Bismuth film electrode for simultaneous adsorptive stripping analysis of trace cobalt and nickel using constant current chronopotentiometric and voltammetric protocol

Electrochemical sensing platform based on Zeolite/Graphite/Dimethylglyoxime nanocomposite for highly selective and ultrasensitive determination of nickel

In this work, the fabrication and analytical application of a novel, unique, mercury-free, and user-friendly voltammetric sensor of Ni(II) based on glassy carbon electrode (GCE) modified with zeolite(MOR)/graphite(G)/dimethylglyoxime(DMG) composite (MOR/G/DMG-GCE) and the voltammetric procedure for highly selective, ultra-trace determination of nickel ions were reported for the first time. Deposition of a thin layer of the chemically active MOR/G/DMG nanocomposite enables the selective and effective accumulation of Ni(II) ions in the form of the DMG-Ni(II) complex. In 0.1 mol L^-1 ammonia buffer (pH 9.0), the MOR/G/DMG-GCE exhibited linear response in the Ni(II) ions concentration range of 0.86 - 19.61 µg L^-1 and 0.57 - 15.75 µg L^-1, for the accumulation time of 30 s and 60 s, respectively. For 60 s of accumulation time, the limit of detection (S/N = 3) was 0.18 µg L^-1 (3.04 nM), and sensitivity of 0.202 µA L µg^-1 was achieved. The developed protocol was validated by the analysis of wastewater certified reference materials. Its practical usefulness was confirmed by the determination of nickel released from metallic jewelry submerged in artificial sweat and stainless steel pot during water boiling. The obtained results were verified by electrothermal atomic absorption spectroscopy as a reference method.

Validation of Voltammetric Methods for Online Analysis of Platinum Dissolution in a Hydrogen PEM Fuel Cell Stack

Platinum dissolution in PEM fuel cells is an increasingly important indicator for the state-of-health and lifetime prediction of fuel cells in real applications. For this reason, portable online analysis tools are needed that can detect and quantify platinum with high sensitivity, selectivity, and accuracy in the product water of fuel cells. We validated the hanging mercury drop electrode (HMDE) and non-toxic bismuth film electrodes for the voltammetric determination of platinum for this purpose. Bismuth films were prepared by reductive deposition on both a glassy carbon solid state electrode and on a screen-printed electrode (film on-chip electrode). Both bismuth film electrodes could be successfully validated for the determination of platinum by adsorptive stripping voltammetry. An LOD of 7.9 μg/L and an LOQ of 29.1 μg/L were determined for the bismuth film solid state electrode, values of 22.5 μg/L for the LOD and of 79.0 μg/L for the LOQ were obtained for the bismuth film on-chip electrode. These numbers are still much higher than the results measured with the HMDE (LOD: 0.76 ng/L; LOQ: 2.8 ng/L) and are not sufficient to detect platinum in the product water of a fuel cell run in different load tests. The amount of dissolved platinum produced by a 100 W fuel cell stack upon dynamic and continuous high load cycling, respectively, was in the range of 2.9–4.1 ng/L, which could only be detected by the HMDE.

Bismuth-coated screen-printed electrodes for the simple voltammetric determination of formaldehyde

For the first time, bismuth modified electrodes have been used for the voltammetric detection of formaldehyde (FM). The well-known method of forming formaldehyde hydrazone (FAH) in the presence of hydrazine sulphate was used to convert the hydrated form of FM into its electrochemically active derivative. Various experimental conditions for differential pulse voltammetry were studied to achieve the best analytical performance. The FAH reduction current (FM response) reaches its maximum value at a pH of a phosphate buffer solution of 5.2 ± 0.1 in the presence of 0.09-0.12 M hydrazine sulfate on a bismuth film preliminarily precipitated for 8-12 min from acidic Bi(III) acetate solutions at an electrolysis potential of -1.0 V on the surface of a screen-printed carbon electrode (SPCE). A dendritic-like film structure was created on the SPCE surface. Under the optimized conditions a linear calibration curve over the range of 0.01-5 mg L^-1 (0.33-167 μM) FM was achieved, with a detection limit of 0.002 mg L^-1 (0.06 μM). The determination of FM in waste water, melt water from snow within the city industrial zone, and a widely used pharmaceutical preparation "Endofalk®" with good results revealed the potential applicability of a bismuth modified SPCE (BiSPCE) for trace analysis.

