Square Wave Anodic Stripping Voltammetry Research Articles

Accurate Detection of Cd2+ and Pb2+ Concentrations in Soils by Stripping Voltammetry Peak Areas under the Mutual Interference of Multiple Heavy Metals

The accurate detection of Cd2+ and Pb2+ in soils by square-wave anodic stripping voltammetry (SWASV) faces great challenges because the interaction between multiple heavy metal ions (HMIs) interferes seriously with their SWASV signals. To detect Cd2+ and Pb2+ by SWASV with high accuracy, an overlooked but informative signal, i.e., stripping current peak area, was employed and combined with chemometric methods to suppress the above mutual interference. An easy-to-prepare electrode, i.e., in-site electroplating bismuth film modified glassy carbon electrode, was used to sense the multiple HMIs. Two machine learning algorithms, including SVR and PLSR, were used to establish the detection models of Cd2+ and Pb2+. In addition, this study developed a homemade algorithm to automatically acquire the stripping peak heights and stripping peak areas of Zn2+, Cd2+, Pb2+, Bi3+, and Cu2+, which acted as the inputs of machine learning models. Then, the detection performance of various SVR and PLSR models were compared based on the R2 and RMSE values of the validation dataset. Results showed that the SVR detection models established by the algorithmically acquired peak areas presented the best stability and accuracy for detecting both Cd2+ and Pb2+ concentrations under the existence of Zn2+ and Cu2+. The R2 and RMSE values of the SVR models built using the peak heights of HMIs acquired by electrochemical workstation control software (Imanu-SVR) were 0.7650 and 5.3916 μg/L for Cd2+, and 0.8791 and 20.0015 μg/L for Pb2+, respectively; the R2 and RMSE values of the SVR models built using the peak area automatically acquired by the developed algorithm (Aalgo-SVR) were 0.9204 and 2.9906 μg/L for Cd2+, and 0.9756 and 13.1574 μg/L for Pb2+, respectively. More importantly, the detection results of the proposed method in real soil extracts for Cd2+ and Pb2+ concentrations were close to those of ICP-MS, verifying its practicability. This study provides a new solution for the accurate detection of targeted heavy metals under the co-existence of multiple HMIs by the SWASV method.

One-step electrochemical elaboration of SnO2 modified electrode for lead ion trace detection in drinking water using SWASV.

A facile method was proposed for the elaboration of an electrochemical sensor for heavy metal's trace detection by using square wave anodic stripping voltammetry (SWASV); this method is based on a simple anodic conversion of tin electrode into Sn/SnO2 modified electrode. Both electrochemical and physico-chemical techniques were used to confirm the modification process and better understand the electrode's behavior. Then, depending on the operating conditions, the response signal was studied and adjusted in order to obtain optimal sensor performance. When optimized, the proposed method reached a lowest detection limit (LOD) of 2.15μg L-1 (0.0104μM), and quantification limit (LOQ) of 5.36μg L-1 (0.0259μM), in linearity range between from 6.2 and 20.7μg L-1. Additionally, after having used the elaborated electrode for ten successive measurements, the repeatability remains very high with an RSD of approximately 5.3%; furthermore, ten other species appear to have very slight effect on Pb(II) detection. Finally, for the method validation, the proposed electrode was able to sense different lead concentration integrated in a local bottled spring water by showing recovery levels ranging from 103.8 to 108.4%.

A Comparison between Different Machine Learning Approaches Combined with Anodic Stripping Voltammetry for Copper Ions and pH Detection in Cell Culture Media

