The short version of primary drying fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-08-01. Anything still debated is marked as such rather than presented as settled.
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.
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.
Misconceptions about lyophilization include the idea that dried products are indefinitely stable or that vacuum sealing eliminates all degradation. Chemical reactions can continue in the solid state, and some proteins lose activity even at low moisture. Another misconception is that any freeze-dryer cycle can be scaled by time alone; heat and mass transfer differ with equipment and load. Open questions remain about predicting long-term stability from short accelerated studies, particularly for amorphous formulations. Real-time stability data remain the standard for shelf-life assignment.
After lyophilization, the dried product is often sealed under vacuum or an inert gas to limit moisture and oxygen exposure. Vials, stoppers, and seals must maintain their barrier throughout shelf life. Storage temperature depends on product sensitivity: some cakes tolerate controlled room temperature, while labile biologics require refrigeration. Humidity is a critical variable because dried cakes are hygroscopic and can absorb water when exposed to air. Handling procedures therefore limit open-vial time and use desiccated environments for sampling.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Freeze-drying; lyophilisation; cryodesiccation | Regional spelling and historical terms. |
| Primary drying pressure | 0.05-0.5 mbar (5-50 Pa) | Kept below the triple point of water; product-specific. |
| Shelf temperature range | -40 to +40 °C | Freezing, primary, and secondary stages use different set points. |
| Cycle duration | 12-72 hours | Depends on fill volume, formulation, and equipment. |
| Condenser temperature | -50 to -80 °C | Must remain below the product's ice temperature. |
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.
Analytical methods for lyophilized solids must account for the low moisture content and the fragile cake. Karl Fischer titration is widely used for water content, while near-infrared spectroscopy can measure moisture non-destructively in sealed containers. X-ray diffraction and modulated differential scanning calorimetry help identify crystalline or amorphous phases. Residual solvent analysis may be needed if organic solvents were used during formulation. The combination of these methods supports batch release and long-term stability assessment.
Lyophilized products are typically stored as sealed solids in vials or syringes. Moisture ingress is a major concern because many dried cakes are hygroscopic and can lose stability when exposed to humid air. Storage temperature depends on the formulation; some products are kept refrigerated, while others are stable at room temperature. Container closure integrity and headspace moisture are often monitored. Light protection may also be required for some photosensitive materials.
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.
== Research == Dayhoff began a PhD in quantum chemistry under George Kimball in the Columbia University Department of Chemistry. In her graduate thesis, Dayhoff pioneered the use of computer capabilities – i.e. mass-data processing – to theoretical chemistry; specifically, she devised a method of applying punched-card business machines to calculate the resonance energies of several polycyclic organic molecules. Her management of her research data was so impressive that she was awarded a Watson Computing Laboratory Fellowship. As part of this award, she received access to "cutting-edge IBM electronic data processing equipment" at the lab.
1.0 L PC, 45 PS (33 kW; 44 hp) / 51 lb⋅ft (69 N⋅m) – export only 1.3 L TC (1977.01–1980) 60 PS (44 kW; 59 hp) / 72 PS (53 kW) in Japan 1.4 L UC (1978.03–1980) 83 PS (61 kW) in Japan In Australia the 1.3 had 45 kW (61 PS; 60 hp) at 5700 rpm while the bigger 1.4, introduced in July 1978, offered 48 kW (65 PS; 64 hp) at a somewhat lower engine speed of 5500 rpm. The 1.4 was accompanied by the new, better-equipped CS model which was only available with five-door bodywork. Van engines:
== Pharmacokinetics == Phenobarbital has an oral bioavailability of about 90%. Peak plasma concentrations (Cmax) are reached eight to 12 hours after oral administration. It is one of the longest-acting barbiturates available – it remains in the body for a very long time (half-life of two to seven days) and has very low protein binding (20 to 45%). Phenobarbital is metabolized by the liver, mainly through hydroxylation and glucuronidation and induces many isozymes of the cytochrome P450 system. Cytochrome P450 2B6 (CYP2B6) is specifically induced by phenobarbital via the CAR/RXR nuclear receptor heterodimer. It is excreted primarily by the kidneys.
The Roast Town concept received poor marks in market tests and was quickly discontinued. Pierce and his team left the company and it sold all of its 354 company-owned locations to RTM Restaurant Group, an existing Arby's franchise, for $71 million. Another marketing concept that was tried was a dual-brand venture that was started in 1995 with ZuZu's Handmade Mexican Grill. The marketing venture was a failure resulting in lawsuits being filed by each company against the other. In 1990, Arby's would acquire Daddy-O's Express, a double drive-through hamburger chain. The chain would expand to 13 locations with all closing by the late 90's. In 1992, Les Franchises P.R.A.G. Inc. opened the first Arby's franchise in the Canadian province of Quebec. It was also the 100th location to open in Canada and joins other locations that were then operating in the provinces of Ontario, Alberta, New Brunswick, Nova Scotia, Manitoba, British Columbia, and Saskatchewan. The Quebec location also sold the uniquely French-Canadian dish called poutine. In 2002, Arby's returned to operating restaurants by purchasing the second largest Arby's franchisee, Sybra Inc., with 293 locations out of bankruptcy outbidding RTM so as to prevent RTM from becoming too large. RTM was purchased by Arby's on July 25, 2005. In November 2002, Access Now filed a lawsuit against RTM, then a franchise of Triarc, that some 800 of their stores did not comply with the Americans with Disabilities Act of 1990 (ADA). The lawsuit had no liability damages except for lawyer fees.
