Precipitates filtering

Zebiihr et al. (29) developed an automated system for determining PAHs, PCBs and PCDD/Fs by using an aminopropyl silica column coupled to a porous graphitic carbon column. This method gives five fractions, i.e. aliphatic and monoaromatic hydrocarbons, polycyclic aromatic hydrocarbons, PCBs with two or more ortho-chlorines, mono-ort/io PCBs, and non-ortho PCBs and PCDD/Fs. This method employed five switching valves and was successfully used with extracts of sediments, biological samples and electrostatic filter precipitates. 

Since, however, K2 is comparatively large, the solvent effect is relatively small this is why in the quantitative separation of barium sulphate, precipitation may be carried out in slightly acid solution in order to obtain a more easily filterable precipitate and to reduce co-precipitation (Section 11.5). 

In some circumstances, separation of solid from a liquid is better achieved by use of a centrifuge than by filtration, and a small, electrically driven centrifuge is a useful piece of equipment for an analytical laboratory. It may be employed for removing the mother liquor from recrystallised salts, for collecting difficultly filterable precipitates, and for the washing of certain precipitates by decantation. It is particularly useful when small quantities of solids are involved centrifuging, followed by decantation and re-centrifuging, avoids transference losses and yields the solid phase in a compact form. Another valuable application is for the separation of two immiscible phases. 

Dimethylglyoxime is almost insoluble in water, and is added in the form of a 1 per cent solution in 90% ethanol (rectified spirit) or absolute ethanol 1 mL of this solution is sufficient for the precipitation of 0.0025 g of nickel. As already pointed out, the reagent is added to a hot feebly acid solution of a nickel salt, and the solution is then rendered faintly ammoniacal. This procedure gives a more easily filterable precipitate than does direct precipitation from cold or from ammoniacal solutions. Only a slight excess of the reagent should be used, since dimethylglyoxime is not very soluble in water or in very dilute ethanol and may precipitate if a very large excess is added (such that the alcohol content of the solution exceeds 50 per cent), some of the precipitate may dissolve. 

Determination of chloride as silver chloride Discussion. The aqueous solution of the chloride is acidified with dilute nitric acid in order to prevent the precipitation of other silver salts, such as the phosphate and carbonate, which might form in neutral solution, and also to produce a more readily filterable precipitate. A slight excess of silver nitrate solution is added, whereupon silver chloride is precipitated ... 

Cool and filter. Dissolve in the minimum volume of hot water, treat with about 0-5 per cent, by weight of decolourising carbon, filter, precipitate the base with 50 per cent, acetic acid imtil just acid to litmus (avoid an excess of acid), filter off the sulphapyridine at the pump, wash thoroughly with hot water, and dry to constant weight at 90° (about 12 horirs). Alternatively, the cold solution of the sodium salt may be just acidified with dilute hydrochloric acid with very vigorous stirring the presence of a local excess of acid must be avoided since sulphapyridine is hydrolysed by mineral acids to sulphanilic acid and 2-aminopyridine. 

Dissolve 4 g (VII) in 78 ml 1.5% KOH and reflux five minutes (under N2 if possible). Add 8.5 g Na arsenate hydrate and 16 g Raney-Ni (wet) (deactivated by boiling in xylene suspension — see JOC 13,455(1948)) and reflux twenty hours (under N2 if possible). Filter, precipitate lysergic acid by taking pH to 5.6 with HC1 filter and wash precipitate with water to get 1 g lysergic acid. Evaporate in vacuum the filtrate to get more product. 

The barium salt is easier to obtain in solid form than is the corresponding potassium salt. Dissolve 15 g. of crystallized barium hydroxide in 50 cc. of warm water and divide the solution into two equal parts. Completely saturate the one portion (in a stoppered flask) with hydrogen sulfide and then add the other portion, thus forming a solution of barium sulfide. Add about 1 cc. of carbon disulfide and shake from time to time. It is better to add the carbon disulfide by conducting a current of coal gas (from the laboratory gas supply) through a little carbon disulfide in a wash flask and thence into the solution of barium sulfide. The barium salt precipitates as a yellow crystalline powder. The filtered precipitate should be washed first with water, then with half alcohol, finally with pure alcohol and dried on a hot plate. A second crop of crystals may be obtained by allowing the wash alcohol to drain into the mother liquor. 

