Karl Fischer raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-04-26. Anything still debated is marked as such rather than presented as settled.
Quality control for freeze-dried lots combines visual inspection with instrumental tests. Cake appearance, color, and shrinkage are recorded against a reference, while residual moisture is measured by Karl Fischer titration or loss on drying. Thermal analysis can reveal phase transitions and crystallization events, and X-ray diffraction distinguishes amorphous from crystalline solids. Microbiological tests and container closure integrity checks are also routine for sterile products. Analytical methods must be validated for the matrix, because excipients and low moisture can affect accuracy. Open questions include how best to predict long-term stability from short-term data.
Lyophilized solids are often hygroscopic, so handling occurs in controlled low-humidity areas or glove boxes when the material is exposed. Vials remain sealed with elastomeric stoppers and aluminum crimps until use, because airborne moisture can raise residual water and shorten shelf life. The porous cake is fragile and may crack, shrink, or powder during transport. Personnel typically avoid repeated warming and cooling of sealed units, which can draw moisture through closures. These practices aim to preserve the low water content achieved during drying.
Storage conditions depend on the formulation and the intended shelf life. Many pharmaceutical and biological freeze-dried products are kept at 2–8 °C, while some stable foods and reagents tolerate room temperature. Others require −20 °C or colder to slow chemical degradation or aggregation. Protection from light and oxygen is common because oxidation can continue in the dry state. Stability studies usually monitor potency, appearance, moisture, and reconstitution time over months or years. Predictions from accelerated studies are useful but may not fully capture real-time changes.
Analytical methods for lyophilized materials include X-ray diffraction for crystallinity, differential scanning calorimetry for thermal transitions, and scanning electron microscopy for pore morphology. Moisture sorption analysis shows how the cake responds to humidity. These methods help distinguish amorphous from crystalline states and detect phase changes. Open questions remain about how pore structure changes during long-term storage and how best to predict collapse under varied conditions. Comparisons across studies are complicated by differences in formulation, cycle, and storage history.
Quality control for lyophilized products focuses on appearance, moisture level, reconstitution time, and structural integrity. A cake should be uniform, intact, and free of meltback or collapse. Moisture level is measured by Karl Fischer titration or thermogravimetric analysis. Reconstitution time reflects pore structure and formulation. Visual inspection and vial integrity checks detect cracks, stopper defects, or particulate matter. These checks are often performed on samples from each batch. They help confirm that the drying cycle performed as intended.
| Property | Value | Notes |
|---|---|---|
| Typical storage temperature | 2–8 °C | Some products tolerate room temperature or require −20 °C. |
| Residual moisture method | Karl Fischer titration | Coulometric or volumetric; specific for water. |
| Cake appearance | Uniform porous plug | Collapse, shrinkage, or meltback indicates process deviation. |
| Reconstitution time | Seconds to several minutes | Depends on cake porosity, diluent, and formulation. |
| Primary container | Glass vial with elastomeric stopper | Crimp seal limits moisture ingress. |
Handling and storage practices aim to keep the cake intact and dry. Vials are typically stored upright at controlled temperatures, often between 2 °C and 8 °C or at -20 °C for longer-term use. Reconstitution involves adding a suitable diluent and gently mixing until the solid dissolves. Shaking or rapid injection of diluent can create foam or damage sensitive molecules. Once reconstituted, the product may require refrigeration and use within a defined period.
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.
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.
Quality control for lyophilized materials includes visual inspection, residual moisture measurement, and reconstitution testing. Cake appearance can reveal process problems such as collapse, shrinkage, or meltback, although appearance alone does not prove potency. Residual moisture is commonly measured by Karl Fischer titration or by loss on drying. Reconstitution time is checked because a slow or incomplete dissolve can indicate a change in pore structure. Stability studies track these attributes over time under defined temperature and humidity conditions.
We're the ninth-safest city. How do you think I did it? How did I reach that title among the world's safest cities? Kill them all [criminals]. Duterte frequently expressed his support for the extrajudicial killings that occurred during his tenure as Davao City mayor, while alternately denying and admitting his links to them. During his