Eutectic temperature is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Last reviewed on 2025-11-29. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Freeze-drying, lyophilisation | Lyophilisation is the British spelling; the process is not simple evaporation. |
| Primary drying pressure | 0.05–0.3 mbar | Pressure must remain below the vapor pressure of ice at the product temperature. |
| Sublimation temperature | Below 0 °C | Ice changes directly to vapor while the product remains frozen. |
| Typical shelf temperature | −40 to −10 °C | Exact setting depends on formulation critical temperature and equipment. |
| Cycle duration | 12–72 hours | Time varies with fill volume, formulation, and dryer performance. |
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.
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.
You can't field the ball deep. You have to get out in front of it." Remarked Bagwell, "I was basically being given a lesson from Ozzie Smith at first base during a pitching change. It's pretty cool." The next year, Bagwell hit .273, driving in 96 runs with 18 home runs. In 1993, the Astros improved to a third-place finish in the National League West division, and in mid-September, Bagwell was batting .320 with 20 home runs and 88 RBI. However, a pitch from the Philadelphia Phillies' Ben Rivera broke the fourth metacarpal bone in Bagwell's left hand, ending his season prematurely. It was the first of three successive seasons that ended early or was interrupted due to an incoming pitch breaking the same bone in that hand. His tendency to dip just before starting to swing made his hand more vulnerable to being hit by inside pitches. His .320 average was sixth in the NL. In February 1994, Bagwell and the Astros agreed to a one-year contract with a $2.4 million base salary (USD, $5.3 million today).
JRT is the analogue of the lysergamide lysergic acid diethylamide (LSD) in which the embedded tryptamine structure within the ergoline ring system of LSD has been replaced with an isotryptamine structure. Hence, JRT is not an ergoline, lysergamide, or tryptamine itself, but could be considered a cyclized isotryptamine. JRT exists as four enantiomers, including (+)-JRT and (–)-JRT, with (+)-JRT being the active enantiomer and the form used in scientific research.
Systematic doping in Russian sports has resulted in 47 Olympic and tens of world championships medals being stripped from Russian competitors—the most of any country, more than four times the number of the runner-up, and more than 30% of the global total. Russia also has the most competitors that have been caught doping at the Olympic Games, with more than 200. Russian doping is distinct from doping in other countries because in Russia the state supplied steroids and other drugs to sportspeople. Due to widespread doping violations, including an attempt to sabotage ongoing investigations by the manipulation of computer data, on 9 December 2019 the World Anti-Doping Agency (WADA) banned Russia from all international sport for four years. As at the 2018 Winter Olympics, WADA will allow individual cleared Russian athletes to compete neutrally under a title to be determined (which may not include the name "Russia", unlike the use of "Olympic Athletes from Russia" in 2018). Russia later filed an appeal to the Court of Arbitration for Sport (CAS) against the WADA decision. The Court of Arbitration for Sport, on review of Russia's appeal of its case from WADA, ruled on 17 December 2020 to reduce the penalty that WADA had imposed. Instead of banning Russia from sporting events, the ruling allowed Russia to participate at the Olympics and other international events, but for a period of two years the team cannot use the Russian name, flag, or anthem and must present themselves as "Neutral Athlete" or "Neutral Team".
Sources: en.wikipedia.org
=== Ab–Ah === John Jacob Abel (1857–1938). American biochemist and pharmacologist. He founded and chaired the first department of pharmacology in the United States at the University of Michigan. Robert Abeles (1926–2000). American biological chemist at Brandeis University. Member Natl. Acad. Sci. USA. John Abelson (b. 1938). American biologist at Caltech, with expertise in biophysics, biochemistry, and genetics, and known for work on RNA splicing. Sir Edward Abraham CBE, FRS (1913–1999). English biochemist at the University of Oxford involved in the development of penicillin and cephalosporin Gary Ackers (1939–2011). American Professor of Biochemistry and Molecular Biophysics at Washington University in St. Louis, who worked on thermodynamic linkage analysis of biological macromolecules. Gilbert Smithson Adair FRS (1896–1979). British protein chemist at the University of Cambridge, the first to identify cooperative binding, in the context of oxygen binding to haemoglobin. Julius Adler (1930–2024). American Professor of Biochemistry and Genetics at the University of Wisconsin–Madison, known for work on chemotaxis. David Agard (20th–21st century). American Professor of Biochemistry and Biophysics at UC San Francisco, whose research is focussed on understanding the basic principles of macromolecular structure and function. Member Natl. Acad. Sci. USA. Natalie Ahn (PhD 1985).
DSC is used widely for examining polymeric materials to determine their thermal transitions. Important thermal transitions include the glass transition temperature (Tg), crystallization temperature (Tc), and melting temperature (Tm). The observed thermal transitions can be utilized to compare materials, although the transitions alone do not uniquely identify composition. The composition of unknown materials may be completed using complementary techniques such as IR spectroscopy. Melting points and glass transition temperatures for most polymers are available from standard compilations, and the method can show polymer degradation by the lowering of the expected melting temperature. Tm depends on the molecular weight of the polymer and thermal history. The percent crystalline content of a polymer can be estimated from the crystallization/melting peaks of the DSC graph using reference heats of fusion found in the literature. DSC can also be used to study thermal degradation of polymers using an approach such as Oxidative Onset Temperature/Time (OOT); however, the user risks contamination of the DSC cell, which can be problematic. Thermogravimetric Analysis (TGA) may be more useful for decomposition behavior determination. Impurities in polymers can be determined by examining thermograms for anomalous peaks, and plasticisers can be detected at their characteristic boiling points.
