Determination of trace selenium by differential pulse adsorptive stripping voltammetry at a bismuth film electrode

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.

Outlook on bismuth-based photocatalysts for environmental applications: A specific emphasis on Z-scheme mechanisms

Semiconductor photocatalysis is thought to be a viable solution for addressing the growing problem of environmental pollution. Bismuth (Bi) metal oxides can function as a direct plasmonic photocatalyst or cocatalyst to accelerate the photogenerated charge separation and thus improve their photocatalytic activity. Hence, Bi-based photocatalysts have received a lot of attention due to their extensive environmental applications, including pollutant remediation and energy concepts. Massive efforts have been undertaken in the recent decade to find superior Bi-metal oxides (Bi₂XO_6, X = MO, W, or Cr) and to uncover the corresponding photocatalytic reaction mechanism for the degradation of organic contaminants in water. Herein, the unique crystalline and electronic properties and main synthesis methods, as well as the major Bi-Based direct Z-scheme photocatalysts, are timely discussed and summarized in their usage in water treatment. Besides, the impact of Bi₂XO₆ in energy storage devices and solar energy conversion is reviewed as an energy application. Finally, the future development and challenges of Z-scheme-based Bi₂XO₆ photocatalysts are briefly explored, summarized, and forecasted.

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.

Determination of selenium and copper in water and food by hierarchical dendritic nano-gold modified glassy carbon electrodes

The sensitive determination of selenium and copper is of importance for environmental monitoring and food safety. A stripping voltammetric determination of selenium and copper in water and selenium-rich foods was developed using hierarchical dendritic gold nanostructure (AuHD) modified glassy carbon electrodes (GCE). The AuHD thin films were electrodeposited potentiostatically onto the GCE from a solution containing 25 mM HAuCl₄ and 0.1 M Na₂SO₄ at -0.6 V for 20 min. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) studies showed that the electrodeposited gold thin film shows a nanoforest-like morphology with a thickness of about 30-40 μm and a hierarchical dendritic structure with primary-, secondary-, and higher-order branches. Se(iv) and Cu(ii) in a 0.1 M H₂SO₄ solution were determined by square-wave anodic stripping voltammetry using the AuHDs/GCE as the working electrode. Prior to anodic stripping, Se(iv) and Cu(ii) were accumulated onto the working electrode surface at -0.2 V for 300 s. The stripping peak currents of Se(iv) at 0.81 V and Cu(ii) at 0.31 V were positively correlated with the concentrations of Se(iv) and Cu(ii) in a range of 50-700 nM. The limits of detection (3σ) for Se(iv) and Cu(ii) were 1.4 nM and 3.7 nM, respectively. The accuracy of the method was verified by analysing certified water standard reference materials, and the results showed that the method has good accuracy and high precision. The method was used to determine selenium and copper in tap water, selenium-rich rice and selenium-rich eggs. The results were compared with those obtained by using inductively coupled plasma-mass spectrometry (ICP-MS) and found to be consistent with those of ICP-MS. The proposed method had the advantages of simplicity, rapidity, good reproducibility, and high sensitivity and it can be used for the analysis of real samples.

Electroanalytical Techniques for the Detection of Selenium as a Biologically and Environmentally Significant Analyte-A Short Review

This short review deals with the properties and significance of the determination of selenium, which is in trace amounts an essential element for animals and humans, but toxic at high concentrations. It may cause oxidative stress in cells, which leads to the chronic disease called selenosis. Several analytical techniques have been developed for its detection, but electroanalytical methods are advantageous due to simple sample preparation, speed of analysis and high sensitivity of measurements, especially in the case of stripping voltammetry very low detection limits even in picomoles per liter can be reached. A variety of working electrodes based on mercury, carbon, silver, platinum and gold materials were applied to the analysis of selenium in various samples. Only selenium in oxidation state + IV is electroactive therefore the most of voltammetric determinations are devoted to it. However, it is possible to detect also other forms of selenium by indirect electrochemistry approach.

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).

