Primary drying comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2026-02-16. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
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.
| 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 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.
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.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen so that water becomes ice; then the surrounding pressure is lowered below the vapor pressure of ice. Heat is applied gently so ice changes directly to vapor without passing through a bulk liquid phase. The vapor is collected on a cold condenser, leaving a dry porous matrix. This process differs from simple evaporation because the material remains frozen during the main drying stage.
The process usually has three stages: freezing, primary drying, and secondary drying. Freezing sets the ice crystal structure and can determine pore size in the final cake. Primary drying removes free ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, although some water may remain as part of the solid. Cycle parameters depend on formulation, fill volume, vial type, and equipment performance.
The physical chemistry of freezing influences whether a formulation forms an amorphous glass or a crystalline solid. Amorphous systems can collapse if product temperature rises above the glass transition temperature of the freeze concentrate. Crystalline systems may show eutectic melting, where ice and solute melt together at a fixed temperature. Formulators add bulking agents, lyoprotectants, and buffers to preserve structure and biological activity. The optimum cycle keeps product temperature below critical thresholds during primary drying while allowing efficient sublimation.
Formulation composition influences whether freeze-drying produces an intact cake or a collapsed mass. Excipients such as sugars and polymers can raise the collapse temperature and provide bulk during drying. The critical temperature for primary drying is often the collapse temperature or the glass transition temperature of the maximally concentrated phase. If the product temperature exceeds this threshold, the frozen matrix may soften and lose structure. Established practice therefore links shelf temperature and chamber pressure to the formulation's thermal properties.
The physics of freeze-drying couples heat transfer, mass transfer, and phase change. Heat supplied through the shelf must reach the sublimation front without melting the ice or degrading the product. Water vapor then travels through the already dried layer and leaves the chamber, where low pressure and cold traps keep it from returning. The dried layer acts as a resistance to vapor flow, so drying rate changes as the front recedes. Open questions remain about how pore structure and formulation heterogeneity affect drying uniformity at larger scales.
=== Dyeing === Xanthoria parietina has been used as a natural dye source for centuries. Historical evidence indicates that ancient civilizations recognized this lichen's dyeing properties. In a 1934 publication, Reginald Campbell Thompson analyzed ancient Assyrian texts that mention lichens and dyeing. Thompson noted that the "yellow wall lichen" was "affirmed to give a good yellow or orange colour, if fixed with alum". Thompson's analysis of these ancient tablets suggests that knowledge of using lichens with alum as a mordant existed in ancient Mesopotamia. Alum (a naturally occurring mineral containing aluminium sulfate) was a mordant used with this lichen primarily to fix the dye to fabrics. Thompson notes that "the discovery of alum was one of the most important events in the history of dyeing." X. parietina was valued for its accessibility, growing readily on tree trunks and walls, and its ability to produce consistent yellow to orange hues when properly processed with mordants. Parietin is responsible for the lichen's dyeing properties, and pure isolated parietin produces the same color characteristics as whole lichen extracts. When processed using different extraction methods and mordants, this lichen yields a diverse range of colors. Extractions in boiling water produce golden-brown, yellow, and caramel hues, whereas 10% ammonia fermentation processes yield purplish-pink, orange, and pink shades. The POD (photo-oxidized) method, which involves exposing the lichen material to sunlight in an alkaline solution over time, can extract blue or purple dyes from X.
=== Drug delivery === Conventional drug delivery methods, such as systemic or topical delivery, are associated with many issues such as low solubility, off-target effects, and disadvantageous pharmacokinetics. Nanoparticles have been employed to increase solubility and target delivery of the drug to the desired tissue, increasing concentration of the drug at the site of action and decreasing drug concentration elsewhere, thereby increasing the efficacy of the drug and decreasing side effects. RGD has been employed to target nanoparticles containing drugs to specific cell types, especially cancer cells expressing integrin αvβ3. Many research groups utilize RGD to target the chemotherapeutic doxorubicin to cancer cells. Like other chemotherapeutics of its class, doxorubicin causes hair loss, nausea, vomiting, and myelosuppression, and can lead to cardiomyopathy and congestive heart failure. Clinically available Doxil utilizes liposomes to reduce accumulation of doxorubicin in myocardial tissue, thereby reducing cardiotoxicity. However, such nanoparticles rely on passive targeting of tumors by the EPR effect, which varies by patient and tumor type. Active targeting strategies aim to increase drug transport into cells to improve efficacy and counter multidrug resistance. In addition to doxorubicin, RGD-conjugated nanomaterials have been used to deliver the chemotherapeutics cisplatin, docetaxel, paclitaxel, 5-fluorouracil, and Gemcitabine to cancer cells. Such nanomaterials have also been used to deliver combination cytotoxic and vascular disrupting therapies.
