A Novel Carbon Paste Electrode Modified with N1-Hydroxy-N1,N2-Diphenylbenzamidine for the Electrochemical Determination of Cadmium(II) in Environmental Samples

The present study introduces a novel electrode for rapid, highly sensitive, and selective electrochemical sensor for cadmium(II) using 5% N1-hydroxy-N1,N2-diphenylbenzamidine (HDPBA) modified carbon paste electrode (CPE) (HDPBA‒CPE). Surface characterizations and structural analysis of the proposed HDPBA‒CPE were performed using several analytical techniques. The voltammetric measurements of Cd(II) were conducted by cyclic voltammetry (CV) and square wave anodic stripping voltammetry (SWASV). Several experimental conditions such as composition and pH of buffer solutions, HDPBA composition, accumulation potential and time, and other voltammetric conditions were optimized. Cd(II) was preconcentrated on the modified electrode surface for 270 s using Britton Robinson (B-R) buffer (0.1 M, pH 4) at −1.0 V versus Ag/AgCl, followed by electrochemical oxidation of the accumulated Cd(II) in the positive scan of SWASV after a quiet time of 10 s. Under optimized parameters, the proposed method showed a linear range of 0.3–100 nM Cd(II) with a detection limit of 0.032 nM. The fabricated HDPBA-modified carbon paste electrode exhibited excellent sensitivity, selectivity, stability, and reproducibility (with RSD of 3.8%). The developed HDPBA‒CPE was used for the quantification of Cd(II) in tobacco and environmental water samples, and it was found to be applicable for the determination of different types of real samples.


Introduction
In recent times, environmental contamination has become a worldwide problem because of population growth, agricultural activities, and the rapid development of industries [1]. e continuous release of heavy metals into the surroundings lead to serious problem throughout the world. Environmental monitoring of toxic metal ions is an area of major concern because of their perniciousness and the ability to accumulate in human organs even at trace levels [2]. erefore, developing a highly selective, sensitive, and fast monitoring methods is very important for the toxic heavy metal ions due to their serious environmental impact and the increased industrial applications [3].
Cd(II) is among the toxic metal ions, which is mostly present in the water around the chemical industries and has become a rising issue of environmental pollution. Cadmium is mostly used in various factories including the plastic industry, coating technology, and battery manufacturing. It is also the major byproduct of Zn smelting work [4]. Food and water samples may have high contents of cadmium(II) when present around cadmium origins. e trace level accumulation of cadmium(II) in the human organs may lead to various health effects such as muscular cramps, renal degradation, erythrocyte destruction, nausea, diarrhea, salivation, and chronic pulmonary problems [5]. Recent research works indicated that the cadmium(II) is a cause for a carcinogenic disease. e United States Environmental Protection Agency set an allowable limit of 5 μg/L Cd(II) in drinking water [4]. erefore, the fabrication of an accurate analytical technique for the quantification of trace concentrations of cadmium(II) has become of great interest in recent times. Different methods have been applied for the detection of Cd(II) at trace contents which include atomic fluorescence spectrometry [6], graphite furnace atomic absorption spectrometry (GFAAS) [7], inductively coupled plasmamass spectrometry (ICP-MS) [8], high performance liquid chromatography (HPLC) [9], inductively coupled plasmaatomic emission spectroscopy (ICP-AES) [10], and X-ray fluorescence [11]. e aforementioned analytical methods are very reliable and accurate for the quantification of Cd(II). But these analytical techniques have major limitations including their expensiveness, tediousness, and time-consuming nature. Furthermore, they are not appropriate for insitu analysis and require various complicated steps and skills [12].
Instead of the aforementioned methods, the voltammetric methods have been used as the most versatile and suitable techniques for the detection of heavy metals including Cd(II), because of their high sensitivity, high selectivity, fast analysis, simplicity, portability, low cost, easy maintenance, and the ability to conduct speciation determination [13].
Nowadays, chemically modified carbon paste electrodes (CMCPEs) have been applied as selective and suitable tools for the analysis of metal ions because of their easily regenerated surface, cost-effectiveness, simple modification, low background current, high sensitivity, and selectivity of electrochemical methods. e working mechanisms of electrodes depend on the nature and characteristics of the modifiers applied [14]. Several types of modifiers including organic ligands, polymers, ion exchangers, and nanomaterials are usually used in the modification of carbon electrodes [15].
Ligands modified carbon paste electrodes (CPEs) have been applied for the electrochemical determination of toxic metal ions because of their specific complexing ability with metal ions. Most of the metal-chelating ligands have acidic groups, such as, −COOH, -SH, -OH, and neutral donating groups which can form stable complexes with metal ions [16].
is study was aimed at fabricating a new HDPBA modified carbon paste electrode (HDPBA-CPE) for sensitive electrochemical determination of Cd(II) using SWASV. Unlike the previous reported electrodes, in this paper, a single modifier (HDPBA) is used for the modification of CPE which is less costly and not time consuming. HDPBA was synthesized by the condensation of N-phenylhydroxylamine with N-phenylbenzimidoyl chloride at 0°C in ether which is an easy and cost-effective preparation method. e modified electrode exhibited the characteristics of cost-effectiveness, simple preparation, excellent stability, and easy renewable ability. e fabricated sensor has also a higher sensing ability for Cd(II) than electrodes with one and more modifiers. e developed electrode was effectively used for the quantification of trace levels of Cd(II) in various types of water samples and tobacco samples.    [26]. e electrodes morphology characterizations were studied by a scanning electron microscope (Cx-200 COXEM, Korea).

