Oxidimetric determination of indigo with iron(III) and hexacyanoferrate(III)

The use of iron(III) in sulphuric acid medium and of potassium hexacyanoferrate(III) in hydrochloric acid medium has been investigated for the oxidimetric determination of indigo and indigo sulphonic acid. Conditions have been established for the assay of the dye with iron(III) sulphate at 100 degrees and with potassium hexacyanoferrate(III) at room temperature.     

Spectrophotometric determination of ascorbic acid with potassium hexacyanoferrate(III)

A new, simple and rapid method of determination of ascorbic acid in amounts of 45-360 mug is described. The ascorbic acid is determined spectrophotometrically at 420 nm from the decrease in absorbance it causes in 1 x 10(-3)M hexacyanoferrate(III) in McIlvaine buffer at pH 5.2. The proposed method is suitable for the determination of ascorbic acid in pharmaceutical preparations and probably natural products.     

Hexacyanoferrate(III) as a mediator in the determination of total iron in potable waters as iron(II)-1,10-phenanthroline at a single-use screen-printed carbon sensor device

Hexacyanoferrate(III) was used as a mediator in the determination of total iron, as iron(II)-1,10-phenanthroline, at a screen-printed carbon sensor device. Pre-reduction of iron(III) at −0.2 V versus Ag/AgCl (1 M KCl) in the presence of hexacyanoferrate(II) and 1,10-phenanthroline (pH 3.5-4.5), to iron(II)-1,10-phenanthroline, was complete at the unmodified carbon electrode surface. Total iron was then determined voltammetrically by oxidation of the iron(II)-1,10-phenanthroline at +0.82 V, with a detection limit of 10 μg l⁻¹.In potable waters, iron is present in hydrolysed form, and it was found necessary to change the pH to 2.5-2.7 in order to reduce the iron(III) within 30 s. A voltammetric response was not found at lower pH values owing to the non-formation of the iron(II)-1,10-phenanthroline complex below pH 2.5.Attempts to incorporate all the relevant reagents (1,10-phenanthroline, potassium hexacyanoferrate(III), potassium hydrogen sulphate, sodium acetate, and potassium chloride) into a modifying coated PVA film were partially successful. The coated electrode behaved very satisfactorily with freshly-prepared iron(II) and iron(III) solutions but with hydrolysed iron, the iron(III) signal was only 85% that of iron(II).     

Amperometric titrations of cobalt(II) with hexacyanoferrate(III) in ammonium citrate and glycine media

An amperometric titration of cobalt(II) with hexacyanoferrate(III) in aqueous ammonium citrate or aqueous glycine solution at pH 9.8 or pH 8.0 respectively, is reported. Cobalt concentrations of 2-30 mg/l were successfully determined. In citrate solutions cerium(III) and iron(III) interfered, and in glycine solutions, copper(II) and vanadium(V).     

Analytical applications of the determination of hexacyanoferrate(III) with ascorbic acid : Determination of hydrogen peroxide,peroxydisulphate and their mixtures

Hydrogen peroxide can be determined by reaction with excess of alkaline hexacyanoferrate(III), the excess being titrated with ascorbic acid. Peroxydisulphate is determined by reaction with hexacyanoferrate (II) in acidic medium, the hexacyanoferrate(III) formed being titrated with ascorbic acid. To determine hydrogen peroxide and peroxydisulphate in the presence of each other, two titrations are needed ; the results arc readily calculated.     

Oxidimetric determination of ascorbic acid with potassium hexacyanoferrate(III) in acid medium

Conditions have been developed for the titrimetric determination of ascorbic acid with hexacyanoferrate(III), with potentiometric and visual end-points, in sulphuric, hydrochloric or phosphoric acid media. Several organic substances likely to be present in plant tissues do not interfere.     

Analytical applications of the determination of hexacyanoferrate(III) with ascorbic acid: Part IV. Determination of hydroxylamine

Hydroxylamine can be determined by reaction with an excess of standard potassium hexacyanoferrate(III) solution at pH 8–10. After 30 min the excess is titrated with ascorbic acid solution in the presence of 2,6-dichlorophenolindophenol indicator.     

