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.     

An investigation into the diastereoselective palladation of oxazoline appended cobalt metallocenes

The diastereoselective reactions of palladium acetate with (η⁵-(S)-2-(4-methylethyl)oxzazolinylcyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt, which gives a planar chiral palladacycle with (_pR) configuration, and (η⁵-(S)-2-(4-dimethylethyl)oxzazolinylcyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt, which results in the opposite (_pS) configuration, are shown to be a consequence of these reactions displaying thermodynamic and kinetic control, respectively.     

Application of the Suzuki reaction to the asymmetric desymmetrisation of 1,2- and 1,3-disubstituted bulky cobalt metallocenes

Reaction of (η⁵-cyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt with Hg(OAc)₂ (2.3 equiv) in 1:1 MeOH/CH₂Cl₂ followed by the addition of LiCl resulted in the formation of (η⁵-1,2-dichloromercuricyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt (33%) and its 1,3-isomer (6%). Following conversion into their corresponding diiodides these compounds were desymmetrised by Suzuki reactions with ArB(OH)₂ employing [(R)-BINAP]PdCl₂, with the highest ee of 24% being obtained for (η⁵-1-iodo-3-(2-methoxyphenyl)cyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt.     

Cloud point formation based on mixed micelles in the presence of electrolytes for cobalt extraction and preconcentration

A new micelle-mediated phase separation of metal ions, applied for preconcentrating trace levels of cobalt as a prior step to its determination by flame atomic spectroscopy, has been developed. Two methods were proposed employing both Triton X-100 and sodium dodecyl sulfate (SDS) as a mixed micellar system while the phase separation was induced by HCl or NaCl addition. Cobalt was complexed with pyridylazo compounds (PAN, PAR, 5-Br-PADAP) in an aqueous surfactant medium and it was concentrated in the surfactant rich phase after phase separation. The chemical variables affecting the cloud point extraction were evaluated, optimized and successfully applied to cobalt determination in pharmaceutical samples. Under the optimized conditions, the preconcentration system permitted limits of detection as 1.1 and 1.6 μg l⁻¹ cobalt, respectively, when HCl and NaCl were used. Both proposed methods showed linear calibration within a 25-200 μg l⁻¹ cobalt range. The extraction efficiency was investigated at different cobalt concentrations (40-185 μg l⁻¹) and good recoveries (98-102%) were obtained by using NaCl as electrolyte. The results obtained were compared with those observed with ET AAS.     

Spectrophotometric determination of cobalt(II) with 2-(3′-sulfobenzoyl)pyridine benzoylhydrazone

A simple method has been described for the Spectrophotometric determination of cobalt(II) with 2-(3′-sulfobenzoyl)pyridine benzoylhydrazone (SBPBH). In aqueous solution, cobalt(II) reacts with SBPBH to form a yellow complex, which is not destroyed even by the addition of 3.8 M perchloric acid. The absorption maximum of the complex in 1.5 M perchloric acid medium was found to be 400 nm; the molar absorptivity was 2.17 × 10⁴ liters mol⁻¹ cm⁻¹. The proposed method is fairly selective and has been applied to the determination of cobalt in standard alloy steel samples.     

Determination of ultra-trace levels of cobalt by ion chromatographic separation and chemiluminescence detection

A luminol chemiluminescence detection/flow injection analysis technique coupled with ion chromatography (IC) has been examined for the selective determination of cobalt (II) at pg ml^?1 levels. A barium chloride solution was used as an eluent in the IC to separate cobalt(II) from interferents. When a 100-μ1 sample injection volume was used, the detection limit was 1.0 pg ml^?1 cobalt; the minimum detectable amount of cobalt was 100 fg. The calibration graph was linear above 10 pg ml^?1 and the linear dynamic range extended over six orders of magnitude. The relative standard deviation for ten replicate measurements of 30 pg ml^?1 cobalt was 3.8%. The results of the analysis of a synthetic sample corresponding to a boiling-water reactor coolant and some commercially available copper(II) standard solutions are given.     

