This is a working overview of secondary drying, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-03-01. Anything still debated is marked as such rather than presented as settled.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Primary phase change | Sublimation | Ice changes directly to vapor under reduced pressure |
| Typical chamber pressure | 0.01–0.5 mbar (1–50 Pa) | Below the triple point of water; product-specific |
| Typical product temperature during primary drying | −40 °C to −10 °C | Kept below collapse temperature |
| Typical residual moisture | 0.5–3% w/w | Target range varies by formulation and use |
| Common synonyms | Freeze-drying; lyophilisation | Lyophilization is the US spelling |
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.
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.
Secondary drying removes bound water that remains after ice sublimation. Shelf temperature is raised gradually while pressure remains low, reducing water content to a target range. Over-drying can cause brittleness or electrostatic issues, while under-drying affects stability. The endpoint is often judged by pressure rise tests, temperature measurements, or water content analysis. Scale-up depends on matching heat and mass transfer across equipment sizes. Small changes in shelf temperature or pressure can alter cycle length substantially.
Lyophilization, or freeze-drying, removes water from a material by freezing it and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intervening liquid state. It is used for heat-sensitive materials that would degrade in conventional drying. The three stages are freezing, primary drying, and secondary drying, each with distinct temperature and pressure requirements. In practice, cycle design balances these variables.
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, also called freeze-drying, is a dehydration process in which a solvent, usually water, is frozen and then removed by sublimation under reduced pressure. The method preserves heat-sensitive materials that would degrade in conventional drying. Large-scale use grew during the mid-twentieth century for blood plasma and antibiotics, and it later expanded to vaccines, enzymes, foods, and advanced materials. The process produces a dry, porous solid that usually reconstitutes rapidly. It is distinct from simple evaporation because the solvent bypasses the liquid phase during primary removal.
Improving metabolism (improving insulin sensitivity, inhibiting de novo lipogenesis, or increasing fatty acid oxidation). Metabolic modulators tested in MASH include glucagon-like peptide-1 receptor agonists (GLP-1 agonists), GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) or glucagon co-agonists and thyromimetics. Some of these drugs may treat MASFLD by significantly reducing body weight. Reducing inflammation, for example reducing oxidative stress and hepatocyte death. These drugs, such as chemokine antagonists, anti-apoptotics, vascular adhesion protein-1 inhibitors, and c-Jun N-terminal kinase inhibitors, have not shown benefit. "Gut-liver axis targets" that either change a person's microbiome, or act on bile acids Anti-fibrotic drugs, such as fibroblast growth factor analogues, which have largely not met their endpoints Other treatments such as farnesoid X receptor (FXR) agonists, peroxisome proliferator-activated receptor (PPAR) agonists, and ASK1 (apoptosis signal-regulating kinase 1) inhibitors may improve MASFLD by multiple mechanisms simultaneously.
A transition metal imidazole complex is a coordination complex that has one or more imidazole ligands. Complexes of imidazole itself are of little practical importance. In contrast, imidazole derivatives, especially histidine, are pervasive ligands in biology where they bind metal cofactors.
== Notable architecture == The county courthouse of Lebanon is notable for its single-piece vertical Ionic order limestone columns. They were at one time believed to be the largest single-piece limestone columns in the world.
