Diphenic acid as an analytical reagent

Summary Diphenic acid can separate thorium completely from moderate amounts of ferrous iron and titanium in almost neutral solutions. As the reagent forms quantitative precipitates with ferric iron and zirconium, workable methods for their separation from thorium and their co-determinations in a mixture with the help of this reagent have also been developed. The reagent can separate thorium from zirconium by precipitating the latter below p_h2, and the same from iron(ic) can be accomplished by the use of ascorbic acid as a masking agent. Ferric iron can be precipitated from solution containing ascorbic acid, by the ammonium salt of the reagent. A convenient process for the estimation and separation of zirconium, thorium, iron(ic) and titanium, when present in a mixture, has also been described, which involves the proper control ofph and the use of ascorbic acid as a complexing agent for ferric iron.My sincere thanks are due to Dr. A.K. Mukherjee of the Indian Association for the Cultivation of Science, Calcutta for his valuable suggestions and to Dr. A. K. Ghosal, Principal, Darjeeling Government College for providing laboratory facilities.     

Etude par effet Mössbauer des composés de type “bronzes fluorés” MxFeF3 (M = K,Rb, Cs,NH4)

The hexagonal, tetragonal and pyrochlore-type nonstoichiometric iron fluorides M_xFeF₃ (M = K, Rb, Cs, NH₄) have been studied by Mössbauer spectroscopy over the temperature range 4.2 to 295 K. The magnetic transition temperatures have been determined. The ferrous and ferric ions remain in discrete oxidation states indicating the absence of charge hopping. The broadened lines of the spectra of the hexagonal and tetragonal phases are consistent with the disordering of Fe²⁺ and Fe³⁺ in the structure. By contrast, the narrow linewidths of the spectra of the pyrochlore-type phases characterize a structural ordering between the ferrous and ferric ions.     

Determination of ferrous and ferric iron in aqueous biological solutions

A solvent extraction method was employed to determine ferrous and ferric iron in aqueous samples. Fe³⁺ is selectively extracted into the organic phase (n-heptane) using HDEHP (bis(2-ethylhexyl) hydrogen phosphate) and is then stripped using a strong acid. After separation, both oxidation states and the total iron content were determined directly by ICP-MS analysis. This extraction method was refined to allow determination of both iron oxidation states in the presence of strong complexing ligands, such as citrate, NTA and EDTA. The accuracy of the method was verified by crosschecking using a refinement of the ferrozine assay. Presented results demonstrate the ability of the extraction method to work in a microbiological system in the presence of strong chelating agents following the bioreduction of Fe³⁺ by the Shewanella alga BrY. Based on the results we report, a robust approach was defined to separately analyze Fe³⁺ and Fe²⁺ under a wide range of potential scenarios in subsurface environments where radionuclide/metal contamination may coexist with strongly complexing organic contaminants.     

Interactions of Ascorbic Acid, 5-Caffeoylquinic Acid,and Quercetin-3-Rutinoside in the Presence and Absence of Iron during Thermal Processing and the Influence on Antioxidant Activity

Bioactive compounds in fruit and vegetables influence each other’s antioxidant activity. Pure standards, and mixtures of the common plant compounds, namely ascorbic acid, 5-caffeoylquinic acid, and quercetin-3-rutinoside (sum 0.3 mM), in the presence and absence of iron, were analyzed pre- and post-thermal processing in an aqueous solution. Antioxidant activity was measured by total phenolic content (TPC), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (TEAC) radical-scavenging assays. Ionic ferrous iron (Fe²⁺) and ferric iron (Fe³⁺) were measured photometrically. For qualification and quantification of reaction products, HPLC was used. Results showed that thermal processing does not necessarily lead to a decreased antioxidant activity, even if the compound concentrations decreased, as then degradation products themselves have an antioxidant activity. In all used antioxidant assays the 2:1 ratio of ascorbic acid and 5-caffeoylquinic acid in the presence of iron had strong synergistic effects, while the 1:2 ratio had strong antagonistic effects. The pro-oxidant iron positively influenced the antioxidant activity in combination with the used antioxidants, while ferrous iron itself interacted with common in vitro assays for total antioxidant activity. These results indicate that the antioxidant activity of compounds is influenced by factors such as interaction with other molecules, temperature, and the minerals present.     

