A practical reference on primary drying: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-05-20. Anything still debated is marked as such rather than presented as settled.
Lyophilization, also called freeze-drying, removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts free water into ice and may also produce a glassy phase. Primary drying then lowers chamber pressure so ice sublimes directly to vapor without passing through a liquid stage. Secondary drying raises the temperature modestly to remove bound water. The result is a porous, dry solid that usually reconstitutes quickly. Each stage influences pore structure, residual moisture, and stability.
The physics of lyophilization depends on phase boundaries and heat and mass transfer. During primary drying, heat supplied to the product must equal the latent heat of sublimation, while water vapor moves through the drying cake to the condenser. If shelf temperature or pressure is set too high, the ice front can exceed the collapse temperature, causing meltback or pore collapse. If conditions are too cold, drying slows and costs rise. Formulation excipients, vial geometry, and freezing rate alter these limits.
Equipment for lyophilization includes a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. A refrigeration system cools the shelves and condenser below the product's freezing point. Process monitoring often uses Pirani and capacitance manometers, thermocouples, and resistance sensors. Cycle development balances product quality with time and energy use. Some products are annealed during freezing to improve crystallization of bulking agents. Open questions remain about scaling cycles between laboratory, pilot, and production freeze-dryers.
Lyophilization is a drying process in which a solvent, usually water, is removed from a frozen material by sublimation under reduced pressure. The material is first solidified, then placed under vacuum so that ice transitions directly to vapor without a bulk liquid phase. This approach suits heat-sensitive substances that would degrade during conventional evaporation. Primary drying removes unbound ice, while secondary drying reduces water that remains adsorbed to the solid matrix. The result is a porous, lightweight solid that can be reconstituted later.
A typical cycle begins with freezing, sometimes including an annealing step to control ice crystal size. Freezing conditions influence the pore network that later allows vapor escape. During primary drying, shelf temperature and chamber pressure are set so heat enters the product while its temperature stays below the collapse or eutectic point. Secondary drying then raises the shelf temperature to desorb bound water and lower residual moisture. Cycle design depends on formulation, fill volume, container type, and equipment capability.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Freeze-drying; lyophilisation; cryodesiccation | Regional spelling and historical terms. |
| Primary drying pressure | 0.05-0.5 mbar (5-50 Pa) | Kept below the triple point of water; product-specific. |
| Shelf temperature range | -40 to +40 °C | Freezing, primary, and secondary stages use different set points. |
| Cycle duration | 12-72 hours | Depends on fill volume, formulation, and equipment. |
| Condenser temperature | -50 to -80 °C | Must remain below the product's ice temperature. |
Lyophilization is a dehydration technique in which a product is frozen and the solvent is removed under reduced pressure. The low pressure allows ice to sublimate directly into vapor without passing through a bulk liquid phase. This differs from conventional drying, where heat drives evaporation and can damage heat-sensitive structures. The process is used for biological materials, pharmaceutical formulations, and some foods. Its main advantage is preservation of porous structure and rapid reconstitution.
Freezing is the first stage and sets the ice structure that later becomes the pore network. The formulation is cooled below its freezing point, often with a controlled ramp, and solutes concentrate as ice forms. Primary drying then lowers chamber pressure and supplies heat to sublime the ice. The product temperature must stay below its collapse or eutectic temperature to prevent structural loss. Secondary drying raises the temperature modestly to remove bound water and achieve a low residual moisture.
The process generally proceeds in three stages: freezing, primary drying, and secondary drying. During freezing, controlled cooling converts water into ice and may also crystallize or vitrify solutes. In primary drying, the pressure is lowered below the triple point, and heat is supplied so ice sublimes directly to vapor. Secondary drying removes water that remains bound to the solid matrix, yielding a low final water content. Product temperature must stay below the collapse or glass transition temperature to maintain structure. Cycle design therefore balances shelf temperature, chamber pressure, and time.