Recently, the scientific community has shown a great interest about the Organ-on-Chip (OoC) devices, a special kind of micro-fabricated platforms capable of recapitulating the human physiology implementing the traditional cell culture methods and the concept of in vivo studies. Copper ions represent a cellular micronutrient that must be monitored for its potential hazardous effects. The application of electrochemical analysis for heavy metal ions detection and quantification in commercial cell culture media presents several issues due to electrolyte complexity and interferents. In fact, to the best of our knowledge, there is a lack of applications and OoC devices that implement the Anodic Stripping Voltammetry as an ion dosing technique due to the reasons reported above. In fact, considering just the peak intensity value from the measurement, it turns out to be challenging to quantify ion concentration since other ions or molecules in the media may interfere with the measurement. With the aim to overcome these issues, the present work aims to develop an automated system based on machine learning algorithms and demonstrate the possibility to build a reliable forecasting model for copper ion concentration on three different commercial cell culture media (MEM, DMEM, F12). Effectively, combining electrochemical measurements with a multivariate machine learning algorithm leads to a higher classification accuracy. Two different pH media conditions, i.e., physiological (pH 7.4) and acidic (pH 4), were considered to establish how the electrolyte influences the measurement. The experimental datasets were obtained using square-wave anodic stripping voltammetry (SWASV) and were used to carry out a machine learning trained model. The proposed method led to a significant improvement in Cu2+ concentration detection accuracy (96.6% for the SVM model and 93.1% for the NB model in MEM) as well as being able to monitor the pH solution.

Carbon microspheres uniformly decorated with ceria nanoparticles as an ultrasensitive platform for electrochemical sensing of antihypertensive drug lacidipine in patient plasma and pharmaceutical formulation

Herein, a novel ultrasensitive lacidipine (LCDP) electrochemical sensing platform was constructed based on functionalized glassy carbon (FGC) microspheres anchored with ceria nanoparticles (CeO2NPs@FGC, ratio 2:1 w/w). The XRD, SEM, HRTEM, and EDX results confirmed the formation of the hybrid CeO2NPs@FGC composite. A molecular wire (MW) modified CeO2NPs@FGC electrode (CeO2NPs@FGC-MWE) was firstly fabricated by mixing CeO2NPs@FGC composite with diphenylacetylene (DPA). The fabricated CeO2NPs@FGC-MWE sensor exhibited high electro-catalytic activity towards the oxidation of antihypertensive drug LCDP. Quantitative LCDP detection was achieved using adsorptive anodic stripping square-wave voltammetry (AdAS-SWV). The LOD and the LOQ are estimated to be 2.3 and 7.6 nM, respectively, with a dynamic range of 7.0–2680 nM and a sensitivity of 206 μA μM−1 cm−2. Moreover, the fabricated sensor also shows good selectivity, favorable reproducibility, good antifouling activity, and long-term stability. The practical utility of the sensor for LCDP monitoring in biological fluids, patient plasma and pharmaceutical formulation was evaluated with satisfactory results. The UHPLC technique was utilized to verify the accuracy of the proposed method.

A novel comparative study for simultaneous determination of Cd (II) and Pb (II) based on ruthenium complex-nanoparticles-nafion modified screen-printed gold electrode

A novel and effective method for immobilization of active ruthenium (II) bipyridine complex on screen printed gold electrode surface was developed for simultaneous determination of Cd (II) and Pb (II) in an environmental water sample. The electrostatic interaction between negatively charged graphene oxide (GO) or citrate-capped gold nanoparticles (AuNPs) and positively charged ruthenium (II) bipyridine complex ([Ru(bpy)3]2+) was studied with the incorporation of cation exchanging Nafion polymer, which enhanced electron transfer rate, reduced the interference caused by active compounds and results in long term stability. The comparison between the hybrid Ru-GO/Nafion and Ru-Au/Nafion nanocomposites’ behavior was electrochemically investigated in this paper through cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and square wave anodic stripping voltammetry (SWASV). Additionally, the surface morphologies of the screen-printed electrode were evaluated using energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). The proposed Ru-GO/Nafion sensor exhibited a higher sensitivity towards cadmium ion with a detection limit of 4.2 ppb compared to the Ru-Au/Nafion assay, which reveals low sensitivity with a limit of detection of 12.01 ppb. The developed assays show excellent electrochemical performance towards lead ions with a detection limit of 5.3 ppb and 2.5 ppb for Ru-GO/Nafion and Ru-Au/Nafion, respectively, indicating that the lead ions can be accumulated more on the surface of Ru-Au/Nafion SPGE. The hybrid nanocomposite assays were successfully employed in river and tap water samples and validated using Atomic Absorption Spectroscopy (AAS).