Role of N,N-dimethyl-para-toluidine and saccharin in the radical polymerization of methyl methacrylate initiated by a redox system. II. Cumene hydroperoxide/iron saccharinate

The role of N,N-dimethyl-p-toluidine (DMPT) and saccharin as accelerators in the polymerization of methyl methacrylate initiated by the redox decomposition of cumene hydroperoxide (CHP) in the presence of iron saccharinate has been kinetically investigated. DMPT reduces ferric ions to ferrous ions, so that an equilibrium is established between the two oxidation states. With the assumption of a steady-state concentration of propagating radicals, the rate of initiation was deduced from the rate of polymerization and the kinetic orders with respect to each compound involved in the initiation step have been determined. The reaction is first-order in CHP, iron saccharinate, and saccharine and second-order in DMPT. In a proposed scheme, Fe²⁺ ions, complexed by two DMPT molecules, are much more reactive than uncomplexed Fe²⁺ and saccharin activates the decomposition of CHP by protonation of the O? O bond. This mechanism, similar to that proposed in the case of copper saccharinate, explains the synergistic effect of both accelerators. © 1994 John Wiley & Sons, Inc.     

Studies of high linear energy transfer dosimetry by 10B(n,α)7Li reactions in aqueous and organic solvents

Advanced chemical treatment processes such as aqueous separation techniques can be used to separate the reusable materials from used nuclear fuel, reducing the radiotoxicity and storage time of the remaining waste. The degradation of chemicals in these processes has been studied utilizing gamma radiation. However, radiolytic degradation by internal alpha emitters has not been as widely investigated due to the difficulty of finding appropriate internal sources. This work presents results using a method to produce alpha particles in situ in aqueous and organic solvents representative of liquid–liquid extraction systems. The method is based on the widely studied ¹⁰B(n,α)⁷Li reaction which has previously been studied in aqueous solutions. Neutrons were supplied from the UCI TRIGA^® nuclear reactor. Comparisons were also made to gamma radiation from a ¹³⁷Cs source. We report that the method is useful for inducing high linear energy transfer (LET) doses in aqueous and organic solutions. We used the classic iron sulfate-based Fricke dosimeter for dosimetry in aqueous solutions and methyl red (2-[(4-dimethylaminophenyl)diazenyl]benzoic acid) dissolved in n-dodecane for organic solvents. High LET doses in both aqueous and organic solvents are well described and a simple linear relationship was found based on the neutron flux and total boron concentration. We have established, using spectroscopic determination, that methyl red degrades in a linear fashion with absorbed dose up to 80 kGy and G-values for the methyl red degradation in n-dodecane were found to be 4.66 × 10^?4 μmol/J for external ¹³⁷Cs gamma radiation and 3.0 × 10^?5 μmol/J for ¹⁰B(n,α)⁷Li induced high LET radiation.     

Mercurous nitrate as a reductimetric reagent : The interference of the more common cations and anions in the determination of iron

The interfering effect of most of the more common cations and anions on the titration of ferric iron with mercurous nitrate has been examined. As would be expected, ions capable of oxidising ferrous iron interfere. Certain other cations and anions interfere, but in several cases this effect can be eliminated. Copper and thallium must be completely absent, and ions which give coloured products with thiocyanate ions, e.g., molybdenum.     

Catalytic Oxidation of Ascorbic Acid at a Polyhistidine Modified Electrode and Its Application to the Voltammetric Resolution of Ascorbic Acid and Dopamine

Abstract

A new polymer (polyhistidine) modified electrode has been fabricated and was applied to the catalytic oxidation of ascorbic acid (AA), reducing the overpotential by 400 mV. The catalytic rate constant of the modified electrode for the oxidation of AA was determined using a rotating electrode. The catalytic current was linearly dependent on the ascorbic acid concentration between 5×10^?5 and 2×10^?3 M. The catalytic effect on the AA resulted in the separation of the overlapping voltammograms of AA and dopamine (DA) in a mixture. This allowed the determination of AA in the presence of DA. The electrode was rather stable even after several months; a reproducible response of AA was obtained.     

