Cobalt spectrophotometric determination

In another spectrophotometric procedure Motomizu [224] adds to the sample (2 litres) 40% (w/v) sodium citrate dihydrate solution (10 ml) and a 0.2% solution of 2-ethylamino-5-nitrosophenol in 0.01 M hydrochloric acid (20 ml). After 30 min, add 10% aqueous EDTA (10 ml) and 1,2-dichloroethane (20 ml), mechanically shake the mixture for 10 minutes, separate the organic phase and wash it successively with hydrochloric acid (1 2) (3 x 5 ml), potassium hydroxide (5 ml), and hydrochloric acid (1 2) (5 ml). Filter, and measure the extinction at 462 nm in a 50 mm cell. Determine the reagent blank by adding EDTA solution before the citrate solution. The sample is either set aside for about 1 day before analysis (the organic extract should then be centrifuged), or preferably it is passed through a 0.45 xm membrane-filter. The optimum pH range for samples is 5.5 - 7.5. From 0.07 to 0.12 p,g/l of cobalt was determined there is no interference from species commonly present in seawater. 

Courtot-Coupez and Le Bihan [209,210] determined non-ionic detergents in sea- and fresh-water samples at concentrations down to 2 pg/1 ppm by benzene extraction of the tetrathiocyanatocobaltate (II) (NH4)2 (Co(SCN)4) [ 182] detergent ion-pair, followed by atomic absorption spectrophotometric determination of cobalt [209]. 

The amount of ammonia volatilized was determined from the amount of standard sulfuric acid consumed in the traps. Ethylenediamine was determined by the salicylaldehyde method (14). The sample for cobalt(II) determination was made slightly acidic with hydrochloric acid immediately upon removal of the sample from the reaction flask, in order to prevent further oxidation of the cobalt (18). The carbon was removed by filtration, and the cobalt (II) concentration was determined spectrophotometrically as the cobalt-ammonium thiocyanate complex, (NH4)2Co(NCS)4 (28). 

Cobalt is determined in this extract by a spectrophotometric procedure involving the reaction of molybdenum with 2-nitrosonaphth-l-ol and evaluation of the carbon tetrachloride soluble complex formed at 307 nm. 

Burke and Yoe (8) described the simultaneous spectrophotometric determination of cobalt and nickel in acidic ethanol. An analogous procedure in acidic dimethylformamide (DMF) was described by Ayers and Annand (3). By simultaneously solving Beer s law equations, the concentration of each metal can be determined (Eqs. 1 and 2). In general, the results of these two methods were similar. However, Burke and Yoe (8) found that iron and copper interfered with the measurement while Ayers and Annand (3) found interference from manganese. 

An alternative to qdt, (.S )-2-(3-mercaptoquinoxalinyl)thiourinium, is stable and soluble in aqueous ethanol solutions unlike qdt (27). At pH 10 in ammonia-ammonium chloride buffer, this reagent hydrolyzes to qdt. (5)-2-(3-Mercapto-quinoxalinyl)thiourinium has been used for the simultaneous detection of nickel and cobalt and the determination of palladium (27, 28). A related reagent, 6-nitro-(S)-2-(3-mercaptoquinoxalinyl)thiourinium has also been used in metal analysis (7). This reagent is hydrolyzed in ammonia buffer to generate 6-nitro-2,3-quinoxalinedithiol (nqdt). Following adjustment to pH 2.0, the mixture is extracted with methyl isobutyl ketone and spectrophotometrically analyzed. 6-Nitro-(5)-2-(3-mercaptoquinoxalinyl)thiourinium has been used for the simultaneous spectrophotometric determination of nickel and cobalt by the quantification of [Ni(nqdt)2]2 (710 nm, e = 20,700 L mol 1cm 1) and [Co(nqdt)2]2 (530 nm, e = 40,000 L moE cm-1), respectively. 

