Multiwall Carbon Nanotube Paste Electrode Research Articles

Electrochemical polymerized DL-phenylalanine modified carbon nanotube sensor for the selective and sensitive determination of caffeic acid with riboflavin

In this study, DL-phenylalanine modified with a multiwall carbon nanotube paste electrode is used as advanced electrochemical sensor for analysing of 0.1 mM caffeic acid (CFA) with simultaneous detection of riboflavin (RFN). The developed sensors include electrochemically polymerized DL-phenylalanine (DL-PA) modified multiwall carbon nanotube paste electrode [DL-PAMMCNTPE] and bare multiwall carbon nanotube paste electrode [BMCNTPE]. The increasing stability in the developed electrochemical sensor for the quantification of CFA is highlighted in detail, along with its characterization using voltammetric techniques such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), differential pulse voltammetry (DPV), and linear Sweep Voltammetry (LSV). Scanning electron microscopy (SEM) technique was used to studied the structural analysis of BMCNTPE and DL-PAMMCNTPE surface. The investigation of 0.1 mM CFA in 0.2 M phosphate buffered solution (PBS) using a 7.0 pH at 0.1 V/s scan rate was highlighted using DL-PAMMCNTPE, which shows good electrochemical responses compared to BMCNTPE. This work characterizes the voltammetric responses by inspecting the pH effect, scan rate effect, and concentration difference of CFA at the DL-PAMMCNTPE surface. The CFA responses specify that the scan rate progress is adsorption controlled. The concentration of CFA detection was started from 20 μM to 600 μM using DPV method, with lower limit of detection (LOD) of 0.280 μM and limit of quantification (LOQ) of 0.936 μM. And for CV method concentration range 20 to 550 μM, with LOD of 0.198 μM and LOQ of 0.702 μM. Furthermore, the developed electrochemical sensor responses are shows good stability, repeatability, and reproducibility, for CFA. The analytical applicability of CFA in apple juice and coffee powder samples was also evaluated.

Simultaneous Electrochemical Detection of Catechol and Hydroquinone Based on a Carbon Nanotube Paste Electrode Modified with Electro-Reduced Graphene Oxide.

Effectively detecting catechol (CC) and hydroquinone (HQ) simultaneously is crucial for environmental protection and human health monitoring. In the study presented herein, a novel electrochemical sensor for the sensitive simultaneous detection of CC and HQ was constructed based on an electrochemically reduced graphene oxide (ERGO)-modified multi-walled carbon nanotube paste electrode (MWCNTPE). Scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and electrochemical techniques were utilized to characterize the sensing interface and investigate the sensing mechanism. Under the optimal detection conditions, the oxidation peak currents of CC and HQ show a good linear relationship with their concentrations in the range of 0.4-400 μM with a detection limit of 0.083 μM for CC and 0.028 μM for HQ (S/N = 3). Moreover, the sensor exhibits good performance and can be applied successfully in the simultaneous detection of CC and HQ in tap water samples and urine samples with satisfactory results, indicating its promising application prospects.

A new strategy for the determination of dinobuton fungicide by square wave stripping voltammetry on the multi-walled carbon nanotube electrode

