Catalytic Adsorptive Stripping Chronopotentiometry of Co(II)‐DMG‐Bromate System at an In Situ Plated Lead Film Electrode

A novel catalytic adsorptive stripping chronopotentiometric (CC‐CAdSCP) procedure for the determination of Co(II) traces was developed using a lead film electrode (PbFE). The PbFE was generated in situ on a glassy carbon support from a 0.1 M ammonia buffer containing 1×10^?5 M Pb(II), 6.5×10^?5 M DMG and the target metals. An addition of 0.2 M NaBrO₃ to the solution yielded an 11‐fold catalytic enhancement of chronopotentiometric response of the Co(II)‐DMG complex. The CC‐CAdSCP curves were well‐developed, sharp and reproducible (RSD 5.0 % for 5×10^?9 M Co(II)). The limit of detection for Co(II) for 210 s of accumulation time was 4×10^?10 M (0.024 µg L^?1). In addition, the elaborated method allowed the simultaneous quantification of Co(II) and Ni(II) simultaneously.     

Simultaneous Adsorptive Cathodic Stripping Voltammetric Determination of Nickel(II) and Cobalt(II) at an In Situ Bismuth‐Modified Gold Electrode

A study on the simultaneous determination of Ni(II) and Co(II) dimethylglyoximates (Ni‐DMG and Co‐DMG) through adsorptive cathodic stripping voltammetry at an in situ bismuth‐modified gold electrode (Bi‐AuE) is reported. The key operational parameters, such as Bi(III) concentration, accumulation potential and accumulation time were optimized and the morphology of the Bi‐microcrystals deposited on the Au‐electrode was studied. The Bi‐AuE allowed convenient analysis of trace concentrations of solely Ni(II) or of Ni(II) and Co(II) together, with cathodic stripping voltammograms characterized by well‐separated stripping peaks. The calculated limit of detection (LOD) was 40 ng L^?1 for Ni(II) alone, whereas the LOD was 98 ng L^?1 for Ni(II) and 58 ng L^?1 for Co(II), when both metal ions were measured together. The optimized method was finally applied to the analysis of certified spring water (NIST1640a) and of natural water sampled in the Lagoon of Venice. The results obtained with the Bi‐AuE were in satisfactory agreement with the certified values and with those provided by complementary techniques, i.e., ICP‐OES and ICP‐MS.     

Selective and Sensitive Determination of Uranyl Ions in Complex Matrices by Ion Imprinted Polymers‐Based Electrochemical Sensor

We report on the design of a UO₂²⁺‐selective electrode based on the use of UO₂²⁺ imprinted polymer nanoparticles (IP‐NPs), and its application for the differential pulse adsorptive cathodic stripping voltammetry determination of uranyl ions. A carbon paste electrode was modified with the IP‐NPs, and differential pulse adsorptive cathodic stripping voltammetry was applied as the detection technique after open‐circuit sorption of UO₂²⁺ ions. The modified electrode responses to UO₂²⁺ was linear in the 0.1 µg L^?1 to 10 µg L^?1 and in the 0.01 mg L^?1 to 10 mg L^?1. The method detection limit of the sensor was 0.03 µg L^?1.     

Enhanced Specificity and Sensitivity for the Determination of Nickel(II) by Square-wave Adsorptive Cathodic Stripping Voltammetry at Disposable Graphene-modified Pencil Graphite Electrodes