In situ detection of heavy metal ions in sewage with screen-printed electrode-based portable electrochemical sensors

The rapid development of industrial technologies continuously increases the heavy metal pollution of water resources. Recently, portable electrochemical analysis-based devices for detecting heavy metal ions have attracted much attention due to their excellent performance and low fabrication costs. However, it has proven difficult to accommodate complex testing needs in a cost-effective manner. To address these limitations, we propose a new system for the in situ detection of heavy metals in wastewater using an organic light-emitting diode-based panel to display data in real time and Bluetooth to transmit data to a smartphone for rapid analysis. The fabricated device integrates an in situ signal analysis circuit, a Bluetooth chip, a photocured 3D-printed shell, and an electrode sleeve interface. In addition, a fully screen-printed functional electrode plate containing chitosan/PANi-Bi nanoparticle@graphene oxide multi-walled carbon nanotubes is utilized for the rapid detection of heavy metal ions. This device can perform wireless data transmission and analysis and in situ signal acquisition and processing. The sensor exhibits a high sensitivity (Hg²⁺: 88.34 μA ppm^-1 cm^-2; Cu²⁺: 0.956 μA ppm^-1 cm^-2), low limit of detection (Hg²⁺: 10 ppb, Cu²⁺: 0.998 ppm) and high selectivity during the detection of copper and mercury ions in tap water under non-laboratory conditions, and the results of real-time tests reveal that parameters measured in the field and laboratory environments are identical. Hence, this small, portable, electrochemical sensor with a screen-printed electrode can be effectively used for the real-time detection of copper and mercury ions in complex water environments.

Determination of Trace Levels of Nickel(II) by Adsorptive Stripping Voltammetry Using a Disposable and Low-Cost Carbon Screen-Printed Electrode

A commercial and disposable screen-printed carbon electrode (SPCE) has been proposed for a fast, simple and low-cost determination of Ni(II) at very low concentration levels by differential pulse adsorptive stripping voltammetry (DPAdSV) in the presence of dimethylglyoxime (DMG) as complexing agent. In contrast with previously proposed methods, the Ni(II)-DMG complex adsorbs directly on the screen-printed carbon surface, with no need of mercury, bismuth or antimony coatings. Well-defined stripping peaks and a linear dependence of the peak area on the concentration of Ni(II) was achieved in the range from 1.7 to 150 µg L−1, with a limit of detection of 0.5 µg L−1 using a deposition time of 120 s. An excellent reproducibility and repeatability with 0.3% (n = 3) and 1.5% (n = 15) relative standard deviation, respectively, were obtained. In addition, the suitability of the SPCE as sensing unit has been successfully assessed in a wastewater certificated reference material with remarkable trueness and very good reproducibility.

Complexation-Based Detection of Nickel(II) at a Graphene-Chelate Probe in the Presence of Cobalt and Zinc by Adsorptive Stripping Voltammetry

