Pages in category "Fractionation"
The following 19 pages are in this category, out of 19 total. This list may not reflect recent changes (learn more).
The following 19 pages are in this category, out of 19 total. This list may not reflect recent changes (learn more).
1. Differential centrifugation – Differential centrifugation is a common procedure in microbiology and cytology used to separate certain organelles from whole cells for further analysis of specific parts of cells. In the process, a sample is first lysed to break the cell membranes. The lysate is subjected to repeated centrifugations, each time removing the pellet. Finally, purification may be done through equilibrium sedimentation, and the layer is extracted for further analysis. Separation is based on size and density, with larger and denser particles pelleting at lower centrifugal forces, as an example, unbroken whole cells will pellet at low speeds and short intervals such as 1, 000g for 5 minutes. Smaller cell fragments and organelles remain in the supernatant and require more force, high g-force makes sedimentation of small particles much faster than Brownian diffusion, even for very small particles. When a centrifuge is used, Stokes law must be modified to account for the variation in g-force with distance from the center of rotation, in this process, a blender, usually a piece of porous porcelain of the same shape and dimension as the container, is used. The container is, in most cases, a boiling tube. The tissue sample is first crushed and a solution is added to it. The buffer solution is a dense, inert, aqueous solution which is designed to suspend the sample in a medium without damaging it through chemical reactions or osmosis. In most cases, the solution used is sucrose solution, in certain cases brine will be used, then, the blender, connected to a high-speed rotor, is inserted into the container holding the sample, pressing the crushed sample against the wall of the container. With the rotator turned on, the sample is ground by the porcelain pores. This grinding process will break the cell membranes of the samples cells and this process is called cell lysis. A portion of cells will remain intact after grinding and some organelles will be damaged, the lysed sample is now ready for centrifugation in an ultracentrifuge. An ultracentrifuge consists of a refrigerated, low-pressure chamber containing a rotor which is driven by an electrical motor capable of high speed rotation, samples are placed in tubes within or attached to the rotor. Rotational speed may reach up to 100,000 rpm for floor model,150,000 rpm for bench-top model, creating centrifugal speed forces of 800, 000g to 1,000 and this force causes sedimentation of macromolecules, and can even cause non-uniform distributions of small molecules. Since different fragments of a cell have different sizes and densities, additional steps can be taken to further refine each of the obtained pellets. Sedimentation depends on mass, shape, and partial specific volume of a macromolecule, as well as solvent density, rotor size, the sedimentation velocity can be monitored during the experiment to calculate molecular weight
2. Fractional freezing – Fractional freezing is a process used in process engineering and chemistry to separate substances with different melting points. The initial sample is thus fractionated, fractional freezing is generally used to produce ultra-pure solids, or to concentrate heat-sensitive liquids. Such enrichment parallels enrichment by true distillation, where the evaporated and re-condensed portion is richer than the portion left behind. The detailed situation is the subject of thermodynamics, a subdivision of physics of importance to chemistry, without resorting to mathematics, the following can be said for a mixture of water and alcohol, Freezing in this scenario begins at a temperature significantly below 0 °C. The first material to freeze is not the water, but a solution of alcohol in water. The liquid left behind is richer in alcohol, and as a consequence, the frozen material, while always poorer in alcohol than the liquid, becomes progressively richer in alcohol. Further stages of removing material and waiting for more freezing will come to naught once the liquid uniformly cools to the temperature of whatever is cooling it. The best-known freeze-distilled beverages are applejack and ice beer, ice wine is the result of a similar process, but in this case, the freezing happens before the fermentation, and thus it is sugar, not alcohol, that gets concentrated. For an in depth discussion of the physics and chemistry, see eutectic point, when a pure solid is desired, two possible situations can occur. If the contaminant is soluble in the solid, a multiple stage fractional freezing is required. If, however, a system forms, a very pure solid can be recovered. When the requirement is to concentrate a liquid phase, fractional freezing can be due to its simplicity. Fractional freezing is used in the production of fruit juice concentrates and other heat-sensitive liquids. Fractional freezing can be used to desalinate sea water, in a process that naturally occurs with sea ice, frozen salt water, when partially melted, leaves behind ice that is of a much lower salt content. Because sodium chloride lowers the point of water, the salt in sea water tends to be forced out of pure water while freezing. Likewise, the water with the highest concentration of salt melts first. Either method decreases the salinity of the water left over. Fractional freezing can be used as a method to increase the alcohol concentration in fermented alcoholic beverages
