secondary 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 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
Handling practices aim to prevent moisture ingress and mechanical damage. Vials should remain stoppered and crimped until use, and reconstitution should follow the labeled diluent and volume. Shipping may involve temperature-controlled containers and desiccants, but direct contact between desiccant and product is avoided. Regulatory guidance expects documented storage conditions, excursion assessments, and stability commitments. Open questions remain about how best to predict long-term stability from short accelerated studies for every formulation class.
After lyophilization, the product is usually a porous cake or powder with a large internal surface area. This structure can absorb moisture quickly if exposed to humid air, so vials are sealed under vacuum or an inert gas. Moisture uptake may lower the glass transition temperature of the dried matrix and accelerate chemical or physical degradation. Storage conditions therefore depend on the formulation, container, and intended shelf life. Some products remain stable at room temperature, while others require refrigeration or freezing.
Quality control for lyophilized products includes appearance, cake structure, reconstitution time, pH, residual moisture, and potency. Residual moisture is a key attribute because excess water can reduce stability, while excessively low moisture may cause structural changes or aggregation in some systems. Stability studies compare real-time and accelerated conditions to estimate shelf life. Analytical methods must be validated for the specific matrix, container, and moisture range. Sterility and container integrity are also monitored for sterile products.
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.
| Property | Value | Notes |
|---|---|---|
| Typical appearance | White to off-white porous cake or powder | Color and structure vary with formulation. |
| Typical reconstitution time | Seconds to several minutes | Diluent, agitation, and temperature affect rate. |
| Typical storage temperature | 2–8 °C, 15–25 °C, or ≤−20 °C | Product-specific; protect from moisture and light. |
| Typical container closure | Glass vial with rubber stopper and crimp seal | Closure must limit moisture ingress. |
| Typical stability indicator | Residual moisture, potency, and reconstitution time | Monitored throughout shelf life. |
Regulatory expectations for lyophilized products focus on consistent manufacture and documented stability. Batches are often monitored for moisture, appearance, potency, and sterility where applicable. Process parameters such as shelf temperature, chamber pressure, and drying time are recorded and controlled within validated ranges. Open questions remain about how best to predict long-term stability from short accelerated studies, especially for complex biologics. Variations in freezing rate and ice crystal size can produce differences that are not always visible but may affect performance.
After drying, a lyophilized product is usually sealed under vacuum or an inert gas to limit moisture uptake. Residual water content is measured because small changes can alter chemical stability and cake appearance. Storage temperature depends on the material; many biological products are kept at 2–8 °C, while some require −20 °C or colder. Exposure to ambient humidity during handling can cause the porous solid to absorb water and collapse. Container closures and stoppers are therefore selected for low moisture transmission and compatibility.
Quality control for lyophilized materials includes visual inspection of the cake, measurement of residual moisture, and tests for reconstitution time. An acceptable cake is typically uniform and may be slightly porous; shrinkage, meltback, or cracks can indicate process deviations. Analytical methods such as Karl Fischer titration, thermogravimetric analysis, and near-infrared spectroscopy quantify water content. Reconstitution time is recorded because a very slow or incomplete dissolution can signal collapse or aggregation. Stability studies compare samples stored under defined temperature and humidity conditions over months or years.
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.
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Oligonucleotide synthesis is the chemical synthesis of relatively short fragments of nucleic acids with defined chemical structure (sequence). The technique is extremely useful in current laboratory practice because it provides a rapid and inexpensive access to custom-made oligonucleotides of the desired sequence. Whereas enzymes synthesize DNA and RNA only in a 5' to 3' direction, chemical oligonucleotide synthesis does not have this limitation, although it is most often carried out in the opposite, 3' to 5' direction. Currently, the process is implemented as solid-phase synthesis using phosphoramidite method and phosphoramidite building blocks derived from protected 2'-deoxynucleosides (dA, dC, dG, and T), ribonucleosides (A, C, G, and U), or chemically modified nucleosides, e.g. LNA or BNA. To obtain the desired oligonucleotide, the building blocks are sequentially coupled to the growing oligonucleotide chain in the order required by the sequence of the product (see Synthetic cycle below). The process has been fully automated since the late 1970s. Upon the completion of the chain assembly, the product is released from the solid phase to solution, deprotected, and collected. The occurrence of side reactions sets practical limits for the length of synthetic oligonucleotides (up to about 200 nucleotide residues) because the number of errors accumulates with the length of the oligonucleotide being synthesized. Products are often isolated by high-performance liquid chromatography (HPLC) to obtain the desired oligonucleotides in high purity.
Other efforts to prevent deaths from overdose include increasing access to naloxone and treatment for opioid dependence. Drug use contributes to 500,000 deaths worldwide, with opioid overdose resulting in approximately 115,000 of these deaths in 2018. This is up from 18,000 deaths in 1990. In 2018, approximately 269 million people had engaged in drug usage at least once, 58 million of which used opioids. Drug use disorders have affected around 35.6 million people worldwide in 2018. The WHO estimates that 70% of deaths due to drug use are in relation to opioids, with 30% being due to overdose. It is believed that the opioid epidemic has partly been caused due to assurances that prescription opioids were safe, by the pharmaceutical industry in the 1990s. This led to unwarranted trust and a subsequent heavy reliance on opioids. Though there are treatment interventions which can effectively reduce the risk of overdose in people with opioid dependence, less than 10% of affected individuals receive it.
