DETERMINATION OF COBALT

The effects of vaiious cationic interferences on percent recovery of Cobalt were studied. The method was successfully applied for the determinations of Cobalt ion from synthetic and water samples. 

Determination of cobalt as cobalt tetrathiocyanatomercurate(II) (mercurithio-cyanate) Discussion. This method is based upon the fact that cobalt (II) in almost neutral solution forms a blue complex salt Co [ Hg( SCN )4] with a reagent... 

Cobalt in steel Discussion. An alternative, but less sensitive, method utilises 2-nitroso-l-naphthol, and this can be used for the determination of cobalt in steel. The pink cobalt(III) complex is formed in a citrate medium at pH 2.5-5. Citrate serves as a buffer, prevents the precipitation of metallic hydroxides, and complexes iron(III) so that it does not form an extractable nitrosonaphtholate complex. The cobalt complex forms slowly (ca 30 minutes) and is extracted with chloroform. 

McIntyre, N. S., Cook M. G., and Boase, D. G. "Flameless Atomic Absorption Determination of Cobalt, Nickel, and Copper - A Comparison of Tantalum and Molybdenum Evaporation Surfaces". Anal. Chem. (1974), 46, 1983-1987. 

Analytical procedures for the determination of cobalt in seawater generally use graphite furnace absorption spectrometry after a preconcentration step... 

Sakamoto [243] determined picomolar levels of cobalt in seawater by flow injection analysis with chemiluminescence detection. In this method flow injection analysis was used to automate the determination of cobalt in seawater by the cobalt-enhanced chemiluminescence oxidation of gallic acid in alkaline hydrogen peroxide. A preconcentration/separation step in the flow injection analysis manifold with an in-line column of immobilised 8-hydroxyquinoline was included to separate the cobalt from alkaline-earth ions. One sample analysis takes 8 min, including the 4-min sample load period. The detection limit is approximately 8 pM. The average standard deviation of replicate analyses at sea of 80 samples was 5%. The method was tested and inter calibrated on samples collected off the California coast. 

Tominaga et al. [682,683] studied the effect of ascorbic acid on the response of these metals in seawater obtained by graphite-furnace atomic absorption spectrometry from standpoint of variation of peak times and the sensitivity. Matrix interferences from seawater in the determination of lead, magnesium, vanadium, and molybdenum were suppressed by addition of 10% (w/v) ascorbic acid solution to the sample in the furnace. Matrix effects on the determination of cobalt and copper could not be removed in this way. These workers propose a direct method for the determination of lead, manganese, vanadium, and molybdenum in seawater. 

Donat and Bruland [217] conducted a direct determination of cobalt and nickel in seawater by differential pulse cathodic scanning voltammetry, preceded by absorptive collection of cyclohexane-1,2 dioxime complexes. 

Huynk et al. [218] also used differential pulse cathodic stripping voltammetry for the determination of cobalt and nickel in seawater by dimetbylgly-oxime complexation. They report detection hmits of 0.002 pg/1 for cobalt and 0.005 xg/l for nickel. 

Stiller et al. [824] have described the determination of cobalt, copper, and mercury in Dead Sea water by neutron activation analysis followed by X-ray spectrometry and magnetic deflection of /i-ray interference. 

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]. 

Two polarographic methods have been developed for the determination of cohalt(II) at concentrations ranging from approximately 1 to 80 mM in an aqueous sample. For the first method [15], which is suitable for samples containing large amounts of nickel]11), the cobalt(II) is oxidized to Co(NH3)6 in an ammoniacal medium with the aid of sodium perborate, after which the cobalt(III) species is determined. A second procedure [16] entails the use of lead dioxide in an acetic acid-acetate buffer containing oxalate to convert cobalt(II) to the 0(0204)3 ion, which can be subjected to polarographic reduction. This latter approach is well suited to the determination of cobalt in the presence of copper(II), iron(III), nickel(II), tin(IV), and zinc(II), whereas the chief interferences are cerium, chromium, manganese, and vanadium. 

