The use of 2,6-dichlorophenolindophenol as indicator in acid-base titrations

2,6-Dichlorophenolindophenol shows acid-base indicator properties. Its colour is red in acidicmedia and blue in alkaline media. 'Ihe transitional pH value is 5.7 and the colour change is sharp and easy to observe. The use of the indicator in various acid-base titrations, as well as the effects of neutral salts, alcohol and temperatures, were checked. The absorption spectra of the acidic and basic forms of the indicator are presented.     

Diphenylcarbazone as an internal indicator in mercurimetric analysis: The determination of cerium by potassium thiocyanate

Summary The quantitative oxidation of thiocyanate by ceric sulphate has been studied and the method utilised for the determination of small quantities of cerium by back titrating the excess (unreacted) KSCN against standard mercuric nitrate with diphenylcarbazone as the internal indicator. Accurate results are obtained under the specified experimental conditions and the procedure is more simple and direct than that adopted during earlier studies of the above redox reaction.Grateful thanks of the author are due to Professor S. S. Joshi for facilities during the work and to the National Institute of Sciences of India for award of a Research Fellowship.     

The use of the molybdenum electrode as indicator for hydrogen ions

The molybdenum clectiode is found to act as a suitable means for the determination of the hydrogen ion concent-ration. Polished electrodes in aerated solutions give potentials which do not vary appreciably with time. The potential measured in solutions of different H⁺-ion activity is a function of pH from 2–11. pKa values determined from neutralization curves of some acids are not much different from those obtained by other authors, using different methods. Polished or aged electrodes in aerated or oxygen-free solutions could be used satisfactorily for determining tlie end-points in neutralization reactions.     

The use of a polymer inclusion membrane in flow injection analysis for the on-line separation and determination of zinc

This paper reports the first use of a polymer inclusion membrane (PIM) for on-line separation in flow injection analysis (FIA) involving simultaneous extraction and back-extraction. The FIA system containing the PIM separation module was used for the determination of Zn(II) in aqueous samples in the presence of Mg(II), Ca(II), Cd(II), Co(II), Ni(II), Cu(II), and Fe(III). The Fe(III) and Cu(II) interferences were eliminated by off-line precipitation with phosphate and on-line complexation with chloride, respectively. The concentration of Zn(II) was determined spectrophotometrically using 4-(2-pyridylazo) resorcinol (PAR). The optimal composition of the PIM consisted of 40% (m/m) di(2-ethlyhexyl) phosphoric acid (D2EHPA) as carrier, 10% (m/m) dioctyl phthalate (DOP) as plasticizer and 50% (m/m) poly(vinyl chloride) (PVC) as the base polymer. The optimized FIA system was characterized by a linear calibration curve in the range from 1.0 to 30.0 mg L⁻¹ Zn(II), a detection limit of 0.05 mg L⁻¹ and a relative standard deviation of 3.4% with a sampling rate of 4 h⁻¹. Reproducible results were obtained for 20 replicate injections over a 5 h period which demonstrated a good membrane stability. The FIA system was applied to the determination of Zn(II) in pharmaceuticals and samples from the galvanizing industry and very good agreement with atomic absorption spectrometry was obtained.     

The tiron radical as indicator substance in catalytic determination of trace metals

The tiron-hydrogen peroxide reaction used for catalytic determination of trace metals is studied with respect to the indicator substance-the oxidation product of tiron absorbing at 44Onm. Contrary to assumptions in the literature, it is shown by electrochemical techniqus EPR spectroscopy and visible spectrophotometry that the indicator substance is not the o-quinone derivative of tiron (lambda(max) = 372 nm) but the tiron semiquinone radical with a g-value of g(o) = 2.0049 and molar absorptivity = (3.5 +/- 0.5) x 10(3) 1.mole(-1).cm(-1) at 440 nm.     

The use of vanadium-sulphosalicylic acid complex as a redox indicator

In a previous communication it was reported that vanadium^V gives an intense turquoise-blue colour with sulphosalicylic acid in concentrated sulphuric acid and that the colour reaction is specific and very sensitive for the detection of vanadium^V. During our studies on the nature of the complex, it was found that vanadium^IV gives a negative colour test and that the blue colour developed by the reagent with vanadium^V is discharged on the addition of a reducing agent like iron^II, uranium^IV or hydroquinone. It was also observed that the blue colour is restored by the addition cerium^IV solution. This reversible property of the complex has been further investigated to see if the complex can be used as a redox indicator.     