3. Fractional distillation – Generally the component parts have boiling points that differ by less than 25 °C from each other under a pressure of one atmosphere. If the difference in boiling points is greater than 25 °C, heat source, such as a hot plate with a bath, and ideally with a magnetic stirrer. g. As an example consider the distillation of a mixture of water, ethanol boils at 78.4 °C while water boils at 100 °C. So, by heating the mixture, the most volatile component will concentrate to a degree in the vapor leaving the liquid. Some mixtures form azeotropes, where the mixture boils at a lower temperature than either component, in this example, a mixture of 96% ethanol and 4% water boils at 78.2 °C, the mixture is more volatile than pure ethanol. For this reason, ethanol cannot be purified by direct fractional distillation of ethanol-water mixtures. The apparatus is assembled as in the diagram, the mixture is put into the round bottomed flask along with a few anti-bumping granules, and the fractionating column is fitted into the top. The fractional distillation column is set up with the source at the bottom on the still pot. As the distance from the stillpot increases, a gradient is formed in the column, it is coolest at the top. As the mixed vapor ascends the temperature gradient, some of the vapor condenses and revaporizes along the temperature gradient, each time the vapor condenses and vaporizes, the composition of the more volatile component in the vapor increases. This distills the vapor along the length of the column, the vapor condenses on the glass platforms, known as trays, inside the column, and runs back down into the liquid below, refluxing distillate. The hottest tray is at the bottom and the coolest is at the top, at steady state conditions, the vapor and liquid on each tray are at equilibrium. The most volatile component of the exits as a gas at the top of the column. The vapor at the top of the column then passes into the condenser, the process continues until all the ethanol boils out of the mixture. This point can be recognized by the rise in temperature shown on the thermometer. The above explanation reflects the theoretical way fractionation works, normal laboratory fractionation columns will be simple glass tubes filled with a packing, often small glass helices of 4 to 7 mm diameter. Such a column can be calibrated by the distillation of a known mixture system to quantify the column in terms of number of theoretical trays, in laboratory distillation, several types of condensers are commonly found. The Liebig condenser is simply a tube within a water jacket
4. Blood fractionation – Blood fractionation is the process of fractionating whole blood, or separating it into its component parts. This is typically done by centrifuging the blood, plasma proteins are separated by using the inherent differences of each protein. Fractionation involves changing the conditions of the plasma so that proteins that are normally dissolved in the plasma fluid become insoluble, forming large clumps. The insoluble protein can be collected by centrifugation, one of the very effective ways for carrying out this process is the addition of alcohol to the plasma membrane pool while simultaneously cooling the pool. This process is called cold alcohol fractionation or ethanol fractionation. It was described by and bears the eponym of Dr Edwin J. Cohn and this procedure is carried out in a series of steps so that a single pool of plasma yields several different protein products, such as albumin and immune globulin. Human serum albumin prepared by this process is used in vaccines, for treating burn victims
5. Field flow fractionation – It was invented and first reported by J. Calvin Giddings. The method of FFF is unique to other separation techniques due to the fact that it can separate materials over a wide size range while maintaining high resolution. Although FFF is a versatile technique, there is no one size fits all method for all applications. In field-flow fractionation the field can be asymmetrical flow through a membrane, gravitational, centrifugal, thermal-gradient, electrical. The ratio of the velocity of a species of particle to the velocity of the fluid is called the retention ratio. Field flow fractionation is based on laminar flow of particles in a solution and these sample components will change levels and speed based on their size/mass. Since these components will be travelling at different speeds, separation occurs, a simplified explanation of the setup is as follows. The sample separation occurs in a thin, ribbon-like, channel in which there is an inlet flow, the inlet flow is where the carrier liquid is pumped into the channel and it creates a parabolic flow profile and it propels the sample towards the outlet of the channel. The relationship between the force field and retention time can be illustrated from first principles. Consider two particle populations within the FFF channel, the cross field drives both particle clouds towards the bottom accumulation wall. Opposing this force field is the particles natural diffusion, or Brownian motion, when these two transport process reach equilibrium the particle concentration c approaches the exponential function of elevation x above the accumulation wall as illustrated in equation 1. C = c 0 e − x l l represents the elevation of the particle cloud. This relates to the height that the group can reach within the channel. The l of each component can be related to the force applied on each individual particle, L = k T F Where k is the Boltzmann constant, T is absolute pressure and F is the force exerted on a single particle by the cross flow. This shows how the characteristic elevation value is dependent to the Force applied. Therefore, F governs the separation process, hence, by varying the field strength the separation can be controlled to achieve optimal levels. The velocity V of a cloud of molecules is simply the velocity of an exponential distribution embedded in a parabolic flow profile. Retention time, tr can be written as, t r = L V Where L is the channel length, subsequently, the retention time can be written as, tr/to = w/6l ⌊coth w/2l- 2l/w⌋−1 Where to is the void time and w is the sample thickness
6. Isotope fractionation – Isotope fractionation describes processes that affect the relative abundance of isotopes, often used in isotope geochemistry. Normally, the focus is on stable isotopes of the same element, for example, in biochemistry processes cause a fluctuation in the amount of isotopes of carbon ratios incorporated into a biological being. The difference between the amount of carbon and the amount in the plant is known as isotope fractionation. Stable isotopes partitioning between two substances A and B can be expressed by the use of the isotopic fractionation factor, values for alpha tend to be very close to 1. When water vapor condenses, the heavier water isotopes become enriched in the liquid phase while the lighter isotopes tend toward the vapor phase
