Nitroso-R acid

Hydroxy-l-nitrosonaphthalene-3,6-disulfonic acid (nitroso-R acid)... 

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. 

Procedure. The test solution should contain between 0.001 and 0.02 mg of cobalt. Evaporate almost to dryness, add 1 mL of concentrated nitric acid, and continue the evaporation just to dryness to oxidise any iron(II) which may be present. Dissolve the residue in 10 mL of water containing 0.5 mL each of 1 1 hydrochloric acid and 1 10 nitric acid. Boil for a few minutes to dissolve any solid material. Add 2.0 mL of a 0.2 per cent aqueous solution of nitroso-R-salt and also 2.0 g of hydrated sodium acetate. The pH of the solution should be close to 5.5 check with bromocresol green indicator or with a pH meter. Boil for 1 minute, add 1.0 mL of concentrated hydrochloric acid, and boil again for... 

Cupferron Nitroso-R-salt 688 Nitrous acid removal of. 514 Nonaqueous titrations 307 indicators for, 284 solvents for. 283... 

Nitroso-R-salt see l-nitroso-2-naphthol-3,6-disulphonic acid, disodium salt, hydrate. 

ASM—actual sulfuric as nitric, ASS—actual sulfuric as sulfuric,MA—mixed acid,N normality of std soln,N A—nitric acid, N-so—nitroso, R-burette reading,SA—sulfuric acid.TA— total acidity, TAA-total actual acidity (the sum of actual sulfuric, actual nitric and actual nitroso),TAN—total acidity as nitric,... 

Nitroso-R-salt, n82 Nitroterephthalic acid, n31 2-Nitro-p-toluidine, m317 4-Nitro-e>-toluidine, m315... 

B. Fuse about 1 mg of sample with about 50 mg of potassium pyrosulfate in a porcelain crucible, cool, and break up the mass with a glass rod. Add 3 mL of water, and dissolve by boiling. Add 1 drop of phenolphthalein TS, mix, and then add drops of a 1 10 solution of sodium hydroxide until just pink. Add 500 mg of sodium acetate, 0.5 mL of 1 N acetic acid, and 0.5 mL of a 1 500 solution of nitroso R salt. A red or orange-red color appears at once. Add 0.5 mL of hydrochloric acid, and boil for 1 min. The red color persists. 

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). 

In acid solution, the reagent is yellow whereas the complex is red. Figure 18.2 shows the absorption spectra. The molar absorptivity of the red cobalt-nitroso-R salt complex at Xmax = 415 nm is 3.5-10" (a = 0.60). At 500 nm, where interference from the colour of the reagent is negligible, e= 1.5-10. ... 

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. 

When the colour reaction takes place in the presence of relatively large amounts of metals which also react in weakly acidic medium with nitroso-R salt, a considerable amount of the reagent should be added to the solution. 

Nitroso-R salt is the disodium salt of a-nitroso-/ff-naphthol-disulfonic acid. This reagent reacts with Co in the same manner as a-nitroso-)5-naphthol, but it is water-soluble. A highly sensitive spot test is based on the formation of the red cobalt complex of this reagent on an ion-exchange resin. 

Procedure. One granule of the colorless resin (Dowex 1-Xl) is placed on a white spot plate and treated with one drop each of 0.05 % nitroso-R salt solution, 0.3 N sodium acetate and the sample. After 6 minutes, one drop of 2 N nitric acid is added and the plate is heated for 3 minutes on a water bath and allowed to cool. The resin acquires a red color in the presence of cobalt. The nitric acid treatment prevents interference by Ni and Cu. 

In an alternative spectrophotometric analysis capable of greater sensitivity to low levels of surfactant, the cation-surfactant-cobaltithiocyanate complex may be broken up and the extracted cobalt measured by a highly sensitive reaction with l-nitrosonaphth-2-ol-3,6-disulphonic acid (also called Nitroso-R salt), (84,85) or 4-(2-pyridylazo)-resorcinol (80). 

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