Dinobuton is a fungicide with a dinitrophenol group pesticide, and its electrochemical behavior was investigated by cyclic voltammetry (CV) and square wave stripping voltammetry (SWSV) on a multi-walled carbon nanotube paste electrode (MWCNTPE). First of all, optimum parameters such as pH, step potential, frequency, puls amplitude, deposition time and, deposition potential were specified by using SWSV on the MWCNTPE. In the negative potential scans, two cathodic peaks appeared at nearly −480 mV and –760 mV due to the nitro groups on the molecule and the second sharp one appeared at −760 mV (versus Ag/AgCl) was used for analytical purposes. The linear working range was found to be within 3.74–25.8 μM on the MWCNTPE by SWSV in pH 7.0 Britton Robinson (BR) buffer solution. The limit of detection (LOD) and limit of quantification (LOQ) values were found to be 0.73 μM and 2.43 μM, respectively. The interference study was conducted in the presence of some pesticides such as triasulfuron, azinphos-methyl, bromoxynil-octanoate, dialifos, fipronil, vinclozolin, iprodione, procymidone, and some selected metal ions withal. Furthermore, the proposed method was also applied to apple juice, tap water, and grape juice, and percent recoveries (%) were detected as 105.9 ± 4.3; 98.3 ± 0.9; 103.7 ± 2.5% with relative standard deviations of 4.0, 1.0, and 2.4%, respectively. On the other hand, percent relative errors were calculated as 5.90, 1.65, and 3.74%, respectively. High recoveries and low relative standard deviations indicate that the applicability of the proposed method in both matrix and real samples is satisfying.

Electrochemical Sensor Design Based on Silver Nanoparticles Modified Multiwalled Carbon Nanotubes Paste Electrode for the Sensitive Determination of Mepivacaine.

Mepivacaine, an amide-type local anesthetic drug widely used in regional anesthesia, was studied by some aspects such as electrochemical behavior, mechanism illumination, and analytical applications by cyclic voltammetry (CV) and different pulse voltammetry (DPV) methods. In this study, a novel, fast, simple, portable, and the inexpensive electrochemical sensor was developed for the determination of mepivacaine. This study was carried out by mepivacaine anodic direction detection for the first time. The modified sensor was fabricated with silver nanoparticles (AgNP) and multiwalled carbon nanotubes paste electrode (MWCNTPE) by using the drop-dry method. Different experimental parameters, such as pulse amplitude, step potential, and scanning rate in the DPV application module, were optimized. Under optimal operation conditions, the limit of detection (LOD) as low as 31 μg L-1 was found over the dynamic range (0.1-8.0 mg L-1). In contrast to its high response towards mepivacaine, the DPV exhibits negligible responses on modified AgNP/MWCNTPE when exposed to interfering species such as dopamine, uric acid, glucose, ascorbic acid, and some heavy metals. Exceptionally, the proposed DPV method on modified AgNP/MWCNTPE was successfully applied to pharmaceutical dosage form and synthetic human serum with a low relative standard deviation (RSD) of 1.35% and 2.02%, respectively.

A Nanocomposite Paste Electrode Sensor for Simultaneous Detection of Uric Acid and Bisphenol A Using Zinc Hydroxide Nitrate-Sodium Dodecylsulfate Bispyribac.

The fabrication of a zinc hydroxide nitrate-sodium dodecylsulfate bispyribac modified with multi-walled carbon nanotube (ZHN-SDS-BP/MWCNT) paste electrode for uric acid and bisphenol A detection was presented in this study. Electrochemical impedance spectroscopy, chronocoulometry, square-wave voltammetry, and cyclic voltammetry were all used to examine the electrocatalytic activities of modified paste electrodes. The modified electrode's sensitivity and selectivity have been considered in terms of the composition of the modifier in percentages, the types of supporting electrolytes used, the pH of the electrolyte, and square-wave voltammetry parameters like frequency, pulse size, and step increment. Square-wave voltammetry is performed by applying a small amplitude square-wave voltage to a scanning potential from -0.3 V to +1.0 V, demonstrating a quick response time and high sensitivity. The ZHN-SDS-BP/MWCNT sensor demonstrated a linear range for uric acid and bisphenol A from 5.0 µM to 0.7 mM, with a limit of detection of 0.4 µM and 0.8 µM, respectively, with good reproducibility, repeatability, and stability as well. The modified paste electrode was successfully used in the determination of uric acid and bisphenol A in samples of human urine and lake water.

