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.     

Sequential potentiometric complexometric redox determination of iron(III) and cobalt(II) with application to alloys

A simple potentiometric method is presented for successive determination of iron(III) and cobalt(II) by complexometric titration of the iron(III) with EDTA at pH 2 and 40 degrees , followed by redox titration of the cobalt(II) complex with 1,10-phenanthroline or 2,2'-bipyridyl at pH 4-5 and 40 degrees , with gold(III). There is no interference in either determination from common metal ions other than copper(II), which severely affects the cobalt determination but can be removed by electrolysis. The method has been successfully applied to determination of iron and cobalt in Kovar and Alnico magnet alloys.     

Determination of cobalt and nickel by graphite-furnace atomic absorption spectrometry after coprecipitation with scandium hydroxide.

Trace amounts of cobalt and nickel in a water sample were quantitatively coprecipitated with scandium hydroxide at pH 8.0-10.5. Because the coprecipitant could be easily dissolved with 1 mol dm(-3) nitric acid, and the presence of up to 10 mg cm(-1) of scandium did not interfere with the graphite-furnace atomic absorption spectrometric determination of cobalt and nickel, the volume of the final solution prepared for the determination could be minimized down to 0.5 cm3. The concentration factor was 400-fold and the detection limits (signal to noise = 2) were 5.0 pg cm(-3) of cobalt and 10.0 pg cm(-3) of nickel in 200 cm3 of the initial sample solution. The 27 diverse ions investigated did not interfere with the determination in at least a 500-fold mass ratio to cobalt or nickel. The proposed method was successfully applied to the determination of trace amounts of cobalt and nickel in river-water samples.     

Solid-phase extraction and atomic absorption spectrometric determination of cobalt using an octadecyl bonded silica membrane disk modified with Cyanex 272

A simple SPE method for determination of cobalt(II) using a C18 bonded silica membrane disk impregnated with Cyanex 272 has been developed. Cobalt(II) was quantitatively sorbed at pH 6.0 from a sample solution and eluted using 10.0 mL 1.0 M HNO3 prior to its flame atomic absorption spectrometric determination. The influence of eluting agents, the minimum volume and maximum flow rate of the eluent, and interfering ions on cobalt(II) was studied. The method developed for cobalt(II) had an LOD of 1.4 microg/L, and a preconcentration factor > 200 with an RSD of 0.6%. The reusability of the modified disk was for 40 cycles. The method was applied for the determination of cobalt in certified samples, urine, and industrial sludge samples.     

Determination of cobalt by substoichiometric extraction with β-hydroxy-naphthaldoxime

A substoichiometric radiochemical solventextraction method is described for the determination of cobalt, employing β-hydroxy-naphthaldoxime and chloroform as reagent and extractant, respectively. The extraction behaviour of the complex of cobalt with the reagent in the pH-range 8–9.5 and the effects of various metal ions on the extraction are critically studied. The method is used to determine the cobalt content in some pharmaceutical drugs.     

The photometric determination of cobalt by extraction with b -nitroso-a-naphthol

An improved procedure has been described for the photometric determination of cobalt by extraction of the β-mtroso-α-naphthol complex with chloroform. This procedure can be applied in the presence of large amounts of foreign elements. Interfering elements are: gold, palladium, platinum and copper (above 25 mg).The method has been applied to the determination of cobalt in steels, non-ferrous alloys and nickel.     

Kinetic determination of cobalt by complexation with pyridine-2-aldehyde 2-pyridylhydrazone and ligand oxidation with bromate

Summary Kinetic Determination of Cobalt by Complexation with Pyridine-2-Aldehyde 2-Pyridylhydrazone and Ligand Oxidation with Bromate Optimum conditions for a kinetic procedure are outlined for the determination of cobalt. The rate of disappearance of pyridine-2-aldehyde 2-pyridylhydrazone (PAPH) in acidic medium is monitored spectrophotometrically at 372 nm. The method is based on the modification of the oxidation rate by complexation of PAPH with cobalt ions. The detection limit has been determined and the limitations to the sensitivity are discussed. A number of foreign ions have been tested for interference and the fundamental basis of their effects is discussed. The method has been used for determination of cobalt in soil samples.     

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 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.     

Gravimetric determination of cobalt and nickel,and their separations from copper with n-benzoylphenylhydroxylamine

N-Benzoylphenylhydroxylamine can be used for the gravimetric determination of cobalt and nickel. The precipitates can be weighed as such, or ignited and weighed as cobalt sulphate or nickclous oxide. Cobalt or nickel can be separated from copper with the reagent.     