Materials and Methods
e Fourier transform infrared (FTIR) spectrometer (PerkinElmer, Spectrum 100, USA) was used for the recording of the FTIR spectra. UV-Vis analyses were done using a UV/Vis/NIR instrument (PerkinElmer Lambda 950, USA). e electrochemical measurements were conducted using the CHI 840C electrochemical analyzer (CHI instruments, USA). ree electrodes system with modified or unmodified CPE as a working electrode, Ag/AgCl as a reference electrode, and Pt-wire as a counter electrode were used in all the voltammetric determinations of the study. A 20 mL cell was used as a solution container. A pH meter (sensION, China), magnetic stirrer, and a stop clock were applied for pH measurements of the solutions, stirring of the solutions, and time measurement, respectively. Atomic spectrometric determination of Cd(II) was conducted using a graphite furnace atomic absorption spectrometer (GFAAS) (Agilent 280Z AA Zeeman, GTA120, USA).

Electrodes Preparation.
Modified CPE was made by mixing of 0.05 g of the modifier (HDPBA), 0.95 g graphite powder (spectroscopic grade, BDH Laboratory Supplies Poole, England), and 0.36 mL paraffin oil (Uvasol Merck, Germany) using a mortar and pestle. In the mixture, the paraffin oil does not dissolve the modifier (HDPBA). e paraffin oil was used to adhere the powder and the HDPBA to form a uniform paste. Hence, the HDPBA still remained solid in the carbon paste. e mixture was ground for 20 min and packed into an electrode prepared from plastic syringe (1 mL) with a 3 mm outer diameter, using a Cu wire connected to measurement instrument. e bare CPE was made in an identical manner, without the addition of the modifier (HDPBA). e renewal of the electrode was performed by removing a small portion of the electrode surface and replacing it with a fresh paste.

Voltammetric Determinations.
e voltammetric determinations were performed using CV and SWASV by applying the following steps: (a) accumulation step: In this step, the accumulation solution, 0.1 M B-R buffer (pH 4) was first added into the cell, and a predetermined concentration of Cd(II) was added to it. After immersion of the electrodes into the cell, Cd(II) was preconcentrated at the electrodes surface with an applied potential of −1.00 V for a known time under stirring solution. After preconcentration, stirring was stopped and a 10 s rest time was permitted to make the solution stable and minimize the background current. (b) Stripping step: e voltammograms of Cd(II) were recorded in the positive potential scan from −1.2 to −0.2 V versus Ag/ AgCl. During each determination, the electrode was renewed using 4 to 5 runs/scans in B-R solution (0.1 M). Fresh buffer solution was applied in each measurement for the prevention of buildup of potential in the cell. e effect of deaeration on the peak currents of Cd(II) was studied by purging the test solution with argon with different times (0, 5, 8, and 10 min).

