Precipitate general requirements

To 5 ml. of water add 1-2 drops of the amine if the amine does not dissolve, add a drop or two of concentrated hydrochloric acid. Add 0-5-1 ml. of this amine solution to 2-3 ml. of the reagent an almost immediate precipitate indicates the presence of a primary amine. A slight turbidity indicates the presence of a primary amine as an impurity. (Primary aromatic amines generally require 2-3 minutes for the test. Urea and other amides, as well as amino acids, do not react.)... 

After the precipitation of the carbonate of lead, which generally requires twelve or fourteen hours, the contenta of the tank arc allowed to settle, and after this the solution of neutral aoetate is drawn off into the... 

Sodium sulfide can also be used as a precipitating agent Filtration of the precipitate is generally required, following by drying to achieve further weight and volume reduction (Hart 1987). 

In this strategy, it is very important to avoid interphage catalysis. Therefore, the phage concentration should be kept low (lower than 10-9 M) and phages should not be precipitated with PEG. Because removal of excess label is generally required before affinity capture, it should be done by phage dialysis or size-exclusion chromatography. 

Palit and Guha (110) drew further attention to the connection between polymerization rate and the colloidal nature of the precipitating polymer. They found that as the amount of redox initiator increased the polymerization rate first increased, then decreased and finally increased again. These regions corresponded to a fine sol, a milky dispersion and a coarse precipitate. Generally the rate of polymerization ran parallel to the amount of electrolyte required to precipitate the colloid. 

Pretreatment involving filtration and clarification for removal of suspended solids and turbidity may improve treatment efficiency. To reduce the interference of inorganic and organic compounds, other treatment processes may have to be combined with UV/H202 systems for effective treatment. In some situations, pH control may be required to prevent precipitation of metal salts during the oxidation process and to avoid a loss in efficiency due to the precipitates. Generally, metal hydroxide precipitation can be avoided for pH less than 6. Alkaline pH can adversely affect the reaction rate, possibly due to the base-catalyzed decomposition of H202. 

Fumed silica is typically available with sizes of 7 to 40 nm and surface areas ranging from 50 to 380 m2/g. Unlike precipitated silica, fumed silica has no internal surface area. The specific gravity of fumed silica is approximately 2.2. Because of its high surface area to weight ratio, formulations generally require only a minor amount of fumed silica (1 to 5 percent by weight) to achieve thixotropic properties. 

The method has been termed the double-antibody technique and can be used for a wide variety of analytesJ The double antibody techniques generally require more time because the second antibody reaction can require days to reach equilibrium. The speed of precipitation clearly depends on the concentration of the second antibody. Polyethylene glycol has been used as a cosolvent to increase the precipitation rate. 

Extraction is equally useful in the preconcentration and separation of small amounts of elements, and in the separation of macrocomponents from traces. Extraction methods generally require less time than precipitation methods. The former give also purer separation of elements owing to the small area of phase contact. Co-extraction occurring in some cases [11] has not been widely used in extraction separations. 

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