Preparation, structural characterisation and release study of novel hybrid microspheres entrapping nanoselenium, produced by green synthesis

The main goal of this study was to synthesise and characterise different formulations based on alginate and alginate/chitosan microspheres containing nanoselenium (nano-Se) for controlled delivery applications. Nanosize elemental selenium was produced by using probiotic yogurt bacteria (Lactobacillus casei) in a fermentation procedure. The structural and morphological characterisation of the microspheres was performed by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. FTIR and XRD pattern indicated that was an effective cross-linking of selenium nanoparticles within the polymeric matrix in both cases. The SEM images reveal that selenium nanoparticles are mainly exposed on the surface of alginate, in contrast to porous structure of alginate/chitosan/nano-Se, interconnected in a regular network. This architecture type has a considerable importance in the delivery process, as demonstrated by differential pulse voltammetry. Selenium release from both matrices is pH sensitive. Moreover, chitosan blended with alginate minimise the release of encapsulated selenium, in simulated gastric fluid, and prolong the duration of release in intestinal fluid. The overall effect is the enhancement of total percentage release concomitant with the longer duration of action. The authors' formulation based on alginate/chitosan is a convenient matrix to be used for selenium delivery in duodenum, caecum and colon.

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.

Improved Bi Film Wrapped Single Walled Carbon Nanotubes for Ultrasensitive Electrochemical Detection of Trace Cr(VI)

We report here the successful fabrication of an improved Bi film wrapped single walled carbon nanotubes modified glassy carbon electrode (Bi/SWNTs/GCE) as a highly sensitive platform for ultratrace Cr(VI) detection through catalytic adsorptive cathodic stripping voltammetry (AdCSV). The introduction of negatively charged SWNTs extraordinarily decreased the size of Bi particles to nanoscale due to electrostatic interaction which made Bi(III) cations easily attracted onto the surface of SWNTs in good order, leading to higher quality of Bi film deposition. The obtained Bi/SWNTs composite was well characterized with electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), the static water contact angle and the voltammetric measurements. The results demonstrates the improvements in the quality of Bi film deposited on the surface of SWNTs such as faster speed of electron transfer, more uniform and smoother morphology, better hydrophilicity and higher stripping signal. Using diethylene triaminepentaacetic acid (DTPA) as complexing ligand, the fabricated electrode displays a well-defined and highly sensitive peak for the reduction of Cr(III)-DTPA complex at -1.06 V (vs. Ag/AgCl) with a linear concentration range of 0-25 nM and a fairly low detection limit of 0.036 nM. No interference was found in the presence of coexisting ions, and good recoveries were achieved for the analysis of a river sample. In comparison to previous approaches using Bi film modified GCE, the newly designed electrode exhibits better reproducibility and repeatability towards aqueous detection of trace Cr(VI) and appears to be very promising as the basis of a highly sensitive and selective voltammetric procedure for Cr(VI) detection at trace level in real samples.

Expression profile of nine novel genes differentially expressed in hepatitis B virus-associated hepatocellular carcinomas

Chronic hepatitis B virus (HBV) infection is known to be one of the major causes in the development of hepatocellular carcinoma (HCC), although the biomolecular mechanism(s) involved remain unclear. To identify the cellular gene(s) involved in HBV-associated hepatocarcinogenesis, we used the mRNA differential display method and examined three paired tumor and nontumor tissues, all of which had chromosomally integrated HBV-DNA through chronic infection. Using 240 different combinations of three one-base anchored oligo-dT primers and 80 arbitrary 13-mers, genes decreased or increased in expression more than twofold between each tumor tissue and its paired nontumor tissue were identified. Twenty-nine known genes and four novel genes were differentially over-expressed in the HCC tumor tissues. In contrast, 27 known genes and five novel genes were under-expressed in those tumor tissues. The nucleotide sequences of the nine novel gene fragments were determined and their expression patterns were examined in 40 HCC samples. HA61T2, PT18, HG63T1, and HG57T1 were preferentially over-expressed in 32 cases (80%, P<0.001), 24 cases (60%), 23 cases (57.5%) and 22 cases (55%) of the 40 tumor tissues, respectively. There was an increased frequency of HG57T1 over-expression in HCC patients with HBV-positive serology and low serum alpha-feto protein (AFP) levels (P<0.05). DNT10, PT8, PT19, ENT25 and HA6T4 were under-expressed in 26 cases (65%), 23 cases (57.5%), 21 cases (53%), 20 cases (50%) and 18 cases (45%) of the 40 tumor samples, respectively. There was a strong correlation of DNT10 under-expression with high serum AFP level in HCC patients, irrespective of HBV serology (P<0.01). HA6T4 was preferentially under-expressed in HCC tumors in patients with HBV-positive serology and high serum AFP levels (P<0.05). Thus, the functional analyses of the known and novel genes identified in this study should prove valuable to further understand the mechanism(s) of hepatocarcinogenesis.