Spectrophotometric determination of cyanocobalamin (as cobalt)

A spectrophotometric method for the determination of cyanocobalamin (as cobalt) in pharmaceutical preparations has been developed. The sample is first decomposed with sulfuric acid and potassium perchlorate. The liberated cobalt is then determined using 2,2′-dipyridyl-2-pyridylhydrazone as reagent in solutions containing 20% sulfuric acid. The presence of other metal cations does not interfere with the determination of cobalt. The method has been applied to the determination of cobalt in pure cyanocobalamin and in two pharmaceutical preparations.     

Spectrophotometric determination of cobalt with isonitrosodimedon

An extraction procedure with iso-amylalcohol for the determination of traces of cobalt was developed using isonitrosodimedon. At 374mμ, the wavelength of maximal absorption, the molar extinction coefficient is as high as 19.680, allowing cobalt determination as low as 0.5μg/ml in the organic phase. The extraction is quantitative between pH 4 and 7. The most common ions in a 100-fold excess do not disturb the determination, though Fe⁺³, Cu⁺², Cr⁺³ and Ni⁺² should be absent.     

Spectrophotometric determination of cobalt with dipyridylglyoxal mono(2-pyridyl)hydrazone

A method for the Spectrophotometric determination of cobalt with dipyridylglyoxal mono(2-pyridyl)hydrazone (DMPH) has been devised. The orange-reddish Co-DMPH chelate (ϵ = 2.7 × 10⁴ liters mol⁻¹ cm⁻¹ at 490 nm) is formed at pH 3–7 in a solution containing 24% (v/v) ethanol. This complex, on addition of a strong acid, shows a bathochromic shift from 490 to 505 nm. A fair degree of selectivity for cobalt is achieved by measuring the absorbance of the orange-reddish coloration at 510 nm (isosbestic point wavelength; ϵ = 2.6 × 10⁴ liters mol⁻¹ cm⁻¹) in solutions of final acidity about 1 M in perchloric acid.     

Spectrophotometric determination of cobalt with gluconic acid

Summary A new spectrophotometric method is proposed for determining cobalt using gluconic acid as a chromogenic reagent. The parameters fundamentally affecting the absorbance of the complex are studied and obeyance of Beer's law between 5.33 and 53.3 g of Co²⁺/ml has been found. Measurements have to be carried out at 330 nm. The complex is formed in the molar ratio 11.

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Spektralphotometrische Bestimmung von Kobalt mit Hilfe von Gluconsäure

Zusammenfassung Die vorgeschlagene Methode verwendet Gluconsäure als farbbildendes Reagens. Untersucht wird der Einfluß verschiedener Parameter auf die Absorption des Kobalt(II)-Gluconsäure-Komplexes. Das Beersche Gesetz gilt im Bereich von 5,33–53,3 g Co²⁺/ml. Die Messung der Absorption erfolgt bei 330 nm. Das Molverhältnis des Komplexes beträgt 11.

     

Spectrophotometric determination of cobalt with mucic acid

A procedure for the spectrophotometric determination of cobalt with mucic acid is proposed. The absorption spectra, pH, amount of reagent, temperature, and time are studied. Beer's law is obeyed in the range 2.3 and 28.3 μg Co(III)/ml, the Ringbom optimal interval falls between about 9.5 and 25.0 μg Co(III)/ml. The molar absorptivity is 1.4 × 10³ liter/ mol · cm. The stoichiometry of the reaction takes place in the metal-to-ligand ratio of 1:1. The stability constants of the complex are calculated. At the same time, the interferences produced by the commonest ions are studied. The method has been successfully applied to the determination of cobalt in vitamin B₁₂.     

Spectrophotometric determination of cobalt with phenanthrenequinone monoxime

Phenanthrenequinone monoxime reacts with cobalt to form a yellow-orange insoluble 1:3 (cobalt:ligand) complex which is extractable into chloroform in the pH range 4.45-8.0. The determination of cobalt is carried out at 470 mmu. Beer's law is obeyed over the concentration range 0-3.0 ppm of cobalt. The sensitivity is 0-00336 mug of Co/cm(2) for 0.001 absorbance. The effect of a number of foreign ions has been studied.     

Spectrophotometric determination of cobalt with nitrosochromotropic acid

A sensitive spectrophotometric method for the determination of trace amounts of cobalt based on the complex formation with nitrosochromotropic acid in ammoniacal medium is described. After its extraction as thiocyanate complex into isobutylmethyl ketone, cobalt is stripped into nitrosochromotropic acid in ammonia buffer. The method has been applied to the determination of cobalt in mild steel, ferrous alloys and multivitamin preparations.     