Radiometric determination of anionic surfactants by two-phase titration method with the use of131I-Rose Bengal as indicator

The paper describes a radiometric variant of the two-phase titration method for the determination of anionic surfactants of nonsoapy type. The method is based on the titration of an anionic surfactant with Septonex in alkaline medium in the presence of¹³¹I-Rose Bengal /abbreviated¹³¹I-RB/. The ion associates are extracted into chloroform. The equivalence point is determined graphically from the activity of¹³¹I-RB-Septonex associate, which is formed after the consumption of the anionic surfactant and which passes into the organic phase. The influence of¹³¹I-RB amount, pH of the titrated medium and of soap presence on the precision of anionic surfactants determination was studied. The detection limit is 2.88 g sodium n-dodecylsulphate in 10 ml of sample.     

The use of Metomega Chrome Blue BBL as a metal indicator and its application for the determination of calcium and magnesium in serum

Summary Metomega Chrome Blue BBL was used as a metal indicator for the detection and titration of calcium, magnesium, manganese, nickel and manganese. A displacement reaction was described for the titration of cadmium using Mn-EDTA. A stepwise titration was conducted for the direct titration of both calcium and magnesium in blood serum.Fenugreek mucilage was used as a media for increasing the sensitivity limits of detection of barium, cadmium, cerous, calcium, copper, cobalt, magnesium, manganese, nickel, lead and zinc.     

The use of 2,6-dichlorophenol-indophenol as indicator in iodometric titrations with ascorbic acid

2,6-Dichlorophenol-indophenol can be used as an indicator in iodometric methods, provided that near the end-point the solutions can be buffered with potassium hydrogen carbonate, so that ascorbic acid can be used as the titrant. Procedures for the determination of iodine, chlorine, bromine, hypochlorite, Chloramine T, bromate, iodate, permanganate, dichromate, copper(II), hydrogen peroxide, peroxydisulphate, thiosulphate, sulphite, sulphide, hydrazine and formaldehyde are described.     

N-Aryl-3-Aminopropionic acids as selective reagents for the determination of copper in metallurgical products

Analytical characteristics of N,N-di(2-carboxyethyl)aniline (I), N,N-di(2-carboxyethyl)-3,4-xylidine (II), N-(2-carboxyethyl)anthranilic acid (III), N,N-di(2-carboxyethyl)-4,5-dimethylaminoazobenzene-4-sulfonic acid (IV), and N-(2-carbamoylethyl)anthranilic acid (V) were studied. The factors affecting the selectivity of I–V for Cu(II) ions (basicity of the amino group, nature and positions of substituents in the benzene ring, and geometry of chelate cycles) were analyzed. The optimum conditions were found and procedures were developed for the spectro-photometric determination of copper in metallurgical products. The high selectivity of I–V for Cu(II) ions allows the determination without preliminary separation of concomitant components in aqueous solutions without organic solvents. Compound II exhibits the best analytical characteristics: the analytical range of copper 3–20 mg/L, detection limit 0.7 mg/L, ( = 252 nm) = 3290 L mol^–1 cm^–1, and pH 6.0 (ammonia-acetate buffer solution).Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 271–277.Original Russian Text Copyright © 2005 by Neudachina, Osintseva, Skorik, Vshivkov.     

The titrimetric micro determination of sulphate using lead nitrate as titrant and dithizone as indicator

Summary The previously reported titrimetric determination of sulphate, using lead nitrate as titrant and dithizone as indicator has been developed for application to the micro scale. Attention has been directed in the titration procedure to the effect of foreign ions and their removal where necessary, the optimum conditions for the highest accuracy, and the precision attainable for the range 0.5 to 5 mg of sulphate (0.16 to 1.6 mg of sulphur). This procedure forms a highly satisf actor y basis for the micro determination of sulphur in organic compounds by oxidation with nitric acid in a sealed tube and subsequent titration of the sulphate ion produced.The procedure has also been extended to the submicro scale giving a direct titration of 10 to 100g of sulphate (4–30g of sulphur), thus enabling the sulphur content of submicro quantities of organic compounds to be readily determined.

