Metal concentrations in transitional and coastal waters measured by passive (Diffusive Gradients in Thin-films) and spot sampling: MONITOOL Project Dataset

The MONITOOL project (2017-2023) was carried out to describe the relationships between total dissolved and labile metal concentrations measured in spot water samples and in concurrently deployed Diffusive Gradients in Thin-films (DGTs) passive samplers, respectively. The ultimate aim was to adapt existing marine metal Environmental Quality Standards (EQS marine water) for DGTs, enabling their use in the context of the European Directives (the Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD)). Time-integrated metal concentrations provided by DGTs, representing several days, are an advantage compared to conventional spot sampling, especially in highly dynamic systems, such as transitional waters. Hence, the MONITOOL project aimed to provide a robust database of dissolved and labile metal concentrations in transitional and coastal waters, based upon co-deployments of DGTs and collection of spot water samples at several sampling sites (England, France, Ireland, Italy, Northern Ireland, Portugal, Scotland and Spain), followed subsequently by DGT and water metal analysis. Samplings were carried out in 2018 and 2022, following agreed protocols developed in the framework of the project. The MONITOOL dataset includes metal concentrations from DGTs, measured with Inductively Coupled Plasma Mass Spectrometry (ICP-MS: Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn) and in concurrently collected spot water samples by ICP-MS (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) and Anodic/Cathodic Stripping Voltammetry (ASV/CSV: Cd, Pb, Ni). Moreover, data on seawater physical-chemical parameters (salinity, temperature, dissolved oxygen, pH, turbidity, total suspended solids, dissolved organic carbon, and total organic carbon) is provided. This database presents the results obtained using, concurrently, different forms of sampling and analytical techniques, enabling the comparison of the results obtained by these strategies and allowing the adaptation of EQS in marine water (EQS marine water) to DGTs (EQS DGT), in the context of the WFD. Moreover, due to the large number of sampling sites, it could also be used for other types of research, such as those dealing with metal speciation or the determination of baseline levels.

Determination of lithium ions by stripping voltammetry using single-crystal LiFePO4

Determination of lithium ions is very important for extraction of lithium from salt lakes. Electrochemical sensor is an ideal choice, but it is not available so far. Here, a voltammetric sensor based on lithium iron phosphate (LiFePO4) was developed. Single-crystal LiFePO4 dominated by the (010) lattice plane was synthesized using hydrothermal method; it had good selectivity for lithium ions. Lithium ions were preferentially intercalated into LiFePO4 even if molar ratio of sodium ions, potassium ions, magnesium ions or calcium ions to lithium ions reached 10:1. The intercalation and deintercalation of interfering ions should be avoided because this reduced the selectivity of LiFePO4 for lithium ions. Lithium ion concentration of synthetic Uyuni Salt Lake solution was determined using the standard addition method. The measurement result was only 0.34 % higher than the theoretical value. The sensor provides a highly selective lithium ion analysis method at an extremely low cost, which was very promising to be widely used.

Adsorptive stripping voltammetric sensor based on Cd zeolitic imidazole framework-67 for electrochemical detection of sarin simulant

A selective and reliable modified glassy carbon sensor, based on a 1.0% Cd zeolitic imidazole framework-67 modified glassy carbon sensor (GCS2), has been developed for ultrasensitive detection of dimethyl methyl phosphonate (DMMP) in human biological fluid. The synthesis of porous nanoparticles of Cd zeolitic imidazole framework-67 (Cd ZIF-67) was carried out via the hydrothermal method. The resulting Cd ZIF-67 powder emerges with good crystallinity, a rhombic dodecahedral morphology with particle size in the range 300 ~ 500 nm, and a specific surface area of 1780 m2·g-1. Furthermore, the fabricated sensor exhibited superior performance in the detection of DMMP with two linearity ranges of 0.02-2.0 nM and 2.0-9.0 nM and a limit of detection (LOD) of 0.06 pM. The fabricated sensor exhibited good reliability, long-term stability, and repeatability, which are favourable attributes for electroanalytical detection. In addition, the fabricated sensor displayed superior performance without significant interference during the assay of DMMP in a biological fluid (human serum sample) within two linearity ranges of 0.1-1.0 nM and 1.0-6.0 nM and a LOD of 0.03 nM.

