New electrochemical sensor with the renewable silver annular band working electrode: Fabrication and application for determination of selenium(IV) by cathodic stripping voltammetry

Microelectrode Voltammetric Analysis of Low Concentrations of Se(IV) Ions in Environmental Waters

The current research is an attempt to analyze on-site selenium(IV) ions in environmental water samples using an eco-friendly miniaturized sensor developed by deposition of a very thin amount of metallic bismuth in a solid Bi electrode tightly closed in miniaturized housing. Numerous experimental variables are optimized, including the composition of the supporting electrolyte and its pH, as well as activation and accumulation conditions. Under optimized measurement conditions, the method shows high sensitivity, permitting a very low limit of detection equal to 7 × 10-10 mol L-1 to be achieved in a short accumulation time of 50 s. The performance of this microsensor was investigated against numerous interference factors and its good anti-interference capability was demonstrated. A series of voltammetric experiments by differential pulse cathodic stripping voltammetry (DPCSV) were carried out and they proved that the miniaturized sensor is characterized by very good accuracy and precision as well as long-term stability. The solid bismuth microelectrode displays a good voltammetric response in the analysis of diverse samples with a complex matrix and demonstrates a good recovery rate.

Voltammetric and impedimetric determinations of selenium(iv) by an innovative gold-free poly(1-aminoanthraquinone)/multiwall carbon nanotube-modified carbon paste electrode

Selenite (Se⁴⁺), a significant source of water pollution above the permissible limits, is considered a valuable metal by environmentalists. In this study, we described a novel electrochemical sensor that utilized a carbon paste electrode (CPE) that was modified using multiwall carbon nanotubes (MWCNTs) and poly(1-aminoanthraquinone) (p-AAQ) for finding Se⁴⁺ in water samples. Electrochemical quantification of Se⁴⁺ depends on the formation of a selective complex (piaselenol) with p-AAQ. In this work, we prepared a CPE modified by physical embedding of MWCNTs and 1-aminoanthraquione (AAQ), while the polymer film was formed by anodic polymerization of AAQ by applying a constant potential of 0.75 V in 0.1 M HCl for 20 s followed by cyclic voltammetry (CV) from −0.2 to 1.4 V for 20 cycles. The modified CPE was used for differential pulse voltammetry (DPV) of Se⁴⁺ in 0.1 M H₂SO₄ from 0 to 0.4 V with a characteristic peak at 0.27 V. Further, the proposed sensor was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electrochemical impedance spectroscopy (EIS). The analytical conditions regarding the electrode performance and voltammetric measurements were optimized, with the accumulation time and potential, supporting electrolyte, differential-pulse period/time, and amplitude. The EIS results indicated that the p-AAQ/MWCNTs-modified CPE sensor (p-AAQ/MWCNTs/CPE) that also exhibited low charge-transfer resistance (R_ct) toward the anodic stripping of Se⁴⁺, exhibited good analytical performance toward different concentrations of Se⁴⁺ in a linear range of 5–50 μg L⁻¹ Se⁴⁺ with a limit of determination (LOD) of 1.5 μg L⁻¹ (3σ). Furthermore, differential-pulse voltammetry was employed to determine different concentrations of Se⁴⁺ in a linear range of 1–50 μg L⁻¹ Se⁴⁺, and an LOD value of 0.289 μg L⁻¹ was obtained. The proposed sensor demonstrated good precision (relative standard deviation = 4.02%) at a Se⁴⁺ concentration of 5 μg L⁻¹. Moreover, the proposed sensor was applied to analyze Se⁴⁺ in wastewater samples that were spiked with Se, and it achieved good recovery values.

The selenite ion is quantified electrochemically by selective complexation with poly(1-aminoanthraquione) to give a piaselenol complex on a modified p-AAQ/MWCNTs/CPE sensor.

Materials interacting with inorganic selenium from the perspective of electrochemical sensing

Inorganic selenium, the most common form of harmful selenium in the environment, can be determined using electrochemical sensors, which are compact, fast, reliable and easy-to-operate devices. Despite progress in this area, there is still significant room for developing high-performance selenium electrochemical sensors. To achieve this, one should take into account (i) the electrochemical process that selenium undergoes on the electrode; (ii) the valence state of selenium species in the sample and (iii) modification of the sensor surface by a material with high affinity to selenium. The goal of this review is to provide a knowledge base for these issues. After the Introduction section, mechanisms and principles of the electrochemical reduction of selenium are introduced, followed by a section introducing the modification of electrodes with materials interacting with selenium and a section dedicated to speciation methods, including the reduction of non-detectable Se(VI) to detectable Se(IV). In the following sections, the main types of materials (metallic, polymers, hybrid (nano)materials…) interacting with inorganic selenium (mostly absorbents) are reviewed to show the diversity of properties that may be endowed to sensors if the materials were to be used for the modification of electrodes. These features for the main material categories are outlined in the conclusion section, where it is stated that the engineered polymers may be the most promising modifiers.

Recent Advancement in Disposable Electrode Modified with Nanomaterials for Electrochemical Heavy Metal Sensors

Heavy metal pollution has gained global attention due to its high toxicity and non-biodegradability, even at a low level of exposure. Therefore, the development of a disposable electrode that is sensitive, simple, portable, rapid, and cost-effective as the sensor platform in electrochemical heavy metal detection is vital. Disposable electrodes have been modified with nanomaterials so that excellent electrochemical properties can be obtained. This review highlights the recent progress in the development of numerous types of disposable electrodes modified with nanomaterials for electrochemical heavy metal detection. The disposable electrodes made from carbon-based, glass-based, and paper-based electrodes are reviewed. In particular, the analytical performance, fabrication technique, and integration design of disposable electrodes modified with metal (such as gold, tin and bismuth), carbon (such as carbon nanotube and graphene), and metal oxide (such as iron oxide and zinc oxide) nanomaterials are summarized. In addition, the role of the nanomaterials in improving the electrochemical performance of the modified disposable electrodes is discussed. Finally, the current challenges and future prospect of the disposable electrode modified with nanomaterials are summarized.

