The short version of secondary drying fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2025-09-19. 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.
Quality control for lyophilized products focuses on appearance, moisture level, reconstitution time, and structural integrity. A cake should be uniform, intact, and free of meltback or collapse. Moisture level is measured by Karl Fischer titration or thermogravimetric analysis. Reconstitution time reflects pore structure and formulation. Visual inspection and vial integrity checks detect cracks, stopper defects, or particulate matter. These checks are often performed on samples from each batch. They help confirm that the drying cycle performed as intended.
Storage stability depends on water content, oxygen exposure, and temperature. Lyophilized solids are hygroscopic and can absorb water if exposed to humid air. Vials are usually sealed under vacuum or inert gas with rubber stoppers and aluminum crimps. Storage temperatures range from room temperature to refrigerated or frozen conditions depending on the material. Stability studies track potency, moisture, and physical form over time. Accelerated conditions can reveal sensitivity but may not predict long-term behavior.
| 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.
Quality control for freeze-dried forms includes visual inspection, water content measurement, and reconstitution time. A satisfactory cake is typically uniform, porous, and intact, although minor shrinkage or cracking may be acceptable if specifications allow. Karl Fischer titration, thermal gravimetric analysis, and near-infrared spectroscopy are used to measure water content. Reconstitution is assessed by adding a specified diluent and recording the time and ease of dissolution. Microbiological and particulate tests are added when the product is sterile or intended for injection.
Stability of a lyophilized solid depends on water content, temperature, and the physical state of the formulation. Amorphous products may slowly absorb moisture and drop below their glass transition temperature, causing collapse or crystallization. Some proteins and peptides can aggregate even in a dry state, especially when exposed to heat or moisture. Accelerated stability studies at elevated temperature and humidity help estimate shelf life, but real-time data remain the basis for expiration dating.
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.
Although there are no official definition to what a member of parliament is, it commonly refers to the elected members of the lower People's Representative Council (Dewan Perwakilan Rakyat, abbr. DPR), known in Indonesian as Anggota DPR (member of the DPR). Members of the upper Regional Representative Council (Dewan Perwakilan Daerah, abbr. DPD) are referred to as senator, although the term Anggota DPD (member of the DPD) is also widely used. These titles are not used in formal naming convention following a member's name unlike the Westminster system. Currently, there are 575 and 136 members in the DPR and the DPD respectively, both elected for a renewable five-year term. Members of the DPR are required to be a member of a registered political party, whereas members of the DPD are independent.
In the Roman Catholic Church, the full-fingered gloves traditionally worn by the pope or other bishops are also known as gauntlets or episcopal gloves, though their use has largely been relaxed since Paul VI.
The Journal of Pharmacy Practice is a bimonthly peer-reviewed healthcare journal that covers the field of pharmacy, including new drugs and therapies, pharmacokinetics, drug administration, and adverse drug reactions. The editor-in-chief is Michael Liu (Touro College of Pharmacy). It was established in 1988 and is currently published by SAGE Publications.
Sources: en.wikipedia.org
C-5 sterol desaturase (also known as sterol C-5 desaturase and C5SD) is an enzyme that is highly conserved among eukaryotes and catalyzes the dehydrogenation of a C-5(6) bond in a sterol intermediate compound as a step in the biosynthesis of major sterols. The precise structure of the enzyme's substrate varies by species. For example, the human C-5 sterol desaturase (also known as lathosterol oxidase) oxidizes lathosterol, while its ortholog ERG3 in the yeast Saccharomyces cerevisiae oxidizes episterol.
Silicon (14Si) has 25 known isotopes, with mass number ranging from 22 to 46. 28Si (the most abundant isotope, at 92.24%), 29Si (4.67%), and 30Si (3.07%) are stable. The longest-lived radioisotope is 32Si, which occurs naturally in tiny quantities from cosmic ray spallation of argon. Its half-life has been determined to be approximately 157 years; it beta decays with energy 0.21 MeV to 32P, which in turn beta-decays, with half-life 14.269 days to 32S; neither step has gamma emission. After 32Si, 31Si has the second longest half-life at 157.2 minutes. All others have half-lives under 7 seconds.