Freeze-drying is used for materials whose activity or structure depends on low temperature and low water content. Examples include certain biologics, diagnostic reagents, starter cultures, coffee, and porous inorganic precursors. The dried product forms a cake whose porosity aids rapid wetting and dissolution. Main drawbacks are high energy use, long cycle times, and sensitivity to formulation and equipment variation. Questions remain about how freezing rates and ice morphology affect batch uniformity, especially when moving from laboratory to production scale.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and fixes the structure of the sample. After freezing, primary drying lowers pressure so ice changes directly to vapor without passing through a liquid phase. Secondary drying then removes bound water that remains after ice sublimation. The result is a dry, porous solid that often retains its original shape.
The low pressure used during drying allows water vapor to move from the ice surface to a cold condenser. Energy supplied as heat drives sublimation but must stay below the collapse temperature of the frozen matrix. If the product becomes too warm, the frozen structure may soften or melt, reducing pore formation and slowing drying. Formulations often include bulking agents, stabilizers, or buffers to support a rigid cake. The final moisture content depends on formulation, freezing rate, and the length of secondary drying.
Freeze-drying is distinct from simple evaporation and from spray drying. Evaporation removes water at temperatures above freezing, while spray drying rapidly dries droplets in a heated gas stream. Lyophilization avoids high temperatures, which can be useful for heat-sensitive materials such as proteins, vaccines, and some foods. The porous cake produced by sublimation dissolves or rehydrates more quickly than a dense dried mass. Not all materials tolerate freezing or the pH shifts that can occur as solutes concentrate during ice formation.
==== Juvenile breast hypertrophy ==== In 1993, the Japanese journal Surgery Today reported on the case of a 12-year-old girl. Only 152 centimetres (60 in) tall and weighing 43 kilograms (95 lb), her breasts began to develop at age 11 before the onset of menstruation. Over the next eight months, both breasts grew abnormally large, and physicians treating her found that her physiological development was normal except for her breasts. The weight produced by their symmetrical and massive enlargement resulted in marked curvature of the spine. Lab tests of her blood for hormones and biochemical substances showed normal values, though tests revealed that it might have been caused by hypersensitivity to estrogen. She underwent a bilateral reduction mammoplasty. Surgeons removed 2 kilograms (4.4 lb) of tissue from her right breast and 1.9 kilograms (4.2 lb) from her left breast. She was administered tamoxifen afterward to suppress breast regrowth. A more severe case of juvenile breast hypertrophy of an 11-year-old girl was reported in 2008. The breasts had begun to grow rapidly at puberty and had reached the point of causing physical and psychological impairment and possible respiratory compromise after ten months. The skin was intact without any ulcerations. Blood chemistry and endocrine investigation was normal. A bilateral reduction mammaplasty with free nipple grafts was performed. 6 kg (13 lb) of the right breast and 6.5 kg (14 lb) of the left breast were removed, resulting in a removal of 12.5 kg (28 lb) of tissue in all (24% of the total body weight).
Coal and oil are possible examples of constituents which may have undergone changes over geologic time periods. Chalk and limestone are examples of secretions (marine animal shells) which are of geologic age. Grass and wood are biogenic constituents of contemporary origin. Pearls, silk and ambergris are examples of secretions of contemporary origin. Biogenic neurotransmitters.
13 October A grenade was thrown in the Vi Thanh District Chieu Hoi center, killing three civilians and wounding 46. The VC kidnapped a Catholic priest and a lay assistant, from the church at Phu Hoi, Biên Hòa Province.
Sources: en.wikipedia.org
In 1979, Bakker and PTL came under investigation by the Federal Communications Commission (FCC) for allegedly misusing funds raised on the air. The FCC report was finalized in 1982 and found that Bakker had raised $350,000 that he told viewers would go towards funding overseas missions but that was actually used to pay for part of Heritage USA. The report also found that the Bakkers used PTL funds for personal expenses. FCC commissioners voted four to three to drop the investigation, after which they allowed Bakker to sell the only TV station that he owned, therefore bypassing future FCC oversight. The FCC forwarded its report to the U.S. Department of Justice, which declined to press charges, citing insufficient evidence. Bakker used the controversy to raise more funds from his audience, branding the investigation a "witch-hunt" and asking viewers to "give the Devil a black eye". A confidential 1985 Internal Revenue Service (IRS) report found that $1.3 million in ministry funds was used for the Bakkers' personal benefit from 1980 to 1983. The report recommended that PTL be stripped of its tax-exempt status, but no action was taken until after the Jessica Hahn scandal broke in 1987. Art Harris and Michael Isikoff wrote in The Washington Post that politics may have played a role in the three government agencies taking no action against PTL despite the evidence against them, as members of the Reagan administration were not eager to go after television ministers whose evangelical followers made up their base.
