Determination of methanol in o,o-dimethyldithiophosphoric acid (DMDTPA) of technical grade by UV/vis spectrophotometry and by HPLC

Two procedures are proposed in this work for the determination of methanol impurities in o,o-dimethyldithiophosphoric acid (DMDTPA). To avoid possible interferences from the main component, DMDTPA was precipitated in the form of insoluble lead complex. Free Pb(II) ions were eliminated with sulfuric acid and methanol was oxidized to formaldehyde with potassium permanganate in methanesulfonic acid medium. Finally, the excess of oxidizing agent was neutralized with saturated sodium oxalate. The above pretreatment procedure was identical for spectrophotometric assay and for chromatographic determination. In the first case, the solution obtained was treated with Nash reagent to form 3,5-diacetyl-1,4-dihydrolutidine (λ_max = 415 nm). In the calibration range 0.1-1.0% (methanol in DMDTPA), the analytical figures of merit were: R² = 0.9993, quantification limit 0.02% methanol in DMDTPA coefficient of variance (n = 5) for 0.1% and 0.4% methanol respectively 6.7% and 2.4%. Recoveries obtained in the sample fortified with 0.1, 0.2, 0.4% of methanol (in DMDTPA) were in the range 99-105%. For chromatographic procedure, formaldehyde was derivatized with 2,4-dinitrophenylhydrazine and separation was achieved on Luna C18(2) column using the isocratic elution with acetonitrile-water (70:30, v/v) and spectrophotometric detection at 360 nm. In the calibration range 0.05-0.25% (methanol in DMDTPA), R² was always higher than 0.999, the quantification limit was 0.004% and the recoveries in these same fortified samples in the range 98-101%. No statistically significant differences were observed between the results obtained in the analysis of technical grade DMDTPA by the two procedures (ANOVA, p < 0.05)     

Lattice dynamics to trigger low temperature oxygen mobility in solid oxide ion conductors

SrFeO(2.5) and SrCoO(2.5) are able to intercalate oxygen in a reversible topotactic redox reaction already at room temperature to form the cubic perovskites Sr(Fe,Co)O(3), while CaFeO(2.5) can only be oxidized under extreme conditions. To explain this significant difference in low temperature oxygen mobility, we investigated the homologous SrFeO(2.5) and CaFeO(2.5) by temperature dependent oxygen isotope exchange as well as by inelastic neutron scattering (INS) studies, combined with ab initio (DFT) molecular dynamical calculations. From (18)O/(16)O isotope exchange experiments we proved free oxygen mobility to be realized in SrFeO(x) already below 600 K. We have also evidence that low temperature oxygen mobility relies on the existence of specific, low energy lattice modes, which trigger and amplify oxygen mobility in solids. We interpret the INS data together with the DFT-based molecular dynamical simulation results on SrFeO(2.5) and CaFeO(2.5) in terms of an enhanced, phonon-assisted, low temperature oxygen diffusion for SrFeO(3-x) as a result of the strongly reduced Fe-O-Fe bond strength of the apical oxygen atoms in the FeO(6) octahedra along the stacking axis. This dynamically triggered phenomenon leads to an easy migration of the oxide ions into the open vacancy channels and vice versa. The decisive impact of lattice dynamics, giving rise to structural instabilities in oxygen deficient perovskites, especially with brownmillerite-type structure, is demonstrated, opening new concepts for the design and tailoring of low temperature oxygen ion conductors.     

Analytical speciation of chromium in in-vitro cultures of chromate-resistant filamentous fungi

In this work, different analytical speciation schemes have been used to study the reduction of Cr(VI) by a chromate-resistant strain of filamentous fungi Ed8 (Aspergillus sp), indigenous to contaminated industrial wastes. As demonstrated previously, this strain has the capability to reduce chromate present in the growth medium without its accumulation in the biomass, yet the reduced chromium end-products have not been characterized. Liquid growth medium, initially containing 50 mg L(-1) Cr(VI), was analyzed for Cr(III)/Cr(VI) and for total Cr at different time intervals (0-24 h) after inoculation with fungi. Three hyphenated procedures, based on the Cr(III)-EDTA formation and species separation by anion-exchange or ion-pairing reversed-phase chromatography with ICP-MS or DAD detection were used. The results obtained for Cr(VI) in each case were consistent, demonstrating efficient reduction of chromate during 24 h of Ed8 growth. However, pre-column complexation with EDTA did not ensure complete recovery of the reduced forms of chromium in the above procedures. An alternative speciation scheme, based on extraction of Cr(VI)-benzyltributylammonium bromide (BTAB) ion pairs into chloroform and subsequent determination of residual chromium by ICP-MS has provided evidence on the effective conversion of chromate into reduced chromium species in the growth medium. The results indicate the feasibility of using Ed8 strain for chromate bioremediation purposes. Analytically it can be concluded that speciation of chromium in biological systems should not be limited to its two most common oxidation states, because the actual reduced chromium species are not converted quantitatively to Cr(III)-EDTA.     