Epoxy/Graphite Composite Electrode Modified with Recycled Silver Nanoparticles: An Eco-Friendly Strategy to Improve Lead Detection

In this work, silver nanoparticles (AgNPs) obtained from photographic waste were synthesized and electrodeposited via cyclic voltammetry using epoxy-graphite composite as an electrochemical substrate. Both electrodes, unmodified (Epoxy/C) and modified (Epoxy/C/AgNPs), were characterized electrochemically by electrochemical impedance spectroscopy (EIS), charge transfer constant (K0 ), and electroactive area. The modified electrode provided lower charge transfer resistance (275 Ω), more kinetically favored electron transfer (K0 = 1.15 × 10-3 cm s-1), and a 1.7- fold increase in the active area compared to the unmodified electrode. Additional characterizations by scanning electron microscopy (SEM) and Raman spectroscopy confirmed the presence of AgNPs structures on the carbonaceous surface. As a proof of concept, Pb2+ was used as a model analyte, and a square wave anodic stripping voltammetry (SWASV) method was developed to evaluate the analytical performance of both electrodes. A wider linear range (4.0 to 40.0 µg L-1), the appropriate limit of detection (1.2 µg L-1), and a 6-fold increase in sensitivity were found using the modified electrode, suggesting that the AgNPs significantly contributed to the performance of the electrode. The proposed method was applied to three real water samples, where the Pb2+ levels varied from 11.3 to 19.5 µg L-1. The proposed protocol (reuse of silver waste) has proven to be a powerful tool for improving the detection of Pb2+, which can be helpful for other electrochemical sensing applications in locations with minimal infrastructure.

Three-dimensional porous high boron-nitrogen-doped carbon for the ultrasensitive electrochemical detection of trace heavy metals in food samples.

Exposure to even trace amounts of Cd(II) and Pb(II) in food can have serious effects on the human body. Therefore, the development of novel electrochemical sensors that can accurately detect the different toxicity levels of heavy metal ions in food is of great significance. Based on the principle of green chemistry, we propose a new type of boron and nitrogen co-doped carbon (BCN) material derived from a metal-organic framework material and study its synthesis, characterization, and heavy-metal ion detection ability. Under the optimum conditions, the BCN-modified glassy carbon electrode was studied using square-wave anodic stripping voltammetry, which showed good electrochemical responses to Cd(II) and Pb(II), with sensitivities as low as 0.459 and 0.509 μA/μM cm2, respectively. The sensor was successfully used to detect Cd(II) and Pb(II) in Beta vulgaris var. cicla L samples, which is consistent with the results obtained using inductively coupled plasma-mass spectrometry. It also has a strong selectivity for complex samples. This study provides a novel approach for the detection of heavy metal ions in food and greatly expands the application of heteroatom-doped metal-free carbon materials in detection platforms.

Electrochemical determination of aripiprazole based on aluminium oxide nanoparticles modified carbon paste electrode.

The electrochemical oxidation of aripiprazole was explored at a carbon paste electrode modified with aluminium oxide nanoparticles by cyclic voltammetry and square-wave anodic adsorptive stripping voltammetry. Experimental parameters such as carbon paste composition, scan rate, buffer pH, accumulation time, and accumulation potential were optimized in order to obtain high analytical performance. The incorporation of aluminium oxide nanoparticles into the carbon paste matrix enhanced the effective surface area of the carbon paste electrode and improved the sensitivity. On the aluminium oxide nanoparticles modified carbon paste electrode, aripiprazole exhibited an irreversible anodic peak at +1.17 V in pH 1.8 BR buffer solution. Under optimum conditions, the peak current exhibited a linear dependence with aripiprazole concentration between 0.03 and 8.0 μM with a detection limit of 0.006 μM. The analytical applicability of the voltammetric method was evaluated by quantification of ARP in human serum samples and pharmaceutical formulations.

