Application of Aminopolycarboxylic Complexes of V(IV) in Catalytic Adsorptive Stripping Voltammetry of Germanium

In the review, voltammetric analytical procedures that employ vanadium(IV) and aminopolycarboxylic complexes of V(IV) are presented and discussed. The focus of the paper is on the mechanism of vanadium-catalyzed reactions responsible for the amplification of the analytical signal of Ge(IV). The analytical efficacy of different catalytic systems is compared, and the optimal parameters of the respective procedures are reported.

Voltammetric Analysis of New Psychoactive Substances

New Psychoactive Substances (NPS) are synthetic drugs that create similar effects as various narcotic drugs and psychotropic substances. Different NPS such as mephedrone, synthacaine, synthetic cannabinoids, etc. are available today which are sold across numerous platforms like drug markets, head shops, the dark web, etc. They are emerging rapidly and becoming popular in society because of their variable nature and ease in avoiding breaking the law. Consequently, their analysis is extremely crucial in the prohibition of drug abuse and the development of laboratory methods. This review introduces a broad overview of the analysis of various new psychoactive substances by voltammetric techniques such as cyclic voltammetry, differential pulse voltammetry, square wave voltammetry, stripping voltammetry etc. It also focuses on various methodologies that were developed for the detection of these NPS which play a leading role in forensic investigation by providing a rapid, sensitive, and cost-effective platform of analysis. The need for the advancement of various detection methods and analysis of more drugs is additionally discussed.

Preparation of Pt electrocatalyst supported by novel, Ti(1−x)MoxO2-C type of composites containing multi-layer graphene

Ball milling is a relative simple and promising technique for preparation of inorganic oxide–carbon type of composites. Novel TiO2-C and Ti0.8Mo2O2-C type of composites containing multi-layer graphene were prepared by ball milling of graphite in order to get electrocatalyst supports for polymer electrolyte membrane fuel cells. Starting rutile TiO2 was obtained from P25 by heat treatment. Carbon-free Ti0.8Mo2O2 mixed oxide, prepared using our previously developed multistep sol–gel method, does not meet the requirements for materials of electrocatalyst support, therefore parent composites with Ti0.8Mo2O2/C = 75/25, 90/10 and 95/5 mass ratio were prepared using Black Pearls 2000. XRD study of parent composites proved that the oxide part existed in rutile phase which is prerequisite of the incorporation of oxophilic metals providing CO tolerance for the electrocatalyst. Ball milling of TiO2 or parent composites with graphite resulted in catalyst supports with enhanced carbon content and with appropriate specific surface areas. XRD and Raman spectroscopic measurements indicated the changes of graphite during the ball milling procedure while the oxide part remained intact. TEM images proved that platinum existed in the form of highly dispersed nanoparticles on the surface of both the Mo-free and of Mo-containing electrocatalyst. Electrocatalytic performance of the catalysts loaded with 20 wt% Pt was studied by cyclic voltammetry, COads-stripping voltammetry done before and after the 500-cycle stability test, as well as by the long-term stability test involving 10,000 polarization cycles. Enhanced CO tolerance and slightly lower stability comparing to Pt/TiO2-C was demonstrated for Pt/Ti0.8Mo2O2-C catalysts.

An overview of methods used for quantification of heavy metal contents in vegetal samples

Continuous monitoring of heavy metals content in vegetal products is a priority for food control and a risk assessment strategy for human health. Having in view the importance of heavy metals surveillance, the aim of this paper is to identify, on the basis of literature data, the most suitable procedures and techniques used for accurate determination of them in vegetal samples. In most cases, quantification of heavy metals in the vegetal matrix is preceded by digestion performed through different protocols chosen carefully because this is a critical step for obtaining accurate results. Among most used techniques for heavy metals’ assessment from vegetal products reported by literature it worth to be mentioned: atomic absorption spectrometry (AAS), inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma - optical emission spectrometry (ICP-OES), X-ray fluorescence (XRF), neutron activation analysis (NAA), anodic stripping voltammetry (ASV).

ПОРІВНЯЛЬНА ХАРАКТЕРИСТИКА ЕФЕКТИВНОСТІ ЕЛЕКТРОХІМІЧНИХ МЕТОДІВ ДОСЛІДЖЕННЯ ВМІСТУ ВАЖКИХ МЕТАЛІВ У СТІЧНИХ ВОДАХ

Сompare the various modern electrochemical research methods effectiveness used to determine the heavy metals concentration in waste water, based on the literature data. Methodology. Analysis of literature data on the possibilities, advantages and disadvantages of voltammetric, potentiometric, coulometric and conductometric methods for the heavy metals content studying in waste water. Findings. The electrochemical methods are the most common methods for analyzing the composition of waste water. Among their advantages, it should be noted high selectivity, low concentration registration limit (up to 10-10 M for stripping voltammetric methods), simplicity in execution, absence of preliminary long-term samples preparation for analysis, the ability to microvolumes measure without samples destroying and automation of the process for continuous metals concentrations determination in waste water treatment, relatively inexpensive equipment, the ability to determine the concentration of several metal ions in a mixture. Originality. The studies have shown that most often the concentration of heavy metals in waste water determine with the using of the different modifications of voltammetric research methods (polarography and varieties of stripping voltammetry) and potentiometric research methods in particular with highly sensitive and specific ion-selective indicator electrodes. Practical value. The theoretical material on modern electrochemical methods for the heavy metal ions content determining in waste water is generalized.