Dispersive liquid–liquid microextraction and spectrophotometric determination of cobalt in water samples

A new simple and rapid dispersive liquid–liquid microextraction has been applied to preconcentrate trace levels of cobalt as a prior step to its determination by spectrophotometric detection. In this method a small amount of chloroform as the extraction solvent was dissolved in pure ethanol as the disperser solvent, then the binary solution was rapidly injected by a syringe into the water sample containing cobalt ions complexed by 1-(2-pyridylazo)-2-naphthol (PAN). This forms a cloudy solution. The cloudy state was the result of chloroform fine droplets formation, which has been dispersed in bulk aqueous sample. Therefore, Co-PAN complex was extracted into the fine chloroform droplets. After centrifugation (2 min at 5000 rpm) these droplets were sedimented at the bottom of conical test tube (about 100 µL) and then the whole of complex enriched extracted phase was determined by a spectrophotometer at 577 nm. Complex formation and extraction are usually affected by some parameters, such as the types and volumes of extraction solvent and disperser solvent, salt effect, pH and the concentration of chelating agent, which have been optimised for the presented method. Under optimum conditions, the enhancement factor (as the ratio of slope of preconcentrated sample to that obtained without preconcentration) of 125 was obtained from 50 mL of water sample, and the limit of detection (LOD) of the method was 0.5 µg L^?1and the relative standard deviation (RSD, n = 5) for 50 µg L^?1 of cobalt was 2.5%. The method was applied to the determination of cobalt in tap and river water samples.     

The simultaneous spectrophotometric determination of nickel and cobalt in mixtures with 3-hydroxypicolinealdehyde azine

The properties of the nickel complex of 3-hydroxypicolinealdehyde azine are described (λ_max = 480 nm, ? = 4.2· 10⁴ l mol^-1 cm^-1). The optimal conditions for a selective and sensitive spectrophotometric determination of nickel are discussed. The absorption spectra of the nickel and cobalt (II) complexes of 3-hydroxypicolinealdehyde azine are sufficiently different to permit the simultaneous spectrophotometric determination of both ions when the absorbances are measured at 480 nm and 540 nm. Mixtures containing nickel and cobalt in ratios from 0.1 to 10 can be analysed. The method has been applied to process catalysts on alumina supports.     

A rapid spectrophotometric method for the determination of cobalt in industrial, environmental, biological, pharmaceutical and soil samples using bis(5-bromosalicylaldehyde)orthophenylenediamine

A very simple, ultra-sensitive and fairly selective spectrophotometric method is presented for the determination of cobalt at trace levels using bis(5-bromosalicylaldehyde)orthophenylenediamine (BBSOPD). The method is based on the reaction of nonabsorbent BBSOPD in a slightly acidic (0.001–0.0025 M H₂SO₄ or pH 3.4–4.0) and 50% N,N-dimethylformamide media with cobalt(II) to produce a highly absorbent orange colored chelate-product with an absorption maximum at 473 nm. The reaction is instantaneous and the absorption remains stable for 24 h. The average molar absorption coefficient and Sandell’s sensitivity were found to be 5.84 × 10⁴ l mol^-1 cm^-1 and 9.0 ng cm^-2 of cobalt(II), respectively. Linear calibration graphs were obtained for 0.02–4.0 mg l^-1 of Co(II). The stoichiometric composition of the chelate is 1:1 (Co(II):BBSOPD). A large excess of over 50 cations, anions and complexing agents do not interfere in the determination. The method was successfully used for the determination of cobalt in several standard reference materials (steels and alloys), environmental waters (potable and polluted), biological samples (human blood and urine), pharmaceutical and soil samples and solutions containing both cobalt(II) and cobalt(III) as well as some complex synthetic mixtures. The method has high precision and accuracy.     

On-line preconcentration and determination of cobalt by chelating microcolumns and flow injection atomic spectrometry

A simple and sensitive flow injection analysis-atomic absorption spectrometric procedure is described for the determination of cobalt. The method is based upon on-line preconcentration of cobalt on a microcolumn of 2-nitroso-1-naphthol immobilized on surfactant coated alumina. The trapped cobalt is then eluted with ethanol (250 μl) and determined by flame atomic absorption spectrometry. The analytical figures of merit for the determination of cobalt are as follows: detection limit (3 S), 0.02 ng ml⁻¹; precision (RSD), 2.8% for 20 ng ml⁻¹ and 1.7% for 70 ng ml⁻¹ of cobalt; enrichment factor, 125 (using 25 ml of sample). The method has been applied to the determination of cobalt in water samples, vitamin B₁₂ and B-complex ampoules and accuracy was assessed through recovery experiment and independent analysis by furnace AAS.     

