A practical reference on residual moisture: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-06-24 and is reviewed periodically as new material appears.
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.
Lyophilization removes water by freezing a material and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intermediate liquid state. Because the material remains frozen during primary drying, the structure often stays porous. This porous matrix can rehydrate quickly when water is added back. The low pressure also allows vapor to leave the solid matrix without boiling.
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.
| 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 |
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.
Secondary drying removes bound water that remains after ice sublimation. Shelf temperature is raised gradually while pressure remains low, reducing water content to a target range. Over-drying can cause brittleness or electrostatic issues, while under-drying affects stability. The endpoint is often judged by pressure rise tests, temperature measurements, or water content analysis. Scale-up depends on matching heat and mass transfer across equipment sizes. Small changes in shelf temperature or pressure can alter cycle length substantially.
Residual moisture is a key quality attribute for lyophilized products. Water that remains after secondary drying can affect chemical stability, cake structure, and shelf life. Karl Fischer titration is a common method for measuring water content in the dried solid. The target range varies by product, but many biologics are dried to between 0.5% and 3% water by weight. Acceptable limits are set during development and confirmed by stability studies.
Stability studies examine how temperature, humidity, and time influence a lyophilized product. Accelerated conditions provide early information about degradation pathways, while long-term studies support shelf-life claims. The glass transition temperature of the dried formulation can indicate its physical stability, and storage above this temperature may increase molecular mobility and lead to collapse or aggregation. Container closure integrity also matters because moisture or oxygen ingress can degrade the product, so vial stoppers and seals are part of the quality system.
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 is a dehydration technique in which a product is frozen and the solvent is removed under reduced pressure. The low pressure allows ice to sublimate directly into vapor without passing through a bulk liquid phase. This differs from conventional drying, where heat drives evaporation and can damage heat-sensitive structures. The process is used for biological materials, pharmaceutical formulations, and some foods. Its main advantage is preservation of porous structure and rapid reconstitution.
Lyophilized products are typically hygroscopic and require protection from moisture during storage. Manufacturers seal them in glass vials, often under vacuum or an inert gas such as nitrogen. The container closure system, including the stopper and crimp seal, must prevent water vapor ingress. Storage temperature varies from controlled room temperature to refrigerated or frozen conditions, depending on the formulation. Humidity-controlled environments are essential because even brief exposure to ambient air can degrade the product.
Stability of a lyophilized product depends on its glass transition temperature, the temperature at which the amorphous cake transitions from a glassy to a rubbery state. Storage below this temperature minimizes molecular mobility and slows chemical degradation. If the storage temperature exceeds the glass transition temperature, the cake may collapse, shrink, or become sticky. Accelerated stability studies at elevated temperatures and humidity help predict shelf life, but they do not always reflect real-time behavior. Residual moisture content also plays a critical role in long-term stability.
Reconstitution involves adding a suitable diluent, often sterile water or a buffer, to the dried cake. Gentle swirling or inversion helps dissolve the material without creating excessive foam. The time required for complete dissolution can range from seconds to several minutes and depends on the cake structure and the diluent. Improper reconstitution, such as vigorous shaking or using the wrong diluent, can cause protein aggregation or loss of activity. After reconstitution, the product may have a limited shelf life and should be used according to its labeling.
Paetongtarn Shinawatra (born 21 August 1986) is a Thai politician and businesswoman who served as the 31st prime minister of Thailand from 2024 until her removal from office in 2025. She led the Pheu Thai Party from 2023 until her resignation in 2025. Paetongtarn was born into the prominent Shinawatra family as the youngest child of the 23rd prime minister Thaksin Shinawatra and niece of the 28th prime minister Yingluck Shinawatra. After graduating from Chulalongkorn University and the University of Surrey, she began a career in business before entering politics. In 2024, Paetongtarn became the youngest prime minister of Thailand, the first to be the child of a previous prime minister, and the second woman to hold the position, following her aunt. She has also served as Minister of Culture since 30 June 2025. On 1 July 2025, Paetongtarn was suspended from office by the Constitutional Court over a leaked phone call between her and former Cambodian leader Hun Sen, in which critics say she appeared deferential to him, in the wake of the border conflict between Thailand and Cambodia. The deputy prime minister, Suriya Juangroongruangkit, took over as Thailand's acting leader. On 29 August 2025, the Constitutional Court ruled 6–3 against Paetongtarn, officially removing her from office.