3-D Viewer of a male American mastodon skeleton, with bones labelled, at the University of Michigan Mammutidae digital fossil repository Interactive views of various primate skeletons at eSkeletons.org (associated with the University of Texas at Austin)
Sources: en.wikipedia.org
Hunter requested greater control by authorities in England and an excise duty on rum. He issued an order restricting the amount of convict labour that officers could use, but again had no means to enforce it. Hunter was strongly opposed by officers of the Corps, and pamphlets and letters against him were circulated. John Macarthur wrote a letter accusing Hunter of ineffectiveness and trading in rum. Hunter was required by the Colonial Office to answer the charges, and soon after was recalled for being ineffective. In 1799 Paterson, now a Lieutenant Colonel, returned from England with orders to stamp out the trading in rum by officers of the Corps. In 1800, he charged Major George Johnston, who had served as Hunter's aide-de-camp, with giving a sergeant part payment in rum at an exorbitant rate. Johnston claimed he was being unfairly persecuted and demanded that he be sent to England for trial. The English courts decided that colonial affairs were not a matter for them and, as all the evidence and witnesses were in Sydney, that any trial should be held there. They decided that, as proper court martial could not be constituted in Sydney, no further action should be taken against Johnston. Governor Philip King, appointed in September 1800, continued Hunter's efforts to prevent the Corps trading in rum. He had the power to levy an excise duty on alcohol, and the Transit Board now required all ships to lodge a bond which was forfeit for disobeying the Governor's orders, which included the prohibition of the landing of more than 500 gallons of rum.
Enzymes that transfer aldehyde or ketone groups and included in EC 2.2. This category consists of various transketolases and transaldolases. Transaldolase, the namesake of aldehyde transferases, is an important part of the pentose phosphate pathway. The reaction it catalyzes consists of a transfer of a dihydroxyacetone functional group to glyceraldehyde 3-phosphate (also known as G3P). The reaction is as follows: sedoheptulose 7-phosphate + glyceraldehyde 3-phosphate
International Proteolysis Society MEROPS - the peptidase database Archived 2006-11-14 at the Wayback Machine List of protease inhibitors Protease cutting predictor List of proteases and their specificities (see also [1] Archived 2011-04-30 at the Wayback Machine) Proteolysis MAP from Center for Proteolytic Pathways Proteolysis Cut Site database - curated expert annotation from users Protease cut sites graphical interface TopFIND protease database covering cut sites, substrates and protein termini Proteases at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
The Crown issued a decree, Código Negro Español (Spanish Black Code), that specified food and clothing provisions, put limits on the number of work hours, limited punishments, required religious instruction, and protected marriages, forbidding the sale of young children away from their mothers. The British made other changes to the institution of slavery in Cuba. However, planters often flouted the laws and protested against them, considering them a threat to their authority and an intrusion into their personal lives.
== Child drownings == As of 2020, Thailand leads ASEAN in child drownings and its death rate for drowning by children less than 15 years of age is twice the world average. From 2000 to 2018, there were more than 22,700 drowned children, averaging about 1,262 children per year or five per day. Drownings are decreasing—in 2018, 727 children drowned, down from 1,244 a decade earlier. Most drownings occur around the time of the Songkran holiday.
Sources: en.wikipedia.org
Chromosome studies are used in the general genetics clinic to determine a cause for developmental delay or intellectual disability, birth defects, dysmorphic features, or autism. Chromosome analysis is also performed in the prenatal setting to determine whether a fetus is affected with aneuploidy or other chromosome rearrangements. Finally, chromosome abnormalities are often detected in cancer samples. A large number of different methods have been developed for chromosome analysis:
=== Cancer diagnosis with the MasSpec Pen === The MasSpec Pen was designed to assist in the detection of positive surgical margins during solid tumor debulking procedures to assist in the complete excision of cancer surgeries. The device was initially used to analyze 253 human tissue biopsies, including normal and cancerous breast, lung, ovary, and thyroid tissues. The mass spectra obtained for each sample contained metabolites, lipids, and some proteins that were representative of the molecular composition of the tissue analyzed. The collected data for each tissue type was then used to develop statistical models that could discriminate between the normal and cancer samples of each tissue type. Leave-one-patient-out cross validation was used to evaluate the accuracy of the models for distinguishing the normal and cancer tissues based on their molecular profiles. The method allowed for diagnosis of the breast tissues with 95.6% accuracy, lung with 96.8% accuracy, and ovary with 94.7% accuracy. Statistical models also allowed for the discrimination of normal thyroid from papillary thyroid carcinomas with 97.8% accuracy and from follicular thyroid adenomas with 94.7% accuracy. The report also demonstrated the ability of the MasSpec Pen technology to detect cancer within regions of mixed tissue containing both normal and cancerous cells from an ovarian cancer sample. Finally, the authors demonstrated the use of this method for in vivo analysis of tumor tissues using an anesthetized murine model.
