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Ammonium sulfate decomposes upon heating above 250 °C, first forming ammonium bisulfate. Heating at higher temperatures results in decomposition into ammonia, nitrogen, sulfur dioxide, and water.[17] As a salt of a strong acid (H2SO4) and weak base (NH3), its solution is acidic; pH of 0.1 M solution is 5.5. In aqueous solution the reactions are those of NH4+ and SO4-2 ions. For example, addition of barium chloride, precipitates out barium sulfate. The filtrate on evaporation yields ammonium chloride. Ammonium sulfate forms many double salts (ammonium metal sulfates) when its solution is mixed with equimolar solutions of metal sulfates and the solution is slowly evaporated. With trivalent metal ions, alums such as ferric ammonium sulfate are formed. Double metal sulfates include ammonium cobaltous sulfate, ferrous diammonium sulfate, ammonium nickel sulfate which are known as Tutton's salts and ammonium ceric sulfate.[2] Anhydrous double sulfates of ammonium also occur in the Langbeinites family.
Airborne particles of evaporated ammonium sulfate comprise approximately 30% of fine particulate pollution worldwide.[18] Legislation and control In November 2009, a ban on ammonium sulfate, ammonium nitrate and calcium ammonium nitrate fertilizers was imposed in the former Malakand Division—comprising the Upper Dir, Lower Dir, Swat, Chitral and Malakand districts of the North West Frontier Province (NWFP) of Pakistan, by the NWFP government, following reports that they were used by militants to make explosives. In January 2010, these substances were also banned in Afghanistan for the same reason Ammonium sulfate precipitation is one of the most commonly used methods for large and laboratory scale protein purification and fractionation that can be used to separate proteins by altering their solubility in the presence of a high salt concentration.

Contents 1 Properties 2 Mechanism 3 Procedure 4 Applications 5 References Properties Ammonium sulfate is an inorganic salt with a high solubility that disassociates into ammonium (NH4+) and sulfate (SO42-) 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. Mechanism Ammonium sulfate, as well as other neutral salts, will stabilize proteins by preferential solvation. Proteins are usually stored in ammonium sulfate because it inhibits bacterial growth. With the addition of ammonium sulfate, proteins unfolded by denaturants can be pushed into their native conformations. This can be seen with the folding of recombinant proteins.[2] The solubility of proteins varies according to the ionic strength of the solution, thus according to the salt concentration. At low ion concentrations (<0.5 M), the solubility of proteins increases with increasing salt concentration, an effect termed "salting in". As the salt concentration is further increased, the solubility of the protein begins to decrease. At a sufficiently high ionic strength, the protein will precipitate out of the solution, an effect termed "salting out".[3] When the ammonium (NH4+) and sulfate (SO42-) ions are within the aqueous solution they are attracted to the opposite charges evident on the compound that is being purified. This attraction of opposite charges prevents the water molecules from interacting with the compound being purified, leading to the precipitation or "salting out".[2] Proteins differ markedly in their solubilities at high ionic strength, therefore, "salting out" is a very useful procedure to assist in the purification of the desired protein. Ammonium sulfate is commonly used for precipitation because of its high solubility, additionally, it forms two ions high in the Hofmeister series. Because these two ions are at the end of Hofmeister series, ammonium sulfate can also stabilize a protein structure.[3] The ammonium sulfate solubility behavior for a protein is usually expressed as a function of the percentage of saturation. A solubility curve can be determined by plotting the log of the experimentally determined solubility, expressed as mg/mL, versus the percentage saturation of ammonium sulfate.[4] With the mechanism of salting-out, there is an omission of the salt from the layer of water, which is closely associated with the surface of the protein, known as the hydration layer. The hydration layer plays a vital role in sustaining solubility and suitable natural conformation. There are three main protein-water interaction: ion hydration between charged side chains, hydrogen bonding between polar groups and water, and hydrophobic hydration. Once salt is added to the mixture, there is an increase in the surface tension of the water, thus increasing hydrophobic interactions between water and the protein of interest. The protein of interest then reduces its surface area, which diminishes its contact with the solvent. This is shown by the folding and self-association, which ultimately leads to precipitation. The folding and self-association of the protein pushes out free water, leading to an increase in entropy and making this process energetically favorable.[2] Procedure Typically, the ammonium sulfate concentration is increased stepwise, and the precipitated protein is recovered at each stage. This is usually done by adding solid ammonium sulfate; however, calculating the amount of ammonium sulfate that should be added to add to a solution to achieve the desired concentration may be difficult because the addition of ammonium sulfate significantly increases the volume of the solution. The amount of ammonium sulfate that should be added to the solution can be determined from published nomograms or by using an online calculator.[5] Each protein precipitate can be dissolved individually in a standard buffer and assayed to determine the total protein content. The ammonium sulfate concentration added should be increased to a value that will precipitate most of the protein of interest whilst leaving the maximum amount of protein contaminants still in the solution. The precipitated protein of interest can subsequently be recovered by centrifugation and dissolved in standard buffer to prepare the sample for the next stage of purification. In the next stage of purification, all this added salt needs to be removed from the protein. One way to do so is using dialysis, but dialysis further dilutes the concentrated protein. The better way of removing ammonium sulfate from the protein is mixing the precipitate protein in a buffer containing a mixture of SDS, Tris-HCl, and phenol and centrifuging the mixture. The precipitate that comes out of this centrifugation will contain salt-less concentrated protein.