=== 1950–2000 === In the 1950s, thiazide diuretics were developed by Merck scientists Karl H. Beyer, James M. Sprague, John E. Baer, and Frederick C. Novello and led to the marketing of the first drug of this class, chlorothiazide, under the trade name Diuril in 1958. The research leading to the discovery of chlorothiazide, leading to "the saving of untold thousands of lives and the alleviation of the suffering of millions of victims of hypertension" was recognized by a special Public Health Award from the Lasker Foundation in 1975. In 1953, Merck & Co. merged with Philadelphia-based Sharp & Dohme, Inc., becoming the largest U.S. drugmaker. Sharp and Dohme had acquired H. K. Mulford Company in 1929, adding smallpox vaccines to its portfolio. The combined company kept the trade name Merck in the United States and Canada, and as Merck Sharp & Dohme (MSD) outside these two countries. In 1965, Merck & Co. acquired Charles Frosst Ltd. of Montreal (founded 1899), creating Merck-Frosst Canada, Inc., as its Canadian subsidiary and pharmaceutical research facility. Merck & Co. closed this facility in July 2010 but reemerged in 2011 as Merck Canada. Maurice Hilleman, a scientist at Merck, developed the first mumps vaccine in 1967, the first rubella vaccine in 1969, and the first trivalent measles, mumps, rubella (MMR vaccine) in 1971. The incidence of rubella-associated birth defects fell from up to 10,000 per year in the U.S. to zero in the aftermath of the rubella vaccine's development.
Sources: en.wikipedia.org
=== Disinfection === Much research has been done in evaluating the ability of the silver ion at inactivating Escherichia coli, a microorganism commonly used as an indicator for fecal contamination and as a surrogate for pathogens in drinking water treatment. Concentrations of silver nitrate evaluated in inactivation experiments range from 10–200 micrograms per liter as Ag+. Silver's antimicrobial activity saw many applications prior to the discovery of modern antibiotics, when it fell into near disuse. Its association with argyria made consumers wary and led them to turn away from it when given an alternative.
Three designer NPs have been bioengineered, tested in cell-based assays and animal models of heart failure, undergone pharmaceutical toxicology studies, and have received FDA approval for clinical studies.
==== Federal drug schedule system introduced ==== The Richard Nixon presidency (1969–74) incorporated his predecessor's anti-drug initiative in a tough-on-crime platform. In his 1968 presidential nomination acceptance speech, Nixon promised, "Our new Attorney General will ... launch a war against organized crime in this country. ... will be an active belligerent against the loan sharks and the numbers racketeers that rob the urban poor. ... will open a new front against the filth peddlers and the narcotics peddlers who are corrupting the lives of the children of this country." In a 1969 special message to Congress, he identified drug abuse as "a serious national threat". On October 27, 1970, Nixon signed into law the Comprehensive Drug Abuse Prevention and Control Act of 1970, establishing his approach to drug control. The act largely repealed mandatory minimum sentences: simple possession was reduced from a felony to a misdemeanor, the first offense carried a maximum of one year in prison, and judges had the latitude to assign probation, parole or dismissal. Penalties for trafficking were increased, up to life depending on the quantity and type of drug. Funding was authorized for the Department of Health, Education and Welfare to provide treatment, rehabilitation and education. Additional federal drug agents were provided, and a "no-knock" power was instituted, that allowed entry into homes without warning to prevent evidence from being destroyed. Licensing and stricter reporting and record-keeping for pharmaceutical manufacturers and distributors occurred under the act.
== History == During the 1980s, Jean-Pierre Raufman worked as a postdoctoral researcher at the National Institutes of Health for John Pisano, a biochemist who specialized in collecting venom from various animals and looking for novel substances that could affect human physiology. In the course of this work, Raufman focused on the Gila monster, because he was curious about its practice of eating once or twice per year. He reported that Gila monster venom had biologically active molecules that provoked inflammation of the pancreas in test animals. In 1992, after learning of Raufman's findings, John Eng of the Veterans Administration Medical Center in New York City used radioimmunoassay to isolate a novel substance from Gila monster venom. The new substance, which Eng called exendin-4, was similar to GLP-1 in that it reduced blood glucose in diabetic mice, but exendin-4 had a much longer half-life than GLP-1, whose extremely short half-life had defeated earlier attempts to turn it into a drug. Eng filed a patent application for exendin-4 in 1993. He then spent three years searching for a pharmaceutical industry partner interested in commercializing exendin-4. In 1996, Amylin Pharmaceuticals licensed Eng's patent and created a synthetic version of exendin-4 called exenatide. In 2002, Eli Lilly and Company partnered with Amylin to develop exenatide and secure approval to market the drug. Exenatide's 2005 approval by the U.S.
Sources: en.wikipedia.org
The main change is sublimation, in which ice becomes water vapor without melting into liquid water. This occurs when the chamber pressure is held below the vapor pressure of ice while mild heat is supplied. The result is a dry, porous solid that retains much of its original shape.
Freezing determines ice crystal size, solute distribution, and the pore network left after drying. A slow or fast freezing rate can produce different cake structures and affect reconstitution. It also sets whether the formulation follows an amorphous or crystalline drying path.
It removes most free water during primary drying and part of the bound water during secondary drying. A small residual moisture content often remains and is specified for each product. Complete removal is generally neither practical nor desirable for stability.
Primary drying removes ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, often under the same vacuum. The two stages differ in the water state being removed.