Extractive spectrophotometric determination of tungsten(VI) in alloy steels using ethopropazine hydrochloride.

Ethopropazine hydrochloride (EPH) has been proposed as a sensitive reagent for the spectrophotometric determination of tungsten(VI). The method is based on the formation of a chloroform-soluble yellow-colored ternary complex by the interaction of EPH and thiocyanate with tungsten(V). The complex exhibits the absorption maximum at 404 nm with Sandell's sensitivity value of 20.03 ng cm-2. The complex obeyed Beer's law in the concentration range of 1-15 micrograms ml-1 with an optimum concentration range of 2.3-12.9 micrograms ml-1. The effects of foreign ions in the determination of tungsten(VI) were investigated. The method has also been successfully applied to the analysis of alloy steels.     

Spectrophotometric determination of molybdenum(VI)

Molybdenum(IV) gives a red colour with ammonium thiocyanate in 5-8M hydrochloric acid medium, the Sandell sensitivity index being 0.018 ppm Mo(VI)/cm(2). Molybdenum(VI) in 4-7M hydrochloric acid medium forms a red complex with ethyl xanthate and ammonium thiocyanate and this can be extracted into acetophenone. Beer's law is obeyed over the range of 1.2-13.8 ppm, and the Sandell indices at 370 and 470 nm are 0.0016 and 0.0068 ppm/cm(2) respectively. The colour is stable for 40 hr. Most cations do not interfere.     

Spectrophotometric determination of vanadium(V) in minerals, steels, soil and biological samples using phenothiazine derivatives.

Two simple, rapid and sensitive spectrophotometric methods have been proposed for the determination of vanadium(V) using butaperazine dimaleate (BPD) and propionyl promazine phosphate (PPP). These methods are based on the formation of red-colored radical cations on reaction with vanadium(V) in phosphoric acid medium, with their absorbance maxima at 513 nm. Beer's law is valid over the concentration range of 0.25-5.0 micrograms ml-1 and 0.2-4.0 micrograms ml-1, with Sandell's sensitivity values of 6.1 ng cm-2 and 6.0 ng cm-2 for BPD and PPP respectively. The proposed methods have been successfully applied to the analysis of vanadium steels, minerals, biological samples and soil samples.     

Spectrophotometric determination of pipazethate hydrochloride in pure form and in pharmaceutical formulations

Three simple, sensitive, and reproducible spectrophotometric methods (A-C) for the determination of pipazethate hydrochloride (PiCl) in pure form and in pharmaceutical formulations are described. The first and second methods, A and B, are based on the oxidation of the drug by Fe3+ in the presence of o-phenanthroline (o-phen) or bipyridyl (bipy). The formation of tris-complex upon reactions with Fe3+-o-phen and/or Fe3+-bipy mixture in an acetate buffer solution of the optimum pH values was demonstrated at 510 and 522 nm, respectively, with o-phen and bipy. The third method, C, is based on the reduction of Fe(III) by PiCl in acid medium and subsequent interaction of Fe(II) with ferricyanide to form Prussian blue, which exhibits an absorption maximum at 750 nm. The concentration ranges are from 0.5 to 8, 2 to 16, and 3 to 15 microg/mL for Methods A-C, respectively. For more accurate analysis, Ringbom optimum concentration ranges were calculated. The molar absorptivity, Sandell sensitivity, and detection and quantitation limits were calculated. The developed methods were successfully applied to the determination of PiCl in bulk and pharmaceutical formulations without any interference from common excipients. The relative standard deviations were < or =0.83% with recoveries of 98.9-101.15%.     

Spectrophotometric determination of microquantities of frusemide using iso- and heteropolyanions of molybdenum(VI) as oxidizing agents

Summary A spectrophotometric method for the determination of microquantities of frusemide (FRS) is described. It is based on the oxidation of the latter by the paramolybdate anion (PMA) or by the molybdatophosphoric anion (MPA). The oxidation is carried out in acid medium at 98° C ±0.5° C for a fixed time of 25 min. The blue coloured reaction product can be measured spectrophotometrically at 690 nm and 700 nm, respectively. Beer's law is obeyed over the range of 5–200 ppm of FRS. The apparent molar absorptivities and Sandell's sensitivities (in l mol^–1 cm^–1 and ng cm^–2 per 10^–3 absorbance unit, respectively) are 2.8×10³ and 118.2 using PMA as oxidizing agent and 2.16×10³ and 153 using MPA for the same purpose. Six replicate analyses of solutions containing seven different concentrations of FRS were realized and gave a mean correlation coefficient of 0.9999 using the first oxidant (PMA) and 0.9998 using the second one (MPA), while the slope and intercept of the regression line equation were calculated. FRS was successfully determined both in the pure form and in pharmaceutical preparations. The results demonstrated that the proposed procedure is at least as accurate, precise and sensitive as the official method, while a statistical analysis indicated that there was no significant difference between the results obtained by the recommended procedure and those of the official method.

