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 2025-10-22. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Common synonym | Freeze-drying | Same dehydration operation |
| Typical vacuum | 10-100 Pa | Pressure during primary drying |
| Primary drying temperature | -40 to -10 °C | Below collapse temperature for many formulations |
| Cycle duration | 12-72 hours | Varies with load, container, and formulation |
| Key phase change | Sublimation | Solid ice to water vapor |
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.
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.
ALDHs function in cell differentiation, proliferation, oxidation, and drug resistance. These enzymes are only one example of the many different types of dehydrogenases in the human body; their wide array of functions, and the impact that their deactivation or mutations has upon crucial cell processes underscores the importance of all dehydrogenases in maintaining body homeostasis.
Ammonium sulfate precipitation is one of the most commonly used methods for large and laboratory scale protein purification and fractionation that can be used to separate proteins by altering their solubility in the presence of a high salt concentration.
This should not be confused with Folin-Ciocalteu reagent, that is used to detect phenolic compounds. The Folin reagent can be used with an acidic secondary reagent to distinguish MDMA and related compounds from PMMA and related compounds.
in the version dated April 30, 2003 - that their specialist knowledge in radiation protection has been updated and must complete a full-day course with a final examination. Specialist knowledge in radiation protection is required by the Technical Knowledge Guideline according to X-ray Ordinance. - R3 for persons who work with baggage screening equipment, industrial measuring equipment and interfering emitters. Since 2019, the regulatory areas of the previous X-ray and radiation protection ordinances have been merged in the amended Radiation Protection Ordinance. The Radiation Protection Commission (SSK) was founded in 1974 as an advisory body to the Federal Ministry of the Interior. It emerged from Commission IV "Radiation Protection" of the German Atomic Energy Commission, which was founded on January 26, 1956. After the Chernobyl nuclear disaster in 1986, the Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection was established in the Federal Republic of Germany. The creation of this ministry was primarily a response to the perceived lack of coordination in the political response to the Chernobyl disaster and its aftermath. On December 11, 1986, the German Bundestag passed the Precautionary Radiation Protection Act (StrVG) to protect the population, to monitor radioactivity in the environment, and to minimize human exposure to radiation and radioactive contamination of the environment in the event of radioactive accidents or incidents. The last revision of the X-Ray Ordinance was issued on January 8, 1987.
One month later, HVEC announced it was mothballing the XTU and closing the Van de Graaff Research Laboratory in Burlington. The market failure of the XTU coincided with new competitive pressures. Operational difficulties with HVEC's Emperor tandems further damaged the company's competitive position. Laboratories reported technical problems with the Emperor requiring costly component replacements. In 1965, fellow physicist and former HVEC consultant Ray Herb founded the National Electrostatics Corporation. The company's durable Pelletron charging technology became the favored platform for federally-funded accelerator research. HVEC sold its final two Emperor models to French national laboratories in 1973.
Sources: en.wikipedia.org
=== Mechanism of action === Levobunolol is a non-cardioselective beta blocker, that is, it blocks beta-1 receptors as well as beta-2 receptors. The latter type dominates in the ciliary body, where it controls aqueous humour production. Blocking this type of receptor reduces aqueous humour production, lowering intraocular pressure. The substance has no relevant membrane stabilizing effect or intrinsic sympathomimetic activity. Like other beta blockers, and unlike the anti-glaucoma medication pilocarpine, levobunolol has no effect on accommodation and pupil size.
21 March – Leo Varadkar launched the Government's national action plan to tackle racism in response to persistent racial discrimination in Ireland. The plan drew on a report published in April 2021 by the Anti Racism Committee, established in 2020 by the Department of Children, Equality, Disability, Integration and Youth. 31 March RTÉ announced that Radio 1 would permanently stop broadcasting on the longwave band on 14 April. The Supreme Court ruled that legislation governing the election of senators to the Seanad university panels was unconstitutional due to the failure for over 40 years to legislate for the Seventh Amendment of the Constitution of Ireland.
== Self-assembled monolayers on solid substrates == Self-assembled monolayers (SAMs) are made of a layer of organic molecules which forms naturally as an ordered lattice on the surface of a desired substrate. Their molecules in the lattice have connections chemically at one end (head group), while the other end (end group) creates the exposed surface of the SAM. Many types of SAMs can be formed. For example: thiols form SAMs on gold, silver, copper, or on some compound semiconductors such as InP and GaAs. By changing the tail group of the molecules, different surface properties can be obtained; therefore SAMs can be used to render surfaces hydrophobic or hydrophilic as well as change surface states of semiconductor. With self-assembly, positioning of SAMs is used to define chemical system precisely to find the target location in a molecular-inorganic device. With this characteristic, SAMs is a good candidates for molecular electronic devices such as use SAMs to build electronic devices and maybe the circuits is an intriguing prospect. Because of their ability to provide the basis for very high-density data storage and high-speed devices.
Nighttime in-laboratory Level 1 polysomnography (PSG) is the gold-standard diagnostic test. Patients are monitored with EEG leads, pulse oximetry, temperature or pressure sensors to detect nasal and oral airflow, respiratory impedance plethysmography or similar resistance belts around the chest and abdomen to detect motion, an ECG lead, and EMG sensors to detect muscle contraction in the chin, chest, and legs. An "event" can be either an apnea, characterized by complete cessation of airflow for at least 10 seconds, or a hypopnea in which airflow decreases by 50 percent for 10 seconds or decreases by 30 percent if there is an associated decrease in the oxygen saturation or an arousal from sleep. To grade the severity of sleep apnea, the number of events per hour is reported as the apnea-hypopnea index (AHI). For adults, an AHI of less than 5 is considered normal, an AHI of [5–15) is mild, [15–30) is moderate, and ≥30 events per hour characterizes severe sleep apnea. For pediatrics, an AHI of less than 1 is considered normal, an AHI of [1–5) is mild, [5–10) is moderate, and ≥10 events per hour characterizes severe sleep apnea.
