N-substituted phenothiazines as indicators in titrations with chloramine-T

Trifluoperazine dihydrochloride, butaperazine dimaleate, promethazine hydrochloride, diethazine hydrochloride, prochlorperazine maleate and chlorpromazine hydrochloride have been studied as redox indicators in titrations of hydroquinone, metol and ascorbic acid with chloramine-T. The end-points obtained are sharper than with conventional indicators. The molar absorptivities of the oxidized indicators are reported. Simple but accurate methods for the determination of hydroquinone and metol are described.     

N-substituted phenothiazines as redox indicators in titrations with chloramine-T and chloramine-B

Profenamine hydrochloride, fluphenazine dihydrochloride, trifluopromazine hydrochloride, cyamepromazine maleate, perphenazine dihydrochloride and mepazine hydrochloride are proposed as redox indicators in the titration of hydroquinone, metol and ascorbic acid with chloramine-T and chloramine-B in sulphuric, hydrochloric and acetic acid media. They give a sharp reversible colour change at the equivalence point. A simple but accurate method for the determination of hydroquinone, metol and ascorbic acid is described. The conditional potentials and molar absorptivities of the indicators and redox potential of chloramine-B are reported.     

Redox indicators in titrations with chloramine-T

Naphthidine, 3,3'-dimethylnaphthidine disulphonic acid, o-dianisidine, di-phenylbenzidine, quinoline yellow, amaranth, methyl red, methyl orange, rhodamine-B and erioglaucine-A are examined as indicators in macro-and micro-titrations of arsenic(III), antimony(III), ascorbic acid, hydroquinone, metol, hydrazinium sulphate, isonicotinic acid hydrazide, semicarbazide hydrochloride and phenylhydrazine hydrochloride with chloramine-T. The indicators give sharp colour changes under optimal conditions. Transition potentials are reported.     

Potentiometric and visual titrations with bromamine-B

Bromamine-B is proposed as an oxidimetric titrant for potentiometric and visual end-point titrations of arsenic(II), hexacyanoferrate(II), antimony(III), hydroquinone, semicarbazide hydrochloride, isonicotinic acid hydrazide, hydrazine sulphate, ascorbic acid, phenylhydrazine hydrochloride and metol. Quinoline Yellow, naphthidine, dimethylnaphthidinedisulphonic acid, o-dianisidine, diphenylbenzidine, Variamine Blue, alpha-naphthoflavone, Amaranth, Methyl Orange and Methyl Red are proposed as indicators in macro and micro titrations of the reductants with bromamine-B. The transition potentials of Quinoline Yellow, naphthidine, dimethylnaphthidinedisulphonic acid, and o-dianisidine in the titration of ascorbic acid are reported. Arsenic(III) and hexacyanoferrate(II) are suggested for the standardization of bromamine-B solutions.     

Complex kinetics and significant influences of bromine removal in ferroin-bromate-metol reaction

This study presents a new bromate-based chemical oscillator that employs metol as the organic substrate. Complex reaction behaviors were observed when the system was subjected to bromine removal and oxygen exposure. Transitions from simple to sequential oscillations took place as a function of the age of the metol stock solution. MS spectroscopy measurements and parallel kinetic experiments with a mixture of metol and hydroquinone suggest that the decomposition of metol to hydroquinone was responsible for the observed influence of oxygen and the age of the metol solution. GS/MS and NMR measurements revealed that 1,4-benzoquinone and bromobenzoquinones were the major final products, regardless of the presence of oxygen and bromine removal. Preliminary exploration in a capillary tube showed some interesting propagating pulse behavior.     