Amperometric ascorbimetric determination of cerium(IV) and Iron(III) with two polarized electrodes

Summary Amperometric ascorbimetric determinations of cerium(IV) and ferric iron have been carried out at 50°C with two polarized electrodes at 200 and 100 mV respectively. The results obtained are fairly accurate and precise within ±1.0 per cent. A simple method for successive determination of cerium and iron has been developed; and conditions for such estimations have been established. At an acidity of 2.5 M with respect to sulphuric acid, it is possible to ward off the reduction of ferric iron and thereby cerium(IV) is successfully titrated with ascorbic acid in this medium. After completion of the reaction and then lowering the acid concentration to p_H 1.5 with aid of ammonium hydroxide, Fe^III is titrated with standard ascorbic acid yielding good results.     

Iron adsorption on SiO2/Si(111)

The adsorption of ferric and ferrous iron onto the native oxide of the SiO₂/Si(111) surface has been evaluated using X‐ray photoelectron spectroscopy (XPS). Through a series of immersion experiments, performed at room temperature and pH 1, it has been shown that the ferric species is strongly adsorbed onto the hydrophilic surface, while ferrous iron remains in solution. Dehydroxylation of the silica surface by etching with hydrofluoric acid reduces the concentration of receptive Si‐OH groups, thereby limiting iron adsorption. The experiments were reproduced in a combined ultrahigh vacuum‐electrochemical system (UHV‐EC), which allowed a carbon‐free surface to be prepared before contacting the iron solutions, and confirmed the strong affinity of ferric iron towards the SiO₂/Si(111) surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Simultaneous voltammetric determination of uric acid and ascorbic acid using carbon paste/cobalt Schiff base composite electrode

Differential pulse and cyclic voltammetry were applied for the oxidation of mixture of uric acid and ascorbic acid at the surface of carbon paste/cobalt Schiff base composite electrode. The electrooxidation of these compounds at bare electrode is sluggish, and there is no suitable peak separation between them. However, using cobalt methyl salophen as modifier, two well-defined anodic waves with a considerable enhancement in the peak current and a remarkable peak potential separation near 315 mV are obtained. It can improve the kinetics of electron transfer for both compounds remarkably. All these improvements are created because of the electrocatalytic property of cobalt Schiff base complex. The effect of some parameters such as pH and scan rates were studied. All the anodic peak currents for the oxidation of ascorbic acid and uric acid shifted toward more negative potential with an increase in pH, revealing that protons have taken part in their electrode reaction processes. The best peak separation with appropriate current was obtained for pH 4.0. A linear range of 5.0?×?10^?4 to 1.0?×?10^?8 and 1.0?×?10^?3 to 1.0?×?10^?8 M with detection limit of 8.0?×?10^?9 and 8.0?×?10^?9 M was obtained for ascorbic acid and uric acid using differential pulse voltammetry at the surface of modified electrode, respectively. Analytical utility of the modified electrode has been examined successfully using human urine samples and vitamin C commercial tablets.     

Indirekte photometrische Bestimmung kleiner Jodmengen in Selen

After separation of selenium by precipitation with ferrous iron, the iodine is employed for catalyzing the Ce⁴⁺/As³⁺-redox reaction. This is stopped by ferrous iron and the ferric iron formed is determined by photometry as thiocyanate. This method enables the determination of about 100 ± 6 ng of iodine in 5–10 mg of selenium. The method was applied for determination of the distribution of iodine in Se-rectifier layers. The layers were dissolved by etching with a solution of alkali cyanide. The usual doping elements showed no disturbance.     

