Solvent Extraction of Vanadium(V) as a Ternary Complex with N-Hydroxy-N-p-Chlorophenyl-N′-(2-Methyl-5-Chloro)-Phenyl-p-Toluamidine Hydrochloride and p-Chlorophenol

N-Hydroxy-N-p-chlorophenyl-N′-(2-methyl-5-chloro)-phenyl-p-toluamidine hydrochloride (HCPMCPTH) reacts with vanadium(V) to form a 1:2 (metal:reagent) blue-violet complex which can be quantitatively extracted into chloroform from acetic acid solutions. The deep blue adduct having 1:2:1 (V:HCPMCPTH:PCP) stoichiometry gets quantitatively extracted into chloroform from 0–2.5 M acetic acid media. The formation of the ternary complex has been made the basis for the development of a simple, rapid, sensitive and selective extractive-photometric method for the determination of microamounts of vanadium(V). The method has been applied to the determination of vanadium in steels.     

A Spectrophotometric Study of the Chelate of Iron (III) with Sorbohydroxamic Acid and Its Analytical Application

Iron (III) chelates of sorbohydroxamic acid have been studied spectrophotometrically in aqueous solution. Formation of sorbohydroxamic acid chelates was pH dependent. The “normalized absorbance” concept proposed by Likussar and Boltz has been utilized in the continuous variation plot method of determining the composition of metal chelates and the formation constants. The mole ratio of sorbohydroxamic acid to ferric ion was found to be 1 to 1 stoichiometry at pH lower than 2. The formation constant of this chelate has been evaluated to be 6.0×10¹¹ at a constant ionic strength of 0.1 M at 30°C A spectrophotometric determination of ferric ion with sorbohydroxamic acid was proposed in conjunction with the present work.     

Photometric determination of N-(p-nitrophenyl)maleimide

A procedure has been developed for the photometric determination of N-(p-nitrophenyl)maleimide based on the formation of a salt of the acinitro form of N-(p-nitrophenyl)maleic acid monoamide, which is formed on the hydrolysis of maleimide in concentrated acetic acid. Maleimide is dissolved in concentrated acetic acid, and the obtained solution is neutralized with an alkali. A bright yellow color of the reaction product appears.     

Zur Chemie der Bromisocyanursäuren: Eigenschaften und Reaktionen der Dibromisocyanursäure

Of the bromo derivatives of isocyanuric acid, unknown until 1967, dibromoisocyanuric acid (DBI) has proved to be a particularly powerful brominating agent, which can be easily handled in the laboratory.The chemistry ofDBI has been studied in depth by determination of the hydrolysis and dissociation constants, the redox potential in aqueous solution, and by investigation of its thermal behaviour, reaction with alkali ions (salt formation) and tertiary nitrogen compounds (formation of complexes). Its superiority as a brominating agent to other N-bromo compounds derives from the highly positive character of the bromine. The differences between the chloro-, bromo- and iodoisocyanuric acids are discussed, and related to the respective N-halogene and C–N bonding strengths.

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Spectrophotometric Determination of N-2-Pyridyl(maleic acid monoamide)

The behavior of N-2-pyridyl(maleic acid monoamide) in various hydrolyzing media has been studied. It is found that the substance is instantly hydrolyzed by 6 M CH₃COOH under normal conditions to form 2-aminopyridine. The molar absorptivity of the hydrolyzate is several times higher than that of N-2-pyridyl(maleic acid monoamide) in various media, which can be used for the sensitive determination of the substance. A procedure for the spectrophotometric determination of N-2-pyridyl(maleic acid monoamide) has been developed.     

Die Komplexbildungstendenz des dreiwertigen Antimons in wässeriger Lösung

The formation of the complexes of trivalent antimony ion with the following ligands has been investigated with pH measurements: D -tartaric acid, L -tartaric acid, catechol, catechol-3,5-disulfonic acid, 2,3-dihydroxybenzoic acid, mercaptoacetic acid, rac-thiomalic acid, meso-, rac-dithiotartaric acid, and mercapto-ethanol. Using the determined equilibrium constants, a classification of the ligands with respect to their ability to sequester the cation studied is given. In a discussion in which data of the literature are also included the structure of the tartar emetic, the possibility of a volumetric determination of the antimony, some problems concerning the coordination number, and the structure of the complexes are examined.     

Benzohydroxamic acid as a reductometric titrant determination of manganese in ores and alloys

Benzohydroxamic acid has been employed as a reductometric titrant for the determination of manganese in various ores and alloys. The determination is based on the fact that benzohydroxamic acid reduces Mn(VII) quantitatively to Mn(II) in 1.5N sulphuric acid.     