Modification of electrodes with polymer nanocomposites: Application to the simultaneous determination of Zn(II), Cd(II), and Cu(II) in water samples

Currently, there is a need for fast and sensitive analytical methods for monitoring metals in water due to the progressive increase in the presence of metal ions in the environment. These metals reach the environment mainly from industrial activity and heavy metals are non-biodegradable. The present work evaluates different polymeric nanocomposites to carry out the simultaneous electrochemical determination of Cu, Cd, and Zn in water samples. Screen-printed carbon electrodes (SPCE) were modified with the nanocomposites, which were obtained by a mixture of graphene, graphite oxide, and polymers, such as polyethyleneimide, gelatin, and chitosan. These polymers have amino groups in their matrix, giving the nanocomposite the ability to retain divalent cations. However, the availability of these groups plays a fundamental role in the retention of these metals. The modified SPCEs were characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. The electrode that presented the best performance was selected to determine the concentration of metal ions in water samples by square-wave anodic stripping voltammetry. The obtained detection limits were 0.23 μg L^-1, 0.53 μg L^-1, and 1.52 μg L^-1 for Zn(II), Cd(II), and Cu(II), respectively, with a lineal range of 0.1-50 μg L^-1. The obtained results made it possible to conclude that the method developed using the SPCE modified with the polymeric nanocomposite presented adequate LODs, reasonable sensitivity, selectivity, and reproducibility. Besides, this platform is an excellent tool for developing devices to simultaneously determine heavy metals in environmental samples.

A strategy for As(III) determination based on ultrafine gold nanoparticles decorated on magnetic graphene oxide

In this work, a new dendrimer modified magnetic graphene oxide (GO) was used as a substrate for electrodeposition of Au nanoparticles. The modified magnetic electrode was employed for sensitive measuring of As(III) ion as a well-established human carcinogen. The prepared electrochemical device exhibits excellent activity towards As(III) detection using the square wave anodic stripping voltammetry (SWASV) protocol. At optimum conditions (deposition potential at -0.5 V for 100 s in 0.1 M acetate buffer with pH 5.0), a linear range from 1.0 to 125.0 μgL-1 with a low detection limit (calculated by S/N = 3) of 0.47 μg L-1 was obtained. In addition to the simplicity and sensitivity of the proposed sensor, its high selectivity against some major interfering agents, such as Cu(II) and Hg(II) makes it an appreciable sensing tool for the screening of As(III). In addition, the sensor revealed satisfactory results for detection of As(III) in different water samples, and the accuracy of obtained data were confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) setup. Accounting for the high sensitivity, remarkable selectivity and good reproducibility, the established electrochemical strategy has great potential for analysis of As(III) in environmental matrices.

On spot detection of nickel and cobalt from exhausted batteries by a smart electrochemical sensor

This work presents the realization and the application of an user-friendly electrochemical platform based on screen-printed electrodes for the simultaneous determination of nickel and cobalt ions in real samples by means of square wave adsorptive stripping voltammetry (SWAdSV). The sensor was realized by electrodepositing in situ a bismuth film onto graphite screen-printed electrodes (GSPEs). The sensor surface was fully characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The experimental conditions for the determination of nickel and cobalt in the form of dimethylglyoximate complexes were studied and optimized. Linear calibration curves for Ni(II) and Co(II), determined individually and together, in the range 10-40 μg/L for nickel and 10-60 μg/L for cobalt, respectively, were obtained. The limits of detection for nickel and cobalt determination were 2.5 μg/L and 2.4 μg/L, respectively. The performance of the sensor in terms of reproducibility and selectivity was also studied. The applicability of the developed platform was assessed by determining nickel and cobalt in samples deriving from an industrial process of recycling exhausted batteries and in soil samples.

Electrochemical sensor based on Bi/Bi2O3 doped porous carbon composite derived from Bi-MOFs for Pb2+ sensitive detection

It is of great significance to develop electrochemical sensors based on novel functional nanomaterials for heavy metal ions detection. In this work, a novel Bi/Bi₂O₃ co-doped porous carbon composite (Bi/Bi₂O₃@C) was prepared by simple carbonization of bismuth-based metal-organic frameworks (Bi-MOFs). The micromorphology, internal structure, crystal and elemental composition, specific surface area and porous structure of the composite were characterized by SEM, TEM, XRD, XPS, and BET. Further, a sensitive electrochemical sensor for Pb²⁺ detection was constructed by modifying Bi/Bi₂O₃@C on the surface of the glassy carbon electrode (GCE) based on the square wave anodic stripping voltammetric (SWASV). The different factors affecting the analytical performance were optimized systematically, such as material modification concentration, deposition time, deposition potential, and pH value. Under optimized conditions, the proposed sensor exhibited a wide linear range from 37.5 nM to 2.0 μM with a low detection limit of 6.3 nM. Meanwhile, the proposed sensor showed good stability, acceptable reproducibility, and satisfactory selectivity. The reliability of the as-proposed sensor was confirmed by the ICP-MS method for Pb²⁺ detection in different samples.