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Zusammenfassung Die kürzlich veröffentlichte Methode der maßanalytischen Schwefelbestimmung mit Bleinitrat unter Verwendung von Dithizon als Indikator wurde dem Mikromaßstab angepaßt. Auf die Störung durch Fremdionen und deren gegebenenfalls notwendige Entfernung wurde Bedacht genommen, die optimalen Bedingungen für größte Genauigkeit für den Bereich von 0,5 bis 5 mg Sulfat (0,16 bis 1,6 mg Schwefel) ermittelt. Das Verfahren bietet einen sehr befriedigenden Weg für die Mikrobestimmung des Schwefels in organischen Substanzen durch deren Oxydation mit Salpetersäure im geschlossenen Rohr und nachfolgende Titration des Sulfats.

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Rèsumè La méthode précédemment décrite pour le dosage titrimétrique des sulfates à l'aide de nitrate de plomb comme réactif titrant et de dithizone comme indicateur a été étendue au domaine microanalytique. La technique de titrage a été particulièrement étudiée des points de vue de l'effet des ions étrangers et de l'éventuelle nécessité de leur élimination, des conditions optimum pour atteindre l'exactitude la plus élevée et pour déterminer la précision qu'il était possible d'obtenir pour le domaine de 0,5 à 5,0 mg de sulfate (0,16 à 1,6 mg de soufre). Cette technique est extrêmement satisfaisante pour son application au microdosage du soufre dans les composés organiques après oxydation par l'acide nitrique en tube scellé et titrage ultérieur de l'ion sulfurique formé.

     

Titrimetric determination of organofluorine using Arsenazo I as indicator

Summary Some improvements of the titrimetrio method for determining fluorine in organic compounds are described. The modifications involve:(a) introduction of a combustion aid for the electrically heated flask combustion to insure complete conversion of fluorine to hydrogen fluoride, (b) employment of a glycine-perchlorate buffer to maintain a consistent stoichiometric titration, and (c) adaptation of an automatic titrimeter for photometric titration to simplify the detection of the end point. It is also suggested that a linear equation be derived from the calibration data in order to calculate the fluorine content.

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Zusammenfassung Einige Verbesserungen der maßanalytischen Bestimmungsmethode für Fluor in organischen Substanzen wurden beschrieben, nämlich: a) Einführung eines Zusatzreagens zur Erzielung einer vollständigen Überführung in Fluorwasserstoff bei der elektrischen Verbrennung im verschlossenen Kolben; b) Verwendung einer Pufferlösung von Glycin und Perchlorat zur Gewährleistung einer stöchiometrischen Titration; c) Anpassung eines automatischen Titriergerätes für photometrische Titrationen zwecks besserer Wahrnehmung des Endpunktes. Außerdem wird empfohlen, zur Berechnung des Fluorgehaltes eine lineare Gleichung zu verwenden.

     

Complexometric determination of gallium with calcein blue as indicator

A metalfluorechromic indicator, Calcein Blue, has been used for the back-titration of milligram amounts of EDTA in presence of gallium complexes. The indicator was used in conjunction with an ultraviolet titration assembly equipped with a cadmium sulphide detector cell and a microammeter for enhanced end-point detection. The result is a convenient and rapid method with an accuracy approaching 0.1% and a relative standard deviation of about 0.4% for 10 mg of gallium.     

The use of cacotheline as an oxidation-reduction indicator before the volumetric oxidation of iron

Caotheline may be used as an oxidation-ieduction indicator in the removal of stannous tin with cerio sulfate befor the titration of ferrous non     

Mineralization procedure for use with the fluorometric determination of zinc in biological samples

Several minerelization procedures have been evaluated for use in conjunction with a method to determine zinc in milk, eggs, water and whole diets, based on the formation and extraction into diethyl ether, of Zn-5,7-dibromo-8-quinolinol. The results were compared with the known contents of standard samples or those obtained by flame atomic-absorption spectrometry. The most satisfactory procedure employed digestion with acid mixtures to destroy organic matter, and yielded a detection limit of 0.3 mg/kg for Zn.