Cobalt is determined spectrophotometrically using the absorption spectrum of CoCU " in 10 M hydrochloric acid. Iodine is determined by precipitation of silver iodide after reduction of the complex with sulfur dioxide. Titratable H" " is determined by a potentiometric pH titration. AnaL Calcd. for H3[Co4l3024Hi2] 3H20 Co, 22.04 I, 35.59 titratable H+, 0.282 ratio CorlrH" " = 1 0.75 0.75. Found Co, 22.0 I, 35.45 titratable H", 0.285 ratio Co.T H = 1 0.75 0.75. 

Spectrophotometric determination at 550 nm is relatively insensitive and is usehil for the determination of vitamin B 2 high potency products such as premixes. Thin-layer chromatography and open-column chromatography have been appHed to both the direct assay of cobalamins and to the fractionation and removal of interfering substances from sample extracts prior to microbiological or radioassay. Atomic absorption spectrophotometry of cobalt has been proposed for the deterrnination of vitamin B 2 feeds. Chemical methods based on the estimation of cyanide or the presence of 5,6-dimethylben2iniida2ole in the vitamin B 2 molecule have not been widely used. 

EXPERIMENT 2.3 ANALYSIS OF COBALT COORDINATION COMPOUNDS I SPECTROPHOTOMETRIC DETERMINATION OF COBALT1-5... 

Thiocyanate complexes play an important role not only in the spectrophotometric determination of cobalt, but also in its separation from other metals [8-11]. The complex has been extracted with Alamine, TOPO [9], methyltrioctylamine [10], and DAM [11]. 

Nitroso-R salt (formula 18.3) is a derivative of l-nitroso-2-naphthol. Both reagents are specific for cobalt. The sulphonate groups in the molecule of nitroso-R salt render this reagent and its cobalt complex soluble in water but insoluble in non-polar solvents. Hence, nitroso-R salt is used to determine cobalt spectrophotometrically in aqueous medium [29]. In acidic solution (pH 4), cobalt(Il) is oxidized to Co(IlI). 

Different components such as reactors, detectors and mini-columns can be added to or removed from the manifold in order to improve system performance but the strategy can lead to occurrence of the Schlieren effect. Reactor interchange has been used to attain two different analytical signals under two different sample handling conditions, thus allowing the implementation of differential kinetics. The feasibility of this approach was demonstrated in relation to the spectrophotometric determination of cobalt and nickel in steels [110]. The method involved complexation with citrate followed by time-dependent dissociation and reaction with 4-(2-pyridylazoresorcinol). 

D.T. Burns, N. Chimpalee, M. Harriott, Flow-injection spectrophotometric determination of cobalt by extraction as tetrathiocyanatocobaltate(II) with the ethyl-enebis(triphenylphosphonium) cation, Anal. Chim. Acta 225 (1989) 123. 

The spectrophotometric determination of cobalt and nickel using 2-hydroxybenzaldehyde thiosemicarbazone [48]. 

Recent contributions to the analytical chemistry of this group include an improved determination of total belladonna alkaloids, expressed as hyoscyamine content, based on a simple extraction and titration procedure. A method for the estimation of hyoscine and hyoscyamine utilizes u.v. spectrophotometric determination of the alkaloids following t.l.c. separation.Another method involves the spectrophotometric determination of cobalt thiocyanate complexes, e.g. of n-butylscopolammonium bromide.Further procedures based on column, t.l.c.,g.l.c., or paper chromatographic separation, have been reported. 

Andac M., Asan A and Isildak I. (2001) Flow-injection spectrophotometric determination of cobalt/fl) at low pg H levels with 4-benzylpiperidinedithiocarbamate. Analytica Chimica Acta, 434,143-147. 

Katiyar, G. S. Haidar, B. C. Rapid extraction and spectrophotometric determination of cobalt(II) with isonitrosothiocamphor. J. Indian Chem. Soc. 1986, 63, 937-938. 

In the case of cobalt(II) the results obtained by the solubility method could be verified by a spectrophotometric determination of the equilibrium constant. The value obtained in this way is given above, the agreement of the two methods being satisfactory. The advantage of the solubility method lies in its applicability in cases in which the spectrophotometric method cannot be used. 