Application of BiNPs/MWCNTs-PDA/GC sensor to measurement of Tl (1) and Pb (II) using stripping voltammetry

Herein, simultaneous determination of Tl (1) and Pb (II) has been carried out at the surface of a modified glassy carbon electrode with polydopamine functionalized multi-walled carbon nanotubes- BiNPs nanocomposite (BiNPs/MWCNTs-PDA/GC) using square-wave anodic stripping voltammetry (SWASV) technique. The morphologies, composition and, electrochemical properties of the BiNPs/MWCNTs-PDA/GC were characterized by scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray energy dispersive spectroscopy (EDX), electrochemical impedance spectroscopy (EIS) and, SWASV. The parameters affecting the stripping current response were investigated and optimized. The large specific area of MWCNTs and good electro-conductibility of BiNPs causes the BiNPs/MWCNTs-PDA/GC electrode to exhibit an excellent electro-catalytic effect with good separation peaks for Tl and Pb oxidation compared to bare GCE under the optimal conditions. The proposed sensor showed wide leaner ranges from 0.4-100 ppb and 100-400 ppb for Tl (I) and Pb (II). Low detection limits of 0.04 ppb for Tl (I) and 0.07 ppb for Pb (II) were achieved. The efficiency of the electrode after thirty days of storage in ambient conditions without using it and also with the ability to reuse for 16 days did not decrease significantly. In addition, the modified electrode with simple preparation method showed good reproducibility, and high selectivity for measuring target ions. The method was successfully implemented for the simultaneous determination of Tl (I) and Pb (II) in tap, mineral and waste water samples with acceptable recovery (from 99.1-103.2 for Tl (I) and 98.4-100.4 for Pb (II)).

Reversed-phase dispersive liquid-liquid microextraction based on decomposition of deep eutectic solvent for the determination of lead and cadmium in vegetable oil

In this work, a reversed-phase dispersive liquid-liquid microextraction procedure based on the decomposition of deep eutectic solvent was suggested for the first time. The procedure was utilized for fast and simple separation of lead and cadmium from vegetable oil samples. The procedure assumed mixing of oil sample and DES based on menthol, formic acid and water. Water as component of DES promoted its decomposition in sample matrix resulting menthol dissolution in the sample phase and dispersion of aqueous formic acid solution. In this procedure menthol acted as a dispersive solvent during DES decomposition for dispersion of aqueous formic acid solution. The metals were determined by the square-wave anodic stripping voltammetry. The limits of detection, were 0.01 µg kg^-1 for lead and 0.006 µg kg^-1 for cadmium. The RSD was less then 6% for both analytes. The enrichment factor was 36 and 39 for lead and cadmium, respectively.

Quercetin-rGO based mercury-free electrode for the determination of toxic Cd (II) and Pb (II) ions using DPASV technique

Metal ion pollution poses serious threat to environment. Analysis of Cd (II) and Pb (II) ions using chemically modified mercury free electrode is a feasible routine analytical tool. Developing an electrode surface modified with conductive 2D carbon and metal complexing ligand created a synergetic effect towards sensitive and selective electrochemical determination of metal ions. The present study focused on green chemistry approach towards synthesis of reduced graphene oxide using a natural flavonoid (Quercetin) that acts as a reducing, functionalizing agent and also as metal complexing agent. This quercetin reduced graphene oxide (Q-rGO) was surface modified over paraffin wax impregnated graphite electrode. The resulting Q-rGO electrode was used as a mercury-free electrode for simultaneous analysis of Pb (II) and Cd (II) ions. Physico-chemical parameters of the synthesized Q-rGO and modified electrodes were characterized using X-ray diffraction, UV-Vis, FT-IR, and Raman spectrometer. The morphology of the material and surface topography of the modified electrode was observed using HR-TEM and FESEM, respectively. Cyclic voltammetry (CV) and AC impedance (EIS) were adopted for electrochemical characterization and Differential pulse anodic stripping voltammetry (DPASV) was chosen for simultaneous sensing of metal ions using Q-rGO electrode. Analytical parameters such as effect of electrolyte, effect of pH, preconcentration time and deposition potential were optimized. The experimental results suggested that the Q-rGO electrode is capable of sensing Pb (II) and Cd (II) ions individually and simultaneously. Inference from the calibration plot showed that the Q-rGO electrode was capable of sensing the concentration range of Cd (II) ion form 0.19 to 2.5 μgL^-1 with LOD-0.05 μgL^-1 and Pb (II) ions from 0.19 to 3.1 μgL^-1 with LOD 0.06 μgL^-1.