Calcium. — Digest 20 gm. of copper oxide with a mixture of 5 cc. of nitric acid and 95 cc. of water for about fifteen minutes, shaking frequently filter, precipitate the copper in the filtrate completely by passing hydrogen sulphide gas, and filter again. Evaporate the filtrate on the water-bath to about 20 cc., add ammonia water in excess, filter once more, and to the filtrate add ammonium oxalate solution. No immediate turbidity should be produced. 

Therefore, it would be possible not only to filter precipitated salts merely as solids but also to filter those low-melting-point salts that are in a molten state. 

Platinum residues from hydrogenation reactions should be carefully preserved and subsequently recovered by conversion into ammonium chloro-platinate by the following method. Dissolve the platinum or platinum residues in aqua regia, evaporate just to dryness several times with concentrated hydrochloric acid, dissolve the final residue in a little water and filter. Precipitate ammonium chloroplatinate from the filtrate by addition of excess of a saturated solution of ammonium chloride. Filter and dry the precipitate at 100°C. 

At very low concentrations, c. 10 4 to 10 3 mol dm-3, the supersaturation is sufficient for extensive nucleation to occur, but crystal growth is limited by the availability of material, with the result that a sol is formed. At moderate concentrations, c. 10 2 to 10 1 mol dm 3, the extent of nucleation is not much greater, so that more material is available for crystal growth and a coarse filterable precipitate is formed. At very high concentrations, c. 2 to 3 mol dm-3, the high viscosity of the medium slows down the rate of crystal growth sufficiently to allow time for much more extensive nucleation and the formation of very many small particles. Owing to their... 

The filtered precipitate was partially dried for several hours under vacuum, and reprecipitated twice from boiling methanolic solution by means of four volumes of ethyl acetate (analytical grade), to yield overnight a pure, white product (about 12 g., together with 2-3 g. of an impure Becond crop). A weighed sample (20-25 mg.) was boiled with 100 ml. of 2 N hydrochloric acid for 2.5 hr. (to complete hydrolysis), neutralized with alkali, made up to standard volume, and the phenolphthalein estimated colorimetrically (theoretical content, 38.8% for the cinchonidine salt of the monoglucuronide). ... 

Add diethyl ether (100 mL) to the reaction mixture and remove the precipitated solids by filtration. Wash the filtered precipitate with ether (50 mL). 

Catalytic amounts of [Pd(PPh3)4] (chiffres ) and Cul were added to a solution of dithienophosphole 80 (1.73 g, 1.5 mmol) and l,4-diiodo-2,5-bis(octyloxy)benzene (0.88 g, 1.5 mmol) in N-methylpyrrolidinone (80 mL). The light-yellow reaction mixture was then stirred for 48 h at 200 °C, after which time the color changed to orange-red. The solution was then cooled to room temperature, the solvent evaporated under vacuum and the resulting amorphous solid taken up in a small amount of THF (ca. 5 mL). The suspension was filtered, precipitated into hexane and the residue dried under vacuum to yield 80 as a reddish brown pow-... 

The solution must be acidic (m in hydrochloric acid) in order to obtain a crystalline, well-filterable precipitate. In the absence of acid, or in very slightly acid solutions a colloidal, brownish-black precipitate or colouration is obtained. By adding some acid and boiling coagulation can be achieved. 

Isolation of Toxic Anions by Protein Precipitation. Prepare a slurry of the sample, coagulate the proteins with ammonium sulphate, filter, precipitate ammoniiun sulphate remaining in the filtrate with meth ol, and evaporate the supernatant liquid (F. Rieders Mid F. J. Frere, J. forens. Set, 1963,5,46-53). 

Boc-Met-Met-OMe (60 g, 152 mmol) was treated with 3M HCl in EtOAc (250 mL). The precipitation was completed by addition of abs EtjO and cooling. The filtered precipitate was dried under reduced pressure yield 49.3 g (98%). 

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