Determination of cobalt by substoichiometric extraction with β-hydroxy-naphthaldoxime

A substoichiometric radiochemical solventextraction method is described for the determination of cobalt, employing β-hydroxy-naphthaldoxime and chloroform as reagent and extractant, respectively. The extraction behaviour of the complex of cobalt with the reagent in the pH-range 8–9.5 and the effects of various metal ions on the extraction are critically studied. The method is used to determine the cobalt content in some pharmaceutical drugs. Received: 10 January 1997 / Revised: 11 March 1997 / Accepted: 25 March 1997     

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 studies on complexation reactions of some water-soluble 5-nitro-2-pyridylhydrazones with cobalt. Spectrophotometric and derivative spectrophotometric determination of trace cobalt with 2-benzimidazolyl-3-sulphophenylmethanone 5-nitro-2-pyridylhydrazone

The complexation reactions of four water-soluble hydrazones, 2-quinolyl-3-sulphophenylmethanone 5-nitro-2-pyridylhydrazone, 3-sulphophenyl-2-thiazolylmethanone 5-nitro-2-pyridylhydrazone (STNPH), 2-benzothiazolyl-3-sulphophenylmethanone 5-nitro-2-pyridylhydrazone and 2-benzimidazolyl-3-sulphophenylmethanone 5-nitro-2-pyridylhydrazone (BISNPH), with cobalt(II) were studied spectrophotometrically. These hydrazones react with cobalt(II) to form stable 1:2 (metal:ligand) complexes, except for STNPH, which forms a 1:1 complex, with high molar absorptivities. A sensitive and selective spectrophotometric method for the determination of cobalt with BISNPH has been developed. The cobalt(II)-BISNPH complex is formed quantitatively in the pH range 2.7–9.4 and oxidized rapidly to give the corresponding cobalt(III) complex with an absorption maximum at 517 nm. Beer's law is obeyed over the range 0.02–1.0 μg ml^?1 and the apparent molar absorptivity of the cobalt(III) complex is 6.65 × 10⁴ l mol^?1 cm^?1 at 517 nm. The method was applied to the determination of cobalt in iron and steel samples with satisfactory results. The sensitivity is increased 11-fold by use of second-derivative spectrophotometry.     

Extraction and spectrophotometric determination of cobalt(II) with isonitroso-5-methyl-2-hexanone

A simple and selective method is proposed for the extraction of cobalt(II) for its spectrophotometric determination using (HIMH) as an extractant. Cobalt(II) forms a yellow coloured complex with HIMH which can be extracted into chloroform. The calibration curve is rectilinear in the concentration range 0.1–5.0 μg ml⁻¹ of cobalt(II). The extracted species shows an absorption maximum at 400 nm with molar absorptivity of 1.135×10⁴ l mol⁻¹ cm⁻¹. The method has been applied for the determination of cobalt in synthetic mixtures, pharmaceutical, biological and high speed steel samples.     

H-point standard addition method--first derivative spectrophotometry for simultaneous determination of palladium and cobalt

H-point standard addition method (HPSAM) has been applied for simultaneous determination of palladium and cobalt in trace levels, using disodium 1-nitroso-2-naphthol-3, 6-disulphonate (nitroso-R salt) as a selective chromogenic reagent. Palladium and cobalt in the neutral pHs form red color complexes with nitroso-R in aqueous solutions and making spectrophotometric monitoring possible. Simultaneous determination of palladium and cobalt were performed by HPSAM--first derivative spectrophotometry. First derivative signals at the two pairs of wavelengths, 523 and 589 nm or 513 and 554 nm were monitored with the addition of standard solutions of palladium or cobalt, respectively. The method is able to accurately determine palladium/cobalt ratio 1:10 to 15:1 (wt/wt). Accuracy and reproducibility of the determination method on the various amounts of palladium and cobalt known were evaluated in their binary mixtures. To investigate selectivity of the method and to ensure that no serious interferences were observed the effects of diverse ions on the determination of palladium and cobalt were also studied. The recommended procedure was successfully applied to real and synthetic cobalt or palladium alloys, B-complex ampoules, a palladium-charcoal mixture and real water matrices.     

