Methods in Chemistry 2 µA R = 0,99 0 2468 10 12 14 1/2 2 µA 0.6 0.8 1.0 1.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Potential (V) vs. SCE Potential (V) vs. SCE (a) (b) Figure 3: (a) Cyclic voltammograms recorded on (A) NiAl-LDH/CPE in 0.1 M acetate buﬀer (pH 4.5); (B) on CPE in 50 μM ISO + 0.1 M −1 acetate buﬀer (pH 4.5); (C) on NiAl-LDH/CPE in 50 μM ISO + 0.1 M acetate buﬀer (pH 4.5); potential scan rate 50 mV s . (b) Inﬂuence of −1 scan rate (v) on peak current of 50 μM of ISO on the NiAl-LDH/CPE (curves a-f, v � 25, 50, 75, 100, 125, and 150 mv.s , respectively). Inset: 1/2 plot of the anodic peak current (Ip ) versus v . 10 µA 10 μA 0.6 0.9 0.6 0.9 0.6 0.9 0.6 0.9 0.6 0.9 Potential (V) vs. SCE 1 2345 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Successive measurement number Potential (V) vs. SCE Figure 5: Typical successive peaks recorded using 25 μM of ISO Figure 4: SWV response of (a) 0.1 M acetate buﬀer on CPE; (b) ISO after 3 min accumulation and detection in 0.1 M acetate buﬀer on 25 μM after 3 min accumulation and detection in 0.1 M acetate NiAl-LDH/CP; inset SWV response recorded in condition the buﬀer on CPE; (c) ISO 25 μM after 3 min accumulation and de- same as in Figure 3. tection in 0.1 M acetate buﬀer on NiAl-LDH/CPE. Other experi- mental conditions: electrolysis potential: 0.8 (V) pulse amplitude: 50 mV, frequency 125 Hz. obeys the following equation: E (V) � −0.025pH + 0.974. pa *e slope of the variations in Ep vs. pH, of 0.025 V/ΔpH, suggests that the same numbers of protons and electrons are which contains positive charge. *e sensibility of the electrode involved in the electrochemical oxidation of ISO, almost is optimal at pH 4.5. *e lower stripping signal recorded for matching the theoretical Nernst equation . pH> 4.5 must probably be due to the quantity of OH in the medium which can react by exchange mechanism with ex- changer ion in the interlayer, thus contributing to the re- 3.4.4. Inﬂuence of the SWV Technique Parameters. duction of the sensibility of the electrode. Square wave parameters are also important in controlling *e relationship between the oxidation peak potential the peak intensity. *ese parameters include the frequency, and pH was shown in Figure 6(d). A linear shift of E the electrolysis potential, and amplitude. All these param- pa towards negative potential with an increasing pH indicated eters were studied and the most suitable values used for the that protons are directly involved in the oxidation of ISO. It detection of ISO are given in Table 1. I (µA) Peak current (μA) Journal of Analytical Methods in Chemistry 7 14 11 0 50 100 150 200 250 300 2 468 10 12 14 16 %Ni AlNO Time of accumulation (s) 3 3 (a) (b) 35 0.96 0.93 20 0.90 0.87 0.84 E = – 0.025 pH + 0.974 0.81 0 123456789 1 23456 pH of detection medium pH (c) (d) Figure 6: (a) Eﬀect of accumulation time on the peak current of ISO; (b) eﬀect of the amount of NiAl-LDH in the composition of the paste on the peak current of ISO; (c) eﬀect of pH of detection medium on the peak current of ISO; (d) variation of the peak potential versus pH of the detection medium. Other conditions are the same as in Figure 4. 