=== Drug-drug interactions === Lamividine/zidovudine interacts with stavudine and zalcitabine by competing intracellularly for activation and results in inhibiting phosphorylation. There is also a known interaction with nephrotoxic or bone marrow suppressive agents (e.g. doxorubicin) which increases the risk of hematologic toxicity of zidovudine. Monitoring renal function and hematologic tests can be used to assess these potential interactions.
During the Migration Period, the Jutland peninsula was home to several tribes. The Jutes inhabited the most northern part of the peninsula from Grenen to Olger's Dyke. This dyke, dating back to around the first century, served as the boundary between the Jutes in the north and the Angles in the south. This dyke lost its relevance in the 200s when the Angles expanded northward, leading to the establishment of a new dyke called the Wendish Dyke. The southern border of the Angles was marked by the marshes surrounding the Eider, that combined with the dense old-growth forest to the south of the river, formed a natural barrier. South of the forest lay the region now known as Holstein, which was divided between the Germanic Saxons, who inhabited the western part, and the Slavic Wagri, who lived in the eastern part. In the 8th century, the Wagri became part of the Slavic tribal confederation known as the Obotrites (also known as the Wends by the Danes and Saxons). During the 4th and early 5th centuries, a significant migration saw the Jutes, Angles, and Saxons depart from their homelands to settle in the British Isles. This mass exodus left much of the Jutland Peninsula sparsely populated, allowing the Danes from southern Scandinavia and the islands of Zealand, Funen, and other smaller Danish isles to migrate into the peninsula. They gradually settled the region, integrating the remaining Jutes and Angles who had not left for Britain. By the mid-5th century, the Danes had established settlements from Grenen in the north to just north of the Eider River and its marshes.
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Upon heating a dilute potassium hydroxide solution with glucose to 100 °C, a strong reddish browning and a caramel-like odor develops. Concentrated sulfuric acid dissolves dry glucose without blackening at room temperature forming sugar sulfuric acid. In a yeast solution, alcoholic fermentation produces carbon dioxide in the ratio of 2.0454 molecules of glucose to one molecule of CO2. Glucose forms a black mass with stannous chloride. In an ammoniacal silver solution, glucose (as well as lactose and dextrin) leads to the deposition of silver. In an ammoniacal lead acetate solution, white lead glycoside is formed in the presence of glucose, which becomes less soluble on cooking and turns brown. In an ammoniacal copper solution, yellow copper oxide hydrate is formed with glucose at room temperature, while red copper oxide is formed during boiling (same with dextrin, except for with an ammoniacal copper acetate solution). With Hager's reagent, glucose forms mercury oxide during boiling. An alkaline bismuth solution is used to precipitate elemental, black-brown bismuth with glucose. Glucose boiled in an ammonium molybdate solution turns the solution blue. A solution with indigo carmine and sodium carbonate destains when boiled with glucose.
==== International drug control conventions ==== In 1990, it was recommended that etizolam not be placed under international control. However, this attitude has changed due to increased abuse. On 13 December 2019, the World Health Organization recommended etizolam be placed in Schedule 4 of the 1971 Convention on Psychotropic Substances. This recommendation was followed by the placement of Etizolam into Schedule IV in March 2020.
== Agriculture == In the farming industry, environmental concerns over air pollution led to research aimed at reducing the odor of manure. A body of evidence emerged that increased sulfur containing amino acid content of feed increased the offensive odor of feces and flatus produced by livestock. This is thought to be due to increased sulfur containing substrate available to gut microbiota enabling increased volatile sulfur compound (VSC) release during gut fermentation (VSC are thought to be the primary contributors to the odor of flatus and feces). This theory is supported by the observation that feces from carnivores is more malodorous than feces from herbivore species, and this appears to apply to human diets as well (odor of human feces shown to increase with increased dietary protein, particularly sulfur containing amino acids).
=== Other governmental positions === Mizell became the Assistant Secretary of Agriculture for Governmental and Public Affairs on August 23, 1982. He was the Agriculture Department's top lobbyist during the Reagan administration. Later he was appointed as Deputy Assistant Secretary for Intergovernmental Affairs in the Department of Veterans Affairs in the George H. W. Bush administration. In 1989, he became the executive director of the President's Council on Physical Fitness and Sports. In this role, he supported the Healthy People 2000 aims of reducing preventable deaths and disabilities. He also helped start local physical fitness and sports councils around the country.
target site The site or locus upon another molecule at which a protein performs a particular biochemical activity; e.g. the nucleotide motif at which a restriction endonuclease cleaves a DNA molecule, often but not necessarily the same as the enzyme's recognition site (i.e. a restriction enzyme may recognize one motif, known as a restriction site, and cleave at another).
Sources: en.wikipedia.org
Collapse occurs when the product temperature rises above its collapse or eutectic temperature during drying. The frozen matrix loses structure, producing a shrunken or melted appearance. This can slow reconstitution and may affect stability.
Karl Fischer titration is a common method, along with loss on drying and thermogravimetric analysis. Each method has different sensitivity and sample requirements. Results should be interpreted with the product's formulation and container in mind.
No. Lyophilization removes water but is not a sterilization step. Sterile products are typically filtered and filled aseptically before freezing, and container closure integrity is maintained afterward.
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.