Some remarks on the Euler ring U(G)

Let G be a compact Lie group and let U(G) denote the Euler ring of G constructed by tom Dieck [5, 6]. The main result of the paper (Theorem 4.1) describes the homomorphism induced by the inclusion . Dedicated to Professor Vladimir Arnold     

Quantitative Analysis of Phenolic Acids in Extracts Obtained from the Fruits of Peucedanum alsaticum L. and Peucedanum cervaria (L.) Lap

Peucedanum alsaticum L. and Peucedanum cervaria (L.) Lap. are, in common with all species belonging to the Apiaceae family, rich in coumarins and essential oils. Phenolic acids also present in the plant are very important pharmacologically, because of their broad spectrum of biological activity. A simple high-performance liquid chromatographic method has been developed for separation and quantitative analysis of the major phenolic acids in extracts obtained from the fruits of P. alsaticum and P. cervaria. Soxhlet extraction, ultrasound extraction, and accelerated solvent extraction under different conditions were used to find the most efficient extraction conditions. Optimum chromatographic performance was obtained with a C₁₈ column and acetonitrile—1% (v/v) aqueous acetic acid as mobile phase. Ferulic, p-coumaric, caffeic, vanillic, syringic, p-hydroxybenzoic, protocatechuic, chlorogenic, and gallic acids were investigated in the fruits of the plants. For all calibration plots linearity was good (R ² > 0.9991) in the ranges tested. The highest yields of most of the phenolic acids were achieved by use of accelerated solvent extraction. The predominant phenolic acid in the fruits of both plants was chlorogenic acid. The amounts, which depended on the method of extraction, were approximately 146 ± 1.616 and 109.92 ± 3.405 mg per 100 g dry weight for P. cervaria and P. alsaticum, respectively.     

Electrochemical oscillations and bistability during anodic dissolution of vanadium electrode in acidic media—part I. Experiment

Dynamic instabilities, current oscillations and bistability observed during anodic dissolution of both stationary and rotating disk vanadium electrode in acidic phosphoric media, were reported using both dc and ac techniques. The effect of various experimental conditions, concentration of H₃PO₄, temperature, disk rotation rate, and external resistance, was analyzed. Systematic studies allowed the construction of bifurcation diagrams, showing the regions of oscillations and bistability, including the complex behaviors like coexistence of both dynamic regimes. Analogous comparative measurements and analyses were performed for other media—sulfuric, nitric, perchloric, and trifluoroacetic acids—also indicating complex dynamic behaviors. These complexities arise not only due to the difficulties with the precise identification of the composition of the passive layer in every acid but are also due to relatively fast dissolution of V electrode, even in the presence of passive layer, which causes permanent drift of the system’s characteristics. Due to these experimental difficulties, theoretical modeling seems to be an appropriate method to analyze the essential nonlinear dynamic properties of the studied system.

     

Temperature Compensation by Embedded Temperature Variation Method for an AC Voltammeric Analyzer of Electroplating Baths

An in‐situ sensor utilizing a variety of DC‐ and AC‐voltammetric techniques is an integral component of the on‐line monitoring system that provides a complete chemical analysis of different plating solutions by predicting concentration values of all deliberately‐added bath constituents with a single device despite differences in the constituents’ chemical properties. Such sensors are employed routinely for electroplating process control in semiconductor manufacturing. This voltammetric approach exploits quantitatively the physicochemical processes (like adsorption) which are temperature dependent. Therefore the accuracy of analyte concentration predictions can be affected adversely by temperature fluctuations. This paper introduces a novel comprehensive method which allows the mitigation of temperature variation effects on voltammetric scans allowing accurate concentration prediction. Specifically, this study introduces a multi‐step rigorous routine for the development and subsequent validation of the analytical method utilizing a chemometric model with temperature variation embedded in regression for exemplary determination of leveler additive concentration. This approach analyses the effect on AC voltammograms resulting from two qualitatively indistinguishable sources of variation: leveler concentration and temperature. A critical step of this routine of fundamental novelty, which aims to select the variables (index points of voltammogram) to be utilized for building of the analytical model in the presence of two concurrent sources of variation, is introduced to incorporate temperature variation.     

Electrochemical oscillations and bistability during anodic dissolution of vanadium electrode in acidic media��part I. Experiment

Dynamic instabilities, current oscillations and bistability observed during anodic dissolution of both stationary and rotating disk vanadium electrode in acidic phosphoric media, were reported using both dc and ac techniques. The effect of various experimental conditions, concentration of H₃PO₄, temperature, disk rotation rate, and external resistance, was analyzed. Systematic studies allowed the construction of bifurcation diagrams, showing the regions of oscillations and bistability, including the complex behaviors like coexistence of both dynamic regimes. Analogous comparative measurements and analyses were performed for other media—sulfuric, nitric, perchloric, and trifluoroacetic acids—also indicating complex dynamic behaviors. These complexities arise not only due to the difficulties with the precise identification of the composition of the passive layer in every acid but are also due to relatively fast dissolution of V electrode, even in the presence of passive layer, which causes permanent drift of the system’s characteristics. Due to these experimental difficulties, theoretical modeling seems to be an appropriate method to analyze the essential nonlinear dynamic properties of the studied system.