=== Marijuana legalization === President Jimmy Carter was an advocate for legalization of marijuana at the national level. Carter argued that possession of less than 28 g of marijuana should be decriminalized. Carter believed in a more treatment-based approach to the addiction problems, with softer penalties for cocaine but was as opposed to heroin as his predecessors. In a speech to Congress in 1977, Carter stated that "penalties against possession of a drug should not be more damaging to an individual than the use of the drug itself." Rather than legalization, congressional lawmakers passed a bill that would criminalize only marijuana "open to public view." Scholars would later criticize the abuse of that bill when they debated stop-and-frisk laws. In 1967, the US Supreme Court ruled in Terry v. Ohio that a "stop-and-frisk" search does not violate the Fourth Amendment if the officer executing the search bears a "reasonable suspicion" that the person being searched has committed or is about to commit a crime. As a result, "stop-and-frisk" searches became much more common during the war on drugs and were generally conducted in minority communities. "Stop-and-frisk" searches have been criticized for being disproportionately carried out against minorities as a result of racial bias, but empirical literature on that count is inconclusive. Certain authors have found that even after controlling for location and crime participation rates, blacks and Hispanics are stopped more frequently than whites.
Sources: en.wikipedia.org
== Mechanism of action == Ptaquiloside has unstable chemical structure and readily undergoes glucose liberation. The resulting ptaquilodienone is the active form of ptaquiloside and accounts for the observed biological effects. The cyclopropyl group in the dienone is highly reactive as an electrophile, not only because it is conjugated with the keto group, but because it also constitutes a cyclopropyl carbinol system, from which the facile formation of the stable non-classical cation is well-known.
Carlos Manuel de Céspedes was either initiated or introduced to the concept of Freemasonry during his time studying in Spain the 1840's, but as well, he studied what secret societies he could of the entire Mediterranean region from Syria to Turkey on his travels. After the death of Narciso López, in 1851, de Céspedes wrote the original version of La Bayamesa with the poet José Fornaris. In 1867, de Céspedes joined Estrella Tropical Lodge No. 19, in the town of Bayamo. Most records indicate that this was his initiation. On August 13, 1867, a meeting was held at Estrella Tropical Lodge No. 19 to discuss the revolution against the Spanish. After the meeting, Francisco Maceo Osorio turned to Perucho Figueredo, and said to him: "...now it's your turn, who are a musician, to compose our own Marseillaise." Figueredo finished the instrumental composition the next day, on August 14. On October 20, 1868, Figueredo finished the lyrics of the current version of Cuba's national anthem as the revolutionary troops entered Bayamo.
Alternatively, a chief resident may describe a resident who has been selected to extend his or her residency by one year and organize the activities and training of the other residents (typically in internal medicine and pediatrics). If a physician finishes a residency and decides to further his or her education in a fellowship, they are referred to as a "fellow". Physicians who have fully completed their training in a particular field are referred to as attending physicians, or consultants (in Commonwealth countries). However, the above nomenclature applies only in educational institutes in which the period of training is specified in advance. In privately owned, non-training hospitals, in certain countries, the above terminology may reflect the level of responsibility held by a physician rather than their level of education.
require that the partial double bond be broken, so that the activation energy is roughly 80 kJ/mol (20 kcal/mol). However, the activation energy can be lowered (and the isomerization catalyzed) by changes that favor the single-bonded form, such as placing the peptide group in a hydrophobic environment or donating a hydrogen bond to the nitrogen atom of an X-Pro peptide group. Both of these mechanisms for lowering the activation energy have been observed in peptidyl prolyl isomerases (PPIases), which are naturally occurring enzymes that catalyze the cis-trans isomerization of X-Pro peptide bonds. Conformational protein folding is usually much faster (typically 10–100 ms) than cis-trans isomerization (10–100 s). A nonnative isomer of some peptide groups can disrupt the conformational folding significantly, either slowing it or preventing it from even occurring until the native isomer is reached. However, not all peptide groups have the same effect on folding; nonnative isomers of other peptide groups may not affect folding at all.
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.
Karl Fischer titration is a common method, using coulometric or volumetric detection. Thermogravimetric analysis can also measure weight loss on heating. Results depend on sample handling because the dried solid can absorb moisture quickly.