A practical reference on Primary drying: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-02-03. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
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.
| 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 |
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.
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.
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 removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and concentrates dissolved solids. Primary drying then lowers chamber pressure so ice changes directly into vapor without passing through a liquid phase. Secondary drying raises the shelf temperature to remove bound water that remains after ice sublimation. The result is a dry, porous structure that can be reconstituted later.
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.
=== Purification methods === Recovering uranium and plutonium from spent nuclear fuel for reuse is one of the major processes of the nuclear fuel cycle. As it has a long half-life of just over 2 million years, the alpha emitter 237Np is one of the major isotopes of the minor actinides separated from spent nuclear fuel. Many separation methods have been used to separate out the neptunium, operating on small and large scales. The small-scale purification operations have the goals of preparing pure neptunium as a precursor of metallic neptunium and its compounds, and also to isolate and preconcentrate neptunium in samples for analysis. Most methods that separate neptunium ions exploit the differing chemical behaviour of the differing oxidation states of neptunium (from +3 to +6 or sometimes even +7) in solution. Among the methods that are or have been used are: solvent extraction (using various extractants, usually multidentate β-diketone derivatives, organophosphorus compounds, and amine compounds), chromatography using various ion-exchange or chelating resins, coprecipitation (possible matrices include LaF3, BiPO4, BaSO4, Fe(OH)3, and MnO2), electrodeposition, and biotechnological methods. Currently, commercial reprocessing plants use the Purex process, involving the solvent extraction of uranium and plutonium with tributyl phosphate.
==== United Kingdom ==== Insulin, and all other medications, are supplied free of charge to people who use it to manage their diabetes by the National Health Services of the countries of the United Kingdom.
== Potential risks == In December 2024, 38 scientists, including several synthetic biology researchers and two Nobel laureates, warned that the creation of mirror-image life could cause "unprecedented and irreversible harm" to human health and ecosystems worldwide. The reversed structure of mirror-image bacteria could allow them to evade many mechanisms critical for immunity and predation that have evolved to recognize natural-chirality structures. As a result, mirror-image bacteria could potentially escape immune defenses and invade natural ecosystems, leading to "pervasive lethal infections in a substantial fraction of plant and animal species, including humans." Given these risks, the scientists concluded that mirror-image organisms should not be created without compelling evidence of safety. As of January 2026, no researchers are known to be pursuing the creation of mirror life; several who had been pursuing it have since renounced it and signed on as coauthors on the 2024 paper. Since the publication of the 2024 paper, 96 biotechnology experts signed a statement agreeing with its conclusions, and attendees of the first international conference on mirror-image life largely agreed that it should not be created. Germany’s Central Commission for Biological Safety (ZKBS) issued a statement that while applied research on mirror biomolecules should continue, mirror bacteria could pose serious risks, and that "a broad scientific and societal debate" was necessary.
Sources: en.wikipedia.org
The UN Single Convention provided a legal framework, and in 1988, the Convention against Illicit Traffic expanded that framework, working the US-style punitive approach into international law. By the end of Reagan's presidency in 1989, illicit drugs were more readily available and cheaper than at the start of his first term in 1981.
== External links == Atrial+Natriuretic+Factor at the U.S. National Library of Medicine Medical Subject Headings (MeSH) Human NPPA genome location and NPPA gene details page in the UCSC Genome Browser. Overview of all the structural information available in the PDB for UniProt: P01160 (Natriuretic peptides A) at the PDBe-KB.
==== Distribution ==== The plasma protein binding of naltrexone is about 20% over a naltrexone concentration range of 0.1 to 500 μg/L. Its apparent volume of distribution at 100 mg orally is 16.1 L/kg after a single dose and 14.2 L/kg with repeated doses.
Sources: en.wikipedia.org
Clinical psychology is an integration of human science, behavioral science, theory, and clinical knowledge aimed at understanding, preventing, and relieving psychological distress or dysfunction as well as promoting well-being and personal growth. Central to its practice are psychological assessment, diagnosis, clinical formulation, and psychotherapy; although clinical psychologists also engage in research, teaching, consultation, forensic testimony, and program development and administration. In many countries, clinical psychology is a regulated mental health profession. In the United States, clinical psychologists operate under the same license as counseling psychologists and school psychologists. The field is generally considered to have begun in 1896 with the opening of the first psychological clinic at the University of Pennsylvania by Lightner Witmer. In the first half of the 20th century, clinical psychology was focused on psychological assessment, with little attention given to treatment. This changed after the 1940s when World War II resulted in the need for a large increase in the number of trained clinicians. Since that time, three main educational models have developed in the US—the PhD Clinical Science model (heavily focused on research), the PhD science-practitioner model (integrating scientific research and practice), and the PsyD practitioner-scholar model (focusing on clinical theory and practice).
=== Pharmacodynamics === MCCAM acts as a selective pseudo-irreversible partial agonist of the μ-opioid receptor (MOR). It shows both opioid agonist- and antagonist-like effects in animals. More specifically, it has analgesic effects, mixed reinforcing effects, appears to lack significant respiratory depression, alleviates opioid withdrawal symptoms, and provides long-lasting blockade and protection against the effects of MOR full agonists (including their reinforcing effects as well as their toxic and lethal effects, for instance in overdose). Due to its pseudo-irreversible nature, MCCAM is insurmountable by conventional reversible MOR ligands, for instance morphine, alfentanil, and naltrexone. MCCAM is buprenorphine-like in many regards, but differs from buprenorphine in its pseudo-irreversibility.
== Research == Lasofoxifene is under development by Sermonix Pharmaceuticals for the treatment of metastatic breast cancer and dyspareunia associated with vaginal atrophy in the United States and Europe. It is also being researched for the potential treatment of ovarian cancer. As of December 2017, lasofoxifene is in phase III clinical trials for breast cancer and phase II clinical studies for dyspareunia.
== Experimental chemistry == The isotopes 284Nh, 285Nh, and 286Nh have half-lives long enough for chemical investigation. From 2010 to 2012, some preliminary chemical experiments were performed at the JINR to determine the volatility of nihonium. The isotope 284Nh was investigated, made as the daughter of 288Mc produced in the 243Am+48Ca reaction. The nihonium atoms were synthesised in a recoil chamber and then carried along polytetrafluoroethylene (PTFE) capillaries at 70 °C by a carrier gas to the gold-covered detectors. About ten to twenty atoms of 284Nh were produced, but none of these atoms were registered by the detectors, suggesting either that nihonium was similar in volatility to the noble gases (and thus diffused away too quickly to be detected) or, more plausibly, that pure nihonium was not very volatile and thus could not efficiently pass through the PTFE capillaries. Formation of the hydroxide NhOH should ease the transport, as nihonium hydroxide is expected to be more volatile than elemental nihonium, and this reaction could be facilitated by adding more water vapour into the carrier gas. It seems likely that this formation is not kinetically favoured, so the longer-lived isotopes 285Nh and 286Nh were considered more desirable for future experiments. A 2017 experiment at the JINR, producing 284Nh and 285Nh via the 243Am+48Ca reaction as the daughters of 288Mc and 289Mc, avoided this problem by removing the quartz surface, using only PTFE.
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.
Yes. Lyophilization and freeze-drying are synonyms for the same vacuum-assisted sublimation process. The term lyophilization is more common in pharmaceutical and laboratory settings, while freeze-drying is widely used in food and general contexts.