Ionic liquid-modified multi-walled carbon nanotube paste electrode for cadmium and lead ion determinations

The detection of trace heavy metal ions is important in monitoring water quality, a vital freshwater source. This study presents the preparation of a multi-walled carbon nanotube (MWCNTs) paste electrode using a pasting mixture of 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid ([Bmim][PF6] IL) and paraffin oil for the determination of Cd2+ and Pb2+. Scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy were applied to characterize the paste composites. The electrochemical behavior of the fabricated electrodes was analyzed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The [Bmim][PF6]-MWCNTs electrode showed enhanced sensitivity for Cd2+ and Pb2+ detections over linear sweep anodic stripping voltammetry (LSASV) performances. Experimental results showed that the MWCNTs-IL-1 electrode using a pasting mixture of 10 μL of [Bmim][PF6] and 190 μL of paraffin oil was the most suitable for Cd2+ and Pb2+ determinations. The LSASV conditions for Cd2+ and Pb2+ analysis at the MWCNTs-IL-1 electrode were optimized, including the deposition potential, deposition time, and pH of the working solution. The stripping peak currents were linearly correlated with the concentration ranges of Cd2+ (1–35 μg/L) and Pb2+ (1–90 μg/L) for both individual and simultaneous determinations. The MWCNTs-IL-1 electrode exhibited high repeatability, reproducibility, and stability over a 30-day storage period. The real applicability of the MWCNTs-IL-1 electrode was demonstrated by successful determinations of Cd2+ and Pb2+ concentrations in tap water and surface water samples, which agreed with the results obtained by inductively coupled plasma mass spectrometry.

A sensitive voltammetric and density functional theory calculations analysis for the direct interaction of sulfide ion with the multiwalled carbon nanotube

A sensitive and simple cyclic voltametric method was investigated for the direct electrochemical determination of sulfide using multiwalled carbon nanotube paste electrode (MWCNTPE). The sulfide exhibited a distinct and remarkable direct oxidation peak at about 0.56 V in a solution containing sodium chloride as a suitable supporting electrolyte. The effect of voltametric behavior of sulfide was also studied in various supporting electrolyte. Among this sodium chloride containing solution showed a well-defined oxidation peak current as compared to the other supporting electrolyte. The direct oxidation behavior of sulfide in sodium chloride solution was mainly attributed to the less hindrance effect of the electrolyte anions on the surface of electrode. Under optimized condition the oxidation peak current values were found to increase in a linear way with increasing sulfide concentration in the range from 1 × 10−7 to 3 × 10−5 M (R2 = 0.9985). The detection limit (DL) was calculated to be 4 × 10−8 M for the sulfide concentrations. The developed method showed excellent selectivity towards the voltametric determination of sulfide as compared to other competing ions like Br−, NO3−, F−, PO43−, NO2−, I−, CH3COO− present in the solution. Moreover, the method demonstrated good and reproducible results with relative standard deviation (RSD) of 3.8% after 40 successive measurements. The method was successfully applied for determination of sulfide in local tap water samples without any matrix effect. Meanwhile to support the voltametric behavior of sulfide, density functional theory (DFT) calculations were performed at ωB97XD/6-31G(d,p) level of theory to get deep insight into the electronic properties of MWCNT and adsorbed analytes (sulfide) using Gaussian 09 package. The highest interaction energy and the decrease in energy gap of multiwall carbon nanotube with sulfide (MWCNT-S2-) complex are consistent with the highest sensing behavior of MWCNT towards sulfide ion in experimental results.

Electrocatalytic response of chitosan modified multiwall carbon nanotube paste electrode toward iodide: A facile voltammetric method for determination of iodide in biological sample

Herein we report, a simple operable, sensitive, and highly selective, voltammetric method for the determination of iodide (Iˉ) using chitosan modified multiwall carbon nanotube paste electrode (chit-MWCNTPE). It is established that chit-MWCNTPE exhibited a pronounced response toward Iˉ oxidation. The peak potential of Iˉ is recorded at 0.69 V vs SCE. The conditions such as scan rate (V.s−1), accumulation time (ta), and pH are thoroughly optimized for the voltammetric determination of Iˉ. A wide range linear response is observed between oxidation peak current and Iˉ concentration (0.1–100 μM). The limit of detection (LOD) for Iˉ on chit-MWCNTPE is found to be 0.03 μM. The developed method is highly selective for Iˉ detection in the presence of various interfering ions. The method is successfully applied for the determination of Iˉ in urine samples. The method has high selectivity for Iˉ detection at comparably low potential as well as amiable LOD and Linear range.

