Extraction-spectrophotometric determination of mercury with 1,2,4,6-tetraphenylpyridinium perchlorate

The characteristics of 1,2,4,6-tetraphenylpyridinium perchlorate (TPPP) as a reagent for the formation of ion-pair complexes with metal-bromide anions, and its application to the spectrophotometric determination of mercury are described. This reagent forms a 1:1 complex with bromomercurate(II) ions that is slightly soluble in water and can be extracted with isopentyl acetate. The optimum conditions are about 0.5 M sulphuric acid and 0.03 M potassium bromide. Mercury can be determined at 310 nm in the range 0.04–0.5 μg ml^?1; the apparent molar absorptivity is 2.63 × 10⁴ l mol^?1 cm^?1, and the conditional stability constant is log K - 4.7 ± 0.1 at 20°C. The main interferences are easily removed. Mercury can be determined in sphalerites and zinc amalgams.     

Extraction-spectrophotometric determination of iron with 1,2,4,6-tetraphenylpyridinium perchlorate

Summary In 7M hydrochloric acid medium, iron(III) forms an ion-association compound with 1,2,4,6-tetraphenylpyridinium perchlorate (TPPP) which is extractable into isoamyl acetate. The extracted ionpair, which has an Fe: TPPP mole ratio of 11, is used for the spectrophotometric determination of iron (=3.10×10⁴l·mole^–1· cm^–1) in the concentration range 0.1–1.5g/ml in the organic phase. The interference of a number of foreign ions has been investigated. The method is applicable to the determination of iron in various materials.     

Spectrophotometric determination of micro-amounts of vanadium with 5,7-di-iodo-8-hydroxyquinoline

A precise spectrophotometric method for the determination of 2.5-25 mug of vanadium in volumes of up to 500 ml of water was developed. The method is based on the simultaneous concentration (100-1000 fold) and complexation of vanadium(V) with di-iodo-oxine in a water-immiscible phase. Interference from iron is eliminated by masking with phosphoric acid. The standard deviation evaluated was +/-0.04 mug for solutions containing 5 mug vanadium.     

Extraction and spectrophotometric determination of vanadium(V) with 8-hydroxyquinoline

The extraction and spectrophotometric determination of vanadium (V) with oxine is investigated at higher acidities than described previously. Under these conditions, n-butanol and other alcohols are found to exert a synergic effect on the extraction of vanadium into benzene. In the presence of alcohol only a 6-fold ligand excess is needed for quantitative extraction in a single operation, the acidity of the aqueous medium being 0.05M with respect to sulphuric or phosphoric acid. The interference of iron(III) in the spectrophotometric determination of vanadium is suppressed by the addition of pyrophosphate. Beer's law is obeyed up to 14.0 mug of vanadium/ml and the sensitivity is 0.008 mug of vanadium/cm(2) at 390 mmu. The composition of the extracted species is found to be vanadium:oxine:n-butanol = 1:2:2.     

Extraction-spectrophotometric determination of vanadium with 3,5-dinitrocatechol and Brilliant Green

The formation and extraction of the ion-associates of the vanadium(V)-3,5-dinitrocatechol (DNC) anionic chelate complex with various basic dyes have been studied and a new sensitive extraction—spectrophotometric method for the determination of vanadium based on the system V(V)-DNC-Brilliant Green has been developed. Beer's law is obeyed up to a vanadium concentration of 0.3 μg/ml and the molar absorptivity is 1.7 × 1O⁵ l.mole⁻¹. cm⁻¹ at 630 nm. The molar ratios of the components and the form of the vanadium(V) cation in the extracted compound have been determined, and the formula [VO(OH)(DNC)²⁻₂][BG⁺]₂ is proposed. Titanium, molybdenum, tungsten, EDTA and thiocyanate interfere seriously. The method becomes specific after a preliminary separation of vanadium by its extraction as the BPHA complex from H₂SO₄-HF medium, and is 40 times more sensitive than the spectrophotometric BPHA method. The proposed method has been applied to determination of traces of vanadium (about 10⁻⁵%) in alums.     

Spectrophotometric determination of zirconium with 5,7-dibromo-8-hydroxyquinoline in presence of thiocyanate

The characteristics of the ternary complex formed between zirconium(IV) and 5,7-dibromo-8-hydroxyquinoline in presence of thiocyanate have been studied with an analytical point of view. The resulting colored species is extractable into chloroform with absorption maximum at 416 nm, which leads to the determination of the trace amounts of the metal ion. The method obeys Beer’s law in the range 0.2–9.0 μg Zr/mL having molar absorbitivity and Sandell’s sensitivity values of 1.05 × 10⁴ L/mol cm and 0.0087 μg Zr/cm², respectively. The ratio of zirconium(IV), 5,7-dibromo-8-hydroxyquinoline and thiocyanate in the extracted species is found to be 1: 2: 2. A large number of foreign ions do not interfere in the proposed method. The applicability of the procedure is tested by carrying out satisfactorily the analysis of a wide variety of samples.     

Colorimetric determination of vanadium with 5,7-dibromo-8-hydroxyquinoline after paper-chromatographic separation from interfering ions

Summary 5,7-Dibromo-8-hydroxyquinoline is recommended as reagent for the colorimetric determination of vanadium. The absorption is measured at 394 nm. Interfering ions are removed by paper chromatography with a collidine containing solvent. With amounts of 45–120 g of vanadium an error of ± 1 g has been obtained.

