Magnetic separation is a process used to separate materials from those that are less or nonmagnetic. All materials have a response when placed in a magnetic field, although with most, the effect is too slight to be detected. The few materials that are strongly affected (magnetised) by magnetic fields are known as Ferromagnetics, those lesser (though noticeably) affected are known as Paramagnetics.
Ferromagnetics require relatively weak magnetic fields to be attracted and devices to separate these materials usually have magnets that are permanently magnetised (Permanent magnets do not require electricity to maintain their magnetic fields). Paramagnetics require stronger magnetic fields and these can only be achieved and maintained by electro magnets (large wire coils around an iron frame current is continuously passed through the coils creating the magnetic field within the iron. The field is concentrated across an air gap in the circuit).
Both ferromagnetic (low intensity) and paramagnetic (high intensity) separation devices (Laboratory Magnetic Separator) may be operated with dry solids or with solids in pulp form. (A complete classification of magnetic separating devices is given in Wills Mineral Processing Technology, pp. 338-356).
(*The units given are kilogauss (kG). These are the units most commonly used. The equivalent S.I. unit is the Tesla (T) * 1 Tesla = 10 kilogauss). The extremes of field strength used are based on experience from a magnetic separation testing laboratory over many years.
Magnetic separation takes advantage of the fact that magnetite is strongly magnetic (ferromagnetic), hematite is weakly magnetic (paramagnetic), and most gangue minerals are not magnetic (diamagnetic).
The current research and development initiatives and needs in magnetic separation, shown in Fig. 7, reveal several important trends. Magnetic separation techniques that have been, to a greater extent, conceived empirically and applied in practice, such as superconducting separation, small-particle eddy-current separation, and biomedical separation, are being studied from a more fundamental point of view and further progress can be expected in the near future.
In addition, methods such as OGMS, ferrohydrostatic separation, magnetic tagging, and magnetic flocculation of weakly magnetic materials, that have received a great deal of attention on academic level, are likely to enter the development and technology transfer stages.
The application of high-Tc superconductivity to magnetic separation, and novel magnetism-based techniques, are also being explored, either theoretically or empirically. It can be expected that these methods, such as magnetic flotation, magnetic gravity separation, magnetic comminution, and classification will take advantage of having a much wider control over these processes as a result of the presence of this additional external force.
Magnetic separation takes advantage of the fact that magnetite is strongly magnetic (ferromagnetic), hematite is weakly magnetic (paramagnetic), and most gangue minerals are not magnetic (diamagnetic). A simple magnetic separation circuit can be seen in Figure 1.2.5 . A slurry passes by a magnetized drum; the magnetic material sticks to the drum, while the nonmagnetic slurry keeps flowing. A second pass by a more strongly magnetized drum could be used to separate the paramagnetic particles from the gangue.
Magnetic separation can significantly shorten the purification process by quick retrieval of affinity beads at each step (e.g., binding, wash, and elution), and reduce sample dilution usually associated with traditional column-based elution. The method can be used on viscous materials that will otherwise clog traditional columns and can therefore simplify the purification process by eliminating sample pretreatment, such as centrifugation or filtration to remove insoluble materials and particulates. The capability of miniaturization and parallel screening of multiple conditions, such as growth conditions for optimal protein expression and buffer conditions for purification, makes magnetic separation amenable to high-throughput analysis which can significantly shorten the purification process (Saiyed et al., 2003).
Paramagnetic particles are available as unmodified, modified with common affinity ligands (e.g., streptavidin, GSH, Protein A, etc.), and conjugated particles with specific recognition groups such as monoclonal and polyclonal antibodies (Koneracka et al., 2006). In addition to target protein purification, they can also be used to immobilize a target protein which then acts as a bait to pull down its interaction partner(s) from a complex biological mixture. See Chapter 16.
Magnetic separation of cells is a simple, rapid, specific and relatively inexpensive procedure, which enables the target cells to be isolated directly from crude samples containing a large amount of nontarget cells or cell fragments. Many ready-to-use products are available and the basic equipment for standard work is relatively inexpensive. The separation process can be relatively easily scaled up and thus large amount of cells can be isolated. New processes for detachment of larger magnetic particles from isolated cells enable use of free cells for in vivo applications. Modern instrumentation is available on the market, enabling all the process to run automatically. Such devices represent a flexible platform for future applications in cell separation.
IMS play a dominant role at present but other specific affinity ligands such as lectins, carbohydrates or antigens will probably be used more often in the near future. There are also many possibilities to combine the process of cell magnetic separation with other techniques, such as PCR, enabling the elimination of compounds possibly inhibiting DNA polymerase. New applications can be expected, especially in microbiology (isolation and detection of microbial pathogens) and parasitology (isolation and detection of protozoan parasites). No doubt many new processes and applications in other fields of biosciences and biotechnologies will be developed in the near future.
Magnetic separation methods are widely used for isolation of a variety of cell types. Magnetic particles with immobilized antibodies to various antigens have been employed for the rapid isolation of populations T-(CD4 +, CD3 +, CD8+) and B- (CD19+) of lymphocytes, NK cells, and monocytes. Similarly, immobilization of glycoconjugates on magnetic beads allows the isolation of cell populations expressing a particular carbohydrate-recognizing molecule [19, 20]. Glycosylated magnetic beads can be prepared by loading biotinylated probes onto streptavidin-coated magnetic beads. The glycoparticles are then incubated with a cell suspension and the subpopulation of interest is fished out by means of a magnetic device .