Spectrophotometric Determination of Palladium with Methylthymol Blue

A new, sensitive spectrophotometric method for the determination of palladium(II) with methylthymol blue has been developed. The palladium methylthymol blue complex has an absorption maximum at 530 nm. The colour reaction has a sensitivity of 0.005 µg of palladium/cm² and obeys Beer's Law over the range 0.4 to 3.24 ppm of palladium. The effects of concentration of perchloric acid, reagent, heating, stability of colour and diverse ions have been investigated. The ratio of metal: ligand in the complex is 1:1 and the formation constant was calculated to be 1.18×10⁴.     

Fluorimetric Determination of p -Hydroxybenzoic Acid in Beer as α -Cyclodextrin Inclusion Complex

Abstract

The inclusion complex of p-hydroxyenzoic acid and α- and β-cyclodextrin has been studied by fluorescence spectroscopy. To describe quantitatively complex formation between α-cyclodextrin (α-CD) and p-hydroxybenzoic acid, an association constant of 967 ± 14 M^?1 at 21°C was obtained. The inclusion complex has been used to determine p-hydroxybenzoic acid in the range 0.15–1.00 mg L^?1 (RSD 4.5%, n = 8). Application of the method to determination of p-hydroxybenzoic acid in beer samples gave an endogenous content of 1.25 mg L^?1.     

Synthesis of Nitrogen Doped Multilayered Graphene Flakes: Selective Non‐enzymatic Electrochemical Determination of Dopamine and Uric Acid in presence of Ascorbic Acid.

Nitrogen doped multilayered graphene (NDMLG) is synthesized by annealing the black fluffy mass obtained by decomposing the complex prepared from Zn(OAc)₂, diethanolamine and triethanolamine. The NDMLG has been characterized by HRTEM, FESEM, XRD, XPS, Raman spectroscopy, BET which indicate formation of nitrogen doped multilayer graphene flakes with high surface area. NDMLG shows better electrochemical oxidation property towards Dopamine, Uric acid and Ascorbic acid. The linear response ranges for determination of DA, UA and AA are 0.5–150 µM, 3–60 µM and 80–2000 µM respectively and the detection limits (S/N=3) are 15 nM, 15 nM, 580 nM, respectively in the mixture.     

Sensitive, selective spectrophotometric determination of phenols with periodic acid

A new spectrophotometric determination of phenols with periodic acid has been developed. The colored product of phenol periodic acid reaction has a λ_max 380 nm. The determination of phenol, pyrocatechol, α-naphthol, β-naphthol, quinol, p-cresol, m-cresol, 8-quinolinol, resorcinol, phloroglucinol, and gallic acid has been done. The effects of possible variables e.g., temperature, reagent, pH buffers have been studied. A study of interferences is made. Mechanism of the reaction is discussed.     

Spectrophotometric determination of bismuth with diethylenetriaminepenta-acetic acid

Diethylenetriaminepenta-acetic acid is used for spectrophotometric determination of bismuth (at 270 nm) in 1.6 M perchloric acid. The system obeys Beer's law in the range 1–40 μg/ml. The method has been tested for the determination of bismuth in pure lead and polymetallic ores.     

Analytical Characterization of Fatty Acids Composition of Bioactive Stem Oil of Maytenus royleanus by Gas Chromatography Mass Spectrometry

The significant inhibition and selectivity for human solid tumor cell by oily fraction of Maytenus royleanus, was subjected to GC‐MS analysis for determination of its chemical constituents. GC‐MS profile of methyl ester derivatives of fatty acids, showed that Palmitic acid (35.41%), Oleic acid (10.91%), Stearic acid (5.31%), Margaric acid (5.13%), Behenic acid (5.18%) and Hexanoic acid (4.97%) were the major components in the isolated oily fraction, while rest of the other fatty acids were present in minor concentration. The literature revealed that no such work has been done for the determination of fatty acids in M. royleanus stem oil.     

Capillary electrophoretic separation of mono- and dimaltosyl-β-cyclodextrins and determination of the stability constants of their benzoate complexes

Summary Capillary zone electrophoresis method has been developed for the separation (and determination) of monoand dimaltosyl-β-cyclodextrins using indirect UV absorbance detection. The separation is based on inclusion complex formation with benzoate ion which is used as background electrolyte and absorbance provider simultaneously. Good resolution of cyclodextrin mixtures can be achieved optimizing the pH and the benzoic acid concentration in the background electrolyte. Capillary zone electrophoresis method has also been developed for the determination of formation constants of inclusion complexes.     

Spectrophotometry Studies of Uranyl Chelate of 7-Iodo-8-Hydroxyquinoline-5-Sulphonic Acid

Uranyl chelate of 7-iodo-8-hydroxyquinoline-5-sulphonic acid (ferron) has been studied spectrophotometrically in aqueous solution at 25° and at an ionic strength of 0.1 M. The formation of this chelate was pH dependent, and the optimum pH range was between 5.4 to 5.9, Its mole ratio of ligand to uranyl ion was found to be 2 to 1 stoichiometry and the stability constant, log K, was determined as 13.32±0.08. By using the wave-length of 365 mu, determination of trace amount of uranyl ion with the sensitivity of 0.54 γ/cm² was possible.     

