Drying, freeze

Freeze drying is used to dry either salt solutions or ceramic suspensions in a gentle way, avoiding thermal decomposition of the metal salts and aggregation of the particles. There are fovir steps in fieeze drying  

Either a mixture of soluble salts containing the desired ratio of metal ions is dissolved in a solvent or a ceramic powder suspension is made. 

The solution is sprayed into droplets between 0.1 and 0.5 mm in diameter and rapidly frozen by a cold flviid (liquid or gas) so that no compositional segregation or aggregation can occur and the solvent crystals that nucleate are very small. Very hig cooling rates can give a solidified solvent that is amorphous. 

The solvent is removed by vacuvim sublimation being carefvil not to form any liquid phase that could cause chemical segregation. 

The resulting powder is either used directly or the metal salts are calcined at a temperature that decomposes the crystallized salts and converts them to very fine crystalites of the desired ceramic powder. 

Freeze-drying (lyophilization) refers to the removal of solvent directly from a solution while in the frozen state. Removal of water directly from (frozen) biopharmaceutical products via 

Freeze-drying is a relatively gentle way of removing water from proteins in solution. However, this process can promote the inactivation of some protein types and specific excipients (cryoprotectants) are usually added to the product in order to minimize such inactivation. Commonly used cryoprotectants include carbohydrates, such as glucose and sucrose proteins, such as human serum albumin and amino acids, such as lysine, arginine or glutamic acid. Alcohols/polyols have also found some application as cryoprotectants. 

As the temperature drops still lower, some of the solutes present may also crystallize, thus being effectively removed from the solution. In some cases, individual buffer constituents can crystallize out of solution at different temperatures. This will dramatically alter the pH values of the remaining solution and, in this way, can lead to protein inactivation. 

As the temperature is further lowered, the viscosity of the unfrozen solution increases dramatically until molecular mobility effectively ceases. This unfrozen solution will contain the protein, as well as some excipients and (at most) 50% water. As molecular mobility has 

The next phase of the freeze-drying process entails the application of a vacuum to the system. When the vacuum is established, the temperature is increased, usually to temperatures slightly in excess of 0°C. This promotes sublimation of the crystalline water, leaving behind a powdered cake of dried material. Once satisfactory drying has been achieved, the product container is sealed. 

The freeze-drying process is initiated by the freezing of the biopharmaceutical product in its final product containers. As the temperature is decreased, ice crystals begin to form and grow. This results in an effective concentration of all the solutes present in the remaining liquid phase, including the protein and all added excipients. For example, the concentration of salts may increase to 

As the temperature is lowered further, the viscosity of the unfrozen solution increases dramatically until molecular mobility effectively ceases. This unfrozen solution will contain the protein, as well as some excipients, and (at most) 50 per cent water. As molecular mobility has effectively stopped, chemical reactivity also all but ceases. The consistency of this solution is that of glass, and the temperature at which this is attained is called the glass transition temperature Tg-. For most protein solutions, Tg- values reside between -40 °C and -60 °C. The primary aim of the initial stages of the freeze-drying process is to decrease the product temperature below that of its Tg- value and as quickly as possible in order to minimize the potential negative effects described above. 

Freeze drying requires small samples, of fhe order of 10 mm in diameter and 5 mm thick, which are quickly frozen using either liquid nitrogen or propane cooled by liquid 

Freeze-drying techniques have been applied for the preparation of Type A, and B materials. For preparation of a Type A catalyst, the initial solution in the organic solvent contains the IL and the molecular catalyst (plus ligands or additives). For preparation of Type B catalysts, a suspension of metal nanoparticles can be used [25]. The metal nanoparticles can also be prepared directly in an IL. This is particularly interesting as ILs are known to stabilize metal nanoparticles 

Walter and Bryant [564] described a method for freeze drying latex specimens in a homemade vacuum system rather than in a commercially available device (as was typical of the state of the art at that time). Later, a freeze drying/image analysis method using commercially available equipment was described [563]. Important details of that method included specimen preparation, placement onto a TEM (or SEM) grid, the hardware for the experiment, and the metal coating. 

An Edwards evaporator with freeze fracture accessory was used in this experiment, although any commercial freeze etch device can be used. The system must have provision for pumping liquid nitrogen into the specimen holder and temperature sensing and controlling devices. 