Structural and Spectroscopic Characterization of a High‐Spin {FeNO}6 Complex with an Iron(IV)−NO− Electronic Structure

Although the interaction of low‐spin ferric complexes with nitric oxide has been well studied, examples of stable high‐spin ferric nitrosyls (such as those that could be expected to form at typical non‐heme iron sites in biology) are extremely rare. Using the TMG₃tren co‐ligand, we have prepared a high‐spin ferric NO adduct ({FeNO}⁶ complex) via electrochemical or chemical oxidation of the corresponding high‐spin ferrous NO {FeNO}⁷ complex. The {FeNO}⁶ compound is characterized by UV/Visible and IR spectroelectrochemistry, Mössbauer and NMR spectroscopy, X‐ray crystallography, and DFT calculations. The data show that its electronic structure is best described as a high‐spin iron(IV) center bound to a triplet NO^? ligand with a very covalent iron?NO bond. This finding demonstrates that this high‐spin iron nitrosyl compound undergoes iron‐centered redox chemistry, leading to fundamentally different properties than corresponding low‐spin compounds, which undergo NO‐centered redox transformations.     

Catalytic effects of metal submonolayers formed by faradaic adsorption on the anodic oxidation of ascorbic acid at a platinum electrode

The catalytic effects of metal ions on the anodic oxidation of ascorbic acid on a Pt electrode in 1 M HClO₄ were studied by linear sweep voltammetry. The anodic peak due to a two-electron oxidation of ascorbic acid shifts to the negative potential side on the addition of Bi³⁺. This indicates the accelerating effect of Bi³⁺ on the oxidation of ascorbic acid. The presence of other metal ions, such as Pb²⁺, Hg²⁺, Tl⁺, Ag⁺ and Sb³⁺, also exerts similar effects. These metal ions were adsorbed on a Pt electrode at underpotentials and the adsorbed metals (denoted as M_ad) still remain on the electrode surface until the electrode potential goes up to and beyond the peak potential of the oxidation of ascorbic acid. On the other hand, metal ions forming no adsorbed layer on Pt, such as Co²⁺, Zn²⁺, Fe³⁺ and Ni²⁺, exhibit no catalytic effect. These facts suggest that the presence of a M_ad on Pt is essential for the promotion of the anodic oxidation of ascorbic acid. However, there is a difference in the catalytic action among the M_ad, for example, Cu_ad, Cd_ad, In_ad, Sn_ad and Mo_ad display no catalytic action.The catalytic activity depends on the degree of surface coverage by the M_ad. The maximal effect of the M_ad is attained in the submonolayer region. The effects of metal ions were discussed on the basis that the M_ad plays its major role in the removal of the adsorbed ascorbic acid occupying active sites on the electrode surface, and provides effective sites for the activation of adjacent water molecules. Furthermore, from the ¹³C NMR spectra for the oxidation products, the adsorbed water on the M_ad appears to function by promoting the subsequent hydration steps, following the electron-transfer step of ascorbic acid.     

Electrochemical Behavior and Detection of Dopamine and Ascorbic Acid at an Iron(II)tetrasulfophthalocyanine Modified Carbon Paste Microelectrode

In this article the electrocatalytic behavior of an iron(II)tetrasulfophthalocyanine modified carbon paste microelectrode for the oxidation of dopamine (DA) and ascorbic acid (AA) is described. Although the oxidation potential of ascorbic acid is shifted by over 100 mV to more positive potentials, no peak separation could be obtained. This can be explained by the immediate homogeneous reduction of the oxidation product of dopamine by ascorbic acid in solution. However, this reaction induces a shift of the half‐wave potential as a function of ratio of concentration of dopamine to ascorbic acid (c_DA/c_AA). Therefore it was possible to determine the c_AA and c_DA from this potential shift and the experimental peak current. Detection limits of 4.5±0.2×10^?7 and 7.5±0.5×10^?7 mol L^?1 were obtained respectively for dopamine and ascorbic acid for c_DA/c_AA>0.01.     

