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Ammonium sulfate is an inorganic salt with a high solubility that disassociates into ammonium (NH + 4) and sulfate (SO 2− 4) in aqueous solutions. [1] Ammonium sulfate is especially useful as a precipitant because it is highly soluble, stabilizes protein structure, has a relatively low density, is readily available, and is relatively inexpensive.
Salting out (also known as salt-induced precipitation, salt fractionation, anti-solvent crystallization, precipitation crystallization, or drowning out) [1] is a purification technique that utilizes the reduced solubility of certain molecules in a solution of very high ionic strength.
Being extremely soluble in water, ammonium sulfate can "salt out" (precipitate) proteins from aqueous solutions. [3] [4] Precipitation by ammonium sulfate is a result of a reduction in solubility rather than protein denaturation, thus the precipitated protein can be resolubilized through the use of standard buffers. [5]
The ideal salt for protein precipitation is most effective for a particular amino acid composition, inexpensive, non-buffering, and non-polluting. The most commonly used salt is ammonium sulfate. There is a low variation in salting out over temperatures 0 °C to 30 °C.
The "salting out" effect is commonly exploited in protein purification through the use of ammonium sulfate precipitation. [16] However, these salts also interact directly with proteins (which are charged and have strong dipole moments) and may even bind specifically (e.g., phosphate and sulfate binding to ribonuclease A).
NaOH reacts the ammonium (NH 4 +) to ammonia (NH 3), which boils off the sample solution. Ammonia bubbles through the standard acid solution and reacts back to ammonium salts with the weak or strong acid. [3] Ammonium ion concentration in the acid solution, and thus the amount of nitrogen in the sample, is measured via titration.
The following chart shows the solubility of various ionic compounds in water at 1 atm pressure and room temperature (approx. 25 °C, 298.15 K). "Soluble" means the ionic compound doesn't precipitate, while "slightly soluble" and "insoluble" mean that a solid will precipitate; "slightly soluble" compounds like calcium sulfate may require heat to precipitate.
The reagent used is ammonium sulfide or Na 2 S 0.1 M added to the ammonia/ammonium chloride solution used to detect group 3 cations. It includes: Zn 2+ , Ni 2+ , Co 2+ , and Mn 2+ . Zinc will form a white precipitate, nickel and cobalt a black precipitate and manganese a brick/flesh colored precipitate.