石墨烯修饰玻碳电极在对苯二酚存在下选择性测定米吐尔

制备了石墨烯修饰玻碳电极(GN/GCE)。 在0.5 mol/L HAc-NaAc(pH=4.8)缓冲溶液中,用循环伏安法(CV)和方波伏安法(SWV)研究了米吐尔在修饰电极上的电化学行为,建立了测定米吐尔的新方法。 研究表明,米吐尔在GN/GCE上的氧化、还原峰电势差比其在裸玻碳电极(GCE)上的小,峰电流显著增加,说明GN/GCE对米吐尔有电催化作用;共存物对苯二酚干扰米吐尔的测定,通过方波伏安法可以消除其干扰。 在方波伏安曲线上,米吐尔的还原峰电流与其浓度在8.0×10^-8~5.0×10^-5 mol/L范围内呈线性关系,检出限为2.0×10^-8 mol/L。 该法可用于照相显影废液中米吐尔的测定。     

2-巯基苯并噻唑自组装膜电极同时测定米吐尔和对苯二酚

在环境污染物中酚类物质由于其难降解和有毒性而引起人们普遍的关注。测定米吐尔和对苯二酚的常用方法有光度法、铈量法和电化学法。但在电化学法测定中较低倍含量的米吐尔会对对苯二酚的测定带来影响,所以同时准确测定较难。本文利用2-巯基苯并噻唑自组装电极对米吐尔和对苯二酚进行同时测定。应用于显影废水测定结果满意,方法简便快速,有实际应用前景。     

Spectrophotometric methods for the determination of prazosin hydrochloride in tablets

Four simple and sensitive methods for the assay of prazosin hydrochloride (PRH) are developed. These methods are based on the formation of coloured species by treating it either with excess N-bromosuccinimide (NBS) and determining the unconsumed NBS with p-N-methyl aminophenol sulphate (metol)-sulphanilamide (SA) reagent (method A, lambda(max) 520 nm): with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) in the presence of eerie ammonium sulphate (CAS) (method B, lambda(max) 620 nm) or with acidic dyes such as orange-II (O-II) (method C, lambda(max) 490 nm) and alizarin violet 3B (AV-3B) (method D, lambda(max) 570 nm) under the specified experimental conditions. Regression analysis of Beer's law plot showed good correlation in the concentration range of 1.0-10.0, 2.5-25.0, 1.0-17.5 and 2.5-30.0 mug ml for methods A, B, C and D respectively.     

Electrochemical behavior and voltammetric determination of metol using a multiwall carbon nanotubes modified electrode

Electrochemical behavior of metol, which coexists with p-benzeneiol (HQ) at a glassy-carbon electrode modified with multiwall carbon nanotubes (MWNT/GCE), is studied in the thesis. The results indicate that metol yields a well-defined peak of which two concomitant reductive peaks separate and the potential separation reaches to 178 mV, and that concomitant HQ has almost no interference with the reduction signal of metol. The values of the reductive peak current (I _pc) are found to be linearly related to metol concentration over the range of 8.0 × 10⁻² −1.0 × 10⁻⁵ M, with a detection limit of 5.0 × 10⁻⁶ M. Some common matter has no interference with the determination of metol. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 1, pp. 31–35. The text was submitted by the authors in English.     

Reduction of metol on mechanically renewed metal electrodes

The electroreduction of metol on mechanically renewed metallic electrodes is studied by direct voltammetry with linear potential sweep. Reduction peaks of metol are found in a neutral supporting electrolyte (0.02–0.5 M Na₂SO₄) on nickel, silver, and mercury electrodes before the potential of hydrogen liberation from the supporting electrolyte. The shape and parameters of the cathodic peak depend on an electrode material, and also on the composition and pH of the supporting solution. A probable mechanism of the electroreduction of metol is proposed. The regeneration of nickel and silver electrodes by in situ mechanical cutting of a 0.5-μm surface layer provides good reproducibility of the value of peak current; it is proportional to the concentration of metol in the range 2 × 10⁻³–1.8 × 10⁻² M.     

