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.
Last reviewed on 2025-08-22. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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 process relies on the phase diagram of water, where the triple point marks the conditions at which ice, liquid water, and vapor coexist. By maintaining pressure below this point, typically around 0.01 to 0.1 millibar, sublimation becomes the dominant mechanism. Formulations often include excipients such as sugars or polymers that act as lyoprotectants and bulking agents. These additives help preserve the structure of the active ingredient and prevent collapse during drying. The choice of excipient and freezing rate influences the final cake morphology and stability.
Industries use lyophilization for pharmaceuticals, biological products, and food preservation. In the pharmaceutical sector, it extends the shelf life of injectable drugs, vaccines, and proteins that are unstable in aqueous solution. Food manufacturers apply freeze-drying to coffee, fruits, and ready meals to retain flavor and texture. The process is energy-intensive and requires specialized equipment, which limits its use to high-value products. Ongoing research examines how formulation and process parameters affect the quality of the final dried product.
| Property | Value | Notes |
|---|---|---|
| Physical state | Solid, porous cake or powder | Depends on formulation and container |
| Typical storage temperature | 2–25 °C, protected from moisture | Some materials require colder conditions |
| Solubility class | Usually readily soluble after reconstitution | Not an intrinsic chemical property |
| Common analytical method | Karl Fischer titration | Used for residual moisture |
| Common synonyms | Freeze-drying; lyophilisation | Lyophilisation is a spelling variant |
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.
A freeze-dryer consists of a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. Vials, ampoules, or bulk trays hold the product during the cycle. The condenser traps water vapor as ice at a temperature lower than the product. Cycle development balances shelf temperature, chamber pressure, and time. Scale-up can be difficult because heat and mass transfer change with equipment size, so process analytical tools and conservative validation are often used.
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.
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.
Freezing determines ice crystal structure and pore size, which affect drying speed and product uniformity. Rapid freezing creates small crystals, while slow freezing creates larger crystals and often faster sublimation. During primary drying, chamber pressure is held below the vapor pressure of ice, and shelf temperature supplies heat for sublimation. The ice front recedes, leaving a porous matrix. Thermal limits such as collapse and eutectic temperatures set safe boundaries for formulation. These limits vary with solute composition and concentration.
Agilent ChemStation is a software package to control Agilent liquid chromatography, gas chromatography, and ultraviolet-visible spectroscopy systems such as the 1050, 1100 and 1200 Series HPLC system and the 8453 and 8454 single-beam diode array detector spectrophotometers. It is an evolution of the Hewlett-Packard ChemStation System. Two versions are available: one ("online") in connection with the modules of the HPLC chain is designed to control instruments and run experiments, and the other ("offline"), without a connection with the HPLC chain, is designed to analyze data. ChemStation is structured around a number of registers. Two of the more important registers are CHROMREG and CHROMRES, the chromatographic data registers. Other special registers exist for the UV-vis implementation of the software. ChemStation has a command line interpreter and can run macros. Those macros are files grouping a set of commands. These files possess a .mac extension. ChemStation can import analysis lists and export result files in XML by adding new lines to the ChemStation.ini configuration file. This is a feature to implement the connection with a Laboratory information management system (LIMS).
At the conclusion of the 2019 AFL season, Ryder requested a trade to St Kilda. The trade was finalised on 15 October and Ryder was traded to St Kilda along with Port Adelaide teammate Dougal Howard and pick 10 and a 2020 fourth-round selection, in return for the Saints' picks 12 and 18 and a 2020 third-round selection. Ryder nominated to join St Kilda ahead of his former club Essendon. He chose to leave Port Adelaide due to a perceived lack of opportunity in the ruck division at the Power. Of the move, Ryder stated that "I guess the way things have panned out at Port Adelaide over the past couple of years is Port Adelaide’s brought in Scotty Lycett, who's a terrific ruckman, and they've got a couple of young blokes on the list that probably need a bit more time to develop. And I guess being my age and stuff I’m taking away that opportunity for them, so I'm very understanding of the football club and respect their decision. But I feel like I've still got a lot more to give, so I'll be going down to Moorabbin." On choosing to join the Saints ahead of his former team, Ryder admitted that he was leaning towards rejoining the Bombers until he toured their facilities; "I just didn't get like a really, really good feeling from going back there", said Ryder in October 2019. "But then I went down to Moorabbin and it was a sense of like excitement and in the end thats what I ended up basing my decision on." Ryder played 14 of a possible 19 games for the Saints in the 2020 season.