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Spektralphotometrische Bestimmung von Mikromengen Frusemid unter Verwendung von Iso- und Heteropolyanionen des Mo(VI) als Oxidationsmittel

     

Adsorptive stripping voltammetry determination of molybdenum(VI) in water and soil

A differential pulse stripping voltammetry method for the trace determination of molybdenum(VI) in water and soil has been developed. In 0.048M oxalic acid and 6 x 10(-5)M Toluidine Blue (pH 1.8) solution, Mo(V), the reduction product of Mo(VI) in the sample solution, can form a ternary complex, which can be concentrated by adsorption on a static mercury drop electrode at -0.1 V (vs. Ag/AgCl). The adsorbed complex gives a well-defined cathodic stripping current peak at -0.30 V, which can be used for determining Mo(VI) in the range 5 x 10(-10)-7 x 10(-9)M, with a detection limit of 1 x 10(-10)M (4 min accumulation). The method is also selective. Most of the common ions do not interfere but Sn(IV) and large amounts of Cu(2+), Ag(+) and Au(3+) affect the determination.     

Spectrophotometric determination of molybdenum(VI) with 2-mercaptobenzo-γ-thiopyrone and ammonium thiocyanate

Molybdenum(VI) in 1.4–3.6 M hydrochloric acid medium forms an acetophenone-extractable orange-red complex with the potassium salt of 2-mercapto-benzo-γ-thiopyrone and ammonium thiocyanate in the presence of tin(II) chloride. The limit of identification of the spot test based on this reaction is 0.1 μg of molybdenum (dilution limit, 1:1·10⁶). The spectrophotometric method is fairly selective, the sensitivity being 0.005μg Mo cm^-2 at 470 nm. The colour system obeys Beer's law; the optimal concentration range is 0.75–8.5 μg Mo ml^-1, the relative photometric error being 1.675%. The complex is stable for over 24 h. Common ions can be tolerated in amounts greater than 1000-fold. Interferences of Co²⁺, Ni²⁺, Cu²⁺ and Ag⁺ are avoided by complexing these ions with 2-mercaptobenzo-γ-thiopyrone at pH 6–10 and extracting with ethyl acetate or chloroform. The proposed method is applied to the determination of molybdenum in steel and in artificial mixtures.     

Spectrophotometric determination of molybdenum in steels with o-nitrophenylfluorone and cetyltrimethylammonium bromide

A method has been developed for determining microamounts of molybdenum(VI) in aqueous solution by means of the Mo-o-nitrophenylfluorone—cetyltrimethylammonium bromide system, in which micellar solubilization is applied. A red complex is formed in 0.2–0.6M hydrochloric acid medium. The sensitivity of the method is high, and the apparent molar absorptivity is 1.55 × 10⁵ l.mole⁻¹. cm⁻¹. The absorption peak of the complex appears at 530 nm. The colour of the complex develops quickly and is stable for more than 24 hr. The composition of the complex is Mo: o-NPF = 1:1, and the system obeys Beer's law in the range 0–10 μg of Mo per 25 ml. The method has been used for the rapid determination of molybdenum in alloy steels with satisfactory results.     

Complexometric determination of molybdenum(VI)

In acidic medium molybdenum(VI) forms a stable complex on boiling with excess of DCTA and hydroxylamine hydrochloride. Molybdenum can then be determined by back-titration of the excess of DCTA either with zinc chloride at pH 5-5.5 or with thorium nitrate at pH 3-4.5, Xylenol Orange being used as indicator in both cases. A simple method for the determination of molybdenum in the presence of moderate amounts of tungsten is also described.     

Extractive spectrophotometric determination of molybdenum(V) in molybdenum steels

An extraction spectrophotometric method has been developed for the determination of traces of molybdenum present in molybdenum steels which is based on the extraction of the orange-red molybdenum-thiocyanate-acetonethiosemicarbazone complex into chloroform from hydrochloric acid medium. The complex has an absorption maximum at 472 nm with a molar absorptivity of 1.9 × 10⁴ liters mol⁻¹ cm⁻¹. Beer's law is valid over the concentration range 0.1–9.5 ppm of molybdenum with an optimum concentration range of 0.4–9 ppm. The equilibrium shift method indicates 1:4:2 composition for molybdenumthiocyanate-acetonethiosemicarbazone complex. The effect of acidity, reagent concentrations, temperature, and interferences from various ions are reported.     