Selenium‐doped Graphite for Electrochemical Sensing and Adsorption of Hg(II) and Cd(II) Ions

AbstractSelenium‐doped Graphite (Se‐DG) has been used for electrochemical (EC) sensing and adsorption of poisonous Hg(II) and Cd(II) ions which can produce acute toxic effects on various organs. Hence, detection and efficient removal of both the metal ions from aquatic sources are very crucial. Herein, square wave anodic stripping voltammetry (SWASV) method was applied for EC detection using Se‐DG coated glassy carbon electrode (GCE) as a working electrode. Corresponding EC responses were observed due to the interaction between the sensing surface and the analytes. Elemental Se (Se0) present in Se‐DG played a crucial role in EC sensing. The limit of detection (LoD) of Hg(II) and Cd(II) were observed to be 4.3 ppb and 1.9 ppb respectively. The limit of quantification (LoQ) were found as ppb 14.3 ppb and 6.3 ppb respectively. Batch method was carried out for adsorption of the same carcinogenic metal ions on the Se‐DG surface. Ultra‐trace concentration of the metal ions was determined in Inductively Coupled Plasma Mass Spectrometry (ICP‐MS). Maximum adsorption capacity (QM) for Hg(II) and Cd(II) were found 210.81 mg g−1 and 205.53 mg g−1 respectively from Langmuir fit. The adsorption process was spontaneous and endothermic and it could be better fitted by a pseudo‐second order rate law, suggesting a chemisorption over physisorption. X‐Ray Photoelectron spectroscopy (XPS) was performed to investigate the binding interaction of different functionalities present in Se‐DG with metal ions.

Co‐detection of Copper and Lead in Artisanal Sugarcane Spirit Using Caffeic Acid‐modified Graphite Electrodes

AbstractCaffeic acid (CA)‐modified graphite electrodes [GE/poly(CA)] was applied to the co‐detection of copper and lead in artisanal sugarcane spirit using square‐wave anodic stripping voltammetry (SWASV). Electrochemical and morphological studies were performed, and a mechanism for polymerization was proposed. Electropolymerization, SWASV, and analysis conditions parameters were optimized. Interferents, repeatability, reproducibility, and addition and recovery tests were carried out. GE/poly(CA) shows a linear range from 15 to 705 μg/L with a limit of detection of 3.01 μg/L for Pb(II) and 4.50 μg/L for Cu(II). Real samples of artisanal sugarcane spirit were used, and the electrochemical results were compared with atomic absorption spectroscopy experiments.

Electrografting a p‐Propylaniline/L–Cys Nanofilm onto a Glassy Carbon Electrode Resulting in Enhanced Electrosensing of Cd(II), Pb(II) and Hg(II)

AbstractA glassy carbon electrode (GCE) was chemically modified with p‐propylaniline/L–Cys molecules for the sensitivity determination of Cd(II), Pb(II) and Hg(II) in aqueous medium. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) characterized passivation of the electrode and 97.4 % surface coverage with p‐propylaniline/L–Cys molecules. Nanofilm coating was characterized by cyclic voltammetry (CV), atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR) techniques to observe the surface morphology. The porous structure uniformly distributed thiol, amine and carboxylate groups throughout the coating to selectively coordinate and preconcentrate the three metal ions. Under the optimized conditions (deposition potential: −1 V vs. SCE, deposition time: 90s), square wave anodic stripping voltammetry (SWASV) electroanalysis results indicated the linear increment of electrochemical signals with an increase in the concentration of Cd(II), Pb(II) and Hg(II) in range of 2.5 to 30 μg L−1. Based on the calibration plot, limit of detection (LOD, 3σ/m) are 0.103 μg L−1, 0.055 μg L−1 and 0.01 μg L−1 respectively. Analysis of drinking and tap water samples demonstrated precision and accuracy of the electrode as a prospective sensor for analysis of more complex aqueous environmental matrices.

Nanoporous gold microelectrode arrays using microchips: A highly sensitive and cost-effective platform for electroanalytical applications