Effect of the reductive treatment on the state and electrocatalytic behavior of Pt in catalysts supported on Ti0.8Mo0.2O2-C composite

Ti(1-x)MoxO2-carbon composites are promising new supports for Pt-based electrocatalysts in polymer electrolyte membrane fuel cells offering exciting catalytic properties and enhanced stability against electrocorrosion. Pt and the mixed oxide form a couple liable for strong metal-support interaction (SMSI) phenomenon, generally manifesting itself in decoration of the metal particles by ultrathin layers of the support material upon annealing under reductive conditions. The aim of this work is to evaluate the SMSI phenomenon as a potential strategy for tailoring the properties of the electrocatalyst. A 20 wt% Pt/50 wt% Ti0.8Mo0.2O2-50 wt% C electrocatalyst prepared on Black Pearls 2000 carbon functionalized with HNO3 and glucose was reduced at 250 °C in H2 in order to induce SMSI. The electrocatalytic properties and the stability of the reduced and the original catalysts were analyzed by cyclic voltammetry and COads stripping voltammetry. Structural investigations as well as X-ray photoelectron spectroscopy (XPS) measurements were performed in order to obtain information about the details of the interaction between the oxide and the Pt particles. The electrochemical experiments pointed out a small loss of the electrochemically active surface area of Pt in the reduced catalyst along with enhanced stability with respect to the original one, while structural studies suggested only a minimal decrease of the Pt dispersion. At the same time, hydrogen exposure experiments combined with XPS demonstrated the presence of Mo species directly adsorbed on the Pt surface. Thus, the properties of the reduced catalyst can be traced to decoration of the surface of Pt by Mo-containing species.

Chemical Detection by Analyte-Induced Change in Electrophoretic Deposition of Gold Nanoparticles

The electrophoretic deposition (EPD) of citrate-stabilized Au nanoparticles (cit-Au NPs) occurs on indium tin oxide (ITO)-coated glass electrodes upon electrochemical oxidation of hydroquinone (HQ) due to the release of hydronium ions. Anodic stripping voltammetry (ASV) for Au oxidation allows the determination of the amount of Au NP deposition under a specific EPD potential and time. The binding of Cr3+ to the cit-Au NPs inhibits the EPD by inducing aggregation and/or reducing the negative charge, which could lower the effective NP concentration of the cit-Au NPs and/or lower the electrophoretic mobility. This lowers the Au oxidation charge in the ASV, which acts as an indirect signal for Cr3+. The binding of melamine to cit-Au NPs similarly leads to aggregation and/or lowers the negative charge, also resulting in reduction of the ASV Au oxidation peak. The decrease in Au oxidation charge measured by ASV increases linearly with increasing Cr3+ and melamine concentration. The limit of detection (LOD) for Cr3+ is 21.1 ppb and 16.0 ppb for 15.1 and 4.1 nm diameter cit-Au NPs, respectively. Improving the sensing conditions allows for as low as 1 ppb detection of Cr3+. The LOD for melamine is 45.7 ppb for 4.1 nm Au NPs.

Seasonal Variation of Dissolved Lead Speciation in Tagus Estuary, Portugal

The behavior of lead species from Tagus estuarine water collected during winter (January), spring (April), and summer (June) seasons were evaluated. Water samples were titrated with Pb+2 followed by differential pulse anodic stripping voltammetry (DPASV). Experimental voltammetric values were interpreted assuming a macromolecular heterogeneous ligand described in a simple way by two types of binding sites, CL1 and CL2, where CL1 is related to stronger binding groups with lower concentration compared to CL2. Water quality parameters like dissolved organic matter (DOC), pH, salinity, temperature, and total lead concentration were measured during the period under study. The results pointed to a higher concentration of CL1 and CL2 sites in April probably due to the phytoplankton bloom. The decrease of KL1 with the increase of salinity from winter to summer may be caused by the increase of major cations (as Ca2+) in solution. The trend of KL2 followed the pH shift in all seasons since an increase of pH favors Pb2+ complexation with CL2 sites. Finally, the decrease of DOC in summer could be responsible for the decrease in the concentration of the different sites in solution from April to June, with a similar decrease of 35±3% for all of them.