On-site determination of Pb2+ and Cd2+ in seawater by double stripping voltammetry with bismuth-modified working electrodes

Cheap and sensitive polymer/bismuth film modified electrode for simultaneous determination of Pb(II) and Cd(II) ions

Different aminonaphetalenesulphonic acid derivatives like 5-aminonaphthalene-1-sulphonic acid (5AN1SA), 2-aminonaphthalene-1-sulphonic acid (2AN1SA), 8-aminonaphthalene-2-sulphonic acid (8AN2SA) and 4-amino-3-hydroxynaphthalene-1-sulphonic acid (4A3HN1SA) were used to construct polymer/bismuth film modified electrode for simultaneous determination of Pb(II) and Cd(II) ions with the aim of developing a cheaper and sensitive electrode that could possibly replace Nafion. Among the different modified electrodes, poly (8AN2SA)/bismuth film modified electrodes showed the highest electrochemical response for both ions. These electrochemical results were also supported by density functional theory (DFT) calculations. Based on these experimental and theoretical results, poly (8AN2SA)/bismuth film glassy carbon modified electrode was further investigated to develop a simple and sensitive electrochemical method for the simultaneous determination of Pb(II) and Cd(II) ions. After optimizing the different experimental parameters, the proposed method gave a linear range of 1-40 μg/L with the detection limit of 0.38 and 0.08 μg/L for the simultaneous determination of Pb(II) and Cd(II) ions, respectively.

Strategies for Surface Modification with Ag-Shaped Nanoparticles: Electrocatalytic Enhancement of Screen-Printed Electrodes for the Detection of Heavy Metals

Screen-printed carbon nanofiber electrodes (SPCNFEs) represent an alternative with great acceptance due to their results, as well as their low impact on the environment. In order to improve their performance, in the present work they were modified with silver nanoparticles (Ag-NPs) and electrochemically characterized by using anodic stripping voltammetry. From the Ag-NP synthesis, silver seeds (Ag-NS) and silver nanoprisms (Ag-NPr) were obtained. The Ag-NP formation was confirmed by micrographs, where Ag-NPs with diameters of 12.20 ± 0.04 nm for Ag-NS and 20.40 ± 0.09 nm for Ag-NPr were observed. The electrodes were modified by using three different deposition methods—drop-casting, spin-coating, and in situ approaches—that offer different nanoparticle distribution and electrode modification times. It was observed that the last methodology showed a low amount of Ag-NS deposited on the electrode surface and deep alteration of this surface. Those facts suggest that the in situ synthesis methodology was not appropriate for the determination of heavy metals, and it was discarded. The incorporation of the nanoparticles by spin-coating and drop-casting strategies showed different spatial distribution on the electrode surface, as proved by scanning electron microscopy. The electrodes modified by these strategies were evaluated for the cadmium(II) and lead(II) detection using differential pulse anodic stripping voltammetry, obtaining detection limit values of 2.1 and 2.8 µg·L⁻¹, respectively. The overall results showed that the incorporation route does not directly change the electrocatalytic effect of the nanoparticles, but the shape of these nanoparticles (spherical for seeds and triangular for prisms) has preferential electrocatalytic enhancement over Cd(II) or Pb(II).

A rapid on-site analysis method for the simultaneous extraction and determination of Pb2+ and Cd2+ in cereals

In order to achieve rapid on-site screening and solve the problem of rapid pretreatment for the determination of lead (Pb²⁺) and cadmium (Cd²⁺) in cereals by a portable electrochemical analyzer with disposable screen-printed electrodes (SPEs), a new reliable and simple extraction method for Pb²⁺ and Cd²⁺ in cereals was developed. The Pb²⁺ and Cd²⁺ in cereals were purified by a mixed solution of 1 mol L⁻¹ potassium iodide (KI)/5% vitamin C (VC)/ethyl acetate after being extracted by 10% HNO₃, which transfers the Pb²⁺ and Cd²⁺ into ethyl acetate after a reaction with KI–VC. Then, the Pb²⁺ and Cd²⁺ were eluted from ethyl acetate with 5% HNO₃ and were determined by an electrochemical analyzer with screen printed electrodes. Under the optimized conditions, the matrix calibration curves of Pb²⁺ and Cd²⁺ in rice and wheat showed good linear relationships with R² > 0.996. The method shows a detection limit (LOD) for Cd²⁺ in rice and wheat of 6.7 μg kg⁻¹ and 11.5 μg kg⁻¹, and the corresponding values for Pb²⁺ were 34.9 and 31.1 μg kg⁻¹, respectively. The relative standard deviation (RSD) was less than 8.7% for Cd²⁺ and Pb²⁺. In addition, the recoveries of the tested reference materials using this method were between 80% and 120%. From sample pretreatment to testing results, the whole process took no more than 25 min, and the operation was simple for operators, green to the environment, cheap in terms of instruments, and above all suitable for on-site detection. The results implied that this portable electrochemical method with new pretreatment may be a good choice for screening Pb²⁺ and Cd²⁺ in cereal samples on-site.