At the northern end of Via Roma stands Piazza Castello, regarded as the heart of the city. The half-pedestrianised square hosts some significant buildings such as Palazzo Reale (Former Savoy Royal House), the Palazzo Madama (which previously hosted the Savoy senate and, for few years, the Italian senate after Italian unification), the former Baroque Teatro Regio di Torino (rebuilt in modern style in the 1960s, after being destroyed by fire), the Royal Library of Turin which hosts the Leonardo da Vinci self-portrait, and the baroque Royal Church of San Lorenzo. Moreover, Piazza Castello hosts a Fascist era building, the Torre Littoria, a sort of skyscraper which was supposed to become the headquarters of the Fascist party, although it never served as such. The building's style is quite different from the Baroque style of Piazza Castello. The square regularly hosts the main open space events of the city, live concerts included.
=== 25 November === According to U.S. and Ukrainian officials, about 1/3 of Western-supplied artillery went out of action in Ukraine due to wear-related mechanical problems. The United States European Command was said to have a repair base in Poland, but there were problems in transporting the weapons there from the front.
The type of analyzer used to run the CBC affects the reference ranges as well. Reference ranges are therefore established by individual laboratories based on their own patient populations and equipment.
Sources: en.wikipedia.org
== External links == Royal Society of Chemistry, Historical Group, short biography of Curtius University of Kiel history of the inorganic department Heidelberg University German Alpen Association, Kiel section
==== United States ==== Diazepam is controlled as a Schedule IV substance. The states of California and Florida offer diazepam to condemned inmates as a pre-execution sedative as part of their lethal injection program. The state of California has not executed a prisoner since 2006. In August 2018, Nebraska used diazepam as part of the drug combination used to execute Carey Dean Moore, the first death row inmate executed in Nebraska in over 21 years.
=== Middle East === Israel: BCG was given to all newborns between 1955 and 1982. Iran: Iran's vaccination policy was implemented in 1984. Vaccination with the Bacillus Calmette–Guerin (BCG) is among the most important tuberculosis control strategies in Iran [2]. According to Iranian neonatal vaccination policy, BCG has been given as a single dose to children aged <6 years, shortly after birth or at first contact with the health services.
It can then be further metabolized to isopropanol which is excreted in breath/urine, or by CYP2E1 into hydroxyacetone (acetol). Acetol can be converted to propylene glycol. This converts to pyruvate (by two alternative enzymes), or propionaldehyde, or to L-lactaldehyde then L-lactate (the common lactate isomer). Another pathway turns acetol to methylglyoxal, then to pyruvate, or to D-lactaldehyde (via S-D-lactoyl-glutathione or otherwise) then D-lactate. D-lactate metabolism (to glucose) is slow or impaired in humans, so most of the D-lactate is excreted in the urine; thus D-lactate derived from acetone can contribute significantly to the metabolic acidosis associated with ketosis or isopropanol intoxication. L-Lactate can complete the net conversion of fatty acids into glucose. The first experiment to show conversion of acetone to glucose was carried out in 1951. This, and further experiments used carbon isotopic labelling. Up to 11% of the glucose can be derived from acetone during starvation in humans. The glycerol released into the blood during the lipolysis of triglycerides in adipose tissue can only be taken up by the liver. Here it is converted into glycerol 3-phosphate by the action of glycerol kinase which hydrolyzes one molecule of ATP per glycerol molecule which is phosphorylated. Glycerol 3-phosphate is then oxidized to dihydroxyacetone phosphate, which is, in turn, converted into glyceraldehyde 3-phosphate by the enzyme triose phosphate isomerase.
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.
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.