Beryllium may be determined by precipitation with aqueous ammonia solution in the presence of ammonium chloride or nitrate, and subsequently igniting and weighing as the oxide BeO. The method is not entirely satisfactory owing to the gelatinous nature of the precipitate, its tendency to adhere to the sides of the vessel, and the possibility of adsorption effects. Beryllium is sometimes precipitated together with aluminium hydroxide, which it resembles in many respects. Separation from aluminium (and also from iron) may be effected by means of oxine. An acetic (ethanoic) acid solution containing ammonium acetate is used; the aluminium and iron are precipitated as oxinates, and the beryllium in the filtrate is then precipitated with ammonia solution. Phosphate must be absent in the initial precipitation of beryllium and aluminium hydroxides.
The precipitation by ammonia solution of such elements as Al, Bi, Cd, Cr, Ca, Cu, Fe, Pb, Mn, Ni, and Zn may be prevented by complexation with EDTA: upon boiling the ammoniacal solution, beryllium hydroxide is precipitated quantitatively.
In all the above methods the element is weighed as the oxide, BeO, which is somewhat hygroscopic. The ignited residue, contained in a covered crucible, must be cooled in a desiccator containing concentrated sulphuric acid or phosphorus(V) pentoxide, and weighed immediately it has acquired the laboratory temperature.
The beryllium solution (200 mL), prepared with nitric acid or hydrochloric acid and containing about 0.1 g of Be, must be almost neutral and contain no other substance precipitable by ammonia solution. Heat to boiling, and add dilute ammonia solution slowly and with constant stirring until present in very slight excess. Add a Whatman accelerator or one-half of a Whatman ashless tablet, boil for 1 or 2 minutes, and filter on a Whatman No. 41 or 541 filter paper. Transfer as much of the precipitate as possible by rinsing with hot 2 per cent ammonium nitrate solution. Remove any precipitate adhering to the walls of the beaker by dissolving in the minimum volume of hot, very dilute, nitric acid, heating to boiling, and precipitating as before. Filter through the same paper, and wash thoroughly with the ammonium nitrate solution. Place the paper and precipitate in a weighed silica or platinum crucible, dry, and then slowly decompose the hydroxide by raising the temperature gradually to 700 °C, and finally ignite at about 1000 °C for at least 1 hour. Cool in a covered crucible in a desiccator charged with concentrated sulphuric acid, phosphorus(V) pentoxide, or anhydrous magnesium perchlorate, and weigh immediately when cold as BeO.
In the presence of interfering elements, proceed as follows. Neutralise 80-120mL of the solution containing 15-25mg of beryllium with ammonia solution until the hydroxides commence to precipitate. Re-dissolve the precipitate by the addition of a few drops of dilute hydrochloric acid. Add 0.5 g of ammonium chloride and sufficient 0.5M EDTA solution to complex all the heavy elements present. Add a slight excess of dilute ammonia solution, with stirring, boil for 2-3 minutes, add a little ashless filter pulp, filter, and complete the determination as above.