Preparation of GO/Fe3O4@PMDA/AuNPs nanocomposite for simultaneous determination of As3+ and Cu2+ by stripping voltammetry

One of the critical challenges in the simultaneous determination of As³⁺ and Cu²⁺ by stripping voltammetry is the overlapping of their oxidation peaks. Therefore, the engineering of nanostructured sensors in order to uplift their electrochemical performance is a significant issue for the codetection of As³⁺ and Cu²⁺. Herein, we modified a glassy carbon electrode with a new nanocomposite based on poly methyldopa along with gold nanoparticles immobilized on the surface of magnetic graphene oxide (GCE/GO/Fe₃O₄@PMDA/AuNPs) that can determine As³⁺ and Cu²⁺ with great sensitivity. Optimization of the measurement conditions by square wave stripping voltammetry (SWSV) caused the oxidation peaks of As³⁺ and Cu²⁺ to be distinguished significantly from each other, while the peak currents of As³⁺ and Cu²⁺ increased 9-12 fold, respectively, compared to the bare electrode. The proposed electrode exhibits low detection limits (S/N ≥ 3): 0.15 ppb for As³⁺ and 0.11 ppb for Cu²⁺. The GCE/GO/Fe₃O₄@PMDA/AuNPs also has good linearity over a wide concentration range from 5 to 500 ppb for As³⁺ and 0.5-750 ppb for Cu²⁺. The good recovery values were obtained for the analysis of As³⁺ and Cu²⁺ in pool and drinking water samples.

Lead toxicity in Lucilia cuprina and electrochemical analysis: a simple and low-cost alternative for forensic investigation

Entomotoxicology allows the detection and analysis of substances such as poisons, drugs, and metals in necrophagous insects using analytical protocols. In a forensic situation related to death by gunshot, the gunshot residue (GSR) is dispersed at the crime scene and may be consumed by necrophagous insects. Lead (Pb) is the most abundant metal in GSR samples and it can be determined using non-portable methods. However, the toxicity effects of GSR samples on Lucilia cuprina (Diptera: Calliphoridae) and the detection of Pb via portable electrochemical methods have not been investigated. This study describes for the first time the toxicity analysis of Pb on immature L. cuprina through their survival rate and influence of Pb on immature development. In addition, the bioaccumulation of Pb in the larvae samples was determined based on square wave anodic stripping voltammetry (SWASV) measurements. The results revealed a low limit of detection to Pb (6.5 μg L^-1) and the analytical performance was satisfactory because it measures Pb levels in larvae exposed to a diet containing 50 μg Pb g^-1. Furthermore, the levels of Pb influenced the survival rate and development time of the immature L. cuprina. Larvae exposed to a high concentration of the metal (50 μg Pb g ^-1) showed statistically significant changes (p < 0.05). The presence of Pb in immature L. cuprina can be used to estimate the post-mortem interval; thus, the present study provides important information in forensic entomology.

Signal amplification by electro-oligomerisation for improved isoproturon detection

A novel concept is introduced for signal amplification in electrochemical sensing: the electro-oligomerisation stripping voltammetry, which has been applied here to the improved detection of the isoproturon herbicide in spring waters as a proof-of-principle. It involves a potentiostatic accumulation step onto a glassy carbon electrode (at +1.5 V vs Ag/AgCl reference electrode for 300 s) leading to the formation of an oligomeric film, which is then detected by cathodic stripping square wave voltammetry (SWV). The presence and composition of the film are confirmed by confocal Raman spectroscopy. Its characterisation by cyclic voltammetry demonstrates the reversible nature of the electrodeposited material, confirming its interest for sensitive detection by SWV. Adding a mesoporous silica membrane with vertically oriented nanochannels further enhances the sensitivity of the sensor, exhibiting a linear response in the 10-100 μM concentration range. This effect was even more interesting for real media analysis thanks to the permselective properties of such nanoporous coating in rejecting interferences and/or surface fouling agents. The method should be applicable to other analytes that are usually not detectable by conventional accumulation/stripping voltammetry.