HCI-n-butanol-acetone (3 1 6) W2S = HCl-n-pentanol-acetone (3 1 6) W27 = HCl-n-hexanol-acetone(3 1 6) M28-M.M = HCl-DMSO-piopanol-2 in 1 1 1, 2 1 1, 1 2 1, and 1 1 2 ratio respectively. Detection Conventional spot test reagents used for detection of Cu, Ni, Coi, 2j, Mn, and Fe . Conditions Ascending technique, run 10 cm. layer thickness 0.25 mm. plate activation at 110 2°C for I h. loading volume 10 Remarks Qualitative separation of transition metal chlorosulphates and quantitative spectrophotometric determination of cobalt chlorosulphate were discussed. Source A. Mohammad, K. T. Nasim, J. Ahmad, and M. Najar P. A.. Analusis. 23 243 (1995). 

Iodine vapor is generally suitable for visualization of nonionics and is compatible with densitometry (14,46,47). The plate must be covered with another glass plate or photographed immediately, since the iodine color fades rapidly in air (48). Acid blue 158 has been shown to be a good, general purpose visualizer for surfactants (49). It was demonstrated for detection of AE and NPE as well as ethoxylated amines and an alkanolamide. Cobalt thiocyanate reagent, commonly used for spectrophotometric determination of nonionic surfactants, has also been used as a visualizer for qualitative TLC analysis (50.51). Formation of the 3,5-dinitrobenzoate ester derivatives allows visualization with UV light of surfactants without chromophores (52). 

Kasahara, 1., K. Hashimoto, T. Kawabe, A. Kunita, K. Magawa, N. Hata, S. Taguchi, K. Goto, Spectrophotometric determination of anionic surfactants in sea water based on ion-pair extraction with te 2-(5-trifluoromethyl-2-pyridylazo)-5-diethylaminophenolato cobalt(lll). Analyst, 1995,120,1803-1807. 

Concentration limits of the diphosphate-ion, admissible to determination of magnesium and cobalt, manganese and cobalt, zinc and cobalt by spectrophotometric method with application of the l-(2-pyridylazo)-resorcinol (PAR) are presented. Exceeding maintenance of the diphosphate-ion higher admissible supposes a preliminary its separation on the anionite in the H+-form. The optimum conditions of cobalt determination and amount of the PAR, necessary for its full fastening are established on foundation of dependence of optical density of the cobalt complex with PAR from concentration Co + and pH (buffer solutions citrate-ammoniac and acetate-ammoniac). 

Lemli and Knockaert [33] described a spectrophotometric method for the determination of miconazole nitrate suspensions and other organic bases in pharmaceutical preparations by the use of cobalt thiocyanate. The drug and the amines (as their anhydrous hydrochlorides in dichloromethane) react with solid cobalt thiocyanate to form an ion-pair complex that contains two molecules of base to one [Co(SCN)4]2. The complex is determined quantitatively by spectrophotometry versus dichloromethane at 625 nm with rectilinear response for up to 400 pg/mL of the base. This method was applied to miconazole nitrate suspensions and the coefficient of variations were generally <2%. 

Various methods have been proposed for the determination of traces of cobalt in seawater and brines, most necessitatingpreconcentration. Solvent extraction followed by spectrophotometric measurements [223-230] is the most popular method but has many sources of error the big difference in the volumes of the two phases results in mixing difficulties, and the solubility of the organic solvent in the aqueous phase changes the volume of organic phase, resulting in decreased reproducibility of the measurements. In many cases, excess of... 

Malahoff et al. [240] used a shipboard flow injection spectrophotometric technique to determine ppt concentrations of cobalt in seawater... 

Nickel has been determined spectrophotometrically in seawater in amounts down to 0.5 xg/l as the dimethylglyoxime complex [521,522], In one procedure [521] dimethylglyoxime is added to a 750 ml sample and the pH adjusted to 9 -10. The nickel complex is extracted into chloroform. After extraction into 1M hydrochloric acid, it is oxidised with aqueous bromine, adjusted to pH 10.4, and dimethylglyoxime reagent added. It is made up to 50 ml and the extinction of the nickel complex measured at 442 nm. There is no serious interference from iron, cobalt, copper, or zinc but manganese may cause low results. 