Real Samples Analysis.
e proposed electrode was employed for the quantification of Cd(II) in tobacco samples and five types of environmental water samples including industrial wastewater, bottled, well, and stream water samples under optimized experimental parameters. Filtration was performed for the water samples before the determination to avoid solid particles. eir pH values were set to 4 and added to the 20 mL·cell, accumulated and determined by voltammetric measurements. A known concentration of Cd(II) was added into each water sample for recovery studies. Furthermore, Cd(II) in the water samples was also determined by the GFAAS method.
A tobacco sample was collected from ten local cigarettes and dried in an oven at 105°C and ground. For the determination of cadmium(II), 500 mg of powdered samples were added into the digestion vessel, and 5.0 mL of H 2 O 2 (30%) plus 3.0 mL of concentrated HNO 3 were added. e vessel was closed and placed in the carousel of the oven and kept for about eight minutes. en the evaporation of the digest was done to near dryness. Finally, HNO 3 was added for the dissolution of the residue, and voltammetric measurement was done after filtration and pH adjustment of the solution [33].

Spectroscopic Studies and Surface Characterization.
e spectral analysis of the modifier (HDPBA) and morphological characterization of unmodified CPE and HDPBA-CPE were performed using the FT-IR, UV-Vis and SEM techniques. Chemical characterization of the modifier (HDPBA) and unmodified and modified CPEs was done by using Fourier transform infrared (FTIR) analysis. e FTIR characterizations of the HDPBA-modified graphite and unmodified graphite were done by mixing the HDPBA and the graphite powder in a mortar and pestle without paraffin oil addition. First, the HDPBA and the graphite powder were mixed properly in a mortar and pestle. en, after, prior to spectra acquisition, about one mg of graphite powder (for unmodified paste), while one mg of the mixture of graphite powder and the modifier, HDPBA (for modified paste), was mixed with approximately 100 mg of KBr powder separately using a mortar and pestle. e paste was then compressed to form a pellet. A KBr pellet was also used as the background reference spectrum. e FTIR spectra were recorded using a PerkinElmer with a spectral resolution of 1 cm −1 between the wave number 4500 and 500 cm −1 .
FTIR spectra of the modifier (HDPBA) and modified and unmodified CPEs were run within the spectral range of 4500-500 cm −1 . As can be seen in Figure 2, no important bands were found in unmodified graphite (spectrum a). But HDPBA-graphite mixture (spectrum b) exhibited bands at 1030, 1435, 1575, 1640, 3000, and 3400 cm −1 characteristics to the stretching of N−O, C−N, C � C (aromatic) , C � N, C−H (aromatic, stretching) , and O−H bonds, respectively, in the ligand chemical structure. e results are consistent with other reported literature [16,23]. e spectral data proved the incorporation of HDPBA in the modified electrode.
e UV spectra of the modifier were recorded in ethanol. e free modifier (HDPBA) showed a band at 317 nm ( Figure 3, curve a) which is assigned to n−π * transition of the C=N group and which is in agreement with the results of previous studies [16,23,24]. However, after incorporation of Cd(II) into the modifier, the spectra resulted in a bathochromic shift (λ max (ethanol) = 334 nm) ( Figure 3, curve b). e spectrum shift after the addition of the analyte to the ligand gives evidence for the complex formation between Cd(II) and ligand. e surface characteristics of the prepared electrodes were studied by SEM. e SEM images exhibited an important difference between the surface morphologies of HDPBA modified CPE and unmodified CPE. e unmodified surface was prevailed by uniformly distributed and homogenous surface with small pores (Figure 4(a)); while after modification, the numbers and pore sizes were much larger, and their distribution on the electrode surface became uneven because of the addition of the ligand into the paste (Figure 4(b)) making it favorable for the adsorption of Cd(II) on the electrode surface resulting in better sensing.