=== Stannane === Organostannane reagents are common. Several are commercially available. Stannane reagents can be synthesized by the reaction of a Grignard or organolithium reagent with trialkyltin chlorides. For example, vinyltributyltin is prepared by the reaction of vinylmagnesium bromide with tributyltin chloride. Hydrostannylation of alkynes or alkenes provides many derivatives. Organotin reagents are air and moisture stable. Some reactions can even take place in water. They can be purified by chromatography. They are tolerant to most functional groups. Some organotin compounds are heavily toxic, especially trimethylstannyl derivatives. The use of vinylstannane, or alkenylstannane reagents is widespread. In regards to limitations, both very bulky stannane reagents and stannanes with substitution on the α-carbon tend to react sluggishly or require optimization. For example, in the case below, the α-substituted vinylstannane only reacts with a terminal iodide due to steric hindrance.
Sources: en.wikipedia.org
There have been many efforts to engineer and improve new AAV variants for both clinical and research purposes. Such modifications include new tropisms to target specific tissues, and modified surface residues to evade detection by the immune system. Beyond opting for particular strains of recombinant AAV (rAAV) to target particular cells, researchers have also explored AAV pseudotyping, the practice of creating hybrids of certain AAV strains to approach an even more refined target. The hybrid is created by taking a capsid from one strain and the genome from another strain. For example:
In a DNA double helix, each type of nucleobase on one strand bonds with just one type of nucleobase on the other strand. This is called complementary base pairing. Purines form hydrogen bonds to pyrimidines, with adenine bonding only to thymine in two hydrogen bonds, and cytosine bonding only to guanine in three hydrogen bonds. This arrangement of two nucleotides binding together across the double helix (from six-carbon ring to six-carbon ring) is called a Watson-Crick base pair. DNA with high GC-content is more stable than DNA with low GC-content. A Hoogsteen base pair (hydrogen bonding the 6-carbon ring to the 5-carbon ring) is a rare variation of base-pairing. As hydrogen bonds are not covalent, they can be broken and rejoined relatively easily. The two strands of DNA in a double helix can thus be pulled apart like a zipper, either by a mechanical force or high temperature. As a result of this base pair complementarity, all the information in the double-stranded sequence of a DNA helix is duplicated on each strand, which is vital in DNA replication. This reversible and specific interaction between complementary base pairs is critical for all the functions of DNA in organisms.
CAMP is an acronym for "Christie–Atkins–Munch-Peterson", for the three researchers who discovered the phenomenon. In their 1944 report, F. H. Christie (Commonwealth Serum Laboratories, Melbourne), L. J. Atkinson (Council for Scientific and Industrial Research, Melbourne), and L. Munch‑Petersen (Veterinary/Animal Health Research Laboratory) described the hemolytic phenomenon now known as the CAMP test. It is often incorrectly reported as the product of four people (counting Munch-Petersen as two people). The true relationship (three people) is the reason for two en dashes and then one hyphen in Christie–Atkins–Munch-Petersen. The name of the test bears no relationship to the name of the second messenger cyclic adenosine monophosphate (commonly referred to as cAMP).
11-Deoxycortisol, also known as cortodoxone (INN), cortexolone as well as 17α,21-dihydroxyprogesterone or 17α,21-dihydroxypregn-4-ene-3,20-dione, is an endogenous glucocorticoid steroid hormone, and a metabolic intermediate toward cortisol. The compound was first described by Tadeusz Reichstein in 1938 as Substance S, thus has also been referred to as Reichstein's Substance S or Compound S. 11-Deoxycortisol acts as a glucocorticoid, though is less potent than cortisol. 11-Deoxycortisol is synthesized from 17α-hydroxyprogesterone by 21-hydroxylase and is converted to cortisol by 11β-hydroxylase.
Sources: en.wikipedia.org
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.
Reduced pressure lowers the boiling point of water and allows ice to sublime at temperatures below freezing. It also helps remove water vapor from the product toward the condenser. The exact pressure is chosen to stay below the triple point of water.
No. Materials with low solids content or high volatile solvents may form weak or collapsed cakes. Some proteins and cells require stabilizers to survive freezing and drying stresses. Feasibility depends on formulation and process design.
No. Freeze-drying removes water but does not reliably kill microorganisms. Sterile lyophilized products are typically prepared aseptically before freezing or are sterilized by a validated method. Microbial control depends on the entire manufacturing process.