In particular, decreased access to public health services such as syringe exchange programs and confiscation of syringes can precipitate a cascade of health harms. Geographic diffusion of epidemics from the northern border states elsewhere is also possible with the rotation of police and military personnel stationed in drug conflict areas with high infection prevalence. With increased drug use, there has been a parallel rise in demand for drug user treatment in Mexico.
van Krevelen, D.W. (1950). "Graphical-statistical method for the study of structure and reaction processes of coal", Fuel, 29, 269–84. van Krevelen, D.W. and Schuyer, J. (1957) Coal science. Elsevier publishing company. The chemistry and technology of petroleum
Sources: en.wikipedia.org
Opioids by themselves put older people at risk of respiratory depression and impaired ability to operate vehicles and other machinery. Combining these two drugs together not only increases a person's risk of the aforementioned adverse effects, but can increase a person's risk of overdose and death. Benzodiazepines are also the second leading cause of teen overdose death after fentanyl. They killed 152 people in 2021, less than a fifth of fentanyl's death toll. Hydrocodone was declared the most widely prescribed opioid between 2007 and 2016, and in 2015 the International Narcotics Control Board reported that greater than 98% of the hydrocodone consumed in the entire world was consumed by Americans.
== Consensus Development Program == The Consensus Development Program is an initiative focused on gathering expert opinions to establish standards and guidelines in various fields, especially in health and medicine. Developed as a collaborative effort by organizations such as the NIH, the program assembles panels of specialists who assess available evidence on critical topics and form recommendations to guide clinical practice and policy. This method helps ensure that healthcare decisions are informed by the latest scientific research and expert consensus.
In carbohydrate anabolism, simple organic acids can be converted into monosaccharides such as glucose and then used to assemble polysaccharides such as starch. The generation of glucose from compounds like pyruvate, lactate, glycerol, glycerate 3-phosphate and amino acids is called gluconeogenesis. Gluconeogenesis converts pyruvate to glucose-6-phosphate through a series of intermediates, many of which are shared with glycolysis. However, this pathway is not simply glycolysis run in reverse, as several steps are catalyzed by non-glycolytic enzymes. This is important as it allows the formation and breakdown of glucose to be regulated separately, and prevents both pathways from running simultaneously in a futile cycle. Although fat is a common way of storing energy, in vertebrates such as humans the fatty acids in these stores cannot be converted to glucose through gluconeogenesis as these organisms cannot convert acetyl-CoA into pyruvate; plants do, but animals do not, have the necessary enzymatic machinery. As a result, after long-term starvation, vertebrates need to produce ketone bodies from fatty acids to replace glucose in tissues such as the brain that cannot metabolize fatty acids. In other organisms such as plants and bacteria, this metabolic problem is solved using the glyoxylate cycle, which bypasses the decarboxylation step in the citric acid cycle and allows the transformation of acetyl-CoA to oxaloacetate, where it can be used for the production of glucose.
Owing to the rapid decline in the populations of the animals that produce it, the importation and sale of ivory in many countries is banned or severely restricted. In the ten years preceding a decision in 1989 by CITES to ban international trade in African elephant ivory, the population of African elephants declined from 1.3 million to around 600,000. It was found by investigators from the Environmental Investigation Agency (EIA) that CITES sales of stockpiles from Singapore and Burundi (270 tonnes and 89.5 tonnes respectively) had created a system that increased the value of ivory on the international market, thus rewarding international smugglers and giving them the ability to control the trade and continue smuggling new ivory. Since the ivory ban, some Southern African countries have claimed their elephant populations are stable or increasing, and argued that ivory sales would support their conservation efforts. Other African countries oppose this position, stating that renewed ivory trading puts their own elephant populations under greater threat from poachers reacting to demand. CITES allowed the sale of 49 tonnes of ivory from Zimbabwe, Namibia and Botswana in 1997 to Japan. In 2007, under pressure from the International Fund for Animal Welfare, eBay banned all international sales of elephant-ivory products. The decision came after several mass slaughters of African elephants, most notably the 2006 Zakouma elephant slaughter in Chad.