Copper Film Modified Glassy Carbon Electrode and Copper Film with Carbon Nanotubes Modified Screen-Printed Electrode for the Cd(II) Determination

A copper film modified glassy carbon electrode (CuF/GCE) and a novel copper film with carbon nanotubes modified screen-printed electrode (CuF/CN/SPE) for anodic stripping voltammetric measurement of ultratrace levels of Cd(II) are presented. During the development of the research procedure, several main parameters were investigated and optimized. The optimal electroanalytical performance of the working electrodes was achieved in electrolyte 0.1 M HCl and 2 × 10⁻⁴ M Cu(II). The copper film modified glassy carbon electrode exhibited operation in the presence of dissolved oxygen with a calculated limit of detection of 1.7 × 10⁻¹⁰ M and 210 s accumulation time, repeatability with RSD of 4.2% (n = 5). In the case of copper film with carbon nanotubes modified screen-printed electrode limit of detection amounted 1.3 × 10⁻¹⁰ M for accumulation time of 210 s and with RSD of 4.5% (n = 5). The calibration curve has a linear range in the tested concentration of 5 × 10⁻¹⁰–5 × 10⁻⁷ M (r = 0.999) for CuF/GCE and 3 × 10⁻¹⁰–3 × 10⁻⁷ M (r = 0.999) for CuF/CN/SPE with 210 s accumulation time in both cases. The used electrodes enable trace determination of cadmium in different environmental water samples containing organic matrix. The validation of the proposed procedures was carried out through analysis certified reference materials: TM-25.5, SPS-SW1, and SPS-WW1.

New Strategies for the Simple and Sensitive Voltammetric Direct Quantification of Se(IV) in Environmental Waters Employing Bismuth Film Modified Glassy Carbon Electrode and Amberlite Resin

An analytical procedure regarding the determination of selenium(IV) by anodic stripping voltammetry exploiting the in situ plated bismuth film electrode is described. Since organics are commonly present in untreated natural water samples, the use of Amberlite XAD-7 resin turns out to be quite important to avoid problems such as the adsorption of these compounds on the working electrode. The optimum circumstances for the detection of selenium in water using differential pulse voltammetry techniques were found to be as follows: 0.1 mol L-1 acetic acid, 1.9 × 10-5 mol L-1 Bi(III), 0.1 g Amberlite XAD-7 resin, and successive potentials of -1.6 V for 5 s and -0.4 V for 60 s, during which the in situ formation of the bismuth film on glassy carbon and the accumulation of selenium took place. The current of the anodic peak varies linearly with the selenium concentration ranging from 3 × 10-9 mol L-1 to 3 × 10-6 mol L-1 (r = 0.9995), with a detection limit of 8 × 10-10 mol L-1. The proposed procedure was used for Se(IV) determination in certified reference materials and natural water samples, and acceptable results and recoveries were obtained.

An electrochemical sensor for detecting selenium in biological fluids on an arenediazonium tosylate-modified metal electrode

This article presents the results on using a new electrochemical sensor modified with arenediazonium salts (MGE-Cu-COOH) to determine selenium in biological fluids (blood serum). It was shown that the sensitivity of the determination of selenite ions using this modified electrode is higher compared to that of the unmodified one (MGE-Cu). The effect of the concentration of arenediazonium tosylates on various substituents was studied, and the conditions for the production of the electrochemical sensor were developed. The surface of the modified electrode was investigated using SEM. The increase in the effective surface area of the electrode was found to be due to the formation of a system of ultramicroelectrodes. In biological samples, the LOD and LOQ of selenium were established at the levels of 0.057 and 0.166 μg l^-1, respectively. Finally, the correctness of the results on selenium determination in real samples by the "input-found" method, which correlates well with the known value, was verified.

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).

Simple multimodal detection of selenium in water and vegetable samples by a catalytic chromogenic method

The determination of selenium (Se) has garnered increasing interest because of its importance to life as a nutrient element as well as its toxicological effects.

Inorganic selenium speciation in water and biological samples by three phase hollow fiber-based liquid phase microextraction coupled with HPLC-UV

A rapid, sensitive, high clean-up and economic three phase hollow fiber liquid phase microextraction method followed by HPLC-UV was applied for speciation of inorganic selenium in water and biological samples.

Determination of trace Se(IV) by anodic stripping voltammetry following double deposition and stripping steps

A procedure of Se(IV) determination by anodic stripping voltammetry using two deposition and stripping steps at gold electrodes was proposed. A well-defined stripping peak of selenium was obtained at potential 0.9 V. The optimization of parameters influencing the selenium peak current including both deposition and stripping steps was performed. A linear relationship was observed between the Se(IV) peak current and its concentration in the range from 5×10^-9 to 1×10^-7mol L^-1. The limit of detection was found to be 8.5×10^-10mol L^-1. Repeatability of the method determined as RSD % for Se(IV) concentration of 5×10^-8mol L^-1 was 4.3% (n=7). The proposed procedure was used for Se(IV) determination in certified reference material and natural water samples and acceptable results and recoveries were obtained.