Sorption-spectrophotometric determination of iron(II, III) with the use of organic reagents immobilized in a polymethacrylate matrix

The interaction of iron(II) with 2,2′-dipyridyl and 1,10-phenanthroline immobilized in a polymethacrylate matrix was studied. The optimum conditions of the complexation of iron(II) with the immobilized reagents and the chemical analytical properties of the complexes in the polymethacrylate matrix were determined. A sorption-spectrophotometric procedure was developed for the determination of iron(II) and the total of iron(II, III) after the reduction of iron(III) by ascorbic acid. The procedure with 2,2′-dipyridyl was used for the analysis of samples of tap, well, and mineral water and a solution of glucose.     

Coprecipitation with lanthanum phosphate as a technique for separation and preconcentration of iron(III) and lead

The usefulness of coprecipitation with lanthanum phosphate for separation and preconcentration of some heavy metals has been investigated. Although lanthanum phosphate coprecipitates iron(III) and lead quantitatively at pH 2.3, iron(II) can barely be collected at this pH. This coprecipitation technique was applicable to the separation and preconcentration of iron(III) before inductively coupled plasma atomic-emission spectrometric (ICP-AES) determination; the recoveries of iron(III) and iron(II) from spiked water samples were 103-105% and 0.2-0.7%, respectively. The coprecipitation was also useful for separation of 20 microg lead from 100 mL of an aqueous solution that also contained 1-100 mg iron. Coprecipitation of iron was substantially suppressed by addition of ascorbic acid, which enabled recovery of 97-103% of lead added to the solution, bringing the recovery to within 1.6-5.0% of the relative standard deviations. Lanthanum phosphate can also coprecipitate cadmium and indium quantitatively, although chromium(III), cobalt, and nickel and large amounts of sodium, potassium, magnesium, and calcium are barely coprecipitated at pH approximately/= 3.     

Determination of cysteine, 3-mercaptopropionic, and mercaptosuccinic acid with neutral hexacyanoferrate(III)

Two procedures are proposed for the determination of -SH groups. In both a known amount of hexacyanoferrate(III) is added to the sample and the excess is then determined. In one procedure an excess of ascorbic acid is added and the excess of that is titrated with iodine. In the other, the excess is determined by direct titration with ascorbic acid. Both procedures avoid errors resulting from side-reactions of iodine which takes place if the excess of hexacyariofcrrate(III) is reacted with potassium iodide.     

Simultaneous determination of iron(II) and iron(III) by micellar electrokinetic chromatography using an off-line selective complexing reaction.

A simultaneous determination with UV detection/capillary electrophoresis for Fe(II) and Fe(III) was achieved using a sulfonated bathophenantholine and desfferioxamine B. When the electrophoretic buffer was 60 mmol l(-1) SDS, 10 mmol l(-1) acetic acid (pH 4.0) and 10 mmol l(-1) ascorbic acid and at -10 kV, the iron(II) and iron(III) could not only be completely separated, but also be sensitively determined.     

Anwendung der ascorbinometrischen Bestimmung von Hexacyanoferrat(III) zu automatischen Mikrotitrationen

Zusammenfassung Nach theoretischen Erörterungen über die Redoxpotentiale des Ascorbinsäure-Dehydroascorbinsäure-Systems und Besprechung der möglichen Reduktionsreaktionen werden Vorschriften gegeben zur ascorbinometrischen Bestimmung von Hexacyanoferrat(III), Hexacyanoferrat(II), Dichromat, Permanganat, Jodat, Bromat und Chloramin T im Mikromaßstab mit Hilfe eines automatischen Mikrotitrators.

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Application of ascorbinometric determination of hexacyanoferrte(iii) to automatic micro-titrations

The reaction between hexacyanoferrate(III) and ascorbic acid has been applied to the ascorbinometric micro-titration of hexacyanoferrate(III), hexacyanoferrate(II), dichromate, permanganate, bromate and iodate ions as well as chloramine T. Titrations are carried out with an automatic titrimeter which records the potentiometric titration curve. Despite the small amounts of ions involved accuracy and precision of these methods are satisfactory.