Clement and Paris [17] have devised a pair of methods for the determination of cobalt in steels, especially materials encountered in the nuclear industry. In the first technique, suitable for the analysis of solutions containing 8 to 160 mM cobalt(II), iron(III) is used to oxidize cobalt(II) in a picolinic acid medium, after which the resulting iron(II) is titrated po-tentiometrically with a standard solution of cerium(IV). An alternative procedure, for concentrations of cobalt(II) below 8 mM, involves a constant-current coulometric titration with electrogenerated cerium (IV) to measure the iron(II) that arises from the original reaction between cobalt(II) and iron(III). 

Preliminary results have been published [18] that describe the voltammet-ric determination of cobalt(II) in molten... 

A Beckman Model DU spectrophotometer was used for the spectrophoto-metric determination of cobalt (II). 

M. Felipe-Sotelo, A. Carlosena, J. M Andrade, E. Fernandez, P. Lopez-Mahia, S. Muniategui and D. Prada, Development of a slurry-extraction procedure for direct determination of cobalt by electrothermal atomic absorption spectrometry in complex environmental samples. Anal. Chim. Acta, 522(2), 2004, 259-266. 

B. S. Iversen, A. Panayi, J. P. Camblor and E. Sabbioni, Simultaneous determination of cobalt and manganese in urine by electrothermal atomic absorption specttrometry. Method development using a simplex optimisation approach, J. Anal. At. Spectrom., 11(8), 1996, 591-594. 

Preparation of an ultrasonic slurry of the sample is occasionally used, as for example in the determination of cobalt, nickel and copper [200], selenium [39] and arsenic and antimony [40]. Extraction of leaves with a chloroform solution of xanthate completely extracted cadmium [41,103]. X-ray fluorescence spectroscopy is a nondestructive method of analysing plant materials if they can be converted into a suitable form for presentation to the instrument. 

The determination of cobalt by atomic absorption spectrometry is discussed under Multi-Metal Analysis of Soils in Sect. 2.55. 

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. 

In general, these findings on the effects of ashing aids support those previously reported for determinations of cobalt and molybdenum in other aliquots of the same plant extract. 

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. 

Heanes [102] compared determinations of cobalt and molybdenum in various plant materials by wet and dry digestion procedures. 

International Standard Organization. 1986. Water quality. Determination of cobalt, nickel, copper, zinc, cadmium and lead. Flame atomic absorption spectrometric methods. ISO 8288. International Organization for Standardization, Case Postale 56, CH-1211, Geneva 20 Switzerland. 

Ion chromatography has been applied to the determination of cobalt, nickel, copper, zinc and cadmium as their EDTA complexes using anion separation and suppressor columns and 0.03pm sodium bicarbonate0.03gm sodium carbonate [28] eluant and a conductiometric detector. 

A. S. Ribeiro, M. A. Vieira, A. F. Silva, D. L. G. Borges, B. Welz, U. Heitmann, A. J. Curtius, Determination of cobalt in biological samples by line-source and high-resolution continuum source graphite furnace atomic absorption spectrometry using solid sampling or alkaline treatment, Spectrochim. Acta, 60B (2005), 693. 

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. 

Furthermore, qdt can be used for the simultaneous determination of cobalt, nickel, and copper in acidic ethanol solutions by monitoring the absorbance maxima (Xmax) at 510, 656, and 625 nm, and solving the simultaneous equations at each wavelength (Scheme 2) (9). In this method, thiourea is added to generate Cu(I), the reactive form of copper. At pH 6, in the absence of thiourea, nickel and cobalt can be determined without interference from copper. 

DeMars, R.D. Voltammetric Determination of Cobalt and Nickel in Hard... 

The determination of cobalt and nickel is discussed by Allan (A8). Sensitivities are considerably higher than those in emission. Apphcations of absorption methods to molybdenum and strontium are reported by David (D4, D7, D8). 

Floret, G., Massa, V. Determination of cobalt, copper, nickel and manganese after chromatographic separation of their complexes with l-(2-pyridylazo)-2-naphthol. Ttav. Soc. Pharm. Montpellier 28, 129 (1969) C. A. 70, 31 731p (1969)... 

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