To achieve rapid on-site screening rapid pretreatment for the determination of Pb²⁺ and Cd²⁺ in cereals by a portable electrochemical analyzer with disposable screen-printed electrodes, a new reliable and simple extraction method for Pb²⁺ and Cd²⁺ was developed.

Inexpensive Bismuth-Film Electrode Supported on Pencil-Lead Graphite for Determination of Pb(II) and Cd(II) Ions by Anodic Stripping Voltammetry

The present work reports the development and application of bismuth-film electrode (BiFE), obtained by in situ method on the pencil-lead graphite surface, for simultaneous Cd(II) and Pb(II) determination at trace levels, as alternative to replace the mercury-film electrodes. Experimental factors, deposition time (t_d), deposition potential (E_d), and Bi(III) concentration (C_Bi), were investigated by applying a 2³ factorial design using 0.10 mol/L acetate buffer solution (pH 4.5) as supporting electrolyte. The analysis conditions of the differential pulse technique were t_d = 250 s, E_d = -1.40 V, and C_Bi = 250 mg L⁻¹. The validation of the method employing BiFE was accomplished by determination of merit figures. The detection limits were of 11.0 μg L⁻¹ for Cd(II) and 11.5 μg L⁻¹ for Pb(II), confirming that proposed method is attractive and suitable for heavy metals determination. Additionally, the BiFE developed was successfully applied for the Cd(II) and Pb(II) determination in wastewater sample of battery industry.

Screen-Printed Electrode Modified by Bismuth /Fe₃O₄ Nanoparticle/Ionic Liquid Composite Using Internal Standard Normalization for Accurate Determination of Cd(II) in Soil

The quality and safety of agricultural products are threatened by heavy metal ions in soil, which can be absorbed by the crops, and then accumulated in the human body through the food chain. In this paper, we report a low-cost and easy-to-use screen-printed electrode (SPE) for cadmium ion (Cd(II)) detection based on differential pulse voltammetry (DPV), which decorated with ionic liquid (IL), magnetite nanoparticle (Fe₃O₄), and deposited a bismuth film (Bi). The characteristics of Bi/Fe₃O₄/ILSPE were investigated using scanning electron microscopy, cyclic voltammetry, impedance spectroscopy, and linear sweep voltammetry. We found that the sensitivity of SPE was improved dramatically after functionalized with Bi/Fe₃O₄/IL. Under optimized conditions, the concentrations of Cd(II) are linear with current responses in a range from 0.5 to 40 µg/L with the lowest detection limit of 0.05 µg/L (S/N = 3). Additionally, the internal standard normalization (ISN) was used to process the response signals of Bi/Fe₃O₄/ILSPE and established a new linear equation. For detecting three different Cd(II) concentrations, the root-mean-square error using ISN (0.25) is lower than linear method (0.36). Finally, the proposed electrode was applied to trace Cd(II) in soil samples with the recovery in the range from 91.77 to 107.83%.

Multi-element determination of metals and metalloids in waters and wastewaters, at trace concentration level, using electroanalytical stripping methods with environmentally friendly mercury free-electrodes: A review

Nowadays, water is no longer regarded as an inexhaustible resource and the excessive release and proliferation of toxic metal(loid)s into aquatic environments has become a critical issue. Therefore, fast, accurate, simple, selective, sensitive and portable methodologies to detect multiple elements in natural waters is of paramount importance. Electrochemical stripping analysis is an efficient tool for trace metal(loid)s determinations and bring new prospects for answering the current environmental concerns. This review presents a survey of the advancements made between 2003 and 2016 on the development and application of non-toxic mercury free electrodes on the simultaneous analysis of metals and metalloids in waters and wastewaters by means of electroanalytical stripping techniques. The advantages, limitations, improvements and real applications of these "green" sensors are discussed from a critical point of view.