When these materials are used in the biological field, special restrictions should be considered and all possible reactions with the biological materials should be predicted. Magnetic properties should be maintained for a specific time during the test. Some applications can be classified as follows:
Magnetic separation is used for clinical application, such as in the separation of proteins, toxemic materials, DNA, and bacteria and viruses. This is also used for real time detecting of viruses. The most important stage in this field is the labeling of molecules with magnetic materials by a reliable connection. Magnetic beads from iron oxide are typically used for biological separation. The main properties of iron oxide are super paramagnetic properties (Meza, 1997).
Effective drug delivery can greatly improve the process of treatment and reduce side effects. In this method, while the amount of drug decreases, the concentration of the drug in the target area increases. Protecting the drug before its gets to the target area is one of the most important factors, because after releasing the drug in the blood stream, white cells detect the drug and swallow them in a short time. An ideal nanoparticle for drug delivery should have the potential to combine with a relatively high-weight drug and disperse uniformly in the blood stream (Shultz et al., 2007).
Also, while chemotherapy is one of most effective methods for cancerous tissues, many of the other healthy cells are destroyed in the process. So the conventional thermotherapy has many side effects. In hyperthermia treatment, after delivering the drug to the target area, an AC magnetic field is used to generate controllable energy and increase temperature. Heat transfer in this process is a balance between blood flow, heat generation, and tissue porosity and conductivity (Sellmyer and Skomski, 2006).
Magnetic Resonance Imaging (MRI) is considered a great help in the diagnoses of many diseases. The advantages of this imaging are high contrast in soft tissue, proper resolution, and sufficient penetration depth for noninvasive diagnosis. In fact, in MRI imaging magnetization of protons is measured when exposed to the magnetic field with radio frequency (Corot, 2006).
Magnetic separation: based on the generation of magnetic forces on the particles to be separated, which are higher than opposing forces such as gravity or centrifugal forces. This principle is used to separate ferromagnetic particles from crushed scrap mixtures.
Eddy current separation: is a particular form of magnetic separation. An alternating magnetic field induces electrical eddy currents on a metal particle. This results in a magnetic field whose direction is opposite to the primary magnetic field. The exchange interactions between the magnetic fields result in a repulsive force on the metallic particle; the net effect is a forward thrust as well as a torque. This force and hence the efficiency of separation is a function of the magnetic flux, or indirectly of the electrical conductivity and density and the size and shape of the metallic particles.
Air separation/zigzag windsifter: Air-based sorting technique, which separates the light materials from the heavier. The most prominent application is in shredder plants producing the shredder light fraction, or in fridge recycling, removing among others the polyurethane (PUR) foam from the shredded scrap.
Screening: Separation of the scrap into different particle size classes is performed to improve the efficiency of the subsequent sorting processes and/or to apply different processing routes for different size fractions (based on material breakage and hence distribution over various size fractions).
Fluidized bed separation: A fluidized bed of dry sand is used to separate materials based on density. This technology is in principle a dry sink-float separation, which is still hampered by several difficulties (tubular or hollow particles filling up with sand and tend to sink; formation of unsteady current due to the use of high velocity air, etc.). The fluidized bed could also be heated for simultaneous de-coating and combustion of organic material.
Image processing (including colour sorting): Colour sorting technologies, which sense the colour of each particle and use computer control to mechanically divert particles of identical colour out of the product stream (red copper, yellow brass, etc.). A complicating issue is that shredding results in mixtures of particles that show a distribution in composition, size, shape, texture, types of inserts, coatings, etc. The variance of these properties complicates identification that is solely based on this principle.
X-ray sorting: Dual energy X-ray transmission imaging (well known for luggage safety inspections at airports) identifies particles based on the average atomic number, particle shape, internal structure (e.g. characteristic variations of thickness) and presence of characteristic insert material. It is rather sensitive to particle thickness and surface contaminations.
LIBS (laser induced breakdown spectroscopy) sorting: A series of focused ablation laser pulses are delivered to the same spot on each particle. A pulse of an ablation laser vaporizes only the first nanometres of the surface, i.e. the first pulses are necessary to clean the surface of oxide layers (different composition than the mother metal), the last pulse vaporizes a tiny amount of metal generating a highly luminescent plasma plume. The light from the plasma is collected and analysed to quantitatively determine the chemical composition. This determines to which bin the particle is directed (e.g. by air pulse).
Iron ore processors may also employ magnetic separation for beneficiation of classifier output streams. Wet high-intensity magnetic separators (WHIMS) may be used to extract high-grade fine particles from gangue, due to the greater attraction of the former to the applied magnetic field.
In addition to beneficiating the intermediate middlings streams from the classifier, WHIMS may be used as scavenger units for classifier overflow. This enables particles of sufficient grade to be recovered that would otherwise be sacrificed to tails.
Testwork has been performed on iron ore samples from various locations to validate the use of magnetic separation following classification (Horn and Wellsted, 2011). A key example was material sourced from the Orissa state in northeastern India, with a summary of results shown in Table 10.2. The allmineral allflux and gaustec units were used to provided classification and magnetic separation, respectively.