== Organoleptic characteristics == The organoleptic characteristics of edible insects vary between species and are influenced by environment. For instance, aquatic edible insects such as water boatmen (family Corixidae) and dragonfly larvae have a fish flavor, while diving beetles taste more like clams. Environment is not always a predictor of flavor, as terrestrial edible insects may also exhibit fish-like flavors (e.g. crickets, grasshoppers). Over 400 volatile compounds responsible for the aroma and flavor of edible insects have been identified. Pheromone chemicals contribute to pungent aromas and flavors in some species and the presence of organic acids (like formic acid in ants) makes some species taste sour. Organoleptic characteristics are dependent on the development stage of the insect (egg, larva, pupa, nymph, or adult) and may change significantly as an insect matures. For example, texture can change from soft to crunchy as an insect develops from larva to adult due to increasing exoskeletal chitin. Cooking method is considered the strongest influence on the final flavor of edible insects. Wet-cooking methods such as scalding or steaming remove pheromones and odor compounds, resulting in a milder flavor, while dry-cooking methods such as frying and roasting introduce more complex flavors. The table below provides common flavor descriptors for a selection of edible insects. Flavors will vary with preparation method (e.g. raw, dried, fried, etc.). Insect development stage is provided when possible.
anticodon A series of three consecutive nucleotides within a transfer RNA which complement the three nucleotides of a codon within an mRNA transcript. During translation, each tRNA recruited to the ribosome contains a single anticodon triplet that pairs with its complementary codon from the mRNA sequence, allowing each codon to specify a particular amino acid to be added to the growing peptide chain. Anticodons containing inosine in the first position are capable of pairing with more than one codon due to a phenomenon known as wobble base pairing.
=== Novel polymerases === Neither the XNA nor the unnatural bases are recognized by natural polymerases. One of the major challenges is to find or create novel types of polymerases that will be able to replicate these new-to-nature constructs. In one case a modified variant of the HIV-reverse transcriptase was found to be able to PCR-amplify an oligonucleotide containing a third type base pair. Pinheiro et al. (2012) demonstrated that the method of polymerase evolution and design successfully led to the storage and recovery of genetic information (of less than 100bp length) from six alternative genetic polymers based on simple nucleic acid architectures not found in nature, xeno nucleic acids.
=== British Army deployed === When war with the Boers seemed imminent in September 1899, a Field Force, referred to as the Army Corps was mobilised and sent to Cape Town. It was "about the equivalent of the I Army Corps of the existing mobilization scheme" and was placed under the command of Gen Sir Redvers Buller, general officer commanding-in-chief of Aldershot Command. In South Africa the corps never operated as such and the 1st, 2nd, 3rd divisions were widely dispersed. Speaking to Alistair McAlpine in the 1950s, participating soldier Lord Morley (1878–1962) recounted his deployment from Southampton:
Sources: en.wikipedia.org
=== Biomolecular research === Researchers often use heterologous expression techniques to study protein interactions. For example, bacteria has been optimized in the heterologous expression and biosynthesis of nitrogenase through NifEN. This is able to be expressed and engineered in E.coli. Through this host, it remains exceedingly challenging to heterologously express a complex, heteromultimeric metalloprotein like NifEN with a full complement of subunits, metalloclusters, and functionality. The NifEN variant engineered in this bacterial host can retain its cofactor efficacy at analogous cofactors-binding sites, which provide proof for heterologous expression and encourage future investigation of this metalloenzyme. Additionally, there have been recent reports of the utility of new filamentous fungal systems in the production of industrial proteins. Advantages include high transformation frequencies, the production of proteins at neutral pH, low viscosity of the fermentation broth due to strain selection for a nonfilamentous format and short fermentation times. Many human gene products, such as albumin, IgG, and interleukin 6, have been expressed in heterologous systems with varying degrees of success. Inconsistent results have hinted at a shift from gene-by-gene studies to a whole-organism approach to post-translational modification. Oocytes are readily optimized for their large size and translational capacity, which is able to observe integrated cell responses.