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Zusammenfassung Zur colorimetrischen Vanadiumbestimmung wird 5,7-Dibrom-8-hydroxychinolin als Reagens empfohlen. Die Messung erfolgt bei 394 nm. Störende Ionen werden durch Papier-Chromatographie mit einem collidinhaltigen Fliemittel entfernt. Der Fehler betrug ±1 g bei Vanadiummengen von 45–120g.

     

Differential-pulse voltammetric determination of molybdenum in nitrate medium in the presence of 8-hydroxyquinoline

The determination of Mo(VI) by differential-pulse voltammetry based on catalytic currents in nitrate medium is described. The existence of catalytic currents in the system Mo(VI)NO₃^? in the presence of 8-hydroxyquinoline was proved by various polarographic techniques. The optimum background electrolyte is 20 ml 0.5 M KNO₃?0.005 M HNO³ with the addition of 1 ml of 1 × 10^?2 M 8-hydroxyquinoline. The detection limit is 7 × 10^?10 M under these conditions. Cr(VI), Cu(II), Cd(II) and Pb(II) interfere when present at higher concentrations then Mo(VI) and W(VI) interferes at an equal concentration to Mo(VI). The method was successfully used in analyses of environmental samples.     

Extraction-spectrophotometric determination of vanadium with 5,5′-dithiodisalicylhydroxamic acid (DTDSHA)

A new method for the extraction-spectrophotometric determination of V(V) is proposed. The violet complex V(V)-5,5′-dithiodisalicylhydroxamic acid formed in aqueous medium (pH 5.0) is extracted into a solution of trioctylmethylammonium chloride (Adogen 464) in toluene, and its spectrophotometric characteristics are studied. The stoichiometry of the complexes formed is 1:1 and 2:1 (reagent:vanadium), and 1:3 for the ionic association complex (2:1):trioctylmethylammonium ion. The system follows Beer's law at pH 5.0 (λ = 550 nm) over the concentration range 0.4 to 2.0 ppm (ε = 7.34 × 10³ liter · mol⁻¹ · cm⁻¹). The method is applied for the determination of vanadium in steel.     

Extraction-spectrophotometric determination of vanadium with N-m-tolyl-N-phenylhydroxylamine and its application to coal and coal fly-ash

N-m-Tolyl-N-phenylhydroxylamine is proposed for the spectrophotometric determination of small amounts of vanadium. The reddish-violet complex formed with the reagent in 3-6M hydrochloric acid after extraction with chloroform shows an absorption maximum at 530 nm, and obeys Beer's law for 0-76.5 mug of vanadium in 10 ml of chloroform. The proposed method has been successfully applied to the determination of vanadium in coal and coal fly-ash.     

Spectrophotometric determination of halogenated 8-hydroxyquinoline derivatives

A spectrophotometric method is proposed for the determination of 8-hydroxyquinoline and three of its iodinated derivatives: 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol), 5,7-di-iodo-8-hydroxy-quinoline (iodoquinol) and 8-hydroxy-7-iodo-quinolone-5-sulphonic acid (chinoform). The suggested method depends on the reaction with 4-aminoantipyrine in the presence of an alkaline oxidizing agent. A red antipyrine dye with an absorption peak at 500 nm is produced in all cases. The reacting ratio has been determined and a reaction mechanism is presented. The proposed method can be applied to the analysis of pharmaceutical preparations containing the compounds studied, and the results obtained compare favourably with those obtained with the standard methods.     

Colorimetric determination of p-aminophenol in the presence of paracetamol with 3-cyano-N-methoxypyridinium perchlorate

Two simple and sensitive calorimetric procedures for the determination of p-aminophenol with 3-cyano-N-methoxypyridinium perchlorate are presented. One is based on reaction in methoxyethanol in presence of sodium acetate, with direct measurement at 410 nm. The reaction product obtained by this procedure has been separated and identified. The other is based on reaction in methoxyethanol in presence of chloramine-T and direct measurement at 448 nm. The method has been applied to the determination of p-aminophenol in pure form and as an impurity in paracetamol and paracetamol- containing tablets, with a coefficient of variation less than 2%.     

Extraction-spectrophotometric determination of chromium with Nitrotetrazolium Blue

The interaction of Cr(VI) and Nitrotetrazolium Blue has been examined. A 12 NTB (CrO₃Cl)₂ ion-associate is formed and is extractable into 1,2-dichloroethane. The optimum conditions have been established. The molar absorptivity at 260 nm was (8.2 ± 0.06) × 10⁴L mol^–1cm^–1. Beer's law was obeyed in the range 0.01–0.4 g ml^–1 Cr(VI). A sensitive and selective method for determination of micro-quantities of Cr(VI) in soils and steels is suggested.     

Extraction-spectrophotometric determination of hydrogen sulphide

A sensitive spectrophotometric method for the determination of trace amounts of hydrogen sulphide (H2S) after fixing in a modified zinc acetate-disodium ethylenediaminetetraacetate-sodium hydroxide solution is described. The fixed H2S is stable for 3 d. The reaction of iodate with H2S in the presence of acid and an excess of chloride leads to the formation of ICI which is stabilised as ICI2-. The species formed reacts with 2',7'-dichlorofluorescein to form 2',7'-dichloro-4',5'-diiodofluorescein which is extracted into a mixture of 15% isoamyl acetate in isoamyl alcohol. The colour system obeys Beer's law in the range 0-2.5 micrograms of H2S. The coefficient of variation is 4.5% for ten determinations of 2.0 micrograms of H2S. The effect of interfering gases on the determination is discussed. The method was applied to the determination of residual amounts of H2S present in a laboratory fume cupboard and the results obtained were compared with those given by the widely used Methylene Blue method. The method can be used to determine down to 0.3 micrograms of H2S.