The starting grade of the sample was a low 42% Fe. It also contained significant ultrafines with 58% passing 20m. This is reflected in the low yield of allflux coarse concentrate; however, a notable 16% (abs) increase in iron grade was eventually achieved. The gaustec results for the middlings and overflow streams demonstrate the ability to recover additional high-grade material. With the three concentrate streams combined, an impressive yield of almost 64% was achieved with minimal decline in iron grade.
The automatic separation system, developed by Magnetic Separation System of Nashville, Tennessee, uses X-ray, IR, and visible spectra sensors for separating the post-consumer recyclate bottles or flakes into individual plastics and into different color groups. X-ray sensors, used for separating PVC, are very accurate and can operate at as high as 99% or better efficiency. IR and visible sensors are used to separate the colored bottles into individual polymers and color groups.
The separation system (Figure 4) essentially consists of a metering inclined conveyer, air knife, special disk screen, singulating infeed conveyor, and sensor module. A motor control system provides operator interface screens which control the sorting functions, including the number of bottles sorted into each fraction, ejection timing, and sort positions. Individual systems currently in use in Germany, Switzerland, and the United States are described in a paper by Kenny and Vaughan.16 The systems are customized, based on the composition of the post-consumer recyclate and the end application of the separated streams. Some systems use X-ray and IR sensors in two locations to achieve better separation. In addition to sorting equipment, some systems also use equipment for breaking the bales and splitting the bottles into more than one stream for smooth operation. Grinders are used when the bottles have to be ground into flakes for further processing. Whereas PVC separation is accomplished at 99%. HDPE and PET separation is between 80 and 90%, depending on the level of contamination.
Automated separation provides two advantages: improved quality and lower labor cost for sorting. The automatic separation system at Eaglebrook Plastics uses the Magnetic Separation System (MSS), which detects and separates the bottles into different categories based on the type of the resin and color, and eliminates impurities such as broken pieces of plastics, rocks, aluminum cans, and other contaminants.17 Metering the feed is critical to obtain maximum throughput at Eaglebrook. This is accomplished by a special debaling device and an incline metering system. Factors contributing to proper operation include clear height, width, spacing, belt speed, and incline angle. Proper presentation of the bottle to the sensor is critical. The bottles are split into four streams and two to three bottles are presented to the sensor per second, one at a time.
The primary identification sensor uses a multibeam, near-IR array to identify the bottles into three classes: Class 1, PVC, PET; Class 2, natural HDPE, PP; Class 3, mixed color HDPE and opaque containers. This sensor is also capable of separating colored PET from clear PET and PP from milk jug HDPE. The X-ray sensor identifies PVC, and a machine vision sensor system provides up to seven color classifications of the plastic bottles. After identification, the containers are ejected from the conveyors into appropriate collection stations using high-speed pulsed air nozzles. The motor control center (MCC) of the separation system controls motor protection, sequential slant up for the system, fault indication, and operation control. In addiiton, a touch screen input panel allows the operator to select any available sort to be directed to any ejection station. Visible light color sensors have been added which sort pigmented HDPE into different colors. The system also includes a decision cross-checking device between the primary sensor and the color sensor. This compares the decisions of the two sensors by comparing them with a logic file. The latter then provides correct identification in case there are discrepancies between the two decisions. The system has successfully operated for the last three to four years at a capacity of 5000 bottles h1.
The debaling system designed for Eaglebrook requires that the bales be presented to the debaling equipment in the same orientation as the original compression. This design feature requires less horsepower, reduces bottle clusters, and requires minimum energy. The debaling and declumping system incorporates a surge bin and metering conveyor to feed the screening system. The improved capacity and higher separation accuracy, due to increased metering efficiency, reduces bottle clusters and provides a more uniform feeding system. The separation efficiency depends on several factors. Timing and catcher bounceback accounts for 12% accuracy loss; contamination, container distortion, and loose labels contribute to about 34%, and nonsingulation of the bottles 510% of accuracy loss.
Asoma Instrument of Austin, TX, is a leading manufacturer of automated bottle sorting equipment. The company uses an X-ray fluorescence spectrophotometer sensor. The identification is completed in 10ms and the separation takes about 20s per bottle. The sorted PET streams have less than 50ppm PVC. National Recovery Technology of Nashville, TN, uses a proprietary electromagnetic screening process which can handle the bottles either in crushed or whole form and does not require any special positioning or orientation of the bottle to achieve high efficiency. Chamberlain/MCR, Hunt Valley, MD, and Automation Industrial Control of Baltimore, MD, offer a paysort bottle sorting system, which uses a sophisticated video camera and color monitor incorporating a strobe to detect and distinguish colors of post-consumer bottles following a near-IR detection system which also determines the primary resin found in each bottle.
A substantial amount of research is focused on microseparation techniques and on techniques which can reject bottles with trace amounts of harmful contaminant. Near-IR spectrometry is being used to separate bottles for household chemicals and ones with hazardous waste residues.