Freeze dried specimens are generally shadowed (at about -150°C) in the vacuum chamber. Shadowing provides a metal cap that is the shape of the frozen, undistorted particle and limits distortion during examination in the electron microscope [566]. Replication of the latex particles, or macromolecules, can also be done if the specimen is expected to change at room temperature. For SEM specimens, the same procedure is used, but the specimens are dried onto small glass coverslips that are attached to the stub with silver paint. 

Results of the experiment described are shown in Fig. 4.48. A monodisperse latex of known particle size (Fig. 4.48A) was used both as a control and for calibration of the particle size distribution measurement [567]. A film forming latex is shown after both air drying 

the steps in the general specimen preparation are as follows  

The material obtained from 5000 L of surface water was further concentrated using a Lyovac GT2 (Leybold Heraeus) Freeze Dryer. Quick freezing was applied to minimise damage to the structure of the molecules. The concentrate was filled into four aluminium plates of a diameter of approximately 20 cm to a height of 5 mm. After operation for about 15 hours the powder was removed from the plates with a spatula and refilled without cleaning (to avoid loss of NOM). The operation was repeated until all the concentrate was dried. 

Standard parameters were flux, temperature, pH, conductivity, TOC/DOC, cations and UV spectra. Further characterisation was carried out with the freeze dried material and is reported in the NOM characterisation section of Chapter 4. 

Results of two batches are shown, the first batch is in standard operation while the last batch is the final concentration step of all previous concentrate batches. In the last concentration step a concentration factor of approximately 250 was attained. 

Researchers have synthesised and characterised a highly conductive, porous and biocompatible MWNT/CHT biocomposite film by the freeze-drying technique. The process was performed by freezing a MWNT/CHT dispersion inside an aluminum mould, followed by drying. 

Gieseler et al. utilized tunable diode laser absorption spectroscopy to detect water vapor concentrations, gas velocities and mass flow during freeze-drying of pure water at different pressure and shelf temperature settings and of a 5%w/w mannitol solution. The analyzer was interfaced to the spool that connected the dryer chamber to the condenser. The reported method was advantageous in that primary and secondary drying end-point control based upon mass flow rate was independent of freeze-dryer size and configuration.  

Thin slices of tissue are placed in clean plastic petri dishes, the loose fitting lids replaced and the dishes inserted into the chamber of the freeze drier. Blood specimens can be poured directly into the dish. It is important that the tissue be thoroughly frozen prior to evacuating the chamber. The time required for complete drying of the sample depends on the nature and weight of the material and the type of equipment employed. Drying is usually completed in 12—48h. The dried tissue is not susceptible to decay and can be stored at room temperature in sealed plastic bags. 

A radio-frequency coil is used to dissociate oxygen molecules in a suitable chamber for the ashing of the sample. A number of systems are commercially available. The sample is placed in a pure-quartz boat and introduced into the oxidation chamber. The chamber is kept under vacuum during the ashing, and oxidation products are vented through a suitable 

CONCENTRATION FACTORS FROM TRACE ELEMENTS IN DRIED AND ASHED ORGANS AND BODY FLUIDS (I.C.R.P.-23 REPORT, [32]) 

In this method, the aqueous, concentrated solution is also atomised into fine droplets, but they are rapidly frozen by blowing them into a low-temperature bath, such as ice-acetone, liquid C6H14 or liquid Nj. The droplets are then dried in vacuum, by sublimation of the ice without melting. This means that the temperature must remain below the eutectic in the salt-H20 system. The anhydrous salts (nitrates, sulphates, chlorides, etc.) are calcined to produce powders which are 0.1 pm in size. A schematic freeze-drying process is shown in Fig. 3.5. 

A non-aqueous solvent can also be used, if it has a higher melting point and a higher vapour pressure at low temperatures than water. Also, a suspension can be used instead of a solution. 

Ni-Zn ferrites have been obtained by freeze-drying a high density with 

Makers of vacuum ovens include Gallenkamp (from Fisher), Heraeus GmbH Co. KG, Jouan, and Townson and Mercer (see http //www. sanyogallenkamp.com http //www.heraeus.com http //www.jouaninc.com http // www.townson-mercer.co.uk). 

A freeze-dryer must be purchased that either has a large built-in chamber, or to which a chamber can be attached. Some smaller ones are mainly for small-scale work when multiple samples are held in glass flasks or ampoules, which are attached to a manifold equipped with isolation valves. 