In another procedure [522] the sample of seawater (0.5-3 litres) is filtered through a membrane-filter (pore size 0.7 xm) which is then wet-ashed. The nickel is separated from the resulting solution by extraction as the dimethylglyoxime complex and is then determined by its catalysis of the reaction of Tiron and diphenylcarbazone with hydrogen peroxide, with spectrophotometric measurement at 413 nm. Cobalt is first separated as the 2-nitroso-1-naphthol complex, and is determined by its catalysis of the oxidation of alizarin by hydrogen peroxide at pH 12.4. Sensitivities are 0.8 xg/l (nickel) and 0.04 xg/l (cobalt). 

A standard official method has been published for the determination of cobalt in plant material [8 ]. The samples are digested with 1 4 v/v perchloric acidmitric acid and the residue dissolved in nitric acid. Cobalt is then extracted into chloroform as the diethyldithiocarbonate. The latter complex is decomposed by bromine and cobalt extracted into dilute hydrochloric acid. Following the addition of a borate buffer, cobalt is then extracted as the o-nitrocresol complex [9]. Excess coupling agent is removed by repeated extraction with copper acetate solution and cobalt determined spectrophotometrically at 360 nm. See Sects. 7.34.1, 7.34.3 and 7.34.4. 

Heanes [97] has described a method for determining copper, manganese and zinc in ashed plant extracts by flame AA spectrophotometry after cobalt and molybdenum have been assayed on separate aliquots of the same plant extracts by a spectrophotometric procedure [102]. (See Sect. 7.34.3). Ashing aids were necessary to maintain accuracy in the determinations. Concentrations of up to 3.5% m/m of silicon and calcium and 4% m/m of chlorine in the plants did not affect the determinations, but in some instances lower concentrations were determined in plant samples containing equal or higher levels of both added silica and calcium. 

Modified spectrophotometric procedures are described for the quantitative determination of cobalt and molybdenum as the 2-nitrosonaphth-l-olate and toluene-3,4-dithiolate complexes in carbon tetrachloride. The extraction, chelation and phase separation steps permitted rapid sample handling, controlled interferences more effectively and provided accurate assays. The molar absorptivities for cobalt and molybdenum were 5.1 x 104 and 2.5 xl04mol/lcm, respectively, and the detection limits for both elements were 4 ng/g. 

Salama et al. [34] developed and validated a spectrophotometric method for the determination of omeprazole and pantoprazole sodium via their metal chelates. The procedures were based on the formation of 2 1 chelates of both drugs with different metal ions. The colored chelates of omeprazole in ethanol were determined spectrophotometrically at 411, 339, and 523 ran using iron(III), chromium(III), and cobalt(II), respectively. Regression analysis of Beer s plots showed good correlation in the concentration ranges 15-95, 10-60, and 15-150 /ig/ ml of pure omeprazole using iron(III), chromium(III), and cobalt(II), respectively. 

The second-order rate constants for reactions of Co(I)(BDHC) with alkyl halides were determined spectrophotometrically at 400 nm (17). These rate constants are listed in Table VII along with those for Co(I)(corrinoid)(vitamin Bi2s) in methanol at 25°C (35). These data indicate that the SN2 mechanism is operative in the reaction of Co(I)(BDHC) the iodides are more reactive with the cobalt complex than the bromides, and the rate decreases with increasing bulkiness of the alkyl donor. The steric effect is more pronounced for Co(I)(BDHC) than for vitamin B12s, which is confirmed by the rate ratios for... 

The thiocyanate method has been used for determining cobalt in vitamin B12 [94], steel [24,94], and nickel [25]. Cobalt present in considerable amounts in alloys with aluminium, nickel, chromium, manganese, copper, and iron was determined by the differential spectrophotometric analysis [95]. 

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