Geography, demography, and tradition contributed to this outcome but did not determine it. It took men, responding unpredictably to circumstances, to forge the chain of causation; and it took [Stalin] in particular, responding predictably to his own authoritarian, paranoid, and narcissistic predisposition, to lock it into place. According to Leffler, the most distinctive feature of We Now Know is the extent to which Gaddis "abandons post-revisionism and returns to a more traditional interpretation of the Cold War". Gaddis is now widely seen as more "orthodox" than "post-revisionist". The revisionist Bruce Cumings had a high-profile debate with Gaddis in the 1990s, where Cumings criticized post-revisionism generally and Gaddis in particular as moralistic and lacking in historical rigor. Cumings urged post-revisionists to employ modern geopolitical approaches like world-systems theory in their work. Other post-revisionist accounts focus on the importance of the settlement of the German Question in the scheme of geopolitical relations between the United States and the Soviet Union.
=== Electrophile === Vinyl halides are common coupling partners in the Stille reaction, and reactions of this type are found in numerous natural product total syntheses. Normally, vinyl iodides and bromides are used. Vinyl chlorides are insufficiently reactive toward oxidative addition to Pd(0). Iodides are normally preferred: they will typically react faster and under milder conditions than will bromides. This difference is demonstrated below by the selective coupling of a vinyl iodide in the presence of a vinyl bromide.
Sources: en.wikipedia.org
[Adenosyl−O−PO2−O−PO2−O−PO3]4− + ROH → [Adenosyl−O−PO2−O−PO3H]2− + [RO−P−O3]2− This equation can be written in several ways that are nearly equivalent that describe the behaviors of various protonated states of ATP, ADP, and the phosphorylated product. As is clear from the equation, a phosphate group per se is not transferred, but a phosphoryl group (PO3-). Phosphoryl is an electrophile. This process and its inverse, dephosphorylation, are common in biology. Protein phosphorylation often activates (or deactivates) many enzymes.
UHDTV potentially allows Rec. 2020, higher dynamic range, and higher frame rates to work on HD services without increasing resolution to 4K, providing improved quality without as high of an increase in bandwidth demand.
==== MeSH D12.125.070 – amino acids, branched-chain ==== MeSH D12.125.070.075 – aminoisobutyric acids MeSH D12.125.070.577 – isoleucine MeSH D12.125.070.637 – leucine MeSH D12.125.070.950 – valine MeSH D12.125.070.950.100 – 2-amino-5-phosphonovalerate
== Pulsed SILAC == Pulsed SILAC (pSILAC) is a variation of the SILAC method where the labelled amino acids are added to the growth medium for only a short period of time. This allows monitoring differences in de novo protein production rather than raw concentration.
Sources: en.wikipedia.org
Simple drying usually removes water by evaporation from a liquid or solid, often with heat. Lyophilization first freezes the material and then removes ice by sublimation under vacuum. This avoids prolonged exposure to liquid water and high temperatures.
Reduced pressure lowers the boiling point of water and allows ice to sublime at temperatures below freezing. It also helps remove water vapor from the product toward the condenser. The exact pressure is chosen to stay below the triple point of water.
No. Materials with low solids content or high volatile solvents may form weak or collapsed cakes. Some proteins and cells require stabilizers to survive freezing and drying stresses. Feasibility depends on formulation and process design.
Freezing only converts liquid to solid. Lyophilization adds vacuum and controlled warming so frozen solvent sublimes, leaving a dry porous solid. The two steps are related but not interchangeable.