Dialysis, crystallization

Ion exchange Reverse osmosis Nano-filtration Electro dialysis Crystallization Evaporation Acid Base Heat treatment UV light Chemical oxidation... 

Variations to the slow-equilibration method include cross-linking of crystals prior to transfer into cryobuffers (Lusty, 1999), transfer of crystals into cryobuffer by dialysis, or the introduction of the cryobuffer during crystallogenesis. 

Dialysis for 6 months at RT of M Fe(N03)3 solution against bidistilled water of pH 5. This gives a mixture of polymeric particles and uniform, rod-like crystals of goethite. The goethite can be separated from the polymer by gel chromatography using a Sephadex 200 substrate (Van der Woude and de Bruyn, 1984). 

Preheat 2 L of distilled water to 75 °C in an oven, then add 20 g unhydrolyzed crystals of Fe(N03)3 9H2O with rapid stirring. Return to the oven and leave there for 10-12 min. During this time the solution changes from gold to dark reddish brown indicating the formation of Fe hydroxy-polymers. No precipitate should form. Cool rapidly by plunging into ice water, transfer to a dialysis bag and dialyse for at least... 

For patients who have ingested more than 30 ml of (pure) methanol or ethylene glycol, dialysis is recommended, and haemodialysis is more effective than peritoneal dialysis. Dialysis both removes the alcohols and their metabolites, and corrects the renal and metabolic disturbances and so is the preferred treatment in severe poisoning. The maintenance dose of ethanol required may be tripled during haemodialysis as ethanol is also removed. Early treatment is indicated if ethylene glycol concentrations are above 20 mg/100 ml (200 mg/1), if the arterial pH is below 7.3, if serum bicarbonate concentrations are less than 20 mM/1, and when there are oxalate crystals in the urine. 

The salt is very soluble in water—100 grms. of cold water dissolve 16 7 parts of the salt, and 100 parts of hot water dissolve 100 parts of salt—the soln. loses ammonia when heated. J. M. Thomson and W. P. Bloxam found that the supersaturated soln. crystallizes when seeded with a crystal of the solid salt—this is taken as. showing the existence of the undissociated solid in the soln. J. M. van Bemmelen fpund that but very little ammonia can be separated by dialysis. J. Thomsen gives —10 8 Cals, for the heat of soln. of a mol. of the salt in 800 mols. of water at 18°. E. Doumer gives 0 303 for the optical refraction of the salt in dil. soln., and 45 for the mol, refraction. 

Conditions sometimes exist that may make separations by distillation difficult or impractical or may require special techniques. Natural products such as petroleum or products derived from vegetable or animal matter are mixtures of very many chemically unidentified substances. Thermal instability sometimes is a problem. In other cases, vapor-liquid phase equilibria are unfavorable. It is true that distillations have been practiced successfully in some natural product industries, notably petroleum, long before a scientific basis was established, but the designs based on empirical rules are being improved by modern calculation techniques. Even unfavorable vapor-liquid equilibria sometimes can be ameliorated by changes of operating conditions or by chemical additives. Still, it must be recognized that there may be superior separation techniques in some cases, for instance, crystallization, liquid-liquid extraction, supercritical extraction, foam fractionation, dialysis, reverse osmosis, membrane separation, and others. The special distillations exemplified in this section are petroleum, azeotropic, extractive, and molecular distillations. 

For crystallization, the RNase Nj fraction eluted from the CM-cellulose column or Sephadex G-75 column was concentrated by lyophilization and then dialyzed against distilled water at 4°. During dialysis, fine needle-shaped crystals were formed. The specific activity of the crystals was about 2200. The solubility of the crystals is small around neutrality and increases below pH 4.0. Thus, the crystals are usually dissolved in dilute acetic acid. 

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