7. Fractionating column – A fractional column is an essential item used in distillation of liquid mixtures so as to separate the mixture into its component parts, or fractions, based on the differences in volatilities. Fractionating columns are used in small scale laboratory distillations as well as for large-scale industrial distillations, a laboratory fractionating column is a piece of glassware used to separate vaporized mixtures of liquid compounds with close volatility. It can also be called a fractional column, most commonly used is either a Vigreux column or a straight column packed with glass beads or metal pieces such as Raschig rings. Fractionating columns help to separate the mixture by helping the mixed vapors to cool, condense, with each condensation-vaporization cycle, the vapors are enriched in a certain component. A larger surface area allows more cycles, improving separation and this is the rationale for a Vigreux column or a packed fractionating column. In a typical fractional distillation, a mixture is heated in the distilling flask. The vapor condenses on glass spurs inside the column, and returns to the distilling flask, the hottest tray is at the bottom of the column and the coolest tray is at the top. At steady-state conditions, the vapor and liquid on each tray reach an equilibrium. Only the most volatile of the stays in gas form all the way to the top, where it may then proceed through a condenser. The separation may be enhanced by the addition of more trays, fractional distillation is one of the unit operations of chemical engineering. Fractionating columns are used in the chemical process industries where large quantities of liquids have to be distilled. That is the origin of the fractional distillation or fractionation. It is often not worthwhile separating the components in these fractions any further based on product requirements, distillation is one of the most common and energy-intensive separation processes. Effectiveness of separation is dependent upon the height and diameter of the column, the ratio of the height to diameter. In a typical plant, it accounts for about 40% of the total energy consumption. Industrial distillation towers are usually operated at a steady state. Unless disturbed by changes in feed, heat, ambient temperature, or condensing, the amount of heat entering the column from the reboiler and with the feed must equal the amount heat removed by the overhead condenser and with the products. The heat entering a distillation column is a crucial operating parameter, addition of excess or insufficient heat to the column can lead to foaming, weeping, entrainment, Figure 3 depicts an industrial fractionating column separating a feed stream into one distillate fraction and one bottoms fraction
8. Fractionation – Fractions are collected based on differences in a specific property of the individual components. A common trait in fractionations is the need to find an optimum between the amount of fractions collected and the purity in each fraction. Fractionation makes it possible to more than two components in a mixture in a single run. This property sets it apart from other separation techniques, fractionation is widely employed in many branches of science and technology. Mixtures of liquids and gases are separated by fractional distillation by difference in boiling point, fractionation of components also takes place in column chromatography by a difference in affinity between stationary phase and the mobile phase. In fractional crystallization and fractional freezing, chemical substances are fractionated based on difference in solubility at a given temperature, in cell fractionation, cell components are separated by difference in mass. The process of blood fractionation involves separation of blood into its main components, blood fractionation refers generally to the process of separation using a centrifuge, after which three major components can be visualized, plasma, buffy coat and erythrocytes. These separated components can be analyzed and often further separated, fractionation is also used for culinary purposes, as coconut oil, palm oil, and palm kernel oil are fractionated to produce oils of different viscosities, that may be used for different purposes. These oils typically use fractional crystallization for the process instead of distillation. Mango oil is an oil fraction obtained during the processing of mango butter, milk can also be fractionated to recover the milk protein concentrate or the milk basic proteins fraction
9. Asymmetric flow field flow fractionation – Asymmetrical flow field-flow fractionation is a fractionation method that is used for the characterization of nanoparticles, polymers and proteins. The theory for AF4 was conceived in 1986 and was established in 1987 and it is a separation technique based on the theory of field flow fractionation. AF4 is distinct from FFF because it only one permeable wall so the cross-flow is caused only by the carrier liquid. The cross-flow is induced by the carrier liquid constantly exiting by way of the wall on the bottom of the channel. It has been used to characterize condensed tannins oxidation, the AF4 experiment can be separated into three stages,1. Sample Injection Samples are injected into the system using an amount of sample volume. This volume will depend on the AF4 instrument being utilized in the experiment and this leads to line broadening and insufficiency. In order to such an error, sample focusing is proposed. Modern AF4 Systems allow both, manual and auto injection, sample focusing A current going opposite of the carrier solvent is used to focus all the particles in the sample to one specified area before fractionation begins. This corrects for any peak broadening that can due to particles being dispersed from the injection port to the channel outlet before fractionation begins. Sample preparation is an option that can be achieved in the focus step. Once all the particles are in the area of the channel. Fractionation There are two components that make up the FFF system, firstly, the laminar flow that carries the sample through the separation chamber and secondly the separation field applied perpendicular to the channel, against the sample flow. As particles flow along the channel the flow separation field pushes the molecules towards the bottom of the channel. As they pass by the bottom they undergo a counter acting diffusion back into the channel against the carrier flow. The extent to which the molecules can diffuse back into the channel is dictated by their natural Brownian motion, smaller particles have a higher Brownian motion than larger ones and are able to diffuse higher into the channel against the carrier flow. The rate of flow within the channel is not uniform. It travels in a pattern with the speed of the flow increasing towards the center of the channel