Electrochemical Characterization.
e electrochemical behaviors of the unmodified carbon paste electrode and HDPBA-CPE were studied using CV and electrochemical impendence spectroscopy (EIS) characterizations in K 3 [Fe(CN) 6 ]/KCl solution. e cyclic voltammograms (CVs) of ferricyanide for both the unmodified and modified electrodes are shown in Figure 5. Intense redox peaks appeared for the unmodified carbon paste electrode (peak a). However, with the HDPBA modified electrode, the peak currents became smaller, and the potential values changed noticeably (peak b). is indicates the ferric cyanide ions repel the lone pair electrons of−OH and −N in HDPBA, consequently the ligand act as blocking layer for mass and electron exchange to obstruct the movement of [Fe(CN) 6 ] 3− towards the electrode surface [13,[34][35][36][37], which evidently confirm HDPBA is effectively incorporated on the carbon paste electrode surface.
EIS is an important tool for investigating the electrochemical characteristics of an electrode's surface. e main parameters in EIS are charge transfer resistance (R ct ), double layer capacitance (C dI ), electrolyte resistance (Rs), and impedance (Z w (W)). Among the mentioned parameters, charge transfer resistance (R ct ) is an important parameter that can be used to explain the electrode interface properties. e semicircle in the impedance plot corresponds to R ct . R ct controls the kinetics of the reaction probe at the electrode surface. In the present study, for electrochemical impendence spectroscopy (EIS) measurements, EIS plots of the developed electrodes were done in 5 mM K 3 [Fe(CN) 6 ]/KCl solution in a frequency range of 0.1-100000 Hz with an amplitude of 0.005 V at a potential of 0 V versus Ag/AgCl. From Figure 6 Figure 7. e unmodified electrode has a higher R ct and semicircle diameter than the HDPBA modified CPE.
is shows the presence of better affinity between HDPBA and Cd(II). is can be explained by the fact that the electrons of −N and −OH in HDPBA attract the Cd(II) (from the solution), and hence, it leads faster electron transfer within the HDPBA-CPE [13,[34][35][36][37].  increment and negative potential shift at HDPBA modified CPE are due to the complex formation of Cd(II) with HDPBA. e results indicate that unmodified CPE is not able to promote an effective interaction between Cd(II) and the electrode surface. However, HDPBA has an effective interaction with Cd(II). Since Cd(II) is a Lewis acid, it has a preference for complexing/bond formation with ligand (HDPBA) that is Lewis base and has electronegative donor atoms (nitrogen and oxygen) (Figure 1). is results in the higher preconcentration of Cd(II) on the HDPBA-CPE surface and hence it makes larger current responses. e anodic peak current of Cd(II) is significantly larger and sharper than the corresponding cathodic peak current. us, the anodic peak of Cd(II) was studied by SWASV for analytical applications. Figure 9(a) shows the square wave anodic stripping voltammograms (SWASVs) of Cd(II) at the developed electrodes.