It is vital to maintain clean contacts on the connection fitting of the Pirani gauge, because it is very sensitive to resistivity changes due to tarnishing or dust. 

Microporous bags can be obtained from Cryovac at the website of Sealed Air Corporation  

ChemLab httpy/home-l. worldonline.nl/ chemlab/ CHRIST http//www.phscientific.co.uk/html/ 

There are some simple freezing methods that provide adequate preparation for some polymers. Cold stage microscopy of colloidal suspensions, microemulsions and liquids is possible by fast freezing and examination of the thin, frozen specimen in an EM. Talmon et ah [404] developed a rather interesting technique in which a thin sample is trapped between two polyimide films. The liquid layer is about 100 nm thick, while the films are about 40 nm thick. Film selection is quite important as the polyimide is more radia- 

Manual methods of freeze fracture are often useful in providing specimens for study in the SEM. An example of a freeze shattering method was described by Stoffer and Bone [406] for comparison with microtomy results. Polymers immersed in liquid nitrogen were mechanically shattered with a hammer, mounted, vacuum pumped and sputter coated for observation. This simple method is useful if the materials cannot be sectioned. However, fine structural details are not conclusive when specimens are prepared by such methods. 

Of the three methods that are used to diminish the surface tension effects resulting from air 

A general method for the preparation of latex for TEM study has been used on film forming 

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Steinbrecht R A and Muiier M 1987 Freeze-substitution and freeze-drying Cryotechniques in Bioiogicai Eiectron Microscopy ed R A Steinbrecht and K Zieroid (Beriin Springer) pp 149-72... 

Figure Bl.24.16. An example of the applieation of the PIXE teelmique using the NMP in the imaging mode. The figures show images of the eross seetion tlirough a root of the Phaseolus vulgaris L. plant. In this ease the material was seetioned, freeze-dried and mounted in vaeuiim for analysis. The seales on the right of the figures indieate the eoneentrations of the elements in ppm by weight. It is elear that the transports of the elements tlirough the root are very different, not only in the eases of the major elements Ca and K, but also in the ease of the traee element Zn.

Then tire pressure is reduced to transfonn tire frozen liquid to a vapour and to remove it. Freeze drying is commonly used to make powders tliat are not agglomerated. 

Endo-exo ratios of the micelle-catalysed reactions have been determined by adding 0.25 mmol of 5.1c and 0.5 mmol of 5.2 to a solution of 5 mmol of surfactant and 0.005 mmol of EDTA in 50 ml of water in carefully sealed 50 ml flasks. The solutions were stirred for 7 days at 26 C and subsequently freeze-dried. The SDS and CTAB containing reaction mixtures were stirred with 100 ml of ether. Filtration and evaporation of the ether afforded the crude product mixtures. Extraction of the Diels-Alder adducts from the freeze-dried reaction mixture containing C12E7 was performed by stirring with 50 ml of pentane. Cooling the solution to -18 C resulted in precipitation of the surfactant. Filtration and evaporation of the solvent afforded the adduct mixture. Endo-exo ratios... 

Free-Wilson method Freeze concentration Freeze drying... 

Citric acid is used in carbonated beverages to provide tartness, modify and enhance flavors, and chelate trace metals. It is often added to jams and jellies to control pH and provide tartness. It is used in cured and freeze-dried meat products to protect the amino acids (qv) and improve water retention. Bakers use it to improve the flavor of fmit fillings in baked goods. Because citric acid is a good chelator for trace metals, it is used as an antioxidant synergist in fats and oils, and as a preservative in frozen fish and shellfish (7) (see Antioxidaisits). 

Pish silage prepared by autolysis of rainbow trout viscera waste was investigated as a substrate for the plastein reaction using pepsin (pH 5.0), papain (pH 6—7), and chymotrypsin (pH 8.0) at 37°C for 24 h (152). Precipitation with ethanol was the preferred recovery method. Concentration of the protein hydrolysate by open-pan evaporation at 60°C gave equivalent yields and color of the final plastein to those of the freeze-dried hydrolysate. 

The development of freeze-drying for the production of blood derivatives was pioneered during World War II (96,97). It is used for the stabilization of coagulation factor (98,99) and intravenous immunoglobulin (IgG iv) products, and also for the removal of ethanol from intramuscular immunoglobulin (IgG im) solutions prior to their final formulation (Fig. 2). 