Sorting of automotive plastics is more difficult than sorting of plastics from packaging recyclates. Whereas only five to six polymers are used for packaging, post-consumer automotive plastics contain large numbers of engineering and commodity plastics, modified in various ways, including alloying and blending, filling, reinforcing, and foaming. Hence, sorting of automotive plastic recyclate poses several challenges. Recently, a systematic study, PRAVDA, was undertaken by a German car manufacturer and the plastic suppliers in Europe to investigate the potential of various analytical techniques in separating post-consumer automotive plastics.18
The techniques examined in this study include near-IR spectroscopy (NIR), middle-IR spectroscopy (MIR), Fourier transform Raman spectroscopy (FTR), pyrolysis mass spectrometry (PY-MS), pyrolysis IR spectroscopy (PYIR), and laser-induced emission spectral analysis (LIESA). X-ray methods were excluded because they have insufficient sensivitity to polymers, other than ones containing chlorine. Since commercial spectrophotometers were not available for most techniques except NIR, either laboratory models (MIR, FTR) or experimental stage instruments (PY-MS, PY-IR, and LIESA) were used in this study. A large number of parts (approximately 7000) were analyzed. The techniques were compared in respect to their success in identification, fault rate, time for identification, degree of penetration, and sensitivity to surface quality. The fault rate is the number of wrong identifications, given as percent. If the sum of the identification and fault rate is less than 100, the difference gives the rate of incomplete correct identification. The biggest stumbling block was the identification of black samples which could not be analyzed by NIR and FTR. MIR is the only technique which not only identified the black samples, but gave the highest identification rate. Some difficulties were experienced, however, in MIR analysis in the case of blends of two similar polymers such as PP/EPDM or nylon 6/nylon 66. The pyrolytic methods showed poorer identification rates and higher fault rates. The LIESA method is very fast and a remote technology, particularly for fast identification of heteroatoms. It is therefore suitable for identifying fillers, minerals, reinforcing fibers, pigments, flame retardants, and stabilizers specific to the individual plastic. The difficulty with MIR is that it is sensitive to surface micro-roughness and, hence, the samples need to be very smooth. Also, paint or surface coats on the part have to be removed for correct identification of the resin used for making the parts. Further, at this stage, no fiber optic or separated probe is available with MIR technology and, hence, the part has to be brought close to the spectrophotometer instead of the probe reaching the part. Another method of measuring efficiency is the level of contamination. Contamination of parts sorted by the MIR method was less than 1%, whereas contamination of parts sorted manually, using a Car Parts Dismantling Manual, is greater than 1015%. When the level of contamination is high, further separation by swim-sink or hydrocyclone techniques are necessary.
The cost of a MIR spectrophotometer is approximately DM 100000. The cost calculated for small dismantlers (dismantling less than 25 cars per day) is approximately DM 0.34 per kg and that for large dismantlers is somewhat less than DM 0.19. Manual sorting, on the other hand, would cost DM0.71 and DM0.23 per kg for small and large dismantlers, respectively. Spectrophotometric identification of plastics in automotive plastics waste therefore makes substantial economic sense.
All substances are not present in their pure form in nature. Most of the substances are present in the form of mixtures. We can separate useful components of the mixtures by using various methods of separation. You must have seen your mother separating stones or other impurities from rice by washing it before cooking it. You generally use different methods of separation in your daily life.
You must have studied many separating techniques in chemistry of class VI, VII and IX. So, here in this article we are going to discuss various separation techniques so that if you have any doubts then you can clear through this article
If you want to separate black grapes from the mixture of black and green grapes, then you will simply pick black grapes using your hands from the mixture. So, the separation method in which components of a mixture can be separated by just picking them out by hands is called handpicking.
This method of separation is generally used by farmers in agriculture during the harvesting of crops as it is used in separating edible part from non-edible part of grain. For example, the grain is separated from the stalks by beating it on the ground or large stone.
It is an agricultural technique being used since ancient times. Now a days many machines are available for winnowing. Winnowing meaning is separation of grains from straw by the use of current of air. The word winnow is originated from old English word windwian which means separation of mixture through wind. Winnowing can be defined as separation of heavier substance from lighter substance of a mixture using current of air or by blowing air. Corns are separated from straw by winnowing.
You must have either used this separation technique or seen someone using this at home. Generally, mothers use this technique in kitchens to separate stones or other larger impurities from rava, rice etc. We use this technique in making tea also.
Sedimentation is a separation technique in which heavier impurities present in water settle down at the bottom after some time if you keep the mixture still at one place. The heavier constituent which get settled at the bottom is known as sediment and the water above it is known as supernatant.
It is used to separate those mixtures in which solvent is liquid and solute is soluble solid. As the name suggests, evaporation is the process of conversion of water into vapour. It is the method of separation in which liquid (solvent or organic solvent) evaporates and leaves the solid residue behind. For example, salt is obtained from sea water by evaporation.
Sublimation is the process in which substance directly changes from solid state to liquid state. It is used as a separation technique for those mixtures which contain sublimable volatile substance and non-sublimable volatile components. Some substances such as ammonium chloride, camphor, naphthalene and anthracene are sublime substances.
It is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling point. In this technique liquid mixtures are boiled, vaporized, condensed and isolated. Mixture of acetone and water is separated by distillation. Boiling point of acetone is 56 and water is 100.
It is same technique as distillation, but its apparatus has fractionating column also. So that it can separate mixture of miscible liquids which has difference in their boiling point less than 25K. Separation of different gases from air can be done by fractional distillation.
It is used to separate two immiscible liquids such as oil and water. This method is used in the extraction of iron also. The principle is that immiscible liquids separate out in layers depending on their densities.