Spectrophotometric determination of cobalt with chlorindazon DS

Summary The optimum experimental conditions for the spectrophotometric determination of trace amounts of cobalt(II) in aqueous solutions using chlorindazon DS were assessed and the procedure was described. A 5.5-fold molar excess of the reagent is required for complete complex formation. Heating at 60° for 20 min or at 100° for 5 min is required for complete colour development. The system conforms to Beer's law; the optimum range for a 1-cm cell is 0.4–1.4 ppm of cobalt, determined with a relative standard deviation of 0.5%. The molar absorptivity at 638 nm is 3.25×10⁴l mole^–1 cm^–1. Cyanide seriously interferes with the determination. A reaction ratio of 1 to 3 for cobalt to the reagent has been deduced from spectrophotometric data. This method was utilized to determine cobalt in a steel sample.

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Zusammenfassung Die optimalen Bedingungen für die spektrophotometrische Bestimmung von Kobalt(II)-Spuren in wäßrigen Lösungen mit Chlorindazon DS wurden ermittelt und die Arbeitsweise angegeben. Ein 5,5-facher molarer Überschuß ist für die vollständige Komplexbildung nötig. Zur endgültigen Farbentwicklung ist es nötig, 20 min auf 60° oder 5 min auf 100° zu erhitzen. Das Reaktionssystem entspricht dem Beerschen Gesetz. Die optimale Menge bei Verwendung von 1-cm-Küvetten ist 0,4–1,4 ppm Co, die relative Standardabweichung 0,5%. Die molare Extinktion bei 638 nm beträgt 3,25·10⁴l·mol^–1·cm^–1. Cyanid stört stark. Kobalt setzt sich mit dem Reagens im Verhältnis 13 um. Das Verfahren wurde zur Co-Bestimmung in Stahlproben verwendet.

     

Spectrophotometric determination of cobalt by extraction of tetrathiocyanatocobaltate(II) with propylene carbonate

Cobalt is extracted as ammonium tetrathiocyanatocobaltate(II) propyelene carbonate. The effects of pH and diverse ions and masking are reported. The system is applied to the determination of cobalt (0.01–0.20%) in mild steels without prior separation of iron.     

Spectrophotometric determination of cobalt(II) and cyanocobalamin with vanillilfluorone and its applications

Spectrophotometric determination of cobalt(II) was accomplished with vanillilfluorone (VF) in the presence of dimethylbenzyltetradecylammonium chloride (Zephiramine, Zep). In the determination of cobalt(II), Beer's law was obeyed in the range of 24-470 ng/ml, with an effective molar absorption coefficient (at 575 nm) and relative standard deviation of 1.35×10(5) l mol(-1) cm(-1) and 0.66% (n=5), respectively. The composition ratio of the colored complex was determined by the mole ratio and continuous variation methods, and it was found to be Co(II) : VF : Zep=1 : 2 : 4. Analysis of cyanocobalamin by the same procedure showed that cyanocobalamin could be determined in the concentration range of 0.5-0.11 μg/ml using the proposed method.     

Spectrophotometric determination of cobalt with 2,2′-Pyridilmonoxime

Summary A visible spectrophotometric method is described for the determination of cobalt with 2,2-pyridilmonoxime. The effects due p_H, time, solvents, reagent concentration and diverse ions are reported. Beer's law is obeyed and the molar extinction coefficient is 1.7 · 10⁴ at 408 nm. A reasonable structure for the cobalt chelate based on analysis and infrared evidence is proposed.

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Zusammenfassung Eine spektrophotometrische Methode zur Kobaltbestimmung mit 2,2-Pyridilmonoxim wurde beschrieben. Der Einfluß des p_H, der Zeit, des Lösungsmittels, der Reagenskonzentration und verschiedener Fremdionen wurde untersucht. Die Reaktion folgt dem Beerschen Gesetz, der Extinktionskoeffizient beträgt 1,7 · 10⁴ bei 408 nm. Auf Grund der Analyse und des IR-Spektrums wird eine Strukturformel für das Kobaltchelat vorgelegt.

     

Spectrophotometric determination of cobalt(II) with 2,2'-dipyridyl-2-pyrimidylhydrazone

Some metallochromic indicators are examined for ion-pair formation with alkaloids, cationic surfactants and some pharmaceutical products. Eriochrome red B is recommended for the determination of quinine at pH 3.6 with extraction into chloroform and measurement at 475 nm.     

Spectrophotometric and fluorometric determination of cobalt

The reaction of Co(II), pyridine-2-aldehyde-2-pyridyl hydrazone (PAPHY) and eosin at pH 5.6 produces the ternary complex Co(L)(HL)E(2) (where HL represents the protonated form of the ligand and E represents the eosinate anion). This complex is extracted by a chloroform-acetone mixture to give a strongly coloured and highly fluorescent extract. Spectrophotometric and fluorometric methods for the determination of Co have been developed with detection limits of 0.017 and 0.008 ppm respectively. Cu(II), Ni, Fe(II), Pd(II) and Hg(II) interfere. The Spectrophotometric method has been successfully applied to the analysis of steels, following ion-exchange separation of Co.