The resuspended and formulated Fraction II precipitate normally contains some aggregated IgG and trace substances that can cause hypotensive reactions in patients, such as the enzyme prekail ikrein activator (186). These features restrict this type of product to intramuscular adininistration. Further processing is required if products suitable for intravenous adininistration are required. Processes used for this purpose include treatment at pH 4 with the enzyme pepsin [9001-75-6] being added if necessary (131,184), or further purification by ion-exchange chromatography (44). These and other methods have been fiiUy reviewed (45,185,187,188). Intravenous immunoglobulin products are usually suppHed in the freeze-dried state but a product stable in the solution state is also available (189). 

J. C. May and F. Brown, eds., "Biological Product Freeze-Drying and Formulation," Derelop. Biol Stand. 74 (1992). 

Lyophilization. LyophiLization is essentially a drying technology. Some dmgs and biologicals are thermolabile and/or unstable in aqueous solution. Utilization of freeze drying permits the production of granules or powders that can be reconstituted by the addition of water, buffered solution, or mixed hydrophilic solvents just prior to use, eg, certain antibiotic suspensions. 

Ereeze casting (59) is a hybrid of sHp casting, gel casting, and freeze drying in which a slurry is poured into a rigid mbber mold, frozen, and the frozen Hquid is removed by sublimation, ie, by freeze drying (see Cryogenics). 

Supercritical and Freeze Drying. To eliminate surface tension related drying stresses in fine pore materials such as gels, ware can be heated in an autoclave until the Hquid becomes a supercritical fluid, after which drying can be accompHshed by isothermal depressurization to remove the fluid (45,69,72) (see Supercritical fluid). In materials that are heat sensitive, the ware can be frozen and the frozen Hquid can be removed by sublimation (45,69). 

Freeze Drying. Commercial freeze drying of instant coffee has been a common practice in the United States since the mid-1960s. The freeze-drying process provides the opportunity to minimize flavor degradation due to heat (34). 

Sublimation of ice crystals to water vapor under a very high vacuum, about 67 Pa (0.5 mm Hg) or lower, removes the majority of the moisture from the granulated frozen extract particles. Heat input is controlled to assure a maximum product end point temperature below 49°C. Freeze drying takes significantly longer than spray drying and requires a greater capital investment. 

Drying is an operation in which volatile Hquids are separated by vaporization from soHds, slurries, and solutions to yield soHd products. In dehydration, vegetable and animal materials are dried to less than their natural moisture contents, or water of crystallization is removed from hydrates. In freeze drying (lyophilization), wet material is cooled to freeze the Hquid vaporization occurs by sublimation. Gas drying is the separation of condensable vapors from noncondensable gases by cooling, adsorption (qv), or absorption (qv) (see also Adsorption, gas separation). Evaporation (qv) differs from drying in that feed and product are both pumpable fluids. 

Freeze drying has also been carried out at atmospheric pressure in fluid beds using circulating refrigerated gas. Vacuum-type vibrating conveyors, rotating multishelf dryers and vacuum pans can be used as can dielectric and microwave heating. 

Specific procedures exist for storing (16,17) and propagating microorganisms to obtain reproducible fermentations. The stock culture is stored frozen (<—80°C) or freeze-dried. To prepare the inoculum (seed) mixture, an aUquot is taken and grown in consecutive soHd or Hquid cultures of increasing volume. The volume of the last step, the seed fermentor, is typically 4—12% of the main fermentor volume. 

Ultrafiltration (qv) (uf) is increasingly used to remove water, salts, and other low molecular-weight impurities (21) water may be added to wash out impurities, ie, diafiltration. Ultrafiltration is rarely used to fractionate the proteins because the capacity and yield are too low when significant protein separation is achieved. Various vacuum evaporators are used to remove water to 20—40% dry matter. Spray drying is used if a powdery intermediate product is desired. Tyophilization (freeze-drying) is only used for heat-sensitive and highly priced enzymes. 

Freeze-drying or dehydrating equipment for sublimation drying of ... 

Shelf Devices Equipment having heated and/or cooled shelves is available but is httle used for divided-sohds heat processing. Most extensive use of stationaiy shelves is freezing of packaged solids for food industries and for freeze drying by sublimation (see Sec. 22). 

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