Voltammetric Determination of Cd(II).
e anodic peak current of Cd(II) at the HDPBA-CPE is enhanced significantly compared to that of the unmodified one. Furthermore, the HDPBA-CPE shows a shift in the peak potential to the negative values (−0.768 V for the HDPBA-modified electrode and −0.756 V for the unmodified CPE) which indicates the formation of a complex between the ligand (HDPBA) and the Cd(II). is is due to the fact that the electrons of −OH and −N groups in HDPBA (Figure 1) attract the Cd(II) and form stable complexes on the HDPBA-CPE surface, which leads to the accumulation of a higher concentration of Cd(II) and hence finally gives higher current responses. us, the use of the HDPBA as a modifier is worthwhile since it highly enhances the analytical peak signal of the electrode. e influence of deaeration on the current response of Cd(II) was studied by purging the test solution with argon at different times (0, 5, 8, and 10 min). e results are shown in Figure 9(b). No significant difference was found between the peak current of non-deaerated and deaerated solutions. e RSD of the responses among nondeaerated and deaerated solutions with different times (0, 5, 8, and 10 min) was found to be 1.80%. e relative error in the peak current between nondeaerated and deaerated solutions was 3.74%. is indicates the results obtained from both solutions are reproducible and deaerating the electrolyte solution has no substantial effect on the peak currents of Cd(II). Since reproducible and stable results were obtained without deaerating the buffer solution, deaeration (which is an additional step) was not required in this study.
Based on the results found and similar research reported [15,19,21,22]

Effect of Modifier Content.
e effect of modifier content in the paste on the peak current of Cd(II) was studied by preparing six separate electrodes made from 2.0%, 3.5%, 5.0%, 7.5%, 10.0%, and 12.5% (w/w) modifiers in the carbon pastes under identical preparation conditions. As presented in Table 1, the highest peak current of Cd(II) was found at the modifier composition of 5.0%. e increase in the peak current response up to 5% modifier composition is due to the fact that the presence of sufficient amount of HDPBA on the electrode surface results in accumulation of a larger amount of analyte ions (Cd(II)). is is because of the complexation of Cd(II) with the HDPBA at the electrode surface. e low peak current at higher modifier content (>5.0%) can be explained by the reduction in the amount of conductive carbon powders within the paste which results in the enhancement in the background current and the decrease in electrode conductivity. While at lower modifier content (<5.0% of HDPBA), there could be a lower extent of complexation between the modifier and Cd(II) and hence it leads to a decrease in the peak current response of Cd(II). us, 5.0% HDPBA modified electrode was used for all further experiments.

Effect of Supporting Electrolyte Solutions and pH.
e effect of supporting electrolyte solutions on the peak current of Cd(II) was determined by applying different buffers including CH 3 COONa, NH 4 Cl, NaClO 4 , HCl, Na 2 HPO 4 /NaH 2 PO 4 , Na 3 C 6 H 5 O 7 , and Britton Robinson (B-R) (0.1 M). Compared to others, the highest peak current was found in the Britton Robinson (B-R) buffer. is may be due to the ionic strength and buffering capacity differences between the solutions. erefore, Britton Robinson (B-R) buffer was selected as a suitable supporting electrolyte solution in the study. e pH effect was studied by varying the pH of the B-R solution between 2 and 9. As shown in Figure 10, the highest voltammetric peak was obtained at pH 4. e low peak currents Cd(II) at extremely low pHs (<4) may be due to the competition of the protons in the solution with Cd(II) for attachment to the modifier, HDPBA. Furthermore, at excessively low pH values, the dissolution and leakage of the modifier (HDPBA) may gradually occur in the acidic medium, which results in the loss of the capability of the HDPBA to immobilizing Cd(II). e hydrolysis of Cd(II) might be carried out at higher pHs (pH > 4), which leads to a decrease in the peak current of Cd(II) due to the lack of preconcentrated Cd(II) on the modified electrode surface [33].

Effect of Accumulation Potential.
e effect of preconcentration potential was determined by changing the potential values between −0.2 V and −1.4 V. As depicted in Figure 11, the peak currents of Cd(II) improved significantly with negative values up to −1.0 V and the highest peak 6 Journal of Analytical Methods in Chemistry current was found at −1.0 V. However, after −1.0 V, the current responses could not be obviously increased; therefore, −1.0 V was chosen for this study. A decrease in the current response at more positive potentials can be explained by the fact that Cd(II)) may not be effectively reduced because of the lack of negative potential. On the other hand, at extremely negative accumulation potentials, a slight reduction of peak currents might be due to impurities that could be easily reduced with the analyte. In addition, at more negative potentials, the evolution of the hydrogen bubbles may affect the deposition of metal at the electrode surface, which results in the decreased current response [38].