Vegetables have been part of the human diet from time immemorial. Some are staple foods but most are accessory foodstuffs, adding variety to meals with their unique flavors and at the same time, adding nutrients necessary for health. Some vegetables are perennials but most are annuals and biennials, usually harvested within a year of sowing or planting. Whatever system is used for growing crops, cultivation follows a similar pattern; preparation of the soil by loosening it, removing or burying weeds, and adding organic manures or fertilisers; sowing seeds or planting young plants; tending the crop while it grows to reduce weed competition, control pests, and provide sufficient water; harvesting the crop when it is ready; sorting, storing, and marketing the crop or eating it fresh from the ground. Different soil types suit different crops, but in general in temperate climates, sandy soils dry out fast but warm up quickly in the spring and are suitable for early crops, while heavy clays retain moisture better and are more suitable for late season crops. The growing season can be lengthened by the use of fleece, cloches, plastic mulch, polytunnels, and greenhouses. In hotter regions, the production of vegetables is constrained by the climate, especially the pattern of rainfall, while in temperate zones, it is constrained by the temperature and day length.
=== Removal and recovery of polar organics from aqueous streams === Some of King's research has dealt with the removal and recovery of polar organic substances from aqueous streams in two contexts. Research on removal of pollutants by solvent extraction was supported by the U. S. Environmental Protection Agency. He later turned to the use of solvent extraction and adsorption, with and without chemical complexation, for recovery of carboxylic acids, glycols and alcohols from aqueous process streams, such as occur in the manufacture of these chemicals from biomass by fermentation. Much of this work also dealt with novel methods of regeneration of the extractants or adsorbents. The research was sponsored by the U. S. Department of Energy through the Lawrence Berkeley National Laboratory.
United States: The U.S. government operates border preclearance facilities at several ports and airports in foreign territory. They are staffed and operated by U.S. Customs and Border Protection officers. Travellers pass through the U.S. Immigration and Customs, Public Health, and Agriculture inspections before boarding their aircraft, ship, or train. This process is intended to streamline border procedures, reduce congestion at ports of entry, and facilitate travel between the preclearance location and American airports that are not equipped to handle international travellers. These facilities are present at the majority of major Canadian airports, as well as selected airports in Bermuda, Aruba, the Bahamas, Abu Dhabi and Ireland. Facilities located in Canada accept NEXUS cards and United States Passport cards (land/sea entry only) in place of passports. A preclearance facility is currently being planned at Dubai International Airport. Citizens of the Bahamas who enter United States through either of the two preclearance facilities in that country enjoy an exemption from the general requirement to hold a visa as long as they can sufficiently prove that they do not have a significant criminal record in either the Bahamas or the U.S. All Bahamians applying for admission at a port-of-entry other than the preclearance facilities located in Nassau or Freeport International airports are required to have a valid visa. Preclearance facilities are also operated at Pacific Central Station, the Port of Vancouver, and the Port of Victoria in British Columbia.
Sources: en.wikipedia.org
Lyophilization relies on sublimation, so water moves from solid ice to vapor without becoming liquid. The material is frozen, pressure is reduced, and controlled heat is supplied. Vapor is captured on a cold condenser, leaving a dry porous solid.
The process has three main stages: freezing, primary drying, and secondary drying. Freezing sets the ice structure, primary drying removes free ice, and secondary drying removes bound water. Each stage uses specific temperature, pressure, and time settings.
No, it is a drying method rather than a sterilization method. Removing water can limit microbial growth, but it does not reliably kill microorganisms. Sterility must come from separate steps such as filtration, heat treatment, or aseptic processing.
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.