It is used in the separation of components of those mixtures in which one component shows magnetic properties and another one doesnt. It is used in the extraction of metals to separate the metal from its impurity.
Electrostatic separation is a process that uses electrostatic charges to separate crushed particles of material. An industrial process used to separate large amounts of material particles, electrostatic separating is most often used in the process of sorting mineral ore. This process can help remove valuable material from ore, or it can help remove foreign material to purify a substance. In mining, the process of crushing mining ore into particles for the purpose of separating minerals is called beneficiation.
Generally, electrostatic charges are used to attract or repel differently charged material. When electrostatic separation uses the force of attraction to sort particles, conducting particles stick to an oppositely-charged object, such as a metal drum, thereby separating them from the particle mixture. When this type of beneficiation uses repelling force, it is normally employed to change the trajectory of falling objects to sort them into different places. This way, when a mixture of particles falls past a repelling object, the particles with the correct charge fall away from the other particles when they are repelled by the similarly charged object.
Charge is the measure of the electric current flowing through an object. A charge can be positive or negative objects with a positive charge repel other positively-charged objects, thereby causing them to push away from each other, while a positively charged object would attract to a negatively charged object, thereby causing the two to draw together. Electrostatic charges are the charges associated with static electricity. Generally, electrostatic charges can build up by friction and can be observed when a balloon attracts a person's hair after the balloon is rubbed against the person's head.
Experiments showing electrostatic sorting in action can help make the process more clear. To exhibit electrostatic separation at home, an experiment can be conducted using peanuts that are still in their shells. When the shells are rubbed off of the peanuts and gently smashed into pieces, an electrostatically charged device, like a comb rubbed quickly against a wool sweater, will pick up the peanut shells with static electricity. The lightweight crushed shells that are oppositely charged from the comb easily move away from the edible peanut parts when the comb is passed nearby.
The electrostatic separation of conductors is one method of beneficiation; another common beneficiation method is magnetic beneficiation. Electrostatic separation is a preferred sorting method when dealing with separating conductors from electrostatic separation non-conductors. In a similar way to that in which electrostatic separation sorts particles with different electrostatic charges magnetic beneficiation sorts particles that respond to a magnetic field. Electrostatic beneficiation is effective for removing particulate matter, such as ash from mined coal, while magnetic separation functions well for removing the magnetic iron ore from deposits of clay in the earth.
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The cell separation method you choose typically depends on what you intend to use the isolated cells for, and the choice may involve a trade-off. For example, if you need very pure cells, you will likely choose a method with high purity but that may result in lower yield.
Due to its speed and simplicity, immunomagnetic cell separation is one of the most commonly used methods by which scientists isolate highly purified populations of specific cell subsets. Immunomagnetic cell separation has several advantages, including:
Both positive and negative selection can be performed using magnetic cell isolation methods. When a positive selection is performed, the supernatant can be discarded and the magnetically-labeled cells of interest remain immobilized until removed from the electromagnetic field. When a negative selection is performed, the desired cells are located in the supernatant.
Fluorescence-activated cell sorting (FACS) is a method that uses flow cytometry and fluorescent probes to sort heterogeneous mixtures of cells. Fluorophore-tagged antibodies bind to epitopes on specific antigens on the target cells within a single-cell suspension. After tagging, the flow cytometer focuses the cell suspension into a uniform stream of single cells. This stream is then passed through a set of lasers that excites the cell-bound fluorophores, causing light scattering and fluorescent emissions. Based on the wavelengths produced by the laser excitation, the resulting photon signals are converted into a proportional number of electronic pulses that assign a charge to the droplet that is formed around the cell. As each droplet falls between the deflection plates, its charge causes the droplet to either be deflected into collection tubes or fall into the waste chamber.
Immunomagnetic cell sorting is a much faster and simpler procedure than FACS, and is often the preferred cell isolation method for common cell types. FACS has several advantages over immunomagnetic cell sorting including the ability to:
Isolating rare cell types by FACS can be time consuming, expensive and can result in low cell recovery. Researchers can pre-enrich their samples for target cells using immunomagnetic cell separation to reduce the sort time and improve purity and recovery. Read our case study:
In addition to ILCs, researchers may choose to pre-enrich for other cell types, including CD4+ T cells, CD8+ T cells, B cells, or dendritic cells, prior to sorting for more specific or rare cell subsets.
In flow cytometry, gates are value limits that allow you to analyze a subset of data from the larger data set. In FACS, these boundaries allow you to analyze cells with common characteristics and allows you to distinguish your cells of interest from other populations. Using an optimal gating strategy is an important factor in ensuring accurate results. For those new to flow cytometry, read the following technical tips to optimize your gating strategy before sorting your samples.
Density gradient centrifugation relies on the varying densities of cells within a heterogeneous sample. The sample is layered on top of a density gradient medium before being centrifuged. During centrifugation, each cell type will sediment to its isopycnic point, which is the place in the medium gradient where the density of the cells and medium are equal.