===== North America ===== Canada - DMT is classified as a Schedule III drug under the Controlled Drugs and Substances Act, but is legal for religious groups to use. In 2017 the Santo Daime Church Céu do Montréal received religious exemption to use ayahuasca as a sacrament in their rituals. United States - DMT is classified in the United States as a Schedule I drug under the Controlled Substances Act of 1970. In 2019, it was decriminalized, along with other naturally derived psychedelics, in the city of Oakland after a campaign by Decriminalize Nature.
=== 2004 === 24 June Human Face Transplant, an Equinox Special, about Jacqui Saburido, after a drunk driver hit her car, work takes place at the University of Louisville School of Medicine; featured the work of John Barker in Kentucky, and his colleague Joe Banis; the French plastic surgeon Laurent Lantieri. Narrated by Lucy Briers, directed by Iain Scollay
== Mechanism of action == After the venom has entered the body via the wasp sting, it enters the bloodstream, where it will be diluted in the blood and distributed through the organism. Pompilidotoxins target the sodium channels, so the toxin reaches its target sites via the distribution by the bloodstream. Research by Sahara et.al. (2000) has suggested that α-PMTX might slow or block the conformational changes that are necessary for the fast inactivation of voltage gated sodium channels. This causes the intracellular sodium concentration to increase. They hypothesise that this effect could be caused by the α-PMTX binding to similar elements of the neurotoxin receptor site 3 on the extracellular surface of the sodium channel. α-PMTX also enhances both the inhibitory postsynaptic potentials (IPSPs) and the excitatory postsynaptic potentials (EPSPs). The eventual paralysis of the spider is caused by the prolonged membrane depolarization, which is induced by the EPSPs. However, when the fast inactivation is slowed or blocked by channel blocker like PMTX, the membrane will not repolarize properly, but stay in a depolarized state instead. The long-lasting depolarisation leads to paralysis. A study by Konno et.al. (2001) has found that the positively charged amino acids in β-PMTX likely bind to the Glu-1616 site on the D4S3-S4 loop of the sodium channel. This indicates that the positive charges of PMTXs are a crucial part of the toxins, as they are likely involved in the electrostatic bonding between the toxin and the sodium channel.
Sources: en.wikipedia.org
=== Design of scientific investigations === Aarons has defined pharmacokinetics (PK) as the study of the complex chain of events that links a dose of drugs administered to a patient and the expected effect or response. PK is based on analysing the concentration of drugs and tracking how they are absorbed, distributed, metabolised and excreted within the patient. Some of his work has involved using optimal design theory to explore what makes a successful scientific investigation for pharmacokinetic studies and has said that this "involves the selection and a careful balance of a number of design factors, including the number and location of measurement times and the number of subjects to include in the study." According to Aarons, population pharmacokinetics studies which focus on what happens to the substances administered to a patient would need specific design factors that apply "statistical experimental design principles to non-linear population pharmacokinetic models." A later paper co-authored by Aarons, reviews the different approaches to optimal design of population pharmacokinetic and pharmacodynamic experiments and notes that some of the options may raise concerns at to their practicality. The paper did, however, conclude "that as the awareness about the benefits of this approach increases, more people will embrace it and ultimately will lead to more efficient population pharmacokinetic and pharmacodynamic experiments."
== 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.
The objective of an atomic bomb is to produce a device, according to Serber, "...in which energy is released by a fast neutron chain reaction in one or more of the materials known to show nuclear fission." According to Rhodes, "Untamped, a bomb core even as large as twice the critical mass would completely fission less than 1 percent of its nuclear material before it expanded enough to stop the chain reaction from proceeding. Tamper always increased efficiency: it reflected neutrons back into the core and its inertia...slowed the core's expansion and helped keep the core surface from blowing away." Rearrangement of the core material's subcritical components would need to proceed as fast as possible to ensure effective detonation. Additionally, a third basic component was necessary, "...an initiator—a Ra + Be source or, better, a Po + Be source, with the radium or polonium attached perhaps to one piece of the core and the beryllium to the other, to smash together and spray neutrons when the parts mated to start the chain reaction." However, any bomb would "necessitate locating, mining and processing hundreds of tons of uranium ore...", while U-235 separation or the production of Pu-239 would require additional industrial capacity.
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.
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.