Nitric acid cobalt complexes

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. 

NOjQH, 4-Pyridinecarboxylic acid, cobalt complexes, 23 113 NOjSCjHj, L-Cysteine, gold complex, 21 31 N03CjH7, Serine, copper complex, 21 115 NO,H, Nitric acid, cerium complexes, 23 178 cobalt complexes, 23 171 N03SC7Hs, o-Benzosulfimide (saccharin), metal complexes, 23 47 N05P2WC4 Hj, Tungstate(l -), pentacarbon-ylhydrido-, p,-nitrido-bis(triphenylphos-phorus)(l + ), 22 182... 

The cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

Berndt et al. [740] have shown that traces of bismuth, cadmium, copper, cobalt, indium, nickel, lead, thallium, and zinc could be separated from samples of seawater, mineral water, and drinking water by complexation with the ammonium salt of pyrrolidine- 1-dithiocarboxylic acid, followed by filtration through a filter covered with a layer of active carbon. Sample volumes could range from 100 ml to 10 litres. The elements were dissolved in nitric acid and then determined by atomic absorption or inductively coupled plasma optical emission spectrometry. 

A series of complex silico-arsenides has been obtained 6 by melting metals with silicon and an excess of arsenic under a layer of molten cryolite and sodium chloride. The following have thus been prepared copper silico-arsenide, a grey crystalline brittle mass zinc silico-arsenide, which behaved as above with hydrochloric acid iron, cobalt and nickel siMco-arsenides, of composition M2SisAs4, similar in appearance to the copper compound. When platinum was treated in the same way, a hard white product of indefinite composition was obtained, almost insoluble in nitric acid. 

The analogous complex [Co(Mej-Pyo[14) trieneN4)Clj] CI-H O is prepared in an identical manner using cobalt(ll) chloride hexahydrate and hydrochloric acid instead of cobalt(II) bromide and hydrobromic acid. Use of cobalt(ll) nitrate and nitric acid yields, after the concentrated reaction mixture is allowed to stand for several days, brown crystalline [CotMej-Pyo[14] trieneN HNOjh) N03-2.5Hj0. 

The absorbance of the Co(III) complex solution may be measured with higher sensitivity at 415-425 nm, or with lower sensitivity at 500-520 nm (a reagent blank, or water as reference). The reaction of cobalt with nitroso-R salt is usually done in a hot weakly acidic medium buffered with sodium acetate. The solution is then made sufficiently acidic with hydrochloric or nitric acid to decompose the nitroso-R salt complexes of other metals (e.g., Cu, Ni, Fe, and Mn), which are less stable than the cobalt(III) complex. Phosphate or fluoride masks iron (III), which has a yellow colour in hydrochloric acid medium. 

Attempts to oxidize cobalt phthalocyanine to a cobalt(III) derivative in neutral or basic solvent were unsuccessful 213). However, it is reported 80) that cobalt phthalocyanine is oxidized to nitratocobalt(III) phthalocyanine by nitric acid in nitrobenzene at 10°-20°C. Unfortunately no data were presented which excluded the alternative formulation of the complex as a nitric acid adduct of cobalt(II) phthalocyanine, which seems more likely. 

The tris(Ar-hydroxethyIethylenediamine)cobalt(III) chloride that was used in these reactions was reported to be an orange crystalline solid (111). In a subsequent investigation (69), attempts to prepare this compound by the air oxidation of a mixture of cobalt (II) and the amine failed. The compound was, however, prepared by the displacement of ammonia from [Co(NH3)e]Cl3 by iV-hydroxyethylethylenediamine and a dark red compound was obtained. Attempts to react the hydroxy groups in this red complex with a variety of reagents (nitric acid, thionyl chloride, benzoyl chloride, and acetyl chloride) were as unsuccessful as the previously reported attempts to react the hydroxy groups in the orange cobalt complex. 

The only jU-superoxo complexes to have been characterized are those which contain cobalt. They are readily prepared by treatment of the corresponding /i-peroxo complexes with strong oxidants. Thompson and Wilmarth observed that MnO, HOCl, Br2, BrOf and NOf are all effective oxidants toward [(en) Co(/r-NH2,02)Co(en)2] in acidic solution whereas Fe ", HjOj, Ag" " and CtjO are not. In other systems CI2, Pb02, persulfate and Ce in nitric acid solution have also effected oxidation. A number of well-characterized //-superoxo cobalt(III) complexes are listed in Table 55. There are no reports of /i-superoxo complexes containing Schiffbase ligands and all that are known contain either terminal amine or cyano groups. 

The first report on the use of ion-exchange columns with chemiluminescence detection was that by Buiguera et aI.[Sl] on the determination of zinc and cadmium through inhibition of the cobalt catalyzed chemiluminescence generation from luminol. The chloro-complexes of zinc and cadmium were retained by an anion exchanger and eluted separately using sodium hydroxide and nitric acid. Apparently, preconcentration effects were not pursued. 

Adsorption by carbon, which is one of the oldest adsorption methods used, has been reviewed and evaluated for the preconcentration of trace metals (794). Many authors have discussed the preparation of activated charcoal and carbon from a wide variety of usually local sources. The applications to water treatment are far too numerous to mention other than a few. Jo (795) carbonized a resin and a gum and hydrated the residue above 600 C to produce an adsorbant selective for cadmium(II). Kuzin et al, 196) used deashed active carbon and oxidized carbon for the quantitative sorption of copper, lead, zinc, and nickel from nearly neutral solutions containing 1-2 M alkali-metal halide. Pearson and Siviour (797) converted the metal-ion species to amine complexes before adsorbing these onto carbonaceous materials such as brown charcoal char or cellulose. Mercury vapor can be removed from a solution by reduction followed by passage of a nitrogen stream and adsorption by activated charcoal (798). Activated carbon, which had been oxidized with nitric acid, has been used to extract several metals including divalent nickel, cadmium, cobalt, zinc, manganese, and mercury from fresh water, brine, and seawater (799, 200). 

The precipitate forms slowly In neutral or dilute acid solutions (up to 0.1 N hydrochloric or 0.3 N nitric acid). The precipitate forms rapidly from an acid solution made ammonlacal. Tlie advantage of the homogeneous precipitation la the production of a coarse, crystalline, easily filtered precipitate and reduction of occluded contaminants (F2). Separations using thloacetamlde can be made more specific by the addition of EDTA (F3). Some cations such as cadmium, cobalt, iron and nickel fall to precipitate from ammonlacal solution due to formation of EDTA complexes. The precipitation of lead is delayed. In the presence... 

It can also be detected with diphenylcarbazide or diphenylcarbazone, which yields a blue-violet color in acidic medium, even in 0.2mol/L nitric acid. The diphenylcarbazone/Hg + complex is extractible into benzene. Copper, iron, and cobalt are not disturbing in 0.2mol/L nitric acid. However, Cr04 , Cr207 , and molybdic anions are. 

---