Chemical sensors relying on graphene-based materials have been widely used for electrochemical determination of metal ions and have demonstrated excellent signal amplification. This study reports an electrochemically reduced graphene oxide (ERGO)/mercury film (HgF) nanocomposite-modified pencil graphite electrode (PGE) prepared through successive electrochemical reduction of graphene oxide (GO) sheets and an in situ plated HgF. The ERGO-PG-HgFE, in combination with dimethylglyoxime (DMG) and square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV), was evaluated for the determination of Ni²⁺ in tap and natural river water samples. A single-step electrode pre-concentration approach was employed for the in situ Hg-film electroplating, metal-chelate complex formation, and non-electrolytic adsorption at –0.7 V. The current response due to nickel-dimethylglyoxime [Ni(II)-DMG₂] complex reduction was studied as a function of experimental paratmeters including the accumulation potential, accumulation time, rotation speed, frequency and amplitude, and carefully optimized for the determination of Ni²⁺ at low concentration levels (μg?L^?1) in pH 9.4 of 0.1 M NH₃–NH₄Cl buffer. The reduction peak currents were linear with the Ni²⁺ concentration between 2 and 16?μg?L^?1. The limits of detection and quantitation were 0.120?±?0.002?µg?L^?1 and 0.401?±?0.007?µg?L^?1 respectively, for the determination of Ni²⁺ at an accumulation time of 120?s. The ERGO-PG-HgFE further demonstrated a highly selective stripping response toward Ni²⁺ determination compared to Co²⁺. The electrode was found to be sufficiently sensitive to determine metal ions in water samples at 0.1?µg?L^?1, well below the World Health Organization standards.     

Highly Sensitive and Selective Adsorptive Stripping Voltammetric Method Employing a Lead Film Screen‐printed Electrode for Determination of Cobalt as its Nioximate Complex

A carbon screen‐printed electrode modified in‐situ with lead film (PbF‐SPCE) was applied for the adsorptive stripping voltammetric determination of Co(II) in the form of a complex with 1,2‐cyclohexanedione dioxime. Lead film was electrochemically deposited in situ on SPCE from a 0.2 M ammonia buffer solution (pH 8.7) containing 5 ? 10^?5 M Pb(NO₃)₂ and 5 ? 10^?5 M nioxime. Due to the very low LOD (0.003 µgL^?1, i.e., 0.05 nmol L^?1 Co(II); t_acc=120s), the developed procedure could be rated among the most sensitive methods employing SPEs. The Ni(II) signal was significantly lower than the Co(II) one and the separation of Ni(II) and Co(II) peaks was even better at the PbF‐SPCE than at the hanging mercury drop electrode.     

Application of the Bismuth Film Electrode for Catalytic Adsorptive Stripping Potentiometric Determination of Cobalt in Dimethylglyoxime‐Nitrite System

Abstract

The application of bismuth film electrodes to the determination of cobalt by constant current adsorptive stripping potentiometry with exploitation of a catalytic effect is presented. The addition of NaNO₂ to the solution containing ammonia buffer and dimethylglyoxime results in a 25‐fold enhancement of the adsorptive stripping potentiometric cobalt signal. Several key parameters of the potentiometric stripping mode were optimized, including the composition of the supporting electrolyte, the stripping current, the accumulation potential, and the accumulation time. The optimized procedure yields favorable and highly stable stripping responses with good precision (RSD=1.4% for a Co concentration of 2 µg L^?1), low detection limit (0.07 µg L^?1), and good linearity (up to 10 µg L^?1, R²=0.998) with a deposition time of 60 s and a stripping current of 10 µA. The method enables the determination of Co in the presence of high excesses of Ni or Zn.     

Determination of Trace Lead and Cadmium in Water Samples by Anodic Stripping Voltammetry with a Nafion‐Ionic Liquid‐Coated Bismuth Film Electrode

A new chemically modified bismuth film electrode coated with an ionic liquid [(1‐ethyl‐3‐methylimidazolium tetracyanoborate (EMIM TCB)] and Nafion was developed for the simultaneous determination Pb²⁺ and Cd²⁺ by anodic stripping voltammetry. Compared with conventional bismuth film electrodes, this electrode exhibited greatly improved electrochemical activity for Pb²⁺ and Cd²⁺ detection due to the unique properties of Nafion polymer and ionic liquid. The key experimental parameters related to the fabrication of the electrode and the voltammetric measurements were optimized on the basis of the stripping signals, where the peak currents increased linearly with the metal concentrations in a range of 10–120 µg L^?1 with a detect limit of 0.2 µg L^?1 for Pb²⁺, and 0.5 µg L^?1 for Cd²⁺ for 120s deposition. High reproducibility was indicated from the relative standard deviations (1.9 and 2.5 %) for nine repetitive measurements of 20 µg L^?1 Pb²⁺ and Cd²⁺, respectively. In addition, the surface characteristics of the modified BiFE were investigated by scanning electron microscopy (SEM), and results showed that fibril‐like bismuth nanostructures were formed on the porous Nafion polymer matrix. Finally, the developed electrode was applied to determine Pb²⁺ and Cd²⁺ in water samples, indicating that this electrode was sensitive, reliable and effective for the simultaneous determination of Pb²⁺ and Cd²⁺.     

