If you have been reading about Primary drying and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2025-08-22. Numbers and descriptions here follow the published literature rather than marketing material.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen to convert liquid water into ice. Next, the pressure is reduced below the triple point of water so that ice changes directly into vapor without passing through a liquid phase. This step is called primary drying. The result is a porous solid or cake that retains the original shape of the frozen solution.
After primary drying, secondary drying removes water that remains bound to the material. This stage raises the shelf temperature while maintaining low pressure, which encourages desorption of unfrozen water. Residual moisture can be reduced to a low percentage, improving stability for many products. The process parameters, including freezing rate, shelf temperature, and chamber pressure, influence the final pore structure and reconstitution behavior. Control of these variables helps prevent collapse or meltback during drying.
A formulation often contains excipients that protect the active ingredient during freezing and drying. Bulking agents provide structure, while lyoprotectants stabilize sensitive molecules. The freezing step can produce ice crystals whose size and distribution affect the drying rate, and cycle design includes freezing, annealing, and drying phases. If the product temperature rises above a critical value, the cake may collapse or lose its porous structure. Successful lyophilization therefore depends on the interaction between formulation, equipment, and cycle design.
A typical cycle begins with freezing, which fixes the material into a solid and determines ice crystal size. Primary drying then raises heat under vacuum so ice sublimes, often near or below the collapse temperature of the formulation. Secondary drying removes bound water that remains after ice is gone, usually by gently warming the product. Each stage balances heat input against pressure to avoid melting or structural damage. Temperature probes and pressure sensors guide the transition between stages.
In practice, lyophilization is slower and more energy intensive than simple drying. Cycle times can range from hours to several days depending on load, container, and formulation. Amorphous materials may require excipients that help preserve structure during freezing and drying. The method is widely used for biological materials, pharmaceuticals, and foods where heat drying would cause unacceptable change. Open questions remain about scaling cycles between laboratory and production equipment, and this gap affects technology transfer.
Lyophilization removes water by freezing a material and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intermediate liquid state. Because the material remains frozen during primary drying, the structure often stays porous. This porous matrix can rehydrate quickly when water is added back. The low pressure also allows vapor to leave the solid matrix without boiling.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Freeze-drying, lyophilisation | Lyophilization is the American spelling; lyophilisation is British |
| Primary drying mechanism | Sublimation of ice | Occurs under vacuum below the triple point |
| Typical chamber pressure | 0.05-0.5 mbar | Range depends on product and equipment |
| Typical shelf temperature during freezing | -40 to -20 °C | Lower temperatures may be used for labile products |
| Resulting product form | Porous cake or powder | Appearance depends on formulation and cycle |
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, 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.
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.
The physics of lyophilization couples heat transfer, mass transfer, and phase behavior. Sublimation requires a vapor pressure difference between the ice front and the chamber, and the dried layer adds resistance to vapor flow. Amorphous formulations are characterized by a glass transition temperature of the maximally freeze-concentrated solute, often denoted Tg'. Crystalline bulking agents can provide structure, while amorphous excipients stabilize labile components. Open questions remain about spatial heterogeneity, edge effects, and how laboratory cycles scale to production.
The mean platelet volume (MPV) measures the average size of platelets in femtolitres. It can aid in determining the cause of thrombocytopenia; an elevated MPV may occur when young platelets are released into the bloodstream to compensate for increased destruction of platelets, while decreased production of platelets due to dysfunction of the bone marrow can result in a low MPV. The MPV is also useful for differentiating between congenital diseases that cause thrombocytopenia. The immature platelet fraction (IPF) or reticulated platelet count is reported by some analyzers and provides information about the rate of platelet production by measuring the number of immature platelets in the blood.
== History == α-Methylfentanyl was discovered by a team at Janssen Pharmaceuticals in the 1960s. In 1976, it began to appear mixed with heroin, as an additive, and the mixture was sometimes also called "China White". It was first identified in the bodies of two drug overdose victims in Orange County, California, in December 1979, who appeared to have died from opiate overdose but tested negative for any known drugs of this type. Over the next year, there were 13 more deaths, and eventually the responsible agent was identified as α-methylfentanyl.