Kinetic-spectrophotometric determination of molybdenum (VI) and tungsten (VI) in mixtures

A simple kinetic-spectrophotometric method is described for the determination of molybdenum(VI) and tungsten(VI) in mixtures, without prior separation. The method is based on the catalytic effect of molybdenum(VI) and tungsten(VI) on the oxidation of 2,4-diaminophenol dihydrochloride (DAP) by hydrogen peroxide in acidic medium. The reaction was followed spectrophotometrically by measuring the rate of change in absorbance with time at 500 nm. A partial inhibition in the catalytic activity of each catalyst, when the other one is present, at all ratios of Mo(VI) W(VI) mixtures studied was observed. On the other hand, the catalytic activity of tungsten(VI) dropped to zero whilst that of molybdenum(VI) decreased slightly, in the presence of citrate ions. Two sets of experiments were carried out, the first in the absence and the other in the presence of citrate, and the resolution of Mo(VI)/W(VI) mixtures was achieved by solving two simultaneous equations. Various molar ratios of Mo(VI) W(VI), at the 10^–6 M level, from 0.2 1 to 5 1 can be determined with satisfactory precision and accuracy. The selectivity of the method was investigated and the method was applied successfully to the determination of molybdenum and tungsten in each other's presence in steel.     

Spectrophotometric determination of molybdenum(VI) with Bromopyrogallol red in the presence of Triton X-114

The complexation of molybdenum(VI) with Bromopyrogallol Red in the presence of the nonionic surfactant Triton X-114 is studied spectrophotometrically. A mixed-ligand complex is formed with the component ratio 1: 1: 1 and a stability constant of logβ = 8.2. The effect of pH, time, temperature, and component concentrations on the formation of the mixed-ligand complex is studied. A highly selective procedure for the spectrophotometric determination of trace molybdenum(VI) in drinking water in the presence of tungsten has been developed.     

Spectrophotometric determination of Chromium(VI) using cyclam as a reagent

A simple, rapid, sensitive, and inexpensive method for spectrophotometric determination of chromium(VI), based on the absorbance of its complex with 1,4,8,11-tetraazacyclotetradecane (cyclam) is presented. The complex showed a molar absorbtivity of 1.5?×?10⁴?L?mol^?1?cm^?1 at 379?nm. Under optimum experimental conditions, a pH of 4.5 and 1.960?×?10³?mg?L^?1 cyclam were selected, and all measurements were performed 10?min after mixing. Major cations and anions did not show any interference; Beer's law was applicable in the concentration range 0.2–20?mg?L^?1 with a detection limit of 0.001?mg?L^?1. The standard deviation in the determination is ±0.5?mg?L^?1 for a 15.0?mg?L^?1 solution (n?=?7). The described method provides a simple and reliable means for determination of Cr(VI) in real samples.     

Spectrophotometric determination of molybdenum(vi) with benzoylacetanilide

Abstract

The complex formed between molybdenum(VI) and benzoylacetanilide in the pH range 0.6 and 1.9 has been extracted into methyl isobutyl ketone and the absorbance has been measured at 410 mμ. Quantities of 0.15 to 2.10 mg of molybdenum have been determined with a standard deviation of 0.6%. The color is stable up to 2 hours. The presence of Co²⁺, Ni²⁺, Zn²⁺, Mn²⁺, Be²⁺, Al³⁺, Cr³⁺, Ce⁴⁺, Th⁴⁺ or UO²⁺ ₂ up to 100 μg causes no interference. Ordinarily, Fe³⁺ interferes with the determination, but when masked with 1 ml of 0.5% solution of ascorbic acid the tolerance limit is 10 mg. Thus, molybdenum can be determined in steel when present in amounts as low as 0.26%.     

Spectrophotometric determination of chromium(VI) with ferron

Chromium(VI) gives a pink coloured solution in chloroform in the presence of ferron when extracted from slightly acidic medium. This reaction is used for the spectrophotometric determination of chromium by measuring the absorbance at 510 nm. Beers law is obeyed in the range of 5–70 g/ml. Most of the important metal ions do not interfere. The relative standard deviation is 2.78%.     

Spectrophotometric determination of tungsten(VI) with rutin

A new spectrophotometric method for the determination of microamounts of tungsten(VI) with rutin has been developed. The effect of a large number of foreign ions was investigated, and the separation and determination of tungsten in the presence of the interfering ions examined are presented.     

Spectrophotometric determination of uranium(VI) with benzoylacetanilide

Ohne Zusammenfassung

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Use of complex forming substitution reactions for the selective enthalpiometric determination of cations and anions