Simultaneous determination of lead and antimony in gunshot residue using a 3D-printed platform working as sampler and sensor

3D-printing is an emerging technique that enables the fast prototyping of multiple-use devices. Herein we report the fabrication of a 3D-printed graphene/polylactic acid (G-PLA) conductive electrode that works as a sampler and a voltammetric sensor of metals in gunshot residue (GSR) using a commercially-available G/-PLA filament. The 3D-printed surface was used as swab to collect GSR and next submitted to a square-wave voltammetric scan for the simultaneous detection of Pb²⁺ and Sb³⁺. The proposed sensor presented excellent analytical performance, with limit of detection values of 0.5 and 1.8 μg L^-1 to Pb²⁺ and Sb³⁺, respectively, and linear ranges between 50 and 1500 μg L^-1. Sampling was performed through the direct contact of G-PLA electrode in hands and clothes of shooters, followed by immersion in the electrochemical cell in the presence of supporting electrolyte for the SWASV scan. The proposed method showed a great performance in the recovery, identification and semi-quantification of Pb²⁺ and Sb³⁺ in the evaluated samples without the need for sample preparation. Moreover, the device can be reused as sampler and sensor (until three times without loss of electrochemical performance) and the fabrication is reproducible (RSD = 7%, for three different devices). Hence, this 3D-printed material is an excellent candidate for the analysis of GSR, an indispensable analysis in the forensic field.

Biomass derived worm-like nitrogen-doped-carbon framework for trace determination of toxic heavy metal lead (II)

The worm-like nitrogen-doped-carbon framework (WNCF) with abundant edge-plane-like defective sites (EDSs) was synthesized by using natural wax gourd (Benincasa hispida) as the main carbon precursor and milk yielded by Chinese Holstein cattle (Holstein Friesian) as the nitrogen precursor for the first time. The Nafion-dispersed WNCF (Nafion-WNCF) was employed to design a highly sensitive electrochemical sensor for the trace determination of toxic heavy metal lead (II) (Pb²⁺) by the differential pulse anodic stripping voltammetry (DPASV). Some key experimental factors including calcination temperature of WNCF, pH value of the buffer solution, deposition potential, deposition time and the concentration of bismuth (Bi³⁺) were optimized for the stripping analysis of Pb²⁺. Under the optimum experimental condition, Nafion-WNCF modified bismuth film glassy carbon electrode (Nafion-WNCF/BFGCE) exhibits a wide linear range from 0.5 μg L^-1 to 100 μg L^-1 and a low detection limit of 0.2 μg L^-1 (S/N = 3) for detecting Pb²⁺. Especially, Nafion-WNCF/BFGCE was successfully applied to determine Pb²⁺ in tap water and lake water samples. All the results suggest that the WNCF can be considered as a green and low-cost nanomaterial for the precision detection of Pb²⁺ in real samples.

High specificity and efficiency electrochemical detection of poly(ADP-ribose) polymerase-1 activity based on versatile peptide-templated copper nanoparticles and detection array

Poly(ADP-ribose) polymerase-1 (PARP-1) activity is closely related to tumor, which is a promising biomarker for cancer diagnosis. So far, only a few methods have been developed for PARP-1 activity assay because both PARP-1 and its catalytic products lack valuable optical or electrochemical property. Herein, we propose a more specific method to label probes on great deal of phosphate groups of PAR. Firstly, versatile peptides were used to prepare CuNPs. This peptide not only worked as reducing agent to prepare CuNPs but also had guanidine groups to label PAR autonomously and specifically. Unlike most previously reported methods based on unspecific electrostatic interactions, CuNPs probes covered by guanidine groups labelled PAR with phosphate groups via intense covalent-like interactions. On the other hand, PARP-1 catalyzed the formation of PAR in each isolated reaction container of the detection array, realizing the high-throughput detection and enhancing the detection efficiency. Ultimately, CuNPs were oxidized into Cu²⁺ and precisely detected by stripping voltammetry. Hence, selectivity and efficiency of PARP-1 detection were both improved. Meanwhile, this approach was successfully used to detect the efficiency of PARP-1 inhibitor and the PARP-1 contents in real cells, indicating its great potential for clinical diagnosis and high-throughput PARP-1 inhibitor screen.