The new Micro‐set for Adsorptive Stripping Voltammetric Simultaneous Determination of Nickel and Cobalt Traces in Aqueous Media

This article the first reports on a fabrication and application of an electrochemical three electrode micro‐set containing: in situ plated lead film on carbon fiber working microelectrode, Ag/AgCl reference electrode and a platinum wire counter electrode placed in one casing for simultaneous Ni(II) and Co(II) traces determination by square wave adsorptive stripping voltammetry (SW AdSV). Ni(II) and Co(II) in forms of their complexes with nioxime were accumulated on the lead film plated on a carbon fibers microelectrode during standard procedure of measurement. Thanks to the fact that measurements were performed in micro‐vessel of a volume of 200 μl small amounts of reagents were used to prepare samples for measurements. In addition, because of the use of microelectrode, sample solutions were not mixed during accumulation step of measurements. This fact creates the possibility of conducting fields analysis. The experimental parameters (composition of the supporting electrolyte, potential and time of accumulation) and possible interference effects were investigated. The linear calibration graphs for Ni(II) and Co(II) were in the range from 2×10^?9 to 1×10^?7 mol L^?1 and from 2×10^?10 to 1×10^?8 mol L^?1 for Ni(II) and Co(II), respectively. The correctness of the proposed method was checked by determining Ni(II) and Co(II) in the certified reference material (SPS‐SW1) with satisfactory results.     

An adsorptive stripping voltammetry of nickel and cobalt at a solid lead electrode

For the first time, a solid lead electrode (PbE) was exploited for adsorptive stripping voltammetric determination of Ni(II) and Co(II) in the presence of nioxime as a complexing agent. The calibration graphs for Ni(II) and Co(II) were linear from 0.059 to 0.59 µg L^?1 and from 0.029 to 0.29 µg L^?1 (accumulation time 120 s), respectively. The analytical parameters such as the detection limit and separation of analytical signals obtained at the solid lead electrode were comparable with those obtained using a lead film electrode while better in comparison to those reported before for the bismuth film or solid bismuth electrodes. Co(II) could be determined in the presence of a large excess of Ni(II) and Zn(II). The proposed electrode was applied to determine Co(II) and Ni(II) traces in certified reference material and a natural water sample with satisfactory results.     

Fast Simultaneous Adsorptive Stripping Voltammetric Determination of Ni(II) and Co(II) at Lead Film Electrode Plated on Gold Substrate

A fast adsorptive stripping voltammetric procedure for simultaneous determination of Ni(II) and Co(II) in the presence of nioxime as a complexing agent at an in situ plated lead film electrode was described. The time of determination of these ions was shortened due to the application of gold as a substrate for lead film. At gold substrate lead film formation and accumulation of Ni(II) and Co(II) complexes with nioxime proceeds simultaneously. To obtain a stable signals for both ions a simple procedure of activation of the electrode was proposed. Calibration graphs for an accumulation time of 20 s were linear from 5×10^?9 to 1×10^?7 mol L^?1 and from 5×10^?10 to 1×10^?8 mol L^?1 for Ni(II) and Co(II), respectively. The procedure with the application of a lead film electrode on a gold substrate was validated in the course of Ni(II) and Co(II) determination in certified reference materials.     