=== Brand names === Propranolol was first marketed under the brand name Inderal, manufactured by ICI Pharmaceuticals (now AstraZeneca), in 1965. "Inderal" is a quasi-anagram of "Alderlin", the trade name of pronethalol (which propranolol replaced); both names are an homage to Alderley Park, the ICI headquarters where the drugs were first developed. Propranolol is also sold under the brand names Avlocardyl, Deralin, Dociton, Hemangeol, Inderalici, InnoPran XL, Indoblok, Sumial, Anaprilin, and Bedranol SR (Sandoz). In India, it is sold under brand names such as Ciplar and Ciplar LA by Cipla.
Sources: en.wikipedia.org
On 14 December 1895, there was a large outbreak of botulism in the Belgian village of Ellezelles that occurred at a funeral where people ate pickled and smoked ham; three of them died. By examining the contaminated ham and performing autopsies on the people who died after eating it, van Ermengem isolated an anaerobic microorganism that he called Bacillus botulinus. He also performed experiments on animals with ham extracts, isolated bacterial cultures, and toxins extracts from the bacteria. From these he concluded that the bacteria themselves do not cause foodborne botulism, but rather produce a toxin that causes the disease when ingested. As a result of Kerner's and van Ermengem's research, it was thought that only contaminated meat or fish could cause botulism. This idea was refuted in 1904 when a botulism outbreak occurred in Darmstadt, Germany, because of canned white beans. In 1910, the German microbiologist J. Leuchs published a paper showing that different strains of Bacillus botulinus caused the outbreaks in Ellezelles and Darmstad and that the toxins were serologically distinct. In 1917, Bacillus botulinus was renamed Clostridium botulinum, as it was decided that the term Bacillus should refer to a group of aerobic microorganisms, while Clostridium would be used only to describe a group of anaerobic microorganisms. In 1919, Georgina Burke used toxin-antitoxin reactions to identify two strains of Clostridium botulinum, which she designated A and B.
=== Amino acid sequence === The linear amino acid sequence of a protein is called the primary structure. The primary structure can be easily determined from the sequence of codons on the DNA gene that codes for it. In most proteins, the primary structure uniquely determines the 3-dimensional structure of a protein in its native environment. An exception is the misfolded prion protein involved in bovine spongiform encephalopathy. This structure is linked to the function of the protein. Additional structural information includes the secondary, tertiary and quaternary structure. A viable general solution to the prediction of the function of a protein remains an open problem. Most efforts have so far been directed towards heuristics that work most of the time.
which means that the divergence of the velocity field is zero everywhere. Physically, this is equivalent to saying that the local volume dilation rate is zero, hence a flow of water through a converging pipe will adjust solely by increasing its velocity as water is largely incompressible.
Amyr Klink (born 25 September 1955) is a Brazilian explorer, sailor and writer. One of his projects, "Antarctica 360", was circumnavigating the Antarctic continent on his own, in 88 days between 1998 and 1999.
== Contact dermatitis == The sap of most species of Vanilla orchid which exudes from cut stems or where pods are harvested can cause moderate to severe dermatitis if it comes in contact with bare skin, though it is water-soluble and can be removed by washing. The sap of vanilla orchids contains calcium oxalate crystals, which appear to be the main causative agent of contact dermatitis in vanilla plantation workers.
Sources: en.wikipedia.org
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.
Reduced pressure keeps the solvent below its triple point, allowing ice to become vapor without melting. Vacuum also helps remove water vapor from the product chamber. The exact pressure is chosen with the formulation and equipment.
Residual moisture is water that remains in the dried solid after secondary drying. It is often measured by Karl Fischer titration, near-infrared spectroscopy, or thermogravimetry. Acceptable levels depend on the material and its stability profile.
Conventional drying uses heat to evaporate water from a material, while lyophilization freezes the material and removes water by sublimation under vacuum. This avoids the liquid phase and reduces thermal damage to sensitive substances. The result is a porous cake that reconstitutes quickly.