Determination of phosphorus based on the formation of a reduced keggin-type 12-molybdophosphate complex in an aqueous-organic solution

Development and validation of the spectrophotometric method of butaphosphan determination in veterinary preparations

A simple and sensitive method has been developed for the determination of butaphosphan in single- and multi-component veterinary preparations. The method is based on the combustion of organic matter prior to the formation of phosphate and the subsequent formation of the phosphoric‑molybdenum complex in the presence of molybdate and ascorbic acid as a reducing agent in the sulfate acid medium. The intensity of light absorption of the colored analytical form of "molybdenum blue" is measured at a wavelength of 830 nm in the range of 0.3-9.0 μg/ml of butaphosphan, where Beer's law is obeyed, has been measured. The reaction conditions and other experimental parameters influencing the reaction transition and the stability of the colored complex have been thoroughly investigated and optimized for the quantitative determination of butaphosphan. Validation of the developed method according to the requirements has been carried out State Pharmacopoeia of Ukraine garmonised with European Pharmacopoeia and its suitability for the analysis of the selected veterinary preparations for the quantitative content of butaphosfan has been confirmed. The results of the determination of butaphosphan in six veterinary preparations of domestic and imported products have been obtained with the help of the developed method. The received results are in agreement with the results obtained by the method of potentiometric titration.

Polyoxometalate-Promoted Electrocatalytic CO2 Reduction at Nanostructured Silver in Dimethylformamide

Electrochemical reduction of CO₂ is a promising method to convert CO₂ into fuels or useful chemicals, such as carbon monoxide (CO), hydrocarbons, and alcohols. In this study, nanostructured Ag was obtained by electrodeposition of Ag in the presence of a Keggin type polyoxometalate, [PMo₁₂O₄₀]^3- (PMo). Metallic Ag is formed upon reduction of Ag⁺. Adsorption of PMo on the surface of the newly formed Ag lowers its surface energy thus stabilizes the nanostructure. The electrocatalytic performance of this Ag-PMo nanocomposite for CO₂ reduction was evaluated in a CO₂ saturated dimethylformamide medium containing 0.1 M [ n-Bu₄N]PF₆ and 0.5% (v/v) added H₂O. The results show that this Ag-PMo nanocomposite can catalyze the reduction of CO₂ to CO with an onset potential of -1.70 V versus Fc^0/+, which is only 0.29 V more negative than the estimated reversible potential (-1.41 V) for this process and 0.70 V more positive than that on bulk Ag metal. High faradaic efficiencies of about 90% were obtained over a wide range of applied potentials. A Tafel slope of 60 mV dec^-1 suggests that rapid formation of *CO₂^•- is followed by the rate-determining protonation step. This is consistent with the voltammetric data which suggest that the reduced PMo interacts strongly with CO₂ (and presumably CO₂^•-) and hence promotes the formation of CO₂^•-.

Selective photoelectrochemical detection of DNA with high-affinity metallointercalator and tin oxide nanoparticle electrode

Selective detection of double-stranded DNA (ds-DNA) in solution was achieved by photoelectrochemistry using a high-affinity DNA intercalator, Ru(bpy)2dppz (bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine) as the signal indicator and tin oxide nanoparticle as electrode material. When Ru(bpy)2dppz alone was irradiated with 470-nm light, anodic photocurrent was detected on the semiconductor electrode due to electron injection from its excited state into the conduction band of the electrode. The current was sustained in the presence of oxalate in solution, which acted as a sacrificial electron donor to regenerate the ground-state metal complex. After addition of double-stranded calf thymus DNA into the solution, photocurrent dropped substantially. The drop was attributed to the intercalation of Ru(bpy)2dppz into DNA and, consequently, the reduced mass diffusion of the indicator to the electrode, as well as electrostatic repulsion between oxalate anion and negative charges on DNA. The degree of signal reduction was a function of the DNA concentration, thus forming the basis for real-time DNA detection. The signal reduction was selective for ds-DNA, as no such effect was observed for single-stranded polynucleotides such as poly-G, poly-C, poly-A, and poly-U. The detection limit of calf thymus ds-DNA reached 1.8 x 10(-10) M in solution.