Density gradient centrifugation is an inexpensive cell separation technique but has limited specificity, low purity, and low throughput. In addition, even though it is a common laboratory technique, density gradient centrifugation can be a slow and laborious process that is difficult to master. Scientists typically need to carefully layer their sample over the density gradient medium, centrifuge for 30 minutes without brakes, then carefully harvest and wash the appropriate layer of cells. Technologies like SepMate make this method easier and faster. SepMate is a specialized tube that allows users to quickly layer blood over the density gradient medium, prevents the layers from mixing and facilitates fast and easy harvesting of the target cells. With SepMate, cells can be obtained in as little as 15 minutes.
Immunodensity cell separation, also referred to as erythrocyte rosetting, is a negative selection method that uses a combination of antibody-based labeling and density gradient centrifugation. With this method, antibodies are added to a whole blood sample, labeling the unwanted cells and cross-linking them to red blood cells. This results in the formation of complexes called immunorosettes that are much denser than the mononuclear cells being isolated. During centrifugation, the unwanted cells pellet with the red blood cells, leaving the target cells in a layer above the density medium.
Immunodensity cell separation doesnt require any specialized equipment beyond a centrifuge, can be easily incorporated into established density gradient centrifugation protocols, and can be used to isolate specific cell subsets directly from whole blood. However, the technique is limited to negative selection, relies on the operators blood sample layering technique, and requires a high concentration of red blood cells in the starting sample.
RosetteSep is an example of a commercially available immunodensity cell separation reagent (Figure 1). RosetteSep can be combined with SepMate PBMC isolation tubes for even faster and easier immunodensity cell separation.
Sedimentation works on the basis that gravity will cause larger and denser components to sediment faster than materials that are smaller and less dense. The largest and densest components in a sample can be pelleted through an initial low-force centrifugation due to their high rate of sedimentation. The supernatant can then be spun again. Through successive centrifugations, components with an increasingly lower rate of sedimentation can be isolated. Leukocytes are commonly separated from erythrocytes through dextran sedimentation. HetaSep is an example of an erythrocyte aggregation agent that is used to separate nucleated cells from red blood cells (RBCs) in whole blood.
The unique adhesion profiles of different cell types can be used to separate target cells from heterogeneous populations. By choosing suitable growth factors and cell culture plates to selectively favor or inhibit adhesion, adherent cells can be separated from cells in suspension.
Macrophages are inherently adherent and often isolated from peripheral blood and bone marrow by adhesion. Mononuclear cells can be cultured with serum and a differentiation cocktail, promoting the formation of an adherent monolayer of macrophages. After removing the supernatant containing unwanted cells, the macrophages can be isolated.
Alternatively, cells that naturally grow in suspension or have lost anchorage dependency can be isolated by culturing the heterogeneous cell population in plates designed for ultra-low attachment. Without a surface to adhere to, adherent cells will fail to survive and the target cells will remain in suspension1.
Microfluidics is an umbrella category of cell separation methods.2 Designed to manipulate fluids on a microscopic level to facilitate single-cell isolation, microfluidic technologies are frequently built onto microchips and are commonly known as "lab-on-a-chip" devices. These devices have several advantages, including the smaller volumes of samples and reagents required for use. Lab-on-a-chip devices are also portable, making them particularly useful as field-based diagnostic tools.
Microfluidic methods can be divided into active and passive systems. Active microfluidic systems involve external forces, whereas passive microfluidics make use of the cells density and mass in combination with gravity. These methods can also be classified by the presence or absence of cell labeling; although some methods involve labeling cells with antibodies, most methods are known for being label-free. There are several different microfluidic methods used for cell isolation, including:
Aptamers are single-stranded RNA or DNA oligonucleotides that form structures that can bind to highly specific targets. Through systematic evolution of ligands by exponential enrichment (SELEX) technology, aptamers can be screened and synthesized to target any cell type. These aptamers have high affinity and specificity toward their targets, and can be labeled with fluorochromes or magnetic particles to facilitate cell separation. The main advantage of aptamers is that they lack immunogenicity.
Buoyancy-Activated cell sorting is a cell separation technique that utilises glass microbubbles labeled with antibodies specific to the target cells. When mixed into the sample, the microbubbles bind to the target cells. Due to the augmented buoyancy force, the microbubbles float to the surface, separating the target cells.
The complement depletion method takes advantage of the proteolytic cascade initiated by the complement system of the immune system. The complement system consists of plasma proteins that can be activated by pathogens or antibodies. Once activated, the plasma proteins induce the formation of a membrane-attack complex on a cell, resulting in cell lysis. With specific monoclonal antibodies, any cell population can be targeted and lysed through the complement cascade.
Laser capture microdissection (LCM) is a technique that uses a narrow laser beam to cleave target cells or areas from mostly solid tissue samples. Through microscopic visualization, LCM can isolate cell populations from heterogeneous mixtures using cell morphology or specific histological and immunological staining. LCM is particularly useful when working with small sample sizes.
Immunoguided laser capture microdissection combines immunostaining with laser capture microdissection (see above). This allows immunophenotypes to be used, in addition to morphology and tissue location, to identify and isolate target cells from the tissue sample. This technique employs immunohistochemistry or immunofluorescence to guide the dissection process for isolating cells expressing a specific molecular marker, and is particularly useful when histological stains do not recognize certain cell populations.
Limiting dilution involves isolating single cells through the dilution of a cell suspension. This technique can be carried out with standard pipetting tools and is commonly used to produce monoclonal cell cultures and single cell cultures for single-cell analysis4.