Spectrophotometric Estimation of Nimesulide and its Formulations

 Four simple and sensitive visible spectrophotometric methods (A–D) have been described for the assay of nimesulide (NMD) either in pure form or in pharmaceutical formulations. Methods A and B are based on the oxidative coupling between the reduced product of NMD (RNMD) and p-N,N-dimethyl phenylenediamine dihydrochloride (DMPD) in presence of chloramine – T (CAT) or 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) in presence of ferric chloride (Fe III) to form coloured products with λ_max at 540 nm and 600 nm respectively. Method C is based on the diazotization of RNMD with excess nitrous acid (HNO₂) and estimating the consumed HNO₂ with cresyl fast violet acetate (CFVA). Method D is based on the formation of the coloured charge-transfer complex, when RNMD is treated with metol (p-methyl aminophenol sulphate, PMAP) in presence of potassium dichromate. All variables have been optimized and the reaction sequence is presented. The concentration measurements are reproducible within a relative standard deviation of 1.0%. Recoveries are 98.6–100.2%. Received February 5, 1998. Revision February 20, 1999.     

Voltammetric Determination of Metol on a Gold Nanoparticle Modified Carbon Molecular Wire Electrode

A carbon molecular wire electrode was fabricated using diphenylacetylene as the modifier and gold nanoparticles were electrodeposited on the surface. The morphology and electrochemical properties of this modified electrode were investigated by scanning electron microscopy and electrochemical impedance spectroscopy. Two well-defined peaks for metol appeared using this gold nanoparticle-modified carbon molecular wire electrode by cyclic voltammetry with a high current response. These results demonstrate a synergistic effect between the gold nanoparticles and the carbon molecular wire electrode resulting in a rapid electrochemical reaction. The electrochemical conditions for metol were optimized on the modified electrode and a detection limit of 0.64?µmol/L and a linear dynamic range between 2.0 to 800.0?µmol/L were obtained. This modified electrode provided good selectivity, high sensitivity, and acceptable reproducibility, demonstrating promise for the determination of metol in the water.     

Correlation of the electrochemical reversibility and resolution of the anode and cathode peaks of the electrode processes of hydroquinone and metol on graphite and platinum

Cyclic and direct voltammetry with linear potential sweep was used to study the potential difference of the anode and cathode peaks for hydroquinone and metol in the cyclic voltammograms (CVA) of their individual solutions on the main factors affecting the reversibility of the electrochemical process on electrodes of a graphite-epoxy composite (GEC), namely, the state of the surface of the indicator electrode, the pH of the buffer solution, and the mode of polarization. The surface state of the GEC electrode was affected by its passivation in air for various periods of time; the reversibility of the electrode process was judged by the difference between the anode and cathode potentials on the CVAs of hydroquinone and metol. A correlation was found between the degree of reversibility and the difference of peak potentials for similar electrode processes of hydroquinone and metol on the GEC electrode and other solid electrodes made of graphite materials and platinum.     

Spectrophotometric determination of some phenols using m-Phenylenediamine and sodium metaperiodate

Summary A new spectrophotometric method for the assay of catechol, guaiacol,o-aminophenol,p-aminophenol and metol using them-phenylenediamine —IO₄-reagent has been developed. The method is simple and accurate within ±1.0%. It has been applied to the estimations of paracetamol through its hydrolysed product and metol in photographic developers.

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Spektrophotometrische Bestimmung einiger Phenole mit m-Phenylendiamin und Natrium-Metaperjodat

Zusammenfassung Ein neues spcktrophotometrisches Verfahren zur Bestimmung von Brenzcatechin, Guajakol,o-Aminophenol und Metol mit Hilfe vonm-Phenylendiamin und Perjodat wurde ausgearbeitet. Es ist einfach und innerhalb ±1,0% genau und wurde zur Bestimmung von Paracetamol über sein Hydrolyseprodukt und Metol in photographischen Entwicklern verwendet.

