Iron determination preventive solution

It must be emphasised that if hydrochloric acid has been employed in the original solution of the iron-bearing material, the volume should be reduced to ca 25 mL and then diluted to ca 150mL with 5 per cent sulphuric acid. The determination is carried out as detailed above, but 25 mL of Zimmermann-Reinhardt or preventive solution must be added before titration with standard potassium permanganate solution. For the determination of iron in hydrochloric acid solution, it is more convenient to reduce the solution in a silver reductor... 

Determination of copper as copper(I) thiocyanate Discussion. This is an excellent method, since most thiocyanates of other metals are soluble. Separation may thus be effected from bismuth, cadmium, arsenic, antimony, tin, iron, nickel, cobalt, manganese, and zinc. The addition of 2-3 g of tartaric acid is desirable for the prevention of hydrolysis when bismuth, antimony, or tin is present. Excessive amounts of ammonium salts or of the thiocyanate precipitant should be absent, as should also oxidising agents the solution should only be slightly acidic, since the solubility of the precipitate increases with decreasing pH. Lead, mercury, the precious metals, selenium, and tellurium interfere and contaminate the precipitate. 

Discussion. Minute amounts of beryllium may be readily determined spectrophotometrically by reaction under alkaline conditions with 4-nitrobenzeneazo-orcinol. The reagent is yellow in a basic medium in the presence of beryllium the colour changes to reddish-brown. The zone of optimum alkalinity is rather critical and narrow buffering with boric acid increases the reproducibility. Aluminium, up to about 240 mg per 25 mL, has little influence provided an excess of 1 mole of sodium hydroxide is added for each mole of aluminium present. Other elements which might interfere are removed by preliminary treatment with sodium hydroxide solution, but the possible co-precipitation of beryllium must be considered. Zinc interferes very slightly but can be removed by precipitation as sulphide. Copper interferes seriously, even in such small amounts as are soluble in sodium hydroxide solution. The interference of small amounts of copper, nickel, iron and calcium can be prevented by complexing with EDTA and triethanolamine. 

Cabrera et al. [95] determined total dissolved and suspended phosphorus in natural waters by a method involving digestion with hydrogen peroxide and sulphuric acid, errors may be caused by adsorption of phosphorus on hydrous iron and aluminium oxides formed during neutralization prior to filtration. It is proposed that this can be prevented by adding extra sulphuric acid after neutralization, to dissolve such oxides and release the adsorbed phosphorus into solution. 

Elemental composition Fe 18.89%, Br 81.11%. The solid material may be analyzed nondestructively by x-ray techniques. The aqueous solution may be acidified with nitric acid (to prevent reduction) and analyzed for iron without further hot digestion by AA or ICP techniques. The bromide ion may be best determined by ion chromatography following appropriate dilution. 

When iron is determined in aqueous media or in the presence of acetone, care should be taken that the concentration of thiocyanate is the same in the sample and the standard solutions. The aqueous solution must be sufficiently acid to prevent hydrolysis of Fe(III), which begins even at pH 3. The solution should not, however, be too acidic, otherwise the concentration of SCN may be too small. Iron(III) thiocyanate complexes are not very stable, and can persist only at a relatively high concentration of SCN. The optimum acidity of the solution with HCl, H2SO4, HNO3, or HCIO4 lies within the concentration range 0.05 - 0.2 M. 

The molar absorptivity of the toluene solution of piazselenol at 420 nm is 1.02-10" (sp. abs. 0.13). This method is specific for selenium. Tellurium does not react with DAB, but V(V) and Fe(III) oxidize DAB to give coloured oxidation products. Iron(III) can be masked with fluoride or phosphate. EDTA is used as masking agent to prevent the precipitation of metals in the neutral medium. Substances capable of reducing selenium to the element interfere in the determination of selenium by the 3,3 -diaminobenzidine method. 

Menendez Garcia et al.[50] combined on-line liquid-liquid extraction separation with hydride generation gas-liquid separation for the determination of arsenic with ICPES. Arsenic in the aqueous sample is extracted as ASI3 into xylene which is continuously mixed on-line with sodium borohydride in dimethylformamide and acetic acid solutions. Arsine is generated in the organic phase and separated in a gas-liquid separator which prevents most of the xylene vapour from entering the plasma. The method was used to improve the sensitivity and to remove interferences from transition metals in the determination of low levels of arsenic in white metal, cast iron, cupro-nickel etc.. 

Interferences caused by transition metal ions have been eliminated or reduced by adding various reagents, such as complexing agents, to the sample solution. The addition of these reagents prevents the reduction or precipitation of the interfering metal ion. The interference caused by cadmium, iron, copper, cobalt, and silver on the determination of arsenic can be eliminated with potassium iodide. An addition of potassium iodide reduces the interference of nickel in the determination of arsenic, that of iron in the determination of antimony, and the influence of copper in the determination of bismuth. 

Preliminary tests were made to determine the feasibility of using the ferrous sulfate solution as a feed for iron electrolysis. The experiments were conducted in a jacketed beaker using a stainless steel cathode blank with 1 cm plating surface. The lead anode was bagged to prevent extensive mixing of any ferric ions generated. 

---