A Combination Bismuth Bulk Electrode and Its Use in Adsorptive Constant‐Current Stripping Chronopotentiometry for Iron Using Solochrome Violet RS

A new combination bismuth bulk electrode allowing potentiostatic control to be maintained in a suspended sample drop is described. The electrode was tested by adsorptive constant‐current stripping chronopotentiometry for iron(III) using Solochrome Violet RS. Optimum conditions were similar to those established with mercury‐based electrodes. With an electropolishing scheme, a reproducibility better than 2 % (n=54) was attainable. The limit of detection was 0.6 µg L^?1 in deoxygenated samples. A partial least squares calibration gave a result of 972±78 µg L^?1 (95 %, n=5) for a 1000±5 µg L^?1 iron reference solution.     

Facile and Simultaneous Stripping Determination of Zinc,Cadmium and Lead on Disposable Multiwalled Carbon Nanotubes Modified Screen‐Printed Electrode

Screen‐printed electrodes (SPEs) are cheap and disposable. But their application for heavy metal detection is limited due to the low sensitivity and poor selectivity. Here we report the ultrasensitive and simultaneous determination of Zn²⁺, Cd²⁺ and Pb²⁺ on a multiwalled carbon nanotubes and Nafion composite modified SPE with in situ plated bismuth film (MWCNTs/NA/Bi/SPE). The linear curves range from 0.5–100 µg L^?1 for Zn²⁺ and 0.5–80 µg L^?1 for Cd²⁺. Uniquely, the linear curve for Pb²⁺ ranges from 0.05–100 µg L^?1 with a detection limit of 0.01 µg L^?1. The practical application was verified in real samples with satisfactory results.     

Carbon Paste Electrode Plated with Lead Film. Voltammetric Characteristics and Application in Adsorptive Stripping Voltammetry

A lead film plated in situ at a carbon paste support was tested as a novel, potential electrode for adsorptive stripping voltammetric determination of cobalt traces in an ammonia buffer solution. To show the practical applicability of the new electrode, a catalytic adsorptive Co system in a supporting electrolyte containing 0.1 M ammonia buffer, 5×10^?4 M nioxime and 0.25 M nitrite was selected and investigated as a model solution. Pb and Co ions were simultaneously accumulated in situ on the electrode surface: Pb ions electrochemically at ?1.3 V) and then at ?0.75 V, at which potential the Co(II)‐nioximate complex was also pre‐concentrated via adsorption. Instrumental parameters, such as the time of nucleation and formation of Pb film deposits, the time of accumulation of the Co‐nioxime complex at the PbF/CPE, and the procedures of electrode regeneration, were optimized to obtain good reproducibility and sensitivity of the Co response. The optimized procedure yields favorable and highly stable stripping responses with good precision (RSD=3% for a 5×10^?8 M Co) and good linearity (up to 5×10^?7 M, coefficient of determination, R=0.996). The detection limit was 4×10^?10 M Co (0.023 μg L^?1) for an accumulation time of 120 s. The method enables the determination of Co in the presence of high excesses of Ni or Zn. The voltammetric data were correlated with the structural characterization by scanning electron microscopy (SEM) and X‐ray fluorescence spectroscopy (XRF).     

Ligandless-ultrasound-assisted emulsification microextraction followed by inductively coupled plasma-optical emission spectrometry for simultaneous determination of heavy metals in water samples