     

Milligram amount determination of thiol groups with ferricyanide. Use of 2,6-dichlorophenolindophenol as titrant

Summary Thiols are reacted at pH 7 with an excess of ferricyanide. The excess of reagent is determined by adding a measured excess of ascorbic acid followed by back titration of ascorbic acid with 2,6-dichlorophenolindophenol. A correction can be made for ascorbic acid, if present with thiols. Tested with dilute solutions of cysteine, glutathione, mercaptoacetic acid and some other water-soluble thiols gave results which are accurate to 0.1%. Glycine, cystine, methionine, etc. do not interfere.

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Zusammenfassung Thiole reagieren bei pH 7 mit überschüssigem Cyanoferrat (III). Der Überschuß läßt sich durch Zusatz einer gemessenen Menge Ascorbinsäure und deren Rücktitration mit 2,6-Dichlorphenolindophenol bestimmen. Ist neben Thiol bereits Ascorbinsäure zugegen, so ist eine entsprechende Korrektur anzubringen. Die Anwendung auf Lösungen von Cystein, Glutathion, Mercaptoessigsäure und einigen anderen wasserlöslichen Thiolen erbrachte auf 0,1% genaue Ergebnisse. Glycin, Cystin, Methionin usw. stören nicht.

     

Flow-injection spectrophotometric determination of ascorbic acid in pharmaceutical products with the Prussian Blue reaction

A lot of modern analytical strategies for exploiting chemistries have been developed by using flow-injection analysis. However, even after 20 years of flow-injection evolution, there still are new quantitative procedures being established using old qualitative assays. The formation of Prussian Blue is a classical test to detect Fe(2+) using hexacyanoferrate(III) as a precipitating reagent. This reaction was evaluated for spectrophotometric determination of ascorbic acid employing Fe(3+) and hexacyanoferrate(III) as chromogenic reagents. An excess of the complexing anion avoids the formation of precipitate and forms a deep blue solution when Fe(3+) is reduced to Fe(2+) by ascorbic acid. The maximum absorbance of the colored complex occurs at 700 nm and the molar absorptivity is 3.0 x 10(4) 1 mol(-1) cm(-1). Under flow-injection conditions the Prussian Blue reaction was employed with an intermittent flow of an oxalate alkaline solution for removing the colored product adsorbed on tube and flow-cell walls. Reference solutions containing 5.0 x 10(-6)-1.0 x 10(-4) M of ascorbic acid were employed to obtain the analytical curve (r = 0.9999). For all solutions the relative standard deviation was lower than 1.0% (n=10). Results obtained for ascorbic acid determination in pharmaceutical products (Cewin, Redoxon and Cebion) are in good agreement with those obtained by using a flow-injection procedure involving the reaction between triiodide and ascorbic acid. The sampling frequency is 140 h(-1) and only 430 microl of reagents is consumed in each determination.     

Inhibition Effect of {Cationic Surfactant-Ascorbic Acid} Premicellar Aggregation on the Rate of Hexacyanoferrate(III) Oxidation of Ascorbic Acid: A Kinetic Study

The kinetics of oxidation of ascorbic acid by acidic hexacyanoferrate(III) have been investigated in presence of cationic surfactant viz. cetyltrimethylammonium bromide (CTAB). An inhibition effect of CTAB (below its critical micelle concentration) on the rate of oxidation has been observed. The spectrophotometric and kinetic data support a 1:1 premicellar association between substrate and surfactant. A mechanism has been proposed and a rate law consistent with kinetic results has been derived.     

Indirect determination of Fe(III) in synthetic samples and iron dextran tablets by capillary electrophoresis with ultraviolet detection

A capillary electrophoresis method based on the oxidation of ascorbic acid is proposed for the indirect determination of Fe(III). Fe(III) concentration corresponds to the decrease in ascorbic acid peak area. The calibration graph was linear in the range of 1.68-112 mg/L for Fe(III), which was easily detected at a concentration of 1.12 mg/L at 3 times the standard deviation of the blank divided by the slope of the calibration graph. The lack of interferences from Fe(II) in synthetic samples and 3 excipients (starch, magnesium strearate, and microcrystalline cellulose) in dextran tablets in the determination of Fe(III) confirmed the high selectivity of the proposed method. Its application to the determination of Fe(III) in several synthetic samples and iron dextran tablets produced excellent results.     