In addition to CYP2B6, CYP2A6 may be involved in the metabolism of selegiline to a lesser extent. Birth control pills containing the synthetic estrogen ethinylestradiol and a progestin like gestodene or levonorgestrel have been found to increase peak levels and overall exposure to oral selegiline by 10- to 20-fold. High levels of selegiline can lead to loss of MAO-B selectivity and inhibition of MAO-A as well. This increases susceptibility to side effects and interactions of non-selective monoamine oxidase inhibitors (MAOIs), such as tyramine-induced hypertensive crisis and serotonin toxicity when combined with serotonergic medications. However, this study had a small sample size of four individuals as well as other methodological limitations. The precise mechanism underlying the interaction is unknown, but is likely related to cytochrome P450 inhibition and consequent inhibition of selegiline first-pass metabolism by ethinylestradiol. In contrast to birth control pills containing ethinylestradiol, menopausal hormone therapy with estradiol and levonorgestrel did not modify peak levels of selegiline and only modestly increased overall exposure (+59%). Hence, menopausal hormone therapy does not pose the same risk of interaction as ethinylestradiol-containing birth control pills when taken together with selegiline. Overall exposure to selegiline with oral selegiline has been found to be 23-fold lower in people taking anticonvulsants known to strongly activate drug-metabolizing enzymes. The anticonvulsants included phenobarbital, phenytoin, carbamazepine, and amobarbital.
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Sources: en.wikipedia.org
=== Israel === Schumer has been a vocal advocate for Israel following the October 7 attacks, a stance for which she has received backlash. Critics have accused Schumer of posting Islamophobic content and misinformation, including sharing a post which depicted pro-Palestinian protesters as holding up signs that read, "Gazans rape Jewish girls only in self-defense". In October 2023, Schumer was one of over 700 Hollywood professionals who signed an open letter condemning Hamas and demanding the release of hostages held in Gaza. That month, she was criticized for a social media post in which she asserted that an Islamic Jihad missile was responsible for the Al-Ahli Arab Hospital explosion and accused media outlets of "blaming Israel" for the explosion. Schumer told Variety in 2024, "I don't agree with anything that Netanyahu is doing, and neither do the Israelis I know. Of course what's going on in Gaza is sickening, horrifying and unthinkable". She added, "The focus is so razor-sharp on Jewish people but not on Hamas", and recommended that people read Israel: A Simple Guide to the Most Misunderstood Country on Earth, a 2021 book by Noa Tishby. In January 2026, Schumer defended Israeli comedian Guy Hochman after a Beverly Hills theater canceled his show when he refused to condemn the Gaza genocide.
== Function == NET functions to transport synaptically released norepinephrine back into the presynaptic neuron. As much as 90% of the norepinephrine released will be taken back up in the cell by NET. NET functions by coupling the influx of sodium and chloride (Na+/Cl−) with the transport of norepinephrine. This occurs at a fixed ratio of 1:1:1. Both the NET and the dopamine transporter (DAT) can transport norepinephrine and dopamine. The reuptake of norepinephrine and dopamine is essential in regulating the concentration of monoamine neurotransmitters in the synaptic cleft. The transporter also helps maintain homeostatic balances of the presynaptic neuron.
=== Negative chemical ionization === Chemical ionization for gas phase analysis is either positive or negative. Almost all neutral analytes can form positive ions through the reactions described above. In order to see a response by negative chemical ionization (NCI, also NICI), the analyte must be capable of producing a negative ion (stabilize a negative charge) for example by electron capture ionization. Because not all analytes can do this, using NCI provides a certain degree of selectivity that is not available with other, more universal ionization techniques (EI, PCI). NCI can be used for the analysis of compounds containing acidic groups or electronegative elements (especially halogens).Moreover, negative chemical ionization is more selective and demonstrates a higher sensitivity toward oxidizing agents and alkylating agents. Because of the high electronegativity of halogen atoms, NCI is a common choice for their analysis. This includes many groups of compounds, such as PCBs, pesticides, and fire retardants. Most of these compounds are environmental contaminants, thus much of the NCI analysis that takes place is done under the auspices of environmental analysis. In cases where very low limits of detection are needed, environmental toxic substances such as halogenated species, oxidizing and alkylating agents are frequently analyzed using an electron capture detector coupled to a gas chromatograph.