Determination of Se(IV) concentration via cathodic stripping voltammetry in the presence of Cu(II) ions and ammonium diethyl dithiophosphate

The development of a methodology for the determination of Se(IV) concentration via cathodic stripping voltammetry is described in this work. The methodology is based on the formation of copper selenide (Cu₂Se), whose reduction signal at -0.60 V has been used as an analytical response to quantify the Se(IV) concentration in solution. The novelty of our methodology is the study of this system in the presence of a ligand such as ammonium diethyl dithiophosphate (ADTTP), which forms complexes with Cu(II) and Se(IV). The results showed that the presence of ADTTP plays an important role, increasing the sensitivity of the determination by almost a factor of two compared with the methodology in the absence of the ligand. The optimized conditions were pH 1.6 (phosphoric acid, 2.0 × 10^-2 mol L^-1), C_Cu(II) = 1.5 mg L^-1, C_ADTTP = 2.0 μmol L^-1, E_acc = -0.40 V and t_acc = 45 s. The detection and the quantification limits obtained were 0.065 and 0.21 μg L^-1, respectively, and linearity was maintained up to 4.0 μg L^-1 of Se(IV). The sensitivity was 10.26 nA L μg^-1. On the other hand, the relative standard deviation for 15 replicate measurements at 1.0 μg L^-1 of Se(IV) was 1.6%. The usefulness of the method was evaluated by determining Se(IV) in two certified reference materials (TMDW and TM-28.4) with relative errors of less than 2.0%. The proposed method was successfully applied to the determination of Se(IV) in spiked tap water and in a liquid pharmaceutical formulation with satisfactory results. The developed methodology presents a low detection limit, good repeatability, selectivity and linear range. Furthermore, the sensibility of the method was achieved by applying a short accumulation time (45 s).

Electrochemical sensing using magnetic molecularly imprinted polymer particles previously captured by a magneto-sensor

The determination of 1-chloro-2,4-dinitrobenzene (CDNB) was used as a proof-of-concept to a simple analytical practical configuration applying magnetic molecularly imprinted particles (mag-MIPs). Mag-MIPs were captured from an emulsion by a home-made magneto-sensor (where a small magnet was entrapped by a graphite-epoxy composite) and then, this sensor, was transferred to the solution containing the analyte, where, after binding to the mag-MIPs, the analyte was directly analysed using differential pulse voltammetry (DPV) since the magneto-sensor acted as the working electrode. After optimization, a detection limit of 6.0 μmol L^-1 with a RSD of 2.7% was achieved along with suitable recoveries and selectivity. This methodology offers a different approach for electroanalytical methodologies using mag-MIPs.

A novel voltammetric sensor for nevirapine, based on modified graphite electrode by MWCNs/poly(methylene blue)/gold nanoparticle

In the present study, a graphite electrode (GE) modified by conductive film (containing functionalized multi-walled carbon nanotubes (f-MWCNTs), poly methylene blue p(MB) and gold nanoparticles (AuNPs)) was introduced for determination of nevirapine (NVP) as an anti-HIV drug by applying the differential pulse anodic stripping voltammetry (DPASV) technique. Modification of the electrode was investigated by scanning electron microscopy (SEM) and impedance electrochemical spectroscopy (EIS). All electrochemical effective parameters on detection of NVP were optimized and the oxidation peak current of drug was used for its monitoring. The obtained results confirmed that the oxidation peak currents increased linearly by increasing in NVP concentrations in the range of 0.1-50 μM and a detection limit of 53 nM was achieved. The proposed sensor (AuNPs/p(MB)/f-MWCNTs/GE) was successfully applied for the determination of NVP in blood serum and pharmaceutical samples. It revealed the excellent stability, repeatability and reproducibility as well.

Selective electrochemical sensing for arsenite using rGO/Fe3O4 nanocomposites

Herein, we report rGO/Fe₃O₄ nanocomposites (NCs) free from noble metals, synthesized by facile one step chemical reduction method, for electrochemical detection of arsenite in water by square wave anodic stripping Voltammetry (SWASV). The synthesized NCs were characterized for its optical, morphological and structural properties. The NCs modified glassy carbon (GCE), NCs/GCE, electrodes showed a higher sensitivity (0.281μA/ppb) and lower LOD (0.12ppb) under optimized experimental conditions. The proposed NCs/GCE electrodes show no interference towards arsenite species in the presence of common cationic interferants, namely, Cu(II), Pb(II), Ni(II), Co(II), Cd(II), Cr(II), Zn(II), etc. In addition, the proposed electrode demonstrates a good stability, reproducibility and potential practical application in electrochemical detection of arsenite.

Adsorptive Behavior and Voltammetric Determination of Hydralazine Hydrochloride at A Glassy Carbon Electrode Modified with Multiwalled Carbon Nanotubes

An electroanalytical method has been introduced for highly sensitive determination of hydralazine hydrochloride (Hy-HCl) based on its oxidation at a glassy carbon electrode modified with multiwalled carbon nanotubes (MWCNT/GCE). Studies showed that the electrochemical oxidation of Hy-HCl was accompanied by adsorption and highly sensitive responses could be achieved by adsorptive stripping voltammetry. The electrooxidation of Hy-HCl at MWCNT/GCE occurred at ~32 mV which was lower than that observed at bare GCE (~52 mV). The optimum working conditions for determination of the drug using differential-pulse adsorptive stripping voltammetry (DPAdSV) were established. The method exhibited linear responses to Hy-HCl in the concentration range 10-220 nM with a detection limit of 2.7 nM. The proposed method was successfully applied to the determination of this compound in pharmaceutical dosage forms.