Selective detection of bismuth(III) and iron(II) ions with certain new reagents

Isoperthiocyanic acid (3-amino-5-thione-1,2,4-dithiazole) (I), tetraethylthiuram monosulphide ("Tetmosol") (II), eosin (III), and mercurochrome (IV) are used as new qualitative reagents for bismuth, III and IV are also used for detection of iron(II). A conc. sulphuric acid solution of I, or an acctone solution of II, when treated with bismuth in presence of potassium iodide, gives a deep red or reddish-orange precipitate, characteristic of bismuth. Bismuth in presence of III or IV gives a heavy and characteristically bright deeppink precipitate on addition of ammonia. With I, 1 mug of bismuth may be detected with a dilution limit of 1:50,000. Sb(III) and As(III) do not interfere in any of these tests. Iodides interfere only when I and II are used as reagents. Pb, Cu(II). and Fe(III) interfere with III and IV. I and II are also proposed as reagents for iodide; nitrites would interfere. III and IV, with iron(II) on addition of ammonia, produce a precipitate with highly intense green fluorescence. No other common cation [including Fe(III)] or anion interferes. The limit of detection is 3 mug ml .     

Model studies on iron(III) ion affinity chromatography. II. Interaction of immobilized iron(III) ions with phosphorylated amino acids, peptides and proteins.

The chromatographic behaviour of phosphoamino acids, phosphopeptides and phosphoproteins and their non-phosphorylated counterparts was studied on Fe(III)-Chelating Sepharose and Fe(III)-Chelating Superose. The phosphorylated compounds, in contrast to their non-phosphorylated or dephosphorylated counterparts, adsorb to immobilized iron(III) ions at pH 5.5 and can be desorbed by an increase in pH. Phosphoamino acids were eluted at pH 6.5-6.7, whereas monophosphopeptides and phosphoprotamine eluted in the pH range 6.9-7.5. Molecules possessing clusters(s) of carboxylic groups are weakly retained (gamma-carboxyglutamic acid, Ala-Ser-Glu5) or bound (polyglutamic acid, beta-casein) to the immobilized iron(III) ions at pH 5.5. Dephosphorylated beta-casein was desorbed at pH 7.0, whereas for elution of native (non-dephosphorylated) beta-casein, phosphate buffer of pH 7.7 was required. The homopolymer of polyglutamic acid was desorbed in the pH range 6.0-6.3, whereas copolymers of glutamic acid and tyrosine require pH 7.0-7.3 or even phosphate buffer at pH 7.7 for elution.     

Investigation of cobalt interference on lead hydride generation with tetrahydroborate(III) in the presence of hexacyanoferrate(III)

The interference of Co(II) on plumbane generation with tetrahydroborate in the presence of hexacyanoferrate(III) was studied with a new mechanism proposed to explain the interference. The products that were obtained, following reactions of a CoCl₂ solution with tetrahydroborate(III), which interfere with plumbane generation, were precipitated and investigated by inductively-coupled plasma-atomic emission spectrometry and -mass spectrometry (ICP-OES and ICP-MS). Batch experiments of the potentiometer analysis and pH determination were performed to investigate a mechanism of Co(II) interference on plumbane generation, the role of hexacyanoferrate(III) on plumbane generation, and the function of the masking agent on Co(II) interference. The preferentially formed nanoscale catalytic and magnetic cobalt borides in the redox system cause a potential for a strong reducing condition and induces the precipitation of Fe(III) and Pb(II) in the solution, which is counter to plumbane generation. Potassium thiocyanate/oxalic acid/1,10-phenanthroline, as the combined masking agent and working with hexacyanoferrate(III), decreases the amount of borides in the precipitates and acts as a kind of buffer of the redox potential, which maintains the conditions for plumbane generation. This hydride generation method has been applied to the direct determination of trace Pb in cobalt oxide standard reference materials with a detection limit of 0.3 µg L^− 1.     

Determination of antimony(III) with potassium hexacyanoferrate(III)

The determination of antimony(III) with potassium hexacyanoferrate(III) in 5M hydrochloric acid medium and in the presence of 40% v/v acetic acid is described. Ferroin is used as the indicator. Antimony has been determined in tartar emetic, solder and pig lead. Arsenic(III) does not interfere.