Micromanipulation, a form of manual cell picking, is a cell isolation technique involving the use of an inverted microscope and ultra-thin glass capillaries connected to an aspiration and release unit. The system moves through motorized mechanical stages, allowing the operator to carefully select a specific cell and apply suction via micropipette to aspirate and isolate the cell.
Mineral processing, art of treating crude ores and mineral products in order to separate the valuable minerals from the waste rock, or gangue. It is the first process that most ores undergo after mining in order to provide a more concentrated material for the procedures of extractive metallurgy. The primary operations are comminution and concentration, but there are other important operations in a modern mineral processing plant, including sampling and analysis and dewatering. All these operations are discussed in this article.
Routine sampling and analysis of the raw material being processed are undertaken in order to acquire information necessary for the economic appraisal of ores and concentrates. In addition, modern plants have fully automatic control systems that conduct in-stream analysis of the material as it is being processed and make adjustments at any stage in order to produce the richest possible concentrate at the lowest possible operating cost.
Sampling is the removal from a given lot of material a portion that is representative of the whole yet of convenient size for analysis. It is done either by hand or by machine. Hand sampling is usually expensive, slow, and inaccurate, so that it is generally applied only where the material is not suitable for machine sampling (slimy ore, for example) or where machinery is either not available or too expensive to install.
Many different sampling devices are available, including shovels, pipe samplers, and automatic machine samplers. For these sampling machines to provide an accurate representation of the whole lot, the quantity of a single sample, the total number of samples, and the kind of samples taken are of decisive importance. A number of mathematical sampling models have been devised in order to arrive at the appropriate criteria for sampling.
After one or more samples are taken from an amount of ore passing through a material stream such as a conveyor belt, the samples are reduced to quantities suitable for further analysis. Analytical methods include chemical, mineralogical, and particle size.
Even before the 16th century, comprehensive schemes of assaying (measuring the value of) ores were known, using procedures that do not differ materially from those employed in modern times. Although conventional methods of chemical analysis are used today to detect and estimate quantities of elements in ores and minerals, they are slow and not sufficiently accurate, particularly at low concentrations, to be entirely suitable for process control. As a consequence, to achieve greater efficiency, sophisticated analytical instrumentation is being used to an increasing extent.
In emission spectroscopy, an electric discharge is established between a pair of electrodes, one of which is made of the material being analyzed. The electric discharge vaporizes a portion of the sample and excites the elements in the sample to emit characteristic spectra. Detection and measurement of the wavelengths and intensities of the emission spectra reveal the identities and concentrations of the elements in the sample.
In X-ray fluorescence spectroscopy, a sample bombarded with X rays gives off fluorescent X-radiation of wavelengths characteristic of its elements. The amount of emitted X-radiation is related to the concentration of individual elements in the sample. The sensitivity and precision of this method are poor for elements of low atomic number (i.e., few protons in the nucleus, such as boron and beryllium), but for slags, ores, sinters, and pellets where the majority of the elements are in the higher atomic number range, as in the case of gold and lead, the method has been generally suitable.
A successful separation of a valuable mineral from its ore can be determined by heavy-liquid testing, in which a single-sized fraction of a ground ore is suspended in a liquid of high specific gravity. Particles of less density than the liquid remain afloat, while denser particles sink. Several different fractions of particles with the same density (and, hence, similar composition) can be produced, and the valuable mineral components can then be determined by chemical analysis or by microscopic analysis of polished sections.
Coarsely ground minerals can be classified according to size by running them through special sieves or screens, for which various national and international standards have been accepted. One old standard (now obsolete) was the Tyler Series, in which wire screens were identified by mesh size, as measured in wires or openings per inch. Modern standards now classify sieves according to the size of the aperture, as measured in millimetres or micrometres (10-6 metre).
In order to separate the valuable components of an ore from the waste rock, the minerals must be liberated from their interlocked state physically by comminution. As a rule, comminution begins by crushing the ore to below a certain size and finishes by grinding it into powder, the ultimate fineness of which depends on the fineness of dissemination of the desired mineral.
In primitive times, crushers were small, hand-operated pestles and mortars, and grinding was done by millstones turned by men, horses, or waterpower. Today, these processes are carried out in mechanized crushers and mills. Whereas crushing is done mostly under dry conditions, grinding mills can be operated both dry and wet, with wet grinding being predominant.
Some ores occur in nature as mixtures of discrete mineral particles, such as gold in gravel beds and streams and diamonds in mines. These mixtures require little or no crushing, since the valuables are recoverable using other techniques (breaking up placer material in log washers, for instance). Most ores, however, are made up of hard, tough rock masses that must be crushed before the valuable minerals can be released.
In order to produce a crushed material suitable for use as mill feed (100 percent of the pieces must be less than 10 to 14 millimetres, or 0.4 to 0.6 inch, in diameter), crushing is done in stages. In the primary stage, the devices used are mostly jaw crushers with openings as wide as two metres. These crush the ore to less than 150 millimetres, which is a suitable size to serve as feed for the secondary crushing stage. In this stage, the ore is crushed in cone crushers to less than 10 to 15 millimetres. This material is the feed for the grinding mill.