A sensitive electrochemical sensor using an iron oxide/graphene composite for the simultaneous detection of heavy metal ions

We report an analytical assessment of an iron oxide (Fe2O3)/graphene (G) nanocomposite electrode used in combination with in situ plated bismuth (Bi) working as an electrochemical sensor for the determination of trace Zn(2+), Cd(2+), and Pb(2+). The as-synthesized nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, thermo-gravimetric analyzer, and X-ray diffraction. The electrochemical properties of the Fe2O3/G/Bi composite modified electrode were investigated. Differential pulse anodic stripping voltammetry was applied for the detection of metal ions. Due to the synergetic effect between graphene and the Fe2O3 nanoparticles, the modified electrode showed improved electrochemical catalytic activity high sensitivity toward trace heavy metal ions. Several parameters such as the preconcentration potential, bismuth concentration, preconcentration time, and pH were carefully optimized to determine the target metal ions. Under optimized conditions, the linear range of the electrode was 1-100μgL(-1) for Zn(2+), Cd(2+), and Pb(2+), and the detection limits were 0.11μgL(-1), 0.08μgL(-1), and 0.07μgL(-1), respectively (S/N =3). Repeatability (% RSD) was found to be 1.68% for Zn(2+), 0.92% for Cd(2+), and 1.69% for Pb(2+) for single sensor with 10 measurements and 0.89% for Zn(2+), 1.15% for Cd(2+), and 0.91% for Pb(2+) for 5 different electrodes. The Fe2O3/G/Bi composite electrode was successfully applied to the analysis of trace metal ions in real samples. The solventless thermal decomposition method applied to the simple and easy synthesis of nanocomposite electrode materials can be extended to the synthesis of nanocomposites and promising electrode materials for the determination of heavy metal ions.

Application of bismuth bulk annular band electrode for determination of ultratrace concentrations of thallium(I) using stripping voltammetry

A study of a new type of mercury-free working electrode - the bismuth bulk annular band working electrode (BiABE) - applied for thallium(I) detection via differential pulse anodic stripping voltammetry (DP ASV), preceded by the complexation of interfering ions (Cd(2+), Pb(2+)) with EDTA in an acetate buffer (pH 4.5), is reported. The optimisation of experimental conditions included selection of the appropriate supporting electrolyte solution, potential and time of preconcentration, and DP mode parameters. The peak current was proportional to the concentration of Tl(I) in the range from 0.5 to 49nmolL(-1) (R=0.9992) and from 0.05 to 1.4nmolL(-1) (R=0.9987) for accumulation times of 60s and 300s, respectively. For 60s of accumulation time, the LOD was 0.005nmolL(-1) (1ngL(-1)) (at S/N=3), and the sensitivity of 18.5nA/nM was achieved. The relative standard deviation for 4.9nmolL(-1) of Tl(I) was 4.3% (n=5). Finally, the proposed method was successfully applied to determine Tl(I) in the certified reference materials-waters (SPS-SW1 and SPS-SW2) as well as the spiked tap and river water samples.

Glutathione modified screen-printed carbon nanofiber electrode for the voltammetric determination of metal ions in natural samples

This work reports the development of a glutathione modified electrode via electrografting on a screen-printed carbon nanofiber substrate (GSH-SPCNFE). GSH-SPCNFE was compared to a classical screen-printed carbon electrode modified with glutathione (GSH-SPCE) for the simultaneous voltammetric determination of Cd(II) and Pb(II). Their electrochemical characterization and analytical performance suggest that SPCNFE could be a much better support for GSH immobilization. The applicability of GSH-SPCNFE for the determination of low concentration levels of Pb(II) and Cd(II) ions in environmental samples was successfully tested in a certified wastewater reference material by means of stripping voltammetry with a very high reproducibility and good trueness.

Penicillamine-modified sensor for the voltammetric determination of Cd(II) and Pb(II) ions in natural samples

A new penicillamine-GCE was developed based on the immobilization of d-penicillamine on aryl diazonium salt monolayers anchored to the glassy carbon electrode (GCE) surface and it was applied for the first time to the simultaneous determination of Cd(II) and Pb(II) ions by stripping voltammetric techniques. The detection and quantification limits at levels of µg L(-1) suggest that the penicillamine-GCE could be fully suitable for the determination of the considered ions in natural samples.