Effect of Accumulation Time.
It was determined by varying the time between 30 s and 360 s. As indicated in Figure 12, the peak current increases quickly up to 270 s and then slowly increases after 270 s, which shows a significant effect of preconcentration time on the detection sensitivity of Cd(II). e gradual increase of current signals of Cd(II) at higher accumulation times is attributed to the

Effect of Scan Rate.
For the investigation of the types of interaction between the Cd(II) and the electrode, the scan rate effect was done by varying the values from 20 mV·s −1 to 140 mV·s −1 . Figure 13 shows the redox peaks at different scan rates (]). e peak currents were linearly proportional to scan rate; the current responses increased with an increase in ] without potential shift. is indicates that Cd(II) undergoes a nondiffusion meaning surface adsorption controlled mechanism at the modified carbon paste electrode.

Effect of Instrumental Parameters.
e effect of frequency on the peak current of Cd(II) was evaluated by changing its values between 20 and 120 Hz. A frequency of 80 Hz was selected as the optimum value based on the peak shape and symmetry. e effect of amplitude was varied from 20 to 150 mV. A 100 mV was selected for subsequent measurements. Similarly, the step potential effect on the current responses was studied by changing the potential values between 2 mV and 12 mV. A 6 mV was selected as the optimum value.

Analytical Performance.
To determine the relationship between the anodic peak current and Cd(II) concentration and to construct calibration curves for the electrode, square wave voltammograms were recorded in B-R buffer solution at pH 4 under optimized experimental parameters. Figure 14 shows the square wave voltammograms and calibration plot for Cd(II) in the linear range of 0.3 to 100 nM. A calibration equation: I p = 2.661 [Cd(II)] + 1.188 with a R 2 value of 0.997 was found in the given linear range. e limit of detection calculated as LOD = 3s/m was found to be 0.032 nM, where LOD, S, and m are the detection limit, standard deviation of 0.3 nM of Cd(II), and the slope of the calibration, respectively. e s was calculated by 8 times measurements of 0.3 nM of Cd(II) peak signals. e calibration results confirm that the developed HDPBA/CPE showed an excellent sensing performance/affinity towards the detection of trace Cd(II). e repeatability of the fabricated electrode was investigated by seven repeated determinations of 50 nM Cd(II) using a similar electrode in identical conditions. RSD value for seven repeated measurements of 50 nM Cd(II) was obtained to be 2.6%. e reproducibility for 50 nM of Cd(II) solution was also performed by applying five separate electrodes, which were made in an identical manner. e RSD of the results found between the five electrodes was 3.8%, which indicates the excellent precision of the proposed sensor. In addition, the stability of the modified electrode was performed by recording the current signals of 100 nM  Journal of Analytical Methods in Chemistry Cd(II) for one month. After one month, the peak current response of 100 nM Cd(II) only decreased by 4.2%. e excellent stability and reproducibility of the modified electrode revealed its applicability for the quantification of Cd(II) in real samples.

Selectivity of the Modified Electrode.
e effect of foreign ions on the current response of Cd(II) was studied by the addition of different concentrations of various ions into 5.0 × 10 −8 M of Cd(II) solution during the accumulation step. e interfering ions were determined in five different groups. e effect of detected interferences on the current signal of Cd(II) is shown in Table 2. As shown in the table, the detected ions had a negligible interference effect on the determination of Cd(II). ere was not a significant effect on the current response of Cd(II) with the addition of 7 to 100 fold molar excess of five groups of the interfering ions in 5.0 × 10 −8 M of Cd(II) solution. is revealed that the developed electrode has excellent selectivity and can be used for the detection of Cd(II) in real samples among other ions.