In this study, a simple and efficient method of ligandless-ultrasound-assisted emulsification microextraction (LL-USAEME) followed by inductively coupled plasma-optical emission spectrometry (ICP-OES) has been developed for simultaneous extraction, preconcentration and determination of manganese, cadmium, cobalt and nickel in water samples. In the proposed approach, tetrachloroethylene was selected as extraction solvent. The effect of important experimental factors such as volume of extraction solvent, pH, sonication time, salt concentration, and temperature was investigated by using a fractional factorial design (2^5?1) to identify important factors and their interactions. In the next step, a Box-Behnken design (BBD) was applied for optimisation of significant factors. The obtained optimal conditions were: 30?µL for extraction solvent, 12 for pH, 5?min for sonication time, and 5% w/v for salt concentration. The limits of detections (LODs) for Cd(II), Co(II), Mn(II) and Ni(II) were 0.20, 0.13, 0.21 and 0.28?µg?L^?1, respectively. Relative standard deviations (RSD, C?=?200.0?µg?L^?1, n?=?9) were between 3.4–7.5% and the calibration graphs were linear in the range of 0.25 to 1000.0?µg?L^?1 for Mn, 0.5–1000.0?µg?L^?1 for Co and Ni and 1.0–250.0?µg?L^?1 for Cd. The determination coefficients (R ²) of the calibration curves for the analytes were in the range of 0.993 to 0.999. The proposed method was validated by using two certified reference materials, and also the method was applied successfully for the determination of heavy metals in different real water samples.     

Sequential Voltammetric Determination of Uranium,Cadmium and Lead by Using the ex situ Bismuth Film Electrode: Application to Phosphate Fertilizers

A sequential voltammetric procedure for the determination of uranium, cadmium and lead was investigated at an ex situ bismuth film electrode (BiFE). First, the adsorptive stripping voltammetry was applied to assay the U(VI)‐cupferron complex in the differential pulse mode (detection limit of 1.0 µg L^?1, 200 s accumulation time). Through the manipulation of the same aliquot of the sample, efforts were made to quantify cadmium and lead by square wave anodic stripping voltammetry. Detection limits of 2.03 µg L^?1 for Cd (II) and 2.43 µg L^?1 for Pb (II) were calculated (100 s accumulation time). The methodology was successfully applied to phosphate fertilizer samples after open vessel wet decomposition (HNO₃/H₂O₂). The following value ranges were evaluated: U (VI) 37.2–150 mg kg^?1, Pb (II) 78.3–204 mg kg^?1 and Cd (II) 44.1–71.6 mg kg^?1. Validation was performed by using the standard reference materials SRM‐695 – phosphate fertilizer – and SRM‐1643e – water.     

Catalytic Adsorptive Stripping Voltammetric Determination of Cobalt and Nickel as Their α‐Furil Dioxime Complexes

The exploitation of the catalytic‐adsorptive effect in the Co(II)‐dioxime‐nitrite systems provides a significant increase of the Co adsorptive stripping voltammetric response and subsequently the influence of the interfering elements such as Ni and Zn is strongly diminished. The purpose of the present paper was to study voltammetric properties of Co and Ni in a supporting electrolyte containing ammonia buffer, α‐furil dioxime in the absence and in the presence of nitrite, by differential pulse polarography and adsorptive stripping voltammetry. Results of detailed studies aimed at optimizing the analytical parameters for simultaneous catalytic adsorptive stripping voltammetric determination of Co and Ni in the form of complexes with α‐furil dioxime in the presence of Zn matrix are presented. In the supporting electrolyte of composition 0.1 M NH₄Cl, 0.5 M NH₃, 4×10^?5 M αFD, 0.5 M NaNO₂ the linearity range amounts from 0.03 to 2.4 μg/L for Co and from 0.3 to 9 μg/L for Ni for 20 s of accumulation. The method enables the determination of Co and Ni in the presence of a great excess of Zn with the detection limit equal to 0.02 μg/L Co and 0.2 μg/L Ni obtained for a 20 s accumulation time.     