• Nanoporous gold structures electrochemically formed at the gold microelectrodes. • Increase in electroactive area (4.4-fold), decrease in resistance to charge transfer. • Energy-dispersive X-ray proves the formation of gold oxide nanostructures. • Improved amperometric detection of dipyrone and cysteine by batch-injection analysis. • Stripping voltammetric detection of lead ions was also improved. In this paper, we investigate the effect of electrochemical treatment on the surface of low-cost and disposable devices (microchips) containing gold microelectrode arrays (Au-µE). This procedure consisted of electrode anodization to generate nanoporous gold structures (NPAu-μE), which contributed to 4.4-fold increase in the electroactive area and decrease in the resistance to charge transfer. Energy-dispersive X-ray spectra revealed the formation of gold oxide nanostructures. The electrochemical response of these sensors was properly investigated using dipyrone (DIP), cysteine (CyS) and lead(II) as target species, and for all the analytes, enhanced analytical performances were obtained using the treated surface. NPAu-μE was combined with a batch-injection analysis (BIA) cell for the amperometric determination of DIP and CyS, which resulted in detection limits lower than 1.2 µmol L -1 , adequate precision (RSD > 4.0 %), wide linear ranges (1.0–200.0 and 5.0–150.0 µmol L −1 ), and high sample throughput (148 and 185 analysis per hour) for DIP and CyS, respectively. Moreover, the NPAu-µE sensor proved to be suitable for Pb 2+ detection by square-wave anodic stripping voltammetry (SWASV), with a detection limit of 2.0 nmol L -1 , linear ranges from 24 to 240 nmol L -1 , and 289 to 531 nmol L -1 , and good precision (RSD = 4.3 %), which enabled a good recovery of Pb 2+ added to drinking water at the level corresponding to the WHO allowed threshold limit (48.2 nmol L -1 or 10.0 µg L -1 ). In summary, we demonstrate that NPAu-μE device can be applied for either organic or inorganic species with satisfactory sensing properties.

Release of free-state ions from fulvic acid-heavy metal complexes via VUV/H2O2 photolysis: Photodegradation of fulvic acids and recovery of Cd2+ and Pb2+ stripping voltammetry currents

Fulvic acid (FA), a ubiquitous organic matter in the environment, can enhance the mobility and bioavailability of Cd2+ and Pb2+ through competitive complexation to form FA-heavy metal ions (FA-HMIs) complexes with excellent solubility. Because FA-HMIs are electrochemically inactive, square wave anodic stripping voltammetry (SWASV) cannot accurately detect the content of bioavailable Cd2+ and Pb2+ in soils and sediments. This study ostensibly aimed to efficiently recover SWASV signals of Cd2+ and Pb2+ in FA-HMIs by disrupting FA-HMIs complexes using the combined vacuum ultraviolet and H2O2 (VUV/H2O2) process. Essentially, this study explored the photodegradation behavior and photolysis by-products of FA and their effects on the conversion of FA-HMIs complexes to free-state Cd2+ and Pb2+ using multiple characterization techniques, as well as revealed the complexation mechanism of FA with Cd2+ and Pb2+. Results showed that reactive groups such as carboxyl and hydroxyl endowed FA with the ability to complex Cd2+ and Pb2+. After FA-HMIs underwent VUV/H2O2 photolysis for 9 min at 125 mg/L of H2O2, FA was decomposed into small molecular organics while removing its functional groups, which released the free-state Cd2+ and Pb2+ and recovered their SWSAV signals. However, prolonged photolytic mineralization of FA to inorganic anions formed precipitates with Cd2+ and Pb2+, thereby decreasing their SWSAV signals. Moreover, the VUV/H2O2 photolysis significantly improved the SWASV detection accuracy toward the Cd2+ and Pb2+ in real soil and sediment samples, verifying its practicality.

Detection of Pertechnetate Using Square Wave Anodic Stripping Voltammetry on Carbon Electrodes

Technetium-99 (Tc-99) is a primary fission product of U-235, U-233, and Pu-239 and is a major constituent of radioactive waste. Tc-99 is commonly found as pertechnetate (TcO4 -), an anion that does not readily adsorb to natural sediment and is extremely mobile in environmental water systems. With concerns that radioactive waste may be leaking from sub-surface storage tanks and potentially reaching groundwater, developing detection methods for TcO4 - is important. Square wave anodic stripping voltammetry (SWASV) is a simple electrochemical technique that has yet to be investigated for pertechnetate due to the high potential required to form solid TcO2. In this work, we use SWASV with a variety of carbon electrodes to determine the optimal conditions for the detection of TcO4 - in a variety of solutions including acidic, basic and neutral pH. Carbon electrodes such as glassy carbon, boron-doped diamond, and nitrogen-doped tetrahedral amorphous carbon were examined. Carbon electrodes are ideal for the detection of pertechnetate due to their robust nature, low background current, and wide windows when compared to metal electrodes. Control studies included optimization of the deposition potential and time. In addition, calibration curves were created for each solution’s optimized parameters. Several analytical figures of merit such as the sensitivity, limit of detection, and limit of quantification were determined. This work expands upon the use of carbon electrodes for trace detection of environmentally relevant analytes.