Electro-oxidation of formoterol fumarate on the surface of novel poly(thiazole yellow-G) layered multi-walled carbon nanotube paste electrode

The current study explicates the electro-oxidation behavior of formoterol fumarate (FLFT) in the presence of uric acid (UA) on the surface of poly thiazole yellow-G (TY-G) layered multi-walled carbon nanotube paste electrode (MWCNTPE). The modified (Poly(TY-G)LMWCNTPE) and unmodified (MWCNTPE) electrode materials were characterized through electrochemical impedance spectroscopy (EIS), field emission scanning electron microscopy (FE-SEM), and cyclic voltammetry (CV) approaches. The characterization data confirms the good conducting and electrocatalytic nature with more electrochemical active sites on the Poly(TY-G)LMWCNTPE than MWCNTPE towards the FLFT analysis in the presence of UA. Poly(TY-G)LMWCNTPE easily separates the two drugs (FLFT and UA) even though they both have nearer oxidation peak potential. The electro-catalytic activity of the developed electrode is fast and clear for FLFT electro-oxidation in 0.2 M phosphate buffer (PB) of pH 6.5. The Poly(TY-G)LMWCNTPE offered a well-resolved peak with the highest electro-oxidation peak current at the peak potential of 0.538 V than MWCNTPE. The potential scan rate and oxidation peak growth time studies show the electrode reaction towards FLFT electro-oxidation is continued through a diffusion-controlled step. The variation of concentration of FLFT in the range from 0.2 to 1.5 µM (absence of UA) and 3.0 to 8.0 μM (presence of UA) provides a good linear relationship with increased peak current and a lower limit of detection (LOD) values of 0.0128 µM and 0.0129 µM, respectively. The prepared electrode gives a fine recovery for the detection of FLFT in the medicinal sample with acceptable repeatability, stability, and reproducibility.

Development and characterization of iron (III) phthalocyanine modified carbon nanotube paste electrodes and application for determination of fluometuron herbicide as an electrochemical sensor

This study is the first electroanalytical study conducted for the determination of fluometuron herbicide. For this purpose, a new electrode was prepared by combining iron (III) phthalocyanine − 4.4′,4′′,4′′′-tetrasulfonic acid, oxygen monosodium salt hydrated compound (FePc) and multi-walled carbon nanotube powders (MWCNTP). The FePc/MWCNTP composite (hybrid) material prepared in this way was coated on glassy carbon electrode (GCE) and multi-walled carbon nanotube paste electrode (MWCNTPE) using the drop-dry method. Compared to both the bare GCE and MWCNTPE, the modified FePc/MWCNTPE increased the anodic peak current of fluometuron by approximately six fold. Calibration plots of the fluometuron were constructed using the standard addition method with differential puls stripping voltammetry (DPSV) and square wave stripping voltammetry (SWSV) under the optimum conditions. While the working range was determined as 0.4–15.0 mg/L in pH 6.0 Britton Robinson (BR) buffer solution on FePc/MWCNTP electrode with DPSV, this range was found to be 0.4–7.5 mg/L with SWSV. In addition, the limit of detection (LOD) and the limit of quantification (LOQ) values ​​were 69.8 µg/L and 233.0 µg/L, respectively, by DPSV. On the other hand, these two validation values ​​(LOD and LOQ) were 101 µg/L and 337 µg/L by SWSV, respectively. Subsequently, cyclic voltammetric (CV) studies were carried out to elucidate the electrochemical behavior and electrode mechanism of the fluometuron herbicide. In addition, the interference effects of some cations and pesticides in the determination of fluometuron were examined. Finally, studies of recovery of fluometuron herbicide from tap water and determination of fluometuron in Cottonex 500 SC® commercial pesticide formulation using the proposed DPSV method and modified FePc/MWCNTP electrode were performed with very low relative error.