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7 and Transitional Provisions) Order 1993 (S.I. 1993/2229) National Assistance (Assessment of Resources) (Amendment No.2) Regulations 1993 (S.I. 1993/2230) National Curriculum Council and School Examinations and Assessment Council (Designation of Staff) Order 1993 (S.I. 1993/2231) Export of Goods (Control) (Haiti) (Revocation) Order 1993 (S.I. 1993/2232) Motor Vehicles (Competitions and Trials) (Amendment) Regulations 1993 (S.I. 1993/2233) Road Traffic (Special Parking Areas) (London Boroughs of Bromley, Hammersmith and Fulham and Lewisham) (London Borough of Wandsworth) (Amendment) Order 1993 (S.I. 1993/2237) Housing (Extension of Right to Buy) Order 1993 (S.I. 1993/2240) Housing (Preservation of Right to Buy) Regulations 1993 (S.I. 1993/2241) Valuation Timetable (Scotland) Amendment (No.3) Order 1993 (S.I. 1993/2242) Housing (Right to Buy Delay Procedure) (Prescribed Forms) (Amendment) Regulations 1993 (S.I. 1993/2245) Housing (Right to Buy) (Prescribed Forms) (Amendment) Regulations 1993 (S.I. 1993/2246) Law Reform (Miscellaneous Provisions) (Scotland) Act 1990 (Commencement No.12) Order 1993 (S.I. 1993/2253) Public Trusts (Reorganisation) (Scotland) (No.2) Regulations 1993 (S.I. 1993/2254) Fish Health (Amendment) Regulations 1993 (S.I. 1993/2255) Royal National Hospital for Rheumatic Diseases National Health Service Trust (Transfer of Trust Property) Order 1993 (S.I. 1993/2256) St Peter's Hospital National Health Service Trust (Transfer of Trust Property) Order 1993 (S.I.
Sources: en.wikipedia.org
== External links == WHO Snake Antivenoms Database Organization (2016). Guidelines for the management of snakebites. Regional Office for South-East Asia, World Health Organization. hdl:10665/249547. ISBN 978-92-9022-530-0.
=== Down syndrome === Adults with Down syndrome had accumulation of amyloid in association with evidence of Alzheimer's disease, including declines in cognitive functioning, memory, fine motor movements, executive functioning, and visuospatial skills.
Birds are tetrapods but though their hind limbs are used for walking or hopping, their front limbs are wings covered with feathers and adapted for flight. Birds are endothermic, have a high metabolic rate, a light skeletal system and powerful muscles. The long bones are thin, hollow and very light. Air sac extensions from the lungs occupy the centre of some bones. The sternum is wide and usually has a keel and the caudal vertebrae are fused. There are no teeth and the narrow jaws are adapted into a horn-covered beak. The eyes are relatively large, particularly in nocturnal species such as owls. They face forwards in predators and sideways in ducks. The feathers are outgrowths of the epidermis and are found in localized bands from where they fan out over the skin. Large flight feathers are found on the wings and tail, contour feathers cover the bird's surface and fine down occurs on young birds and under the contour feathers of water birds. The only cutaneous gland is the single uropygial gland near the base of the tail. This produces an oily secretion that waterproofs the feathers when the bird preens. There are scales on the legs, feet and claws on the tips of the toes.
==== Corporate logos on pills ==== A number of ecstasy manufacturers brand their pills with a logo, often that of an unrelated corporation. Some pills depict logos of products or media popular with children, such as Shaun the Sheep.
Sources: en.wikipedia.org
Lyophilization removes water by sublimation from a frozen material, while evaporation changes liquid water into vapor. The low-pressure freezing step avoids the liquid phase and can preserve heat-sensitive structures.
Vacuum lowers the pressure below the triple point of water, allowing ice to sublimate directly into vapor. It also helps remove water vapor from the product chamber and shortens primary drying.
Many aqueous solutions and suspensions can be freeze-dried, but some formulations collapse or do not form a stable cake. The process requires careful formulation and cycle development.
Primary drying removes ice by sublimation under vacuum. Secondary drying removes water that is bound to the material, often by warming the product after most ice has left. Both stages occur below temperatures that would cause unwanted melting.