3.4.5. Interference Studies. Under optimal experimental relationship between these two parameters is linear, with a conditions, the eﬀects of other coexisting substances and slope (μA/M) of 0.14 and a correlation coeﬃcient of 0.998. anions were studied. *e results summarized in Table 2 show *e detection limit for this work was estimated to be − − − −9 −1 that 5-fold excess of Cl , NO , and HCO did not interfere 1 × 10 mol L on the basis of signal-to-noise ratio equal to 3 3 with the analysis of ISO. However, when the concentration 3. A comparison of the performance of NiAl-LDH/CPE − − of these ions increases up to 50-fold excess (Cl , NO , and including the limit of detection and the linear range with HCO ), they interfere with the analysis of ISO by increasing those reported in the literature is shown in Table 3 which the peak current due to the ion exchange properties of NiAl- indicates that the proposed sensor exhibited detection limits 3+ 2+ LDH. We have also studied the eﬀect of cations (Al , Pb ). lower than those reported by certain authors. 3+ 2+ *e results obtained show that Al and Pb were found to *e analytical applicability of the modiﬁed electrode was interfere slightly at 50-fold excess with the analysis of ISO. applied to the determination of ISO in real sample. A volume *e eﬀect of anionic dye (orange II) shows that it interferes of 50 mL of the spring water was ﬁrst analyzed by using the with ISO when the concentration is 10 times larger than ISO. optimized parameters established in this study and ISO was not detected. However, if these samples were spiked with −1 0.16 μmol L of ISO, the content was determined by the 3.4.6. Inﬂuence of ISO Concentration. *e relationship be- standard addition method (the results are summarized in tween the oxidation peak current of ISO and the concen- Table 4). *e obtained values are in good agreement with the tration was studied by SWV under optimized conditions spiked value, indicating that the proposed method is a good (Figure 7). *e peak current increases with the concentra- alternative for the analytical determination of this pesticide −8 −7 tion of ISO over the range from 2 ×10 to 1.8 ×10 M. *e in the sample. Peak current (µA) Peak current (µA) E (V) Peak current (µA) 8 Journal of Analytical Methods in Chemistry Table 1: Optimum experimental conditions used in SWV of ISO. Instrumental parameter Range examined Optimum value Electrolysis potential (mV) −0.2 to 1.6 0.8 Frequency (Hz) 25 to 220 125 Amplitude (V) 25 to 100 50 Table 2: Eﬀect of interference ions on the response of the NiAl-LDH/CPE to 25 μM ISO in acetate buﬀer (pH 4.5). Interference ions Added amount over [ISO] % variation in the anodic peak current (Ip � 100%) 5 0 Cl 25 +32.1 50 +52.4 5 0 NO 25 +21.7 50 +33.21 10 +10.9 Orange II 25 +21.4 50 +54.45 HCO 50 +33.26 3+ Al 50 −1.5 2+ Pb 50 −3 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 –7 [ISO]. 10 M 0.5 µA 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Potential (V) vs. SCE −8 −8 −8 −7 Figure 7: Dependence of the SWV peak current with increased ISO concentration from (a) to (i) 2 ×10 ; 4 ×10 ; 8 ×10 ; 1 × 10 ; −7 −7 −7 −7 1.2 ×10 ; 1.4 ×10 ; 1.6 ×10 ; 1.8x10 M. *e inset shows the corresponding calibration curve. Table 3: Comparison of the proposed method with literature methods for the determination of phenyl urea herbicides. Electrode conﬁguration Linearity range (M) Detection limit (M) Ref −8 −5 −8 Graphene modiﬁed/ GCE 9.69 ×10 -4.84 ×10 9.69 ×10  ∗ −6 −3 −6 GO-MWCNT ﬁlm-modiﬁed/ GCE 9 ×10 –0.38 ×10 0.645 ×10  −9 −6 −9 Polypyrrole/ GCE 2.42.10 –1.42.10 2.42 ×10  ∗ −6 −6 −6 Sodium montmorillonite ﬁlm/ GCE 0.206 ×10 –61.8 ×10 0.206 ×10  −9 −6 −9 Organomontmorillonite/ GCE 4.84 ×10 –1.45 ×10 4.84 ×10  ∗ −8 −4 −10 PANI/MWCNTs/ GCE 4.84 ×10 –4.84 ×10 4.84 ×10  −7 −3 −7 Well-jet electrode 4.84 ×10 –7.27 ×10 4.84 ×10  −6 −4 −6 Ph-CN-SWCNT/ GCE 1 × 10 –2 ×10 0.20 ×10  −8 −7 −9 ∗∗ NiAl-LDH/ CPE 2 ×10 –1.8 ×10 1 × 10 *is work ∗ ∗∗ GCE: glassy carbon electrode. CPE: carbon paste electrode. GO-MWCNTs: graphene-multiwalled carbon nanotubes. PANI/MWCNTs: polyaniline multiwalled carbon nanotubes. Ph-CN-SWCNT: phthalocyanine-single walled carbon nanotube. I (µA) p Journal of Analytical Methods in Chemistry 9 Table 4: Determination of ISO in spring water. in three soil proﬁles,” Chemosphere, vol. 64, no. 67, pp. 1053–1061, 2006. ISO added (M) ISO found (M) Recovery (%)  M. Chicharro, E. Bermejo, A. Sanchez, ´ A. Zapardiel, Spring water 0.160(μM) 0.156± 0.012 μM 97.5 A. Fernandez-Gutierrez, and D. Arraez, “Multiresidue anal- Number of samples assayed � 5. ysis of phenylurea herbicides in environmental waters by capillary electrophoresis using electrochemical detection,” Analytical and Bioanalytical Chemistry, vol. 382, no. 2, 4.Conclusion pp. 519–526, 2005.  A. Wong, M. R. de Vasconcelos Lanza, and In this work, NiAl-LDH was shown to be eﬀective material M. D. P. T. Sotomayor, “Sensor for diuron quantitation based for the elaboration of an amperometric sensor for ISO. Prior on the P450 biomimetic catalyst nickel(II) 1,4,8,11,15,18,22,25- to its use for sensing purposes, this material was charac- octabutoxy-29H,31H-phthalocyanine,” Journal of Electroana- terized by X-ray diﬀraction, infrared spectroscopy, and lytical Chemistry, vol. 690, pp. 83–88, 2013.  M. Ren-Xiang, C. Ming-Xue, and Z. Jian-Liang, “Simulta- thermal analysis. *e determination of ISO was examined at neous determination of 15 phenylurea herbicides in rice and a bare CPE and NiAl-modiﬁed CPE by using square wave corn using HPLC with ﬂuorescence detection combined with voltammetric techniques. Results showed that the peak UV decomposition and post-column derivatization,” Journal current was greatly enhanced (more that 2.6-fold) compared of Chromatography B, vol. 875, no. 2, pp. 437–443, 2008. to the response obtained using bare CPE. It was also found  Y. Wang, L. Xiao, and M. Cheng, “Determination of phe- that the sensitivity of this modiﬁed electrode depends on the nylureas herbicides in food stuﬀs based on matrix solid-phase loading of NiAl-LDH on the paste composition and mainly dispersion extraction and capillary electrophoresis with on the parameters involved in the detection step by square electrochemiluminescence detection,” Journal of Chroma- wave voltammetry. After optimization, a detection limit of tography A, vol. 1218, no. 50, pp. 9115–9119, 2011. −1 1x10-9 mol.L was achieved. *e proposed method was  J. Fenoll, P. Hell´ın, C. M. Mart´ınez, P. Flores, and S. Navarro, applied to quantify ISO in real media. *e obtained results “High performance liquid chromatography-tandem mass clearly indicated that the proposed voltammetric procedure spectrometry method for quantifying phenylurea herbicides could be applied for ISO sensing in environmental polluted and their main metabolites in amended and unamended soils,” Journal of Chromatography A, vol. 1257, pp. 81–88, media.  G. Shiqian, J. You, X. Zheng et al., “Determination of phe- Data Availability nylurea and triazine herbicides in milk by microwave assisted ionic liquid microextraction high-performance liquid chro- *e data used to support the ﬁndings of this study are matography,” Talanta, vol. 82, no. 4, pp. 1371–1377, 2010. available from the corresponding author upon request.  P. A. Sundari and P. 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