The adsorptive stripping voltammetric detection of nickel and cobalt in water samples at metal film electrodes has been extensively studied. In this work, a novel, environmentally friendly, metal-free electrochemical probe was constructed for the ultra-trace determination of Ni2+ in water samples by Adsorptive Cathodic Stripping Voltammetry (AdCSV). The electrochemical platform is based on the adsorptive accumulation of Ni2+ ions directly onto a glassy carbon electrode (GCE) modified with dimethylglyoxime (DMG) as chelating agent and a Nafion-graphene (NGr) nanocomposite to enhance electrode sensitivity. The nafion-graphene dimethylglyoxime modified glassy carbon electrode (NGr-DMG-GCE) shows superior detection capabilities as a result of the improved surface-area-to-volume ratio and enhanced electron transfer kinetics following the incorporation of single layer graphene, while limiting the toxic effects of the sensor by removal of the more common mercury, bismuth and lead films. Furthermore, for the first time the NGr-DMG-GCE, in the presence of common interfering metal ions of Co2+ and Zn2+ demonstrates good selectivity and preferential binding towards the detection of Ni2+ in water samples. Structural and morphological characterisation of the synthesised single layer graphene sheets was conducted by Raman spectrometry, HRTEM and HRSEM analysis. The instrumental parameters associated with the electrochemical response, including accumulation potential and accumulation time were investigated and optimised in addition to the influence of DMG and graphene concentrations. The NGr-DMG-GCE demonstrated well resolved, reproducible peaks, with RSD (%) below 5% and a detection limit of 1.5 µg L-1 for Ni2+ reduction at an accumulation time of 120 s., the prepared electrochemical sensor exhibited good detection and quantitation towards Ni2+ detection in tap water samples, well below 0.1 mg L-1 set by the WHO and EPA standards. This comparable to the South African drinking water guidelines of 0.15 mg L-1.

Direct Quantification of Cd2+ in the Presence of Cu2+ by a Combination of Anodic Stripping Voltammetry Using a Bi-Film-Modified Glassy Carbon Electrode and an Artificial Neural Network

Abstract: In this study, a novel method based on a Bi/glassy carbon electrode (Bi/GCE) for quantitatively and directly detecting Cd²⁺ in the presence of Cu²⁺ without further electrode modifications by combining square-wave anodic stripping voltammetry (SWASV) and a back-propagation artificial neural network (BP-ANN) has been proposed. The influence of the Cu²⁺ concentration on the stripping response to Cd²⁺ was studied. In addition, the effect of the ferrocyanide concentration on the SWASV detection of Cd²⁺ in the presence of Cu²⁺ was investigated. A BP-ANN with two inputs and one output was used to establish the nonlinear relationship between the concentration of Cd²⁺ and the stripping peak currents of Cu²⁺ and Cd²⁺. The factors affecting the SWASV detection of Cd²⁺ and the key parameters of the BP-ANN were optimized. Moreover, the direct calibration model (i.e., adding 0.1 mM ferrocyanide before detection), the BP-ANN model and other prediction models were compared to verify the prediction performance of these models in terms of their mean absolute errors (MAEs), root mean square errors (RMSEs) and correlation coefficients. The BP-ANN model exhibited higher prediction accuracy than the direct calibration model and the other prediction models. Finally, the proposed method was used to detect Cd²⁺ in soil samples with satisfactory results.

Optimization of Stripping Voltammetric Sensor by a Back Propagation Artificial Neural Network for the Accurate Determination of Pb(II) in the Presence of Cd(II)

An easy, but effective, method has been proposed to detect and quantify the Pb(II) in the presence of Cd(II) based on a Bi/glassy carbon electrode (Bi/GCE) with the combination of a back propagation artificial neural network (BP-ANN) and square wave anodic stripping voltammetry (SWASV) without further electrode modification. The effects of Cd(II) in different concentrations on stripping responses of Pb(II) was studied. The results indicate that the presence of Cd(II) will reduce the prediction precision of a direct calibration model. Therefore, a two-input and one-output BP-ANN was built for the optimization of a stripping voltammetric sensor, which considering the combined effects of Cd(II) and Pb(II) on the SWASV detection of Pb(II) and establishing the nonlinear relationship between the stripping peak currents of Pb(II) and Cd(II) and the concentration of Pb(II). The key parameters of the BP-ANN and the factors affecting the SWASV detection of Pb(II) were optimized. The prediction performance of direct calibration model and BP-ANN model were tested with regard to the mean absolute error (MAE), root mean square error (RMSE), average relative error (ARE), and correlation coefficient. The results proved that the BP-ANN model exhibited higher prediction accuracy than the direct calibration model. Finally, a real samples analysis was performed to determine trace Pb(II) in some soil specimens with satisfactory results.

