Physical methods of separation

Chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of which is stationary (the stationary phase), while the other (the mobile phase) moves in a definite direction. A mobile phase is described as a fluid which percolates through or along the stationary bed in a definite direction . It may be a liquid, a gas or a supercritical fluid, while the stationary phase may be a solid, a gel or a liquid. If a liquid, it may be distributed on a solid, which may or may not contribute to the separation process. ... 

The advent of the newer physical methods of separation and identification, together with the impetus given to the field by the imposition of anti-pollution legislation, has resulted in a flood of new and often unproven methods. While most of these methods were specifically designed to measure materials added to the environment by man s activities, in many cases they have added greatly to our knowledge of the naturally occurring compounds as well. 

The mixture to be separated and analyzed may be either a gas, liquid, or a solid in some instances. All that is required is that the materials be stable, have a vapor pressure of 0.1 torr at the operating temperature and interact with the column material (either a solid adsorbent or a liquid stationary phase) and the mobile phase (carrier gas). The result of this interaction is the differing distribution of the sample components between the two phases, resulting in the separation of the sample components into zones or bands. The principle that governs the chromatographic separation is the foundation of most physical methods of separation, for example, distillation and liquid-liquid extraction. 

Chromatography may be defined as a physical method of separation in which the components to be separated are partitioned between two phases. One of these is stationary(solid or liquid), the -other being mobile(liquid or gas) percolates thru stationary phase(Refs 58, 77 78)... 

The development of newer techniques (chromatography, thermodiffusion) for the separation of the different groups of hydrocarbons from mineral oil fractions allows a better characterization of such type-concentrates with the aid of physical constants. Combination of physical methods of separation with the statistical analysis of the products obtained, may lead to a more detailed and more complete knowledge of the composition of oils. 

Centrifugation is a simple physical method of separation that relies on applying a centrifugal force to a sample in order to separate out components from a mixture. 

Asphalt Solubility in Normal Alkanes. The separation of an asphalt into two fractions—asphaltenes and maltenes—by precipitation with low molecular weight alkanes is a physical method of separation based on solubility. Figure 1 shows that pentane precipitates more asphalt components (17.0 wt %) than does heptane (10.6 wt %). It would be expected that when pentane asphaltenes are treated with heptane, the amount of material equal to 10.6 wt % (based on asphalt) would be precipitated. However, more—14.8 wt %—is precipitated. A similar, but even more pronounced, effect can be seen when heptane and decane treatments are compared (see Figure 1). 

Chromatography, a physical method of separation in which the components are partitioned between two phases, was invented simultaneously and independently by American geologist D.T. Day and Russian botanist M.S. Tsvet (Tswett). Their methods and later modifications are described in Vol 3 of Encycl, pp C289 to C298. Qualitative method of separation of ingredients by adsorption was known for centuries. This is described on p C289-R... 

Physical methods of separation are preferred to those using chemical reagents or organic solvents. These are the standard methods of separation of minerals. Iron oxides can be recovered magnetically.12 The iron oxide in kaolin clay is removed by high-intensity magnetic separation. The treated clay is used as a filler for paper. Ores can be separated by a variety of methods involving radiation. If the... 

Because it is impossible to completely avoid some degree of aflatoxin contamination, a variety of strategies for their detoxification in foodstuffs have been proposed. These strategies have included physical methods of separation, thermal inactivation, irradiation, solvent extraction, adsorption from solution, microbial inactivation, chemical methods of inactivation and fermentation. Two of these strategies are described in more detail below. 

Chromatography is a physical method of separation, in which the components to be separated are carried by a mobile phase along or through a layer of a stationary phase. In the process, the... 

Chromatography is a physical method of separation in which the components to... 

Physical methods of separation, filtration, and extraction also had a positive effect on the release patterns of any dmg or active matter. Progress was also made in the characterization of the parameters and mechanisms that are involved in the coalescence, aggregation, and rupture of doubleemulsion droplets, and effective control of the rheological parameters was achieved by a better understanding of their effect on the static and shear-induced stability. 

Nevertheless, there are still justifiable and legal reasons to carry out such opaations in the laboratory when hazards can be reduced safely. Neutralizatiorr, oxidation, reductiorr, and various otho" chemical conversions as well as physical methods of separation and concentration can be applied prudently to many laboratory-scale mixed wastes. However, the dual character of the hazard, chemical and radioactive, requires that additional precautions be exercised. Treatment for the chemical hazard must not create a radioactivity risk for personnel or the environment. For example, vapors or aerosols from a reaction, distillation, or evaporation must not lead to escape of unsafe levels of radioactive materials into the atmosphere. Fume hoods appropriate for such operations should be designed to trap any radioactive effluent. When mixed waste is made chemically safe for disposal into the sanitary sewer, the laboratory must ensure that the radioactivity hazard is below the standards set by the publicly owned treatment works (POTW). Several examples for reducing the hazard of mixed waste are described below ... 

Flotation a physical method of separating a mineral from the gangue that depends on differences in their wettabilities by a liquid solution. (13.2)... 

Chromatography. A physical method of separation of sample components in which these components distribute themselves between two phases, one stationary and the other mobile. The stationary phase may be a solid or a liquid supported on a solid. 

FIGURE 3.3 A mixture of spaghetti and water is separated using a strainer, a physical method of separation. 

Physical methods of separating a given solubility fraction consist in the application of fractional distillation, fractional crystallization, crystallization from solvents of various types, steam distillation, sublimation, etc. Such operations are already familiar to the student but nevertheless abundant opportunity remains for the exercise of his ingenuity when relatively small amounts of material are available. 

Chromatography permits the separation and partial description of substances whose presence is unknown or unsuspected. As an exploratory method, chromatography is indispensable in all sciences dealing with chemical substances and their reactions. Chromatography is, in fact, a physical method of separation in which mixtures are separated by distribution between two phases a mobile phase and a stationary phase. The mobile phase can be a gas (as in gas chromatography) or a liquid (as in liquid chromatography). 

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