An Efficient Voltammetric Sensor Based on Graphene Oxide-Decorated Binary Transition Metal Oxides Bi2O3/MnO2 for Trace Determination of Lead Ions

Herein we present a facile synthesis of the graphene oxide-decorated binary transition metal oxides of Bi2O3 and MnO2 nanocomposites (Bi2O3/MnO2/GO) and their applications in the voltammetric detection of lead ions (Pb2+) in water samples. The surface morphologies, crystal structures, electroactive surface area, and charge transferred resistance of the Bi2O3/MnO2/GO nanocomposites were investigated through the scanning electron microscopy (SEM), power X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) techniques, respectively. The Bi2O3/MnO2/GO nanocomposites were further decorated onto the surface of a glassy carbon electrode (GCE), and Pb2+ was quantitatively analyzed by using square-wave anodic stripping voltammetry (SWASV). We explored the effect of the analytical parameters, including deposition potential, deposition time, and solution pH, on the stripping peak current of Pb2+. The Bi2O3/MnO2/GO nanocomposites enlarged the electroactive surface area and reduced the charge transferred resistance by significant amounts. Moreover, the synergistic enhancement effect of MnO2, Bi2O3 and GO endowed Bi2O3/MnO2/GO/GCE with extraordinary electrocatalytic activity toward Pb2+ stripping. Under optimal conditions, the Bi2O3/MnO2/GO/GCE showed a broad linear detection range (0.01–10 μM) toward Pb2+ detection, with a low limit of detection (LOD, 2.0 nM). The proposed Bi2O3/MnO2/GO/GCE electrode achieved an accurate detection of Pb2+ in water with good recoveries (95.5–105%).

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.

Zinc detection in oil-polluted marine environment by stripping voltammetry with mercury-free nanoporous gold electrode

Detection of Zn(II) in oil-polluted seawater via square-wave anodic stripping voltammetry (SW-ASV) utilizing thin gold electrodes sputtered onto nanoporous poly(acrylic acid)-grafted-poly(vinylidene difluoride) (PAA-g-PVDF) membrane is herein reported. Prior to SW-ASV, PAA grafted nanopores demonstrated to efficiently trap Zn(II) ions at open circuit. This passive adsorption followed a Langmuir law. An affinity constant of 1.41 L upmu mol^{-1} and a maximum Zn(II) adsorbed mass q_{max} of 1.21 upmu mol g^{-1} were found. Applied SW-ASV protocol implied an accumulation step (− 1.2 V for 120 s) followed by a stripping step (− 1.2 to 1 V; 25 Hz; step: 4 mV; amplitude: 25 mV; acetate buffer (pH 5.5)). It revealed a Zn redox potential at − 0.8 V (Ag/AgCl pseudo-reference). Multiple measurements in synthetic waters close to the composition of production waters exhibited a decreasing precision with the number of readings R (1.65% (R = 2) and 6.56% (R = 3)). These membrane-electrodes should be used as disposable. The intra-batch mean precision was 14% (n = 3) while inter-batches precision was 20% (n = 15). Linear and linear-log calibrations allow exploitation of Zn(II) concentrations ranging from 10 to 500 upmu g L^{-1} and 100 to 1000 upmu g L^{-1} respectively. The LOD was 4.2 upmu g L^{-1} (3S/N). Thanks to obtained calibration, a detected Zn(II) content of 1 ppm in a raw production water from North Sea oil platform was determined.

Electrochemical Sensor for Detection and Degradation Studies of Ethyl Violet Dye.