     

The mechanism of chain growth in oxidative polycondensation of phenols

A new mechanism of chain extension in oxidative polycondensation of phenols has been proposed. Between the two accepted mechanisms: quinol ether redistribution and quinol ether rearrangement, the second mechanism seems to be the most important for the chain growth. The first mechanism, quinol ether redistribution, preserves the system average degree of polymerization and assures a permanent equilibration of the polymeric chains, but has only a minor contribution to the molecular weight increase. The second mechanism, quinol ether rearrangement, proved to be the most important for chain extension and was interpreted as a repeated Claisen rearrangement (a particular case of a sigmatropic rearrangement), characteristic to allyl ethers of phenols. Experimental data proved that the above mentioned mechanisms probably take place simultaneously and the real growth of the molecular weight is a result of the cumulative contributions of both mechanisms.     

Indirect spectrophotometric methods for the determination of antibiotics with iodine or periodate, and metol and sulphanilamide

Two spectrophotometric methods are described for the determination of antibiotics. In the first method, penicillins, cephalosporins, streptomycin and griseofulvin are estimated by oxidizing them under neutral or slightly acidic conditions, after alkaline hydrolysis, by means of a known and excessive quantity of iodine solution. The excess of iodine is determined at pH 3.0 with metol and sulphanilamide. In the second method, dihydrostreptomycin, framycetin and the acid hydrolysis product of chloramphenicol are determined by a method involving oxidation with sodium metaperiodate, masking the excess of periodate with sodium molybdate, and using metol and sulphanilamide at pH 3.0 to determine the iodate formed. In both methods the absorbance of the resulting p-N-methylbenzoquinonemonoimine sulphanilamide charge-transfer complex is measured at 520 nm.     

Phthalocyanines as oxidation-reduction indicators

Summary Copper phthalocyanine tetrasulphonic acid has been found to work satisfactorily as an inside indicator in the cerimetric titration of hydro-quinone and metol. It has the advantage that the indicator correction in titrations with 0.01 N solutions of ceric sulphate is much less than with the ferroin indicator, amounting to only 0.02 ml for two drops of the indicator solution.Part II: See Z. analyt. Chem. 163, 1 (1958).     

Effect of stabilizers on the tolerance of copper nanopowders for oxidation by molecular oxygen

The effect of various stabilizers, phenol, 1-naphthol, hydroquinone, hydroxylamine sulfate, metol, guanidine, and dimethylphenylbenzylammonium chloride, on the rate of oxidation of copper nanopowders by molecular oxygen was studied.     

Chromatographic behaviour of closely related aromatic amines on phenol-impregnated thin-layers

Summary The TLC behaviour of closely related aromatic amines on silica gel plates impregnated with phenol, o-cresol, p-nitrophenol, quinol, catechol and pyrogallol has been studied. An attempt has been made to correlate the chromatographic behaviour of amines with the equilibrium constants of the adducts formed by the interaction of amines with absorbed phenol. Suitable adsorbent system and solvent systems for an efficient separation of closely related isomers of this class of compound of physiological importance have been developed.     

Determination of quinol in volumetric analysis

Summary A short review is given of the literature concerning volumetric determination of quinol. Comparison of various titration procedures and their possible application shows that the cerimetric determination must be preferred for the standardization of pure quinol solutions; when determining the amount of quinol in mixtures, however, one must usually be content with a titration procedure using dichromate, vanadate, ferricyanide and zinc or bromate-bromide, which each have their special applications. In these cases it is recommended to compare the results of the method chosen with the results of a cerimetric determination using a pure quinol solution.

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Zusammenfassung Es wird ein kurzer Überblick über die Möglichkeiten zur volumetrischen Hydrochinonbestimmung gegeben. Ein Vergleich verschiedener Verfahren zeigt, daß zur Titerstellung reiner Hydrochinonlösungen die Cerimetrie am besten geeignet ist. Zur Hydrochinonbestimmung in Mischungen muß jedoch eine Titration mit Dichromat, Vanadat, Hexacyanoferrat(III) und Zink oder Bromat-Bromid verwendet werden, von denen jede ihre besondere Anwendungsmöglichkeiten besitzt. In diesen Fällen ist es empfehlenswert, die erhaltenen Werte mit denen einer cerimetrischen Bestimmung an einer reinen Hydrochinonlösung zu vergleichen.