Sources: en.wikipedia.org
=== Acoustic droplet ejection === Acoustic droplet ejection (ADE) uses a pulse of ultrasound to move low volumes of fluids (typically nanoliters or picoliters) without any physical contact. This technology focuses acoustic energy into a fluid sample to eject droplets as small as a millionth of a millionth of a litre (picoliter = 10−12 litre). ADE technology is a very gentle process, and it can be used to transfer proteins, high molecular weight DNA and live cells without damage or loss of viability. This feature makes the technology suitable for a wide variety of applications including proteomics and cell-based assays.
According to the Human Rights Watch, Xi has "started a broad and sustained offensive on human rights" since he became leader in 2012. The HRW also said that repression in China is "at its worst level since the Tiananmen Square massacre." Since taking power, Xi has cracked down on grassroots activism, with hundreds being detained. He presided over the 709 crackdown on 9 July 2015, which saw more than 200 lawyers, legal assistants and human rights activists being detained. His term has seen the arrest and imprisonment of activists such as Xu Zhiyong, as well as numerous others who identified with the New Citizens' Movement. Prominent legal activist Pu Zhiqiang of the Weiquan movement was also arrested and detained. According to activists, "Xi is waging the most severe systematic suppression of Christianity in the country since religious freedom was written into the Chinese constitution in 1982," and according to pastors and a group that monitors religion in China, has involved "destroying crosses, burning bibles, shutting churches and ordering followers to sign papers renouncing their faith." Under Xi, the CCP has embraced assimilationist policies towards ethnic minorities, scaling back affirmative action in the country by 2019, and scrapping a wording in October 2021 that guaranteed the rights of minority children to be educated in their native language, replacing it with one that emphasized teaching the national language. In 2014, Xi called to foster a sense of community for the Chinese nation among ethnic minorities.
Sample acquisition: the most commonly used samples for metagenomic sequencing are blood, stool, cerebrospinal fluid (CSF), urine, or nasopharyngeal swabs. Among these, blood and CSF are the cleanest, having less background noise, while the others are expected to have a great amount of commensals and/or opportunistic infections and thus have more background noise. Samples should be collected with much caution as surgical specimens could be contaminated during handling of the biopsy; for example, lumbar punctures to obtain CSF specimens may be contaminated during the procedure. RNA/DNA extraction: the DNA and the RNA of the sample is extracted by using an extraction kit. If there is a strong previous suspicion of the pathogen genome composition and since the amount of pathogen nucleic acid in more noise samples is overwhelmed by the RNA/DNA of other organisms, selecting an extraction kit of only RNA or DNA would be a more specific and convenient approach. Some commerciable available kits are for example RNeasy PowerSoil Total RNA kit (Qiagen), RNeasy Minikit (Qiagen), MagMAX Viral Isolation kit (ABI), Viral RNA Minikit (Qiagen). Optimization strategies for library preparation: because of high levels of background noise in metagenomic sequencing, several target enrichment procedures have been developed that aim to increase the probability of capturing pathogen-derived transcripts and/or genomes. Generally there are two main approaches that can be used to increase the amount of pathogen signal in a sample: negative selection and positive enrichment.
Butorphanol is a morphinan-type synthetic agonist–antagonist opioid analgesic developed by Bristol-Myers. Butorphanol is most closely structurally related to levorphanol. Butorphanol is available as the tartrate salt in injectable, tablet, and intranasal spray formulations. The tablet form is only used in dogs, cats and horses due to low bioavailability in humans. It was patented in 1971 and approved for medical use in 1979.
== Chemistry == Selegiline is a substituted phenethylamine and amphetamine derivative. It is also known as (R)-(–)-N,α-dimethyl-N-(2-propynyl)phenethylamine, (R)-(–)-N-methyl-N-2-propynylamphetamine, or N-propargyl-L-methamphetamine. Selegiline (L-deprenyl) is the enantiopure levorotatory enantiomer of the racemic mixture deprenyl, whereas D-deprenyl is the dextrorotatory enantiomer. Selegiline is a derivative of levomethamphetamine (L-methamphetamine), the levorotatory enantiomer of the psychostimulant and sympathomimetic agent methamphetamine (N-methylamphetamine), with a propargyl group attached to the nitrogen atom of the molecule. Selegiline is a small-molecule compound, with the molecular formula C13H17N and a low molecular weight of 187.281 g/mol. It has high lipophilicity, with an experimental log P of 2.7 and predicted log P values of 2.9 to 3.1. Pharmaceutically, selegiline is used almost always as the hydrochloride salt, though the free base form has also been used. At room temperature, selegiline hydrochloride is a white to near white crystalline powder. Selegiline hydrochloride is freely soluble in water, chloroform, and methanol.
Sources: en.wikipedia.org
Primary drying removes ice by sublimation under vacuum. Secondary drying removes water that is bound to the material, often by warming the product after most ice has left. Both stages occur below temperatures that would cause unwanted melting.
Sublimation requires the solvent to remain solid so vapor leaves without passing through a liquid phase. If the product melts, the porous structure can collapse and drying becomes uneven. Maintaining frozen conditions preserves the intended physical form.
No, freeze-drying is a dehydration method, not a sterilization step. It can reduce water activity and limit microbial growth during storage, but it does not reliably kill microbes or remove endotoxins. Sterility must come from separate validated processes.
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.