Spectrophotometric determination of cobalt(II) with 2-(3′-sulfobenzoyl)pyridine benzoylhydrazone

A simple method has been described for the Spectrophotometric determination of cobalt(II) with 2-(3′-sulfobenzoyl)pyridine benzoylhydrazone (SBPBH). In aqueous solution, cobalt(II) reacts with SBPBH to form a yellow complex, which is not destroyed even by the addition of 3.8 M perchloric acid. The absorption maximum of the complex in 1.5 M perchloric acid medium was found to be 400 nm; the molar absorptivity was 2.17 × 10⁴ liters mol⁻¹ cm⁻¹. The proposed method is fairly selective and has been applied to the determination of cobalt in standard alloy steel samples.     

Spectrophotometric Determination of Carbon Disulfide Using Bis(4-(4′-Nitrophenyl)azo-2-Nitrophenyl) Disulfide

Bis(4-(4-nitrophenyl)azo-2-nitrophenyl) disulfide (NADS) has been synthesized for the first time and proposed for the indirect photometric determination of carbon disulfide by dithiocarbamic acid. The reaction, which involves the breaking of the disulfide bond with the formation of colored azothio anions, is carried out in a mixture of dimethylsulfoxide and n-butanol. The high value of the apparent molar absorptivity (2 × 10⁵) is probably due to the autocatalytic character of the reaction. Using NADS, procedures for the determination of carbon disulfide in the atmospheric air of populated areas and in the model gas mixtures designed for the calibration of gas analyzers have been developed and certified. The procedures show high sensitivity and good reproducibility.     

Self‐Assembled Monolayer of L‐Cysteine on a Gold Electrode as a Support for Fatty Acid. Application to the Electroanalytical Determination of Unsaturated Fatty Acid

This article describes the formation of a SAM with chemisorbed cysteine to a gold surface by the thiol group to obtain a surface electrode with an amino and an acid group free for later reaction and accumulation with other molecules on the electrode surface. We explore the accumulation of unsaturated fatty acid and the electrochemical response of the electrode after modification with cysteine. The electrochemical study confirmed the accumulation of linoleic acid on the modified electrode. The optimum conditions for the determination of linoleic acid by differential pulse voltammetry of linoleic acid are studied a detection limit (3σ) of 0.03 μg mL^?1 and a determination limit (10σ) of 0.10 μg mL^?1 were obtained and applied to determination in olive oil and ham from Iberian breed hams.     

Vinyl polymerization initiated by chromic acid–reducing agent systems

A kinetic study of the thermal polymerization of acrylonitrile initiated by chromic acid–reducing agent (n-butanol, ethylene glycol, cyclohexanone, and acetaldehyde) systems was made. Chromic acid alone did not initiate polymerization under deaerated or undeaerated conditions. On the basis of the experimental determination of the dependencies of various variables on the rate of polymerization R_p, the rate of chromium (VI) disappearance ?R_M, the degree of polymerization DP, etc., a reasonable kinetic scheme was arrived at. The mechanism with the reducing agents, n-butanol, cyclohexanone, and ethylene glycol, was found to be similar but different from that with acetaldehyde. Evidence has been presented to prove the formation of radical intermediates formed by the oxidation of the reducing agent by Cr(IV). Rate parameters for oxidation of the reducing agent and polymerization of the monomer were evaluated.     

Optosensing of hydrochloric acid based on the fluorescence quenching of a flavone copolymer

An optical fiber sensor for the continuous determination of hydrochloric acid is presented. It is based on the fluorescence quenching of a flavone containing copolymer membrane by hydrochloric acid. The quenching efficiency is greatly enhanced in the presence of Fe(III). This enhancement is attributed to the primary inner filter effect, as well as the formation of a complex between the 4′-N,N-dimethylaminoflavone group in the copolymer and the Fe(III) species extracted from hydrochloric acid solution. The optical response is linear and reversible for 0.10–6.00 mol L^–1 HCl with a response time of the order of a second. The standard deviations for repeated alternative measurements of 0.20 and 2.00 mol L^–1 hydrochloric acid are 0.32% and 0.46% (n = 10), respectively, indicating a good reproducibility. Because of the covalently bonding of the dye to polymer, the sensor exhibits also a good stability. Selectivity has also been evaluated for some potential interferents. The sensor in conjunction with a flow-injection system can be used for on-line determination of hydrochloric acid. Received: 15 January 1998 / Revised: 14 April 1998 / Accepted: 18 April 1998