Adsorptive voltammetric determination of the trace amount of cobalt

The synthesis of 5-Br-PADNm and the polarographic characteristics of this cobalt(II) complex are reported. In 0.15 mol/l sodium hydroxide cobalt(II) forms a 1 2 complex with 5-Br-PADNm. In the presence of 0.0030% Triton X-100 the complex gives an adsorptive polarographic wave at — 0.90 V, which is recommended for determination of cobalt down to 10^–10 mol/l. The proposed method has been applied to the trace cobalt in natural water, hair and tea samples, with a relative error less than 10%.     

A kinetic method of determination of cobalt in zinc and cadmium selenide

Summary A kinetic method of cobalt determination has been applied for the determination of this element in zinc and cadmium selenides. The method is based on the catalytic effect of cobalt on the oxidation of Direct Blue 6B (C. I. 24410) by hydrogen peroxide at pH=10.8 and in the presence of tiron as an activator. The trace amounts of cobalt have been separated from the bulk zink and cadmium by means of the ion exchanger Lewatit 5080. In samples of 20–100 mg cobalt can be determined in the range of 7.1·10^–5%–2.4·10^–4%.

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Eine kinetische Methode zur Bestimmung von Kobalt in Zink- und Cadmiumselenid

Zusammenfassung Das Verfahren beruht auf dem katalytischen Effekt von Kobalt bei der Oxydation von Direkt Blau 6B (C. I. 24410) durch Wasserstoffperoxid bei pH 10,8 in Gegenwart von Tiron als Aktivator. Die Kobaltspuren wurden von der Hauptmenge Zink und Cadmium mit Hilfe des Ionenaustauschers Lewatit 5080 abgetrennt. In 20–100 mg Probe kann Kobalt in Mengen von 7,1·10^-5 bis 2,4·10^–4% bestimmt werden.

     

Direct spectrophotometric method for the determination of cobalt with indane 1,2,3-trionetrioxime in aqueous medium

A simple, sensitive and selective Spectrophotometric method has been developed for the determination of cobalt using indane 1,2,3-trionetrioxime (ITT): The method is based on the colour reaction between ITT and cobalt(II) in sodium acetate-acetic acid buffer (pH 4.5–7.5) medium. The calibration graph for measurement at 320 nm is linear in the range 1.18–23.60g of cobalt per 25 ml, with molar absorptivity of 5.32×10⁴1mol^–1 cm^–1. The effect of interfering ions has been studied and the method was applied to the determination of cobalt in alloys, with good results.     

The relaxation spectra of nickel(II) and cobalt(II) arginine complexes

The temperature-jump method has been used to determine the nickel(II)- and cobalt(II)-arginine complexation kinetics. In the pH range studied, the neutral form of the ligand, HL, is the attacking, as well as the complexed, ligand species. The reactions reported on are of the type where n = 1, 2, 3 and M is Ni or Co. At 25° and ionic strength 0.1M the association rate constants are: for nickel(II) k₁ = 2.3 × 10³(±20%), k₂ = 2.4 × 10⁴(±20%), k₃ = 3.5 × 10⁴(±40%) M^?1 sec^?1; for cobalt(II) k₁ = 1.5 × 10⁵(±20%), k₂ = 8.7 × 10⁵(±20%), k₃ = 2.0 × 10⁵(±40%) M^?1 sec^?1. Arginine binds to metal ions less well than homologous chelating agents due to the electrostatic repulsion arising from the positively charged terminus of the zwitterion. Kinetically, the effect appears in the association rate constants with nickel reactions more strongly influenced than cobalt.     

Complexation of cobalt(II) perchlorate with crown ethers. Synthesis,properties and structure of complexes of cobalt(II) perchlorate with 16-crown-5 and its lariat derivatives

Complexes of cobalt(II) perchlorate with 16-crown-5 (L¹) and its two lariat derivatives, 15,15-dimethyl-16-crown-5 (L²) and 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (L³), have been prepared and characterized. The crystal structure of [Co(L³)H₂O)](ClO₄)_{_2} has been determined by X-ray crystallography. The cobalt(II) ion is heptacoordinated with five crown ether oxygen atoms at the equatorial plane, a side arm oxygen atom and a water molecule at the apical position. The coordination polyhedron of cobalt is a distorted pentagonal bipyramid with the average Co-O(crown) distance of 2.20(2)Å.     