Simultaneous preconcentration and determination of nickel and cobalt using functionalised mesoporous silica spheres by ICP-OES

In this work functionalised mesoporous silica spheres have been utilised for the simultaneous preconcentration of nickel and cobalt. The silica spheres (SiSPs) prepared by the sol-gel method were functionalised with sodium diethyldithiocarbamate (DDTC-SiSPs). They were characterised by SEM, TEM, XRD, FTIR, CHN and nitrogen adsorption. The adsorption efficiency of DDTC-SiSPs was examined by batch equilibrium technique. The DDTC-SiSPs showed 100% adsorption for Ni (II) and Co (II). The effect of changing variables such as pH, shaking time, sample volume, preconcentration factor, eluent type and volume were investigated so as to obtain maximum recovery with high selectivity over interfering ions. The maximum adsorption capacity was found to be 15.15 mg g^?1 and 11.80 mg g^?1 for Ni (II) and Co (II) respectively using DDTC-SiSPs. 100% recovery was achieved with 5 mL of 2 M HNO₃. The maximum preconcentration factor was 400 and the 3σ limits of detection were 0.201 µg L^?1 and 0.198 µg L^?1 for Ni (II) and Co (II) respectively. Thermodynamic studies showed that adsorption of Ni (II) and Co (II) on DDTC-SiSPs is exothermic with enthalpy changes of –0.514 KJ mol^?1 and –0.854 KJ mol^?1 for Ni (II) and Co (II) respectively. The method was applied to the preconcentration and determination of Ni (II) and Co (II) from tap, river and sea water.     

ABTS‐Multiwalled Carbon Nanotubes Nanocomposite/Bi Film Electrode for Sensitive Determination of Cd and Pb by Differential Pulse Stripping Voltammetry

A 2,2′‐azinobis (3‐ethylbenzothiazoline‐6‐sulfonate) diammonium salt (ABTS)‐multiwalled carbon nanotubes (MWCNTs) nanocomposite/Bi film modified glassy carbon (GC) electrode was constructed for the differential pulse stripping voltammetric determination of trace Pb²⁺ and Cd²⁺. This electrode was more sensitive than ABTS‐free Bi/GC and Bi/MWCNTs/GC electrodes. Linear responses were obtained in the range from 0.5 to 35 μg L^?1 for Cd²⁺ and 0.2 to 50 μg L^?1 Pb(II), with detection limits of 0.2 μg L^?1 for Cd²⁺ and 0.1 μg L^?1 for Pb²⁺, respectively. This sensor was applied to the simultaneous detection of Cd²⁺ and Pb²⁺ in water samples with satisfactory recovery.     

Simultaneous Electrochemical Determination of Hydroquinone and Catechol at MWNTs and Cobalt(II) Tetrakisphenylporphyrin Modified Electrode

A multi-wall carbon nanotubes (MWNTs) and cobalt(II) tetrakisphenylporphyrin (Co(II)TPP) modified glassy carbon electrode (MWNTs/Co(II)TPP/GCE) has been prepared. It can be used for individual or simultaneous determination of hydroquinone (HQ) and catechol (CC). The anodic peaks of HQ and CC can be separated well. Owing to the unique properties of MWNTs and special synergistic effect of MWNTs and Co(II)TPP, the modified electrode exhibited a remarkable and stable current response for CC and HQ. The linear ranges for CC and HQ were 1.0–450.0 µmol L^?1 and 0.8–400.0 µmol L^?1 with detection limits of 0.8 µmol L^?1 and 0.5 µmol L^?1, respectively. Furthermore, Co(II)TPP, MWNTs, and Co(II)TPP/MWNTs composite were also used to construct modified electrodes and the electrochemical performances were studied.     

Sensitive Stripping Determination of Cadmium(II) and Lead(II) on Disposable Graphene Modified Screen‐Printed Electrode

In the present work, a sensitive, facile and disposable sensing platform for trace analysis of heavy metal ions was developed at the Bi modified graphene‐poly(sodium 4‐styrenesulfonate) composite film screen printed electrode (GR/PSS/Bi/SPE). The GR/PSS/Bi/SPE improved sensitivity and linearity due to the functionalization of graphene with negatively charged PSS providing more absorbing sites. The detection limit of the GR/PSS/Bi/SPE is found to be 0.042 µg L^?1 for Cd²⁺ and 0.089 µg L^?1 for Pb²⁺ with linear responses of Cd²⁺ and Pb²⁺ in the range of 0.5–120 µg L^?1. Finally, the practical application was confirmed in real water with satisfactory results.