Mercury(II) trace detection by a gold nanoparticle-modified glassy carbon electrode using square-wave anodic stripping voltammetry including a chloride desorption step

Gold nanoparticles (AuNPs) were deposited on a glassy carbon (GC) substrate by constant potential electrolysis and characterized by cyclic voltammetry in H2SO4 and field emission gun scanning electron microscopy (FEG-SEM). The modified AuNPs-GC electrode was used for low Hg(II) concentration detection using a Square Wave Anodic Stripping Voltammetry (SWASV) procedure which included a chloride desorption step. The comparison of the obtained results with our previous work in which no desorption step was used showed that this latter step significantly improved the analytical performances, providing a three time higher sensitivity and a limit of detection of 80pM for 300s preconcentration, as well as a lower average standard deviation. The influence of chloride concentration on the AuNPs-GC electrode response to Hg(II) trace amounts was also studied and its optimal value confirmed to be in the 10(-2)M range. Finally, the AuNPs-GC electrode was used for the determination of Hg(II) in a natural groundwater sample from south of France. By using a preconcentration time of 3000s, a Hg(II) concentration of 19±3pM was found, which compared well with the result obtained by cold vapor atomic fluorescence spectroscopy (22±2pM).

Antimony film screen-printed carbon electrode for stripping analysis of Cd(II), Pb(II), and Cu(II) in natural samples

An in-situ antimony film screen-printed carbon electrode (in-situ SbSPCE) was successfully used for the determination of Cu(II) simultaneously with Cd(II) and Pb(II) ions, by means of differential pulse anodic stripping voltammetry (DPASV), in a certified reference groundwater sample with a very high reproducibility and good trueness. This electrode is proposed as a valuable alternative to in-situ bismuth film electrodes, since no competition between the electrodeposited copper and antimony for surface sites was noticed. In-situ SbSPCE was microscopically characterized and experimental parameters such as deposition potential, accumulation time and pH were optimized. The best voltammetric response for the simultaneous determination of Cd(II), Pb(II) and Cu(II) ions was achieved when deposition potential was -1.2 V, accumulation time 120 s and pH 4.5. The detection and quantification limits at levels of μg L(-1) suggest that the in-situ SbSPCE could be fully suitable for the determination of Cd(II), Pb(II) and Cu(II) ions in natural samples.

Implications of effluent organic matter and its hydrophilic fraction on zinc(II) complexation in rivers under strong urban pressure: aromaticity as an inaccurate indicator of DOM-metal binding

The zinc binding characteristics of dissolved organic matter (DOM) fractions from the Seine River Basin were studied after being separated and extracted according to their polarity: hydrophobic, transphilic, and hydrophilic. The applied experimental methodology was based on a determination of labile zinc species by means of differential pulse anodic stripping voltammetry (DPASV) at increasing concentrations of total zinc on a logarithmic scale and at fixed levels of: pH, ionic strength, and temperature. Fitting the DOM fractions with two discrete classes of ligands successfully allowed determining the conditional zinc binding constants (Ki) as well as total ligand density (LiT). The binding constants obtained for each DOM fraction were then compared and discussed with respect to the hydrophobic/hydrophilic nature and sample origin. Results highlighted a strong complexation of zinc to the effluent organic matter and especially the most hydrophilic fraction, which also displayed a very low specific UV absorbance. Although the biotic ligand model takes into account the quality of DOM through UV absorbance in the predictions of metal bioavailability and toxicity, this correction is not efficient for urban waters.

Role of Fe(III) in preventing humic interference during As(III) detection on gold electrode: spectroscopic and voltammetric evidence

A drawback of As(III) detection using square wave anodic stripping voltammetry (SWASV) is that it is susceptible to interferences from various metals or organic compounds, especially in real sample water. This study attempts to understand the interference of co-existing of Fe(III) and humic acid (HA) molecules to the electrochemical detection of As(III) using Fourier transform infrared (FTIR) spectrum and X-ray photoelectron spectroscopy (XPS). The electrochemical experiments include stripping of As(III) in the solutions containing HA with different concentrations, cyclic voltammetry in 0.5M H2SO4 in the presence of HA or Fe(III) with/without addition of Fe(III) or HA, and stripping of As(III) in the presence of HA or Fe(III) with/without addition of Fe(III) or HA. FTIR and XPS are employed to confirm the affinity of HA to Fe(III) or As(III) in acidic condition.