Preconcentration of trace amounts of cobalt (II) ions in water and agricultural products samples using of 5-(4-dimethylaminobenzylidene) rhodanin modified SBA-15 sorbent prior to FAAS determination

In the present study, the ?5-(4-dimethylaminobenzylidene)rhodanin-modified SBA-15? was applied as stable solid sorbent for the separation and preconcentration of trace amounts of cobalt ions in aqueous solution. SBA-15 was modified by ?5-(4-dimethylaminobenzylidene)rhodanin reagent. The sorption of Co²⁺ ions was done onto modified sorbent in the pH range of 6.8–7.9 and desorption occurred in 5.0 mL of 3.0 mol L^?1 HNO₃. The results exhibit a linear dynamic range from 0.01 to 6.0 mg L^?1 for cobalt. Intra-day (repeatability) and inter-day (reproducibility) for 10 replicated determination of 0.06 mg L^?1 of cobalt was ±1.82% and ?±1.97%?. Detection limit was 4.2 µg L^?1 (3S_b, n = 5) and preconcentration factor was 80. The effects of the experimental parameters, including the sample pH, flow rates of sample and eluent solution, eluent type and interference ions were studied for the preconcentration of Co²⁺. The proposed method was applied for the determination of cobalt in standard samples, water samples and agricultural products.     

Electrothermal atomic absorption spectrometric determination of cobalt in steel after chloroform extraction of its 1-nitroso-2-naphthol complex

Direct determination of μg g^-1 levels of cobalt in steels and corrosion products by electrothermal atomic absorption is difficult because of suppression of the cobalt signal by mineral acids and other metals. Extraction or cobalt with 1-nitroso-2-naphthol into chloroform in the presence of citrate overcomes this problem. Samples (0.4–10 mg) may be dissolved in a variety of acids, and a detection limit of 0.005 μg g^-1 in the chloroform extract is obtained.     

Le dosage spectrophotometrique du cobalt dans le fer de tres haute purete

A spectrophotometric study of the cobalt-β-nitroso-α-naphthol complex between 200 and 350 nm showed the existence of a very sensitive absorption maximum at 308 nm. Utilization of this wavelength allows cobalt in the range 10^-6–10^-5 g to be determined with good precision. The proposed method is very suitable for the determination of cobalt in high-purity iron.     

The application of photo-oxidation to the determination of stable cobalt in sea water

A method is described for the determination of nanogram quantities of cobalt in a 1-1 sample of sea water after preconcentration with sub-milligram quantities of manganese dioxide formed by the oxidation of manganese(II) in a photochemical reactor. The cobalt is measured by pulse polarography as the dimethylglyoximate after dissolving the manganese dioxide deposit adhering to the quartz jacket surrounding the ultraviolet lamp. The detection limit of the method is ca. 0.6 ng Co 1^-1.     

Synthesis and spectroscopic characterization of cobalt porphyrins and their catalytic activity towards dioxygen reduction

The synthesis and spectroscopic characterization of cobalt(Ⅱ) 5-(4-pyridyl)-10,15,20-triphe-nylporphyrin,cobalt(Ⅱ) 5-(4-N-hexadecylpyridiniumyl)-10,15,20-triphenylporphyrin bromide andcobalt(Ⅱ) 5-(2-aminophenyl)-10,15,20-triphenyl-porphyrin are reported.The corresponding copperand vanadyl derivatives ((TriP)Cu,[(hTriP)Cu]~+Br~- and [(hTriP)VO]~+Br~-) were also studied.Eachmetalloporphyrin was characterized by UV-visible,ESR and ~1H NMR spectroscopy.These me-talloporphyrins can be firmly adsorbed on the glassy carbon (GC) surface.The catalytic reduction ofdioxygen at GC electrodes modified by these catalysts was studied by cyclic voltammetry (CV).Thekinetic process of dioxygen reduction at the cobalt porphyrin-modified electrodes was studied with arotating ring disk electrode.