Increased rates of initiation of polymerization by 4-4′-dicyano-4-4′-azopentanoic acid in the presence of ferric salts

The initiation of the polymerization of acrylamide by 4-4′-dicyano-4-4′-azopentanoic acid in aqueous solution has been studied kinetically at 25°C. Ferric chloride and ferric sulfate were used to terminate polymerization so that rates of initiation could be calculated from the rates of production of ferrous iron. Velocity coefficients at 25°C. for the initiation reaction were found to be (25.7 ± 2.8) × 10^?7 sec.^?1 for the ferric chloride terminated reaction and (73.6 ± 0.6) × 10^?7 sec.^?1 for the ferric sulfate-terminated polymerization. The value reported for the initiation reaction when acrylamide is polymerized in the absence of metal salts is 1.29 × 10^?7 sec.^?1. Velocity coefficients for the termination reaction have been calculated from the overall rates of polymerization obtained with ferric salts present. In the case of the ferric chloride-terminated reaction, it has been shown that the rate of polymerization is reduced by increasing the total concentration of chloride ions. Termination velocity coefficients at 25°C. for the inner sphere complexes FeCl²⁺·5H₂O and FeSO₄⁺·4H₂O have been calculated to be 18.9 × 10⁴ and 7.98 × 10⁴ l./mole-sec., respectively. The dependence on the concentration of ferric chloride of the molecular weights of the polymers produced has also been considered.     

The preparation of the 239Np tracer from 243Am and the purification of the stock solution

The present work describes preparation of ²³⁹Np tracer from ²⁴³Am stock solution and the purification of this solution from ferric cation. The method of the preparation of tracer involves stabilization of Np(IV) by ascorbic acid and ferric nitrate, separation of ²³⁹Np from ²⁴³Am by extraction chromatography and determination of recoveries of ²³⁹Np by means of gamma spectroscopy. We used the commercially available sorbents TEVA^®Resin for the ²³⁹Np preparation and DGA Resin for ²⁴³Am purification. All sorbents were purchased from Eichrom Industries, Inc. The first eluate from the column can be stored for a future preparation of the tracer and fraction with ²³⁹Np will be used to monitor radiochemical yield of ²³⁷Np.     

Mercurous nitrate as a reductimetric reagent : The determination of copper

It has been found that in the presence of excess thiocyanate ions, cupric copper will oxidise ferrous ions. Use has been made of this reaction to determine copper by titration of the ferric iron produced, with mercurous nitrate. Although this reaction is the reverse of that usually observed, where the cuprous ion reduces the ferric iron, it has been found that the large excess of thiocyanate is responsible for this effect.     

A Fast Cation Exchange Separation of Iron(II) and Iron(III) on Zirconium(IV) Arsenophosphate Columns Using Potassium Thiocyanate as a Complexing Agent

Abstract

A new quantitative method has been developed for the separation of ferrous and ferric iron on zirconium(IV) arsenophosphate columns using the cation exchange properties of this material and the complex forming ability of potassium thiocyanate. The method is rapid and requires simply water as the eluant, the results obtained being precise and accurate within the experimental error range (±3%).     

Gas–liquid partition coefficients and Henry's law constants of methyl mercaptan in aqueous solutions of Fe(II)–CDTA chelate complex

Utilization of ferric chelate complex of trans-1,2-cyclohexanediaminetetraacetic acid (CDTA) for the oxidative scrubbing of H₂S and CH₃SH in Kraft mill streams can be beneficial from the standpoints of iron protection against precipitation and oxygen-mediated regenerative oxidation of the ferrous chelate CDTA. The physical solubility of methyl mercaptan in CDTA–Fe(III) complex cannot be measured directly because of oxidation of the sulfur-bearing gaseous species with the ferric chelate. Therefore, this investigation was carried out to determine the gas–liquid partition coefficients and Henry's law constants of methyl mercaptan in aqueous iron-free CDTA solutions and non-reacting ferrous chelate solutions (CDTA–Fe(II) complex), using the static headspace method with an estimated accuracy of about 2%. Experiments with aqueous solutions of chelate concentrations varying between 38 and 300 mol m⁻³ were carried out at temperatures between 298 and 333 K and atmospheric pressure. It was shown that the methyl mercaptan solubility decreases with increasing temperature for all systems but was not much influenced, in the studied conditions, by the chelate concentration especially at larger temperatures.