钴(Ⅱ)催化偶氮胭脂红B的褪色反应特性及应用

基于氢氧内介质中痕量钴对过氧化氢氧化偶氮胭脂红Ｂ的褪色反应的强烈催化作用,建立了催化光度法测定痕量钴的新方法。方法灵敏度为５．２４×１０＾－１２ｇ／ｍＬ,测定范围为０￣３５ｎｇ／１０ｍＬ,对质量浓度为３μｇ／Ｌ的Ｃｏ（Ⅱ）重复测定１１次的相对标准偏差为２．１６％。方法应用于维生素Ｂ１２和矿泉水中痕量钴的测定,结果满意。     

Water-soluble polymers for spectrophotometric and flow injection determination of cobalt with nitroso-R-salt

The water-soluble polymers poly(ethylenimine), quaternized poly(ethylenimine), and poly-4-vinyl-(N-benzyltrimethyl) ammonium chloride were found to be able to change the kinetics of the reaction of cobalt with nitroso-R-salt and the optical density of the cobalt complex formed. The optimum pH range for the complex formation was a wide range from 1 to 10 and at pH 2 the reaction developed instantly. The calibration graph was linear in the range 0.005-2 mug ml(-1). The effective molar absorptivity coefficient of the complex was equal to (2.8+/-0.08)10(3). A spectrophotometric determination method for cobalt with nitroso-R-salt in the presence of water-soluble polymers (before and after membrane preconcentration) and a colorimetric flow injection method were developed. For the flow injection-based spectrophotometric determination, the calibration graph was linear in the concentration range of 0-4.0 mug ml(-1) cobalt with a regression coefficient of 0.9992. The relative standard deviation (R.S.D.) for the determination of 1.0 mug ml(-1) cobalt was 0.9% (ten replicate injections), and at all concentration measured, the R.S.D. of the data was below 5.0%. The proposed FI procedure was applied to river water samples after membrane preconcentration of cobalt. The limit of detection was 4 ng ml(-1).     

Rapid coprecipitation-separation and flame atomic absorption spectrometric determination of lead and cadmium in water with cobalt (II) and ammonium pyrrolidine dithiocarbamate

A coprecipitation technique which does not require complete collection of the precipitate was proposed for the determination of trace lead and cadmium in water with flame atomic absorption spectrometry (FAAS) after preconcentration of lead and cadmium by using cobalt (II) and ammonium pyrrolidine dithiocarbamate (Co-APDC) as coprecipitant and known amount of cobalt as an internal standard. Since lead, cadmium and cobalt were well distributed in the homogeneous precipitate, the concentration ratio of lead to cobalt, and cadmium to cobalt remained unchanged in any part of the precipitate. The amount of lead and cadmium in the original sample solution can be calculated respectively from the ratio of the absorbance values of lead and cadmium to cobalt in the final sample solution that is measured by FAAS and the known amount of the lead and cadmium in the standard series solutions. The optimum pH range for quantitative coprecipitation of lead and cadmium is from 3.0 to 4.5. The 16 diverse ions tested gave no significant interferences in the lead and cadmium determination. Under optimised conditions, lead ranging from 0 to 40?µg and cadmium ranging from 0 to 8?µg were quantitatively coprecipitated with Co-APDC from 100?mL sample solution (pH?～?3.5). This coprecipitation technique coupled with FAAS was applied to the determination of lead and cadmium in water samples with satisfactory results (recoveries in the range of 94.0–108%, relative standard deviations <6.0%).     

The determination of nickel with dimethylglyoxime in the presence of iron and cobalt

A method for the determination of nickel in the presence of both ferric iron and cobalt is presented. The nickel is precipitated directly with dimethylglyoxime, without the prior reduction of the iron. The interference of the iron and cobalt is eliminated by the addition of N,N-dihydroxyethylglycine, which chelates the iron and prevents the formation of the iron-cobalt-dimethylglyoxime contaminant.     

A sensitive and simple extractive-spectrophotometric method for the determination of microgram amount of cobalt by using alpha-benzilmonoxime.

Alpha-benzilmonoxime has been used for the extraction and determination of cobalt at microgram amount. The reagent reacts with cobalt(II) in the pH range of 8.8 - 9.3 to form a yellow-color chelate, which is extracted in chloroform, toluene, and some other non-polar solvents. The chelate is stable in chloroform for about one day. Under the optimum conditions of the a-benzilmonoxime concentration and pH of 9.0, Beer's law was obeyed in the concentration range of 0.08 - 2.2 microg/ml cobalt. The molar absorptivity of the extracted species was 2.55 x 10(4) dm3/mol cm at 380 nm, with a detection limit of 0.01 microg/ml cobalt. Relative standard deviations of 0.4, 0.8 and 2.3% were found for the determination of cobalt concentrations of 2.2, 1.1 and 0.08 microg/ml, respectively. The effect of diverse ions on the determination of 1.00 microg/ml of cobalt has been studied. The method was applied to the determination of cobalt in vitamin B12 and B-complex ampoules, a Co2O3-Co3O4 laboratory chemical mixture and some synthetic alloy samples. The method is sensitive, simple, rapid and accurate.