Comparison of the Proposed Electrode's Analytical Performance with Reported Electrodes.
e performance of the present electrode was compared with several previous electrodes for the determination of Cd(II) described in the literature. As shown in Table 3, the LOD obtained in the present study is much better than other electrodes except one electrode [44]. However, this electrode has a relatively long extraction/preconcentration time (15 min) compared to the present study (4.5 min). A fast preconcentration time used in the present method enables faster measurements. Furthermore, the present method has better and comparable linear range and accumulation/preconcentration time to most of the reported electrodes.
e results indicate the excellent analytical performance of the proposed method and its applicability for the determination of Cd(II) at trace concentrations.

Novelty of the Study.
In this study, a new modified CPE has been fabricated using laboratory prepared ligand, HDPBA, as a modifier for the detection of Cd(II) at low concentrations using the SWASV technique. e developed modified electrode using a single modifier has achieved a better sensing ability with a lower limit of detection than other reported electrodes having more than one modifiers which made them more costly and time-consuming during electrode preparation. Moreover, the fabricated electrode exhibited many attractive features including cost-effectiveness, simple preparation, easily regenerated surface, and fast analysis. It also has a great potential for the analysis of various types of real samples without significant matrix effects due to its high sensitivity and selectivity and excellent reproducibility.  PPy-CO 2 @PGE: a pencil graphite electrode modified with pyrrole-1-carboxylic acid; Nafion-G: Nafion-graphene composite film; Ligand L/ CP: 2,2'-((pyridine-2,6-diylbis (azanylylidene))bis(methany-alkylidene)) bis(4-bromo-phenol); and Fe 3 O 4 @G2-PAD: second-generation polyamidoamine dendrimer functionalized magnetic nanoparticles.

Analytical Applications.
To determine the suitability and feasibility of the developed electrode for real samples, the fabricated electrode was employed to detect Cd(II) in tobacco samples and environmental water samples such as wastewater, bottled water, well water, and spring water from different sources. As given in Table 4, the Cd(II) concentration was found to be 7.94 nM in wastewater while it was not detected in the remaining three water samples. Cd(II) was found to be 16.1 ng g −1 in tobacco samples. e recovery of Cd(II) in the samples was determined by using standard addition method and it was between 96.00% and 105.2%, which shows the good recovery of the method. Graphite furnace atomic absorption spectroscopic (GFAAS) technique was also used to the determination of Cd(II) in the given samples for the comparison purpose. e results found from the two methods were similar and acceptable (Table 4). Paired t test with a 95% confidence limit (p � 0.05) was used to check the significant similarity or difference of the results from the methods. e t test proved that there is no significant difference in the Cd(II) concentrations by the two methods at a 95% confidence limit. e results confirm the applicability of the developed electrode for accurate and reliable quantification of Cd(II) in the real samples.

Conclusion
In this work, a novel, simple, highly sensitive, and selective CPE modified with HDPBA has been fabricated for the detection of Cd(II) in several environmental water samples and tobacco samples.
e developed electrode has many attractive features including low cost, simple preparation, easy renewable ability, portability, and low background noise. Furthermore, the proposed electrode showed various interesting electrochemical behaviors such as excellent selectivity, high sensitivity, good stability, high speed, and capability for the quantification of Cd(II) at very low concentrations compared to unmodified CPE and most other reported electrodes in the literature.
Under optimized experimental parameters, the developed electrode displayed a wide linear range (0.3-100 nM), a very low detection limit (0.032 nM Cd(II)), and good reproducibility (RSD of 3.8%). e developed method and the GFAAS method were effectively employed for the determination of Cd(II) in tobacco and water samples. e recoveries obtained from the two methods were compared, and it was found that they had good agreement. Even though the developed method was applied to the determination of Cd(II) in tobacco and different types of water samples, it can also be employed for Cd(II) determination in other matrices.

Data Availability
All data analyzed or generated in this research work are included in this paper. e authors declare that there are no additional data with the authors.

Conflicts of Interest
e authors declare that they have no conflicts of interest.