[6] Applications Ammonium sulfate precipitation is a useful technique as an initial step in protein purification because it enables quick, bulk precipitation of cellular proteins.[4] It is also often employed during the later stages of purification to concentrate protein from dilute solution following procedures such as gel filtration. The drawback of this method is that oftentimes different substances can precipitate along with the protein, and other purification techniques must be performed, such as ion chromatography or size-exclusion chromatography.[3] Centrifugation is the technique which involves the application of centrifugal force to separate particles from a solution according to their size, shape, density, viscosity of the medium and rotor speed.[1] Not only is this process used to separate two miscible substances, but also to analyze the hydrodynamic properties of macromolecules.[2] More-dense components of the mixture migrate away from the axis of the centrifuge (move to the outside), while less-dense components of the mixture migrate towards the axis, i. e., move to the center. Chemists and biologists may increase the effective gravitational force on a test tube so as to more rapidly and completely cause the precipitate (pellet) to gather on the bottom of the tube. The remaining solution (supernatant) may be discarded with a pipette.[citation needed]. Centrifugation of protein solution, for example, allows elimination of impurities into the supernatant. There is a correlation between the size and density of a particle and the rate that the particle separates from a heterogeneous mixture, when the only force applied is that of gravity. The larger the size and the larger the density of the particles, the faster they separate from the mixture. By applying a larger effective gravitational force to the mixture, like a centrifuge does, the separation of the particles is accelerated. This is ideal in industrial and lab settings because particles that would naturally separate over a long period of time can be separated in much less time.[3] The rate of centrifugation is specified by the angular velocity usually expressed as revolutions per minute (RPM), or acceleration expressed as g. The conversion factor between RPM and g depends on the radius of the centrifuge rotor. The particles' settling velocity in centrifugation is a function of their size and shape, centrifugal acceleration, the volume fraction of solids present, the density difference between the particle and the liquid, and the viscosity. The most common application is the separation of solid from highly concentrated suspensions, which is used in the treatment of sewage sludges for dewatering where less consistent sediment is produced.[4] In the chemical and food industries, special centrifuges can process a continuous stream of particle-laden liquid. Centrifugation is the most common method used for uranium enrichment, relying on the slight mass difference between atoms of U238 and U235 in uranium hexafluoride gas.[citation needed]. Contents 1 Mathematical formula 2 Centrifugation in biological research 2.1 Microcentrifuges 2.2 High-speed centrifuges 2.3 Fractionation process 2.4 Ultracentrifugations 2.5 Density Gradient Centrifugation 2.6 Differential Centrifugation 3 Other applications 4 History 5 See also 6 Sources 7 References Mathematical formula The general formula for calculating the revolutions per minute (RPM) of a centrifuge is {\displaystyle RPM={\sqrt {g \over r}}}{\displaystyle RPM={\sqrt {g \over r}}}, where g represents the respective force of the centrifuge and r the radius from the center of the rotor to a point in the sample.[5] However, depending on the centrifuge model used, the respective angle of the rotor and the radius may vary, thus the formula gets modified. For example, the Sorvall #SS-34 rotor has a maximum radius of 10.8 cm, so the formula becomes {\displaystyle RPM=299{\sqrt {g \over r}}}{\displaystyle RPM=299{\sqrt {g \over r}}}, which can further simplify to {\displaystyle RPM=91{\sqrt {g}}}{\displaystyle RPM=91{\sqrt {g}}}.[6] the applied centrifugation field is square angular velocity in radians per sec .the radial distance o the particle from the axis; The most common formula used for calculating Relative Centrifugal Force (x g) is: RCF (x g) = 1.118 x Radius (mm) x (rpm/1000)² Many clinical separations have historically been carried out at 3000 rpm. This is a somewhat arbitrary approach as the RCF applied is dependent upon the radius in a linear fashion - so a 10% larger radius means that a 10% higher RCF is applied at the same speed. To discover the RCF that you have been applying at 3000 rpm, the above formula can be simplified to: [Short cut for 3000 rpm, with only a 0.62% error:] RCF (x g) = 10 x Radius (mm) Centrifugation in biological research Microcentrifuges Microcentrifuges are used to process small volumes of biological molecules, cells, or nuclei. Microcentrifuge tubes generally hold 0.5 - 2.0 mL of liquid, and are spun at maximum angular speeds of 12,000–13,000 rpm. Microcentrifuges are small enough to fit on a table-top and have rotors that can quickly change speeds. They may or may not have a refrigeration function. High-speed centrifuges High-speed or superspeed centrifuges can handle larger sample volumes, from a few tens of millilitres to several litres. Additionally, larger centrifuges can also reach higher angular velocities (around 30,000 rpm). The rotors may come with different adapters to hold various sizes of test tubes, bottles, or microtiter plates. Fractionation process General method of fractionation: Cell sample is stored in a suspension which is: Buffered - neutral pH, preventing damage to the structure of proteins including enzymes (which could affect ionic bonds) Isotonic (of equal water potential) - this prevents water gain or loss by the organelles Cool - reducing the overall activity of enzyme released later in the procedure Cells are homogenised in a blender and filtered to remove debris The homogenised

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