Metallic modified (bismuth, antimony, tin and combinations thereof) film carbon electrodes

In this paper in situ bismuth, antimony, tin modified electrodes and combinations thereof are explored towards the model target analytes cadmium(II) and lead(II), chosen since they are the most widely studied, to explore the role of the underlying electrode substrate with respect to boron-doped diamond, glassy carbon, and screen-printed graphite electrodes. It is found that differing electrochemical responses are observed, dependent upon the underlying electrode substrate. The electrochemical response using the available range of metallic modifications is only ever observed when the underlying electrode substrate exhibits relatively slow electron transfer properties; in the case of fast electron transfer properties, no significant advantages are evident. Furthermore these bismuth modified systems which commonly employ a pH 4 acetate buffer, reported to ensure the bismuth(III) stability upon the electrode surface can create create a problem when sensing at low concentrations of heavy metals due to its high background current. It is demonstrated that a simple change of pH can allow the detection of the target analytes (cadmium(II) and lead(II)) at levels below that set by the World Health Organisation (WHO) using bare graphite screen-printed electrodes.

Validation of bismuth film electrode for determination of cobalt and cadmium in soil extracts using ICP-MS

A study is presented on the use of the bismuth film electrode (BiFE) operated in the anodic stripping and the cathodic adsorptive stripping voltammetry (ASV, CAdSV) modes, for the determination of two trace heavy metals (Cd and Co, respectively), in soil extract samples. Two types of BiFE were examined in this study: the in situ prepared BiFE, which was employed in ASV determination of Cd, and the ex situ prepared BiFE, which was used in CAdSV of Co with dimethylglyoxime (DMG) as complexing agent. A series of unpretreated soil extracts with varying Cd and Co concentrations were analyzed, and the results obtained compared to those determined using inductively coupled plasma-mass spectrometry (ICP-MS). The results revealed the suitability of stripping analysis at the BiFE for determination of mugl(-1) levels of heavy metals in soil extracts. The promising results obtained here, coupled with the non-toxic nature of bismuth (in comparison to commonly used mercury electrodes employed in stripping analysis), offer great promise in centralized and decentralized analysis of trace heavy metals in complex environmental matrices.

Stripping voltammetric determination of palladium, platinum and rhodium in freshwater and sediment samples from South African water resources

Stripping voltammetry as technique has proved to be very useful in the analysis of heavy and other metal ions due to its excellent detection limits and its sensitivity in the presence of different metal species or interfering ions. Recent assessments of aquatic samples have shown increased levels of platinum group metals (PGMs) in aquatic ecosystems, caused by automobile exhaust emissions and mining activities. The development of an analytical sensor for the detection and characterisation of PGMs were investigated, since there is an ongoing need to find new sensing materials with suitable recognition elements that can respond selectively and reversibly to specific metal ions in environmental samples. The work reported shows the successful application of another mercury-free sensor electrode for the determination of platinum group metals in environmental samples. The work reported in this study entails the use of a glassy carbon electrode modified with a bismuth film for the determination of platinum (Pt(2+)), palladium (Pd(2+)) or rhodium (Rh(2+)) by means of adsorptive cathodic stripping voltammetry. Optimised experimental conditions included composition of the supporting electrolyte, complexing agent concentration, deposition potential, deposition time and instrumental voltammetry parameters for Pt(2+), Pd(2+) and Rh(2+) determination. Adsorptive differential pulse stripping voltammetric measurements for PGMs were performed in the presence of dimethylglyoxime (DMG) as complexing agent. The glassy carbon bismuth film electrode (GC/BiFE) employed in this study exhibit good and reproducible sensor characteristics. Application of GC/BiFE sensor exhibited well-defined peaks and highly linear behaviour for the stripping analysis of the PGMs in the concentration range between 0 and 3.5 μg/L. The detection limit of Pd, Pt and Rh was found to be 0.12 μg/L, 0.04 μg/L and 0.23 μg/L, respectively for the deposition times of 90 s (Pd) and 150 s (for both Pt and Rh). Good reproducibility was also observed and the practical applicability of the sensor was demonstrated with the analysis of environmental water and sediment samples.