In this process stage, the crushed material can be further disintegrated in a cylinder mill, which is a cylindrical container built to varying length-to-diameter ratios, mounted with the axis substantially horizontal, and partially filled with grinding bodies (e.g., flint stones, iron or steel balls) that are caused to tumble, under the influence of gravity, by revolving the container.
A special development is the autogenous or semiautogenous mill. Autogenous mills operate without grinding bodies; instead, the coarser part of the ore simply grinds itself and the smaller fractions. To semiautogenous mills (which have become widespread), 5 to 10 percent grinding bodies (usually metal spheres) are added.
Yet another development, combining the processes of crushing and grinding, is the roll crusher. This consists essentially of two cylinders that are mounted on horizontal shafts and driven in opposite directions. The cylinders are pressed together under high pressure, so that comminution takes place in the material bed between them.
Most of the time the substances that we see around us are not in their pure form. They are basically a mixture of two or more substances. Interestingly, mixtures tend to also come in different forms. Therefore, there are several types of separation techniques that are used in segregating a mixture of substances. As for the need for separation, it is usually done to remove all the unwanted materials and obtain useful components.
This method involves simply picking out all the unwanted substances by hand and separating them from useful ones. The separated substances may be an impurity that has to be thrown away or maybe that both the separated substances are useful. For example if you separate black grapes from green ones from a mixture of the two.
This method is mostly done during the harvesting of crops. Normally, the stalks of the wheat are dried once it is harvested. The grain is then separated from the stalks and grounded into the floor by beating the dry stalks to shake off the dried grains.
When the grains are collected from the process of threshing, it needs to be cleared out of husks and chaffs before it is turned into flour. Normally the separation of the mixture is carried out with the help of wind or blowing air. The husk and chaff are blown away by the strong wind when the farmers drop the mixture from a certain height to the ground. The heavier grains are collected at one place.
It is done to separate mixtures that contain substances mostly of different sizes. The mixture is passed through the pores of the sieve. All the smaller substances pass through easily while the bigger components of the mixture are retained.
Evaporation is a technique that is used in separating a mixture usually a solution of a solvent and a soluble solid. In this method, the solution is heated until the organic solvent evaporates where it turns into a gas and mostly leaves behind the solid residue.
When mixtures consist of two or more pure liquids than distillation is used. Here the components of a liquid mixture are vaporized, condensed and then isolated. The mixture is heated and the component which is volatile vaporizes first. The vapour moves through a condenser and is collected in a liquid state.
The most common method of separating a liquid from an insoluble solid is the filtration. Take, for example, the mixture of sand and water. Filtration is used here to remove solid particles from the liquid. Various filtering agents are normally used like filtering paper or other materials.
Separating funnel is used mainly to segregate two immiscible liquids. The mechanism involves taking advantage of the unequal density of the particles in the mixture. Oil and water can be easily separated using this technique.
Frequently Asked Questions FAQsWhat are chemical methods of separation? Distillation, crystallisation, adsorption, membrane procedures, absorption and stripping, and oxidation are the typical chemical engineering methods of isolation and purification. How can you separate sand and salt? It either remains in the bath as sand is applied to the bath or forms a film on the bottom of the bottle. Consequently, sand does not dissolve in water and is unsoluble. Through separating the mixture, it is easy to segregate sand and water. Salt by evaporation may be isolated from a solution. What are two types of mixtures? Two types of mixtures exist: heterogeneous and homogeneous. Two or more ingredients (or phases, regions with standardised structure and properties) intermingle in heterogeneous mixtures but remain physically distinct. Is Coca Cola a mixture? Although the sugar and water are blended equally in the solution, Coca cola is a homogeneous mixture. You can also see the basic ingredients in a homogeneous mixture such as coca cola, but heterogeneous means that you can see the basic ingredients such as a salad. Can homogeneous mixtures be separated? Components in homogeneous mixtures can typically be distinguished by taking account of the varying properties of the different components. A mixture can be heated until the component that boils at the lowest temperature becomes a vapour and can be distinguished during the distillation process.
It either remains in the bath as sand is applied to the bath or forms a film on the bottom of the bottle. Consequently, sand does not dissolve in water and is unsoluble. Through separating the mixture, it is easy to segregate sand and water. Salt by evaporation may be isolated from a solution.
Two types of mixtures exist: heterogeneous and homogeneous. Two or more ingredients (or phases, regions with standardised structure and properties) intermingle in heterogeneous mixtures but remain physically distinct.
Although the sugar and water are blended equally in the solution, Coca cola is a homogeneous mixture. You can also see the basic ingredients in a homogeneous mixture such as coca cola, but heterogeneous means that you can see the basic ingredients such as a salad.
Components in homogeneous mixtures can typically be distinguished by taking account of the varying properties of the different components. A mixture can be heated until the component that boils at the lowest temperature becomes a vapour and can be distinguished during the distillation process.
Sedimentation is a physical water treatment process that uses gravity to remove suspended solids from water. Solid particles formed by the turbulence of moving water can be naturally removed by sedimentation in the still water of lakes and oceans.
Decantation is the process of separating liquids, and the potential benefit of decantation is to separate liquid from precipitate. An example of this gain can be seen when making brewed coffee, decanting the blend of coffee, and removing the coffee from the coffee grounds.
Magnetic separation is the process of separating components of mixtures by using magnets to attract magnetic materials. The process that is used for magnetic separation detaches non-magnetic material with those that are magnetic.