In this work, a simple and sensitive electrochemical method was developed to determine ethyl violet (EV) dye in aqueous systems by using square wave anodic stripping voltammetry (SWASV) employing a glassy carbon electrode modified with acidic-functionalized carbon nanotubes (COOH-fCNTs). In square wave anodic stripping voltammetry, EV exhibited a well-defined oxidation peak at 0.86 V at the modified GCE. Impedance spectroscopy and cyclic voltammetry were used to examine the charge transduction and sensing capabilities of the modified electrode. The influence of pH, deposition potential, and accumulation time on the electro-oxidation of EV was optimized. Under the optimum experimental conditions, the limit of detection with a value of 0.36 nM demonstrates high sensitivity of COOH-fCNTs/GCE for EV. After detection, it was envisioned to devise a method for the efficient removal of EV from an aqueous system. In this regard a photocatalytic degradation method of EV using Ho/TiO2 nanoparticles was developed. The Ho/TiO2 nanoparticles synthesized by the sol–gel method were characterized by UV–vis, XRD, FTIR, SEM, and EDX. The photocatalytic degradation studies revealed that basic medium is more suitable for a higher degradation rate of EV than acidic and neutral media. The photodegradation kinetic parameters were evaluated using UV–vis spectroscopic and electrochemical methods. The results revealed that the degradation process of EV follows first-order kinetics.

Simultaneous detection of Lead and Cadmium using a composite of Zeolite Imidazole Framework and Reduced Graphene Oxide (ZIF-67/rGO) via electrochemical approach

Present work reports the application of a composite of ZIF-67/rGO for the simultaneous detection of traces of lead and cadmium via square wave anodic stripping voltammetry (SWASV) technique. For this, graffoil sheets were modified with synthesized composite for the electrode fabrication [(ZIF-67/rGO)/Graffoil] for its use in sensing studies. The SWASV response of (ZIF-67/rGO)/Graffoil electrode was optimized against deposition potential (-1.0 V) and time (350 s), required for the accumulation of metal ions onto the sensor electrode. The performance of the sensing electrode was then evaluated for lead (Pb<sup>2+</sup>) and cadmium (Cd<sup>2+</sup>) ions at various concentrations. The sensor displayed linear response in a wide concentration range of 5-100 ppb. The peak current of the electrode was found to be shifted towards the higher potential at higher metal ion concentrations. Based on the response measured, the limit of detection (LOD) of the fabricated sensor has been estimated and found to be 5 and 2.93 ppb for Pb<sup>2+</sup> and Cd<sup>2+</sup> ions, respectively. The results obtained revealed good specificity of the proposed sensor towards Pb<sup>2+</sup> and Cd<sup>2+</sup> ions in the co-presence of several other ions. In addition, the sensor exhibited good reproducibility with a relative standard deviation (RSD) of ~2% for both Pb<sup>2+</sup> and Cd<sup>2+</sup> ions.

Facile fabrication of new sensing platforms decorated with quinalizarin and PtNi alloy nanoparticles for highly sensitive aluminum determination

The presented work demonstrates a rapid, selective, ultrasensitive, and low operating cost voltammetric method for the determination of total aluminum at ultra-trace levels. New nanocomposite sensing platforms coated glassy carbon electrodes (GCE) were fabricated and tested for aluminum determination using square wave anodic stripping voltammetry (SWASV). Incorporation of quinalizarin (HAQ) and PtNi nanoparticles (PtNiNPs) into the carbon black ionic liquid paste (Vulcan XC72-IL) modified with Nafion solution was tested. The synthesized PtNiNPs were characterized by TEM, and the shape was octahedra with an average particle size of ca. 9 nm. SEM was used to examine the surface morphologies of the bare and modified electrodes. Vulcan XC72-IL@PtNiNPs@HAQ/GCE showed surprisingly higher activity than Vulcan XC72-IL@PtNiNPs/GCE and Vulcan XC72-IL@HAQ/GCE. The promising results were obtained after optimized the experimental conditions. The calibration curve was linear from 0.05 to 170 µg/L (R2 = 0.989) with a detection limit of 0.21 ng/L and repeatability below 2.1 %. The reproducibility of the sensing platform preparation was equal to 5.3 % (n = 4). Results were verified using recovery (98.6 ± 3.0) and GFAAS. Thus, the proposed sensing platform enhanced the sensitivity due to its large surface area and high electrical conductivity of its components. The study clearly showed that a small change in aluminum content could be followed with satisfactory results employing this approach.