Electrochemical Analysis of Indigo Carmine in Food and Water Samples Using a Poly(Glutamic Acid) Layered Multi-walled Carbon Nanotube Paste Electrode

Some colourants are hazardous to living species; hence, a powerful and fast methodology is required for the analysis of those colourants in food and water samples. A modest electrochemically polymerised glutamic acid layered multi-walled carbon nanotube paste electrode [P(GA)LMWCNTPE] was functionalised for the sensing of indigo carmine (IC) by powerful differential pulse voltammetry (DPV) and cyclic voltammetry (CV) approaches. Within the optimised experimental conditions, the P(GA)LMWCNTPE holds an acceptable and high rate of electro-catalytic activity towards the redox behaviour of IC. The projected P(GA)LMWCNTPE shows a decent selectivity for IC in the presence of methyl orange. The modified sensor shows an acceptable linear growth between oxidative peak current and concentration in both CV and DPV methods with fine limit of detection values of 4.2 µM and 0.36 µM, respectively. Additionally, the developed sensor was effectively applied to detect IC in food and water samples. The morphological and surface activities of the modified and unmodified electrodes were determined through field emission scanning electron microscopy, electrochemical impedance spectroscopy, and CV techniques. The P(GA)LMWCNTPE requires a simple preparation procedure and is low-cost, with acceptable storage stability, sensitivity, and reproducibility.

A Review: Square Wave Adsorptive Stripping Voltammetry Determination ofPesticide and Ultra-trace Inorganic Ions in Environmental Samples

Environmental pollution caused by pesticides and ultra-trace amounts of inorganic ions in the different environmental samples has become an issue of serious concern in the last years. Thus, the development of novel, simple, fast, sensitive, and cheap methods for the detection of pesticide residues and ultra-trace inorganic ions in the environmental sample is very significant task now days. The SWAdSV can be conjuncted with different modified electrode such as SWAdSV with modified Hanging mercury drop electrode, SWAdSV with multi-walled carbon nanotube paste electrode, SWAdSV with boron-doped diamond electrode, SWAdSV with flow-injection analysis detection and etc. SWAdSV can be used to perform an experiment much faster than normal and differential pulse techniques, which typically run at scan rates of 1 to 10 mV/sec. Square wave voltammetry employs scan rates up to 1 V/sec or faster, allowing much faster determinations. A typical experiment requiring three minutes by normal or differential pulse techniques can be performed in a matter of seconds by square wave voltammetry. The aim of the review was the use of square wave adsorptive stripping voltammetry in conjunction with different modified electrode for the determination of pesticide and ultra-trace inorganic ions in environmental samples.

Electrochemical Reversible Copper Oxide (CuO) System on Multiwalled Carbon Nanotube Paste Electrode (CPE) as Sensor for Hydrogen Peroxide in Wound Cleaning Solution

An electrochemical sensor for hydrogen peroxide (H2O2) was prepared and optimized in this study. The sensor recognition element consisted of mainly copper oxide (CuO) particles electrodeposited on an anodized multiwalled carbon nanotube paste electrode (MWCPE), which is composed of multiwalled carbon nanotubes (MWCNT) and polydimethylsiloxane (PDMS). Chronoamperometry (CA) was used as the electrodeposition technique both for Cu deposition and oxidation to CuO. The layer of CuO was shown to react with H2O2, which lead to measurable voltammetric current at varying concentrations of H2O2. Different parameters were optimized as follows: Cu deposition time, Cu oxidation time, and equilibration time. Differential pulse voltammetry (DPV) was used as the main sensing technique for CuO-CPE. DPV measurements showed that the average peak current (ave. Ip) was found to be increasing linearly with increasing H2O2 concentration. Two H2O2 concentration ranges, low concentration (20 μM – 100 μM) and high concentration (400 μM – 1200 μM), were observed to have a linear correlation with ave. Ip. The limits of detection (LODs) were calculated to be equal to 11.40 µM using the low concentration range, while 13.04 μM using the high concentration range. The H2O2 measurements using CuO-CPE were found to be reproducible and repeatable. Real sample analysis was also performed on a wound cleaning solution (aqua oxigenada, 6% H2O2 w/w) as a sample. From the measurements, the H2O2 concentration of the analyte was found to be 6.16% w/w; the calculated % error was equal to 2.67%. Overall, CuO-CPE composite was shown to be an effective electrochemical sensor for H2O2 analysis.

Square wave stripping voltammetric determination of cyprodinil fungicide in food samples by nanostructured multi walled carbon nanotube paste electrode

Cyprodinil is a fungicide from an anilinopyrimidine group and is widely used in agricultural fields to control fungi that are harmful to vegetables and plants, and therefore requires a reliable, sensitive and selective method for its analysis in food samples. The electrochemical behavior of cyprodinil was investigated by square wave stripping and cyclic voltammetric techniques by using both glassy carbon electrode and multi-walled carbon nano tube paste electrode (MWCNTPE). Prior to analytical determinations, parameters such as pH, frequency, deposition time and deposition potentials were optimized. The oxidation peak potential of cyprodinyl fungicide was + 1160 mV (vs Ag/AgCl). The linear dynamic range was 0.25–4.0 mg/L. The limit of detection and the limit of quantification were calculated as 0.076 and 0.25 mg/L, respectively. In addition, the interference effects of other fungicides in the same class with cyprodinil (pyrimidine fungicides) such as pyrimethanil, nuarimol, fenarimol and another class of dioxacarb (carbamate insecticide) were also investigated. The recommended electroanalytical method was successfully applied to the commercial formulation of Fragman®50 WG containing 50% cyprodinil and apple juice and tap water samples. The percentage of cyprodinil in commercial formulation was calculated as 50.3 ± 3.5% with a relative standard deviation of 6.9% and relative error of 0.65, respectively. The calculated relative standard deviations and high recoveries indicate that the accuracy and precision of the recommended method for is highly acceptable.

Voltammetric determination of nitrite by using a multiwalled carbon nanotube paste electrode modified with chitosan-functionalized silver nanoparticles.

A cyclic voltammetric method is described for the determination of nitrite by using a multiwalled carbon nanotube paste electrode (MWCNT) that was modified with chitosan-functionalized silver nanoparticles (Chit-AgNPs). The AgNPs were prepared by one step procedure using chitosan as stabilizing agent. The resulting modified AgNPs were drop-coated onto the electrode. By combining the advantages of chitosan, AgNPs (in the form of Chit-AgNPs) and MWCNT, the assay exhibits a remarkable improvement in the cyclic voltammetric response towards the oxidation of nitrite at a typical peak potential of 0.81V (vs. SCE) in buffer of pH4.0. The accumulation of nitrite on the electrode also was achieved, and this further enhances the analytical sensitivity. Under optimized conditions, the oxidation peak current increases linearly in the 100nM to 50μM nitrite concentration range, and the detection limit is 30nM. The method has high selectivity for nitrite even in the presence of other potentially interfering ions. Graphical abstract Schematic illustration of the prepared chitosan functionalized silver nanoparticles (transmission electron microscope image) and modification of multi-walled carbon nanotube paste electrode with chitosan functionalized silver nanoparticles for the electrochemical oxidation of nitrite to nitrate.

Phenolic profiling and antioxidant capacity of Morchella esculenta L. by chemical and electrochemical methods at multiwall carbon nanotube paste electrode

The present investigation was carried out to know the aboriginal usage of Morchella esculenta L. as an ethnomedicinal food by tribals of Kashmir, an extreme northern state of India for curing of arthritis, osteoporosis, general bone weakness and cure child labour pain and post menopause pain of women. The average long-life expectancy (~ 80 years) and delayed aging ensured the abundant use of M. esculenta L. as the bases of their daily foods as well as their traditional medicine. The antioxidant character of this mushroom was carried out by chemical and electrochemical assays. The chemical assay was done by DPPH, nitric- oxide, super-oxide scavenging and reducing power while as, electrochemical assay was done by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) using multi-wall carbon nanotube paste electrode (MWCNTPE) at 0.02 M acetate buffer (pH 4.5). The phenolic profiling of the mushroom was evaluated through Folin–Ciocalteu reagent using gallic acid/ascorbic acid as standard which were qualified and quantified by HPLC-UV technique, respectively. The IC50 values found were 57.02 µg ml−1, 58.02 µg ml−1 and 40.01 µg ml−1 for DPPH, nitric-oxide and superoxide. The electrochemical results have shown one oxidation potential at 1.12 V and positive potential at 1.119 ± 0.01 V in CV and 1.19 V in DPV. DPV at superoxide radical scavenging level of mushroom at dropping mercury electrode (DME) in 0.1 M KCl, produced a reduction peak potential at − 0.160 V. HPLC-UV have confirmed the presence of eight phenolic compounds namely, p-coumaric acid, tocopherol, catechol, rutin, hyperoside, quercetin, ellagic acid and cinnamic acid with quercetin at highest percentage (169.76%).

Zinc/Aluminium⁻Quinclorac Layered Nanocomposite Modified Multi-Walled Carbon Nanotube Paste Electrode for Electrochemical Determination of Bisphenol A.

This paper presents the application of zinc/aluminium-layered double hydroxide-quinclorac (Zn/Al-LDH-QC) as a modifier of multiwalled carbon nanotubes (MWCNT) paste electrode for the determination of bisphenol A (BPA). The Zn/Al-LDH-QC/MWCNT morphology was examined by a transmission electron microscope and a scanning electron microscope. Electrochemical impedance spectroscopy was utilized to investigate the electrode interfacial properties. The electrochemical responses of the modified electrode towards BPA were thoroughly evaluated by using square-wave voltammetry technique. The electrode demonstrated three linear plots of BPA concentrations from 3.0 × 10−8–7.0 × 10−7 M (R2 = 0.9876), 1.0 × 10−6–1.0 × 10−5 M (R2 = 0.9836) and 3.0 × 10−5–3.0 × 10−4 M (R2 = 0.9827) with a limit of detection of 4.4 × 10−9 M. The electrode also demonstrated good reproducibility and stability up to one month. The presence of several metal ions and organic did not affect the electrochemical response of BPA. The electrode is also applicable for BPA determination in baby bottle and mineral water samples with a range of recovery between 98.22% and 101.02%.

Voltammetric determination of phenmedipham herbicide using a multiwalled carbon nanotube paste electrode

Phenmedipham is an herbicide used especially in the sugar beet harvest to fight against broad-leaved weeds and studies of its voltammetric behavior and detection have not been done before. The superior properties of carbon nanotubes such as electrical conductivity, mechanical strength, and wide potential ranges make them attractive for chemical sensors and the phenmedipham compound gave an oxidation peak at + role=presentation> + + + 1320 mV (vs. Ag/AgCl) on the nanostructured multiwalled carbon nanotube paste electrode. Square wave voltammetric measurements recorded for phenmedipham showed that the peak current increased linearly between 0.02 and 2.0 mg/L with a regression coefficient of r role=presentation> r r r = 0.9989, and the limit of detection and limit of quantification were calculated as 6.96 μ role=presentation> μ μ \mu g/L and 23.2 μ role=presentation> μ μ \mu g/L, respectively. The applicability and the selectivity of the improved square wave voltammetric method for the phenmedipham assay were investigated in the presence of certain herbicides and fungicides such as carbendazim, benomyl, aclonifen, ethofumesate, metamitron, and p-acetanisidide (methacetin). Phenmedipham at 1 mg/L with the same amount of these pesticides was determined to have recoveries of 103.5 ± role=presentation> ± ± \pm 0.7, 94.5 ± role=presentation> ± ± \pm 2.8, 104.3 ± role=presentation> ± ± \pm 1.8, 101.9 ± role=presentation> ± ± \pm 3.1, 93.8 ± role=presentation> ± ± \pm 1.7, and 101.3 ± role=presentation> ± ± \pm 1.8, respectively (n = 3). The method was also applied to the phenmedipham assay in saturated tea sugar prepared as a spiked natural sample and 1.0 g/L phenmedipham in the sugar solution was successfully determined with a relative error of --5.0% and a relative standard deviation of 3.16%.

Determination of Ophthalmic Drug Proparacaine Using Multi-walled Carbon Nanotube Paste Electrode by Square Wave Stripping Voltammetry.

Proparacaine, one of the most common local anesthetics to facilitate diagnosis and treatment of eye diseases, was assayed by square wave voltammetry using a paste electrode prepared with carbon nanotubes. In cyclic voltammetric studies, proparacaine has exhibited a single irreversible anodic peak at around + 900 mV vs. Ag/AgCl in pH 6.0 Britton-Robinson buffer solution. It was suggested that the peak had appeared due to the oxidation of the NH2 group on the proparacaine molecule. Prior to the determination of the proparacaine by square wave stripping voltammetry (SWSV) on the fabricated multi-walled carbon nanotube paste electrode (MWCNTPE), the accumulation potential (Eacc), accumulation time (tacc), pulse amplitude (ΔE), step potential (ΔEs) and frequency (f ) parameters were optimized. The peak currents plotted in the range of 0.5 - 12.5 mg/L proparacaine exhibited two linear sections with a detection limit of 0.11 mg/L. The results for the determination of proparacaine on a pharmaceutical local anesthetic (Alcaine®) showed that relative standard deviation (RSD) and relative error (RE) were 4.1 and -2.0%, respectively. Selectivity has also been investigated and results showed recoveries of 5.0 mg/L proparacaine in the presence of 5.0 mg/L dopamine, ascorbic acid and uric acid as 106.9 ± 0.8, 99.9 ± 1.2 and 94.1 ± 0.7, respectively.

A highly sensitive sensor of paracetamol based on zinc-layered hydroxide-L-phenylalanate-modified multiwalled carbon nanotube paste electrode

A new zinc-layered hydroxide-L-phenylalanate (ZLH-LP)-modified multiwalled carbon nanotube (MWCNT) was prepared as a new material of paste electrode for the detection of paracetamol (PCM) in 1.0 × 10−1 M phosphate buffer solution and at pH 7.5. The electrochemical characterization of the MWCNTs/ZLH-LP paste electrode was characterized by square wave voltammetry, electrochemical impedance spectroscopy, and cyclic voltammetry while the morphology properties of the MWCNTs, ZLH-LP, and MWCNTs/ZLH-LP were investigated using transmission electron microscopy and scanning electron microscopy. Under optimized conditions, the MWCNTs/ZLH-LP paste electrode demonstrated an excellent electrocatalytic activity towards oxidation of PCM in the linear responses’ ranges from 7.0 × 10−7 M to 1.0 × 10−4 M (correlation coefficient, 0.996) with the limit of detection obtained at 8.3 × 10−8 M. As a conclusion, the MWCNTs/ZLH-LP paste electrode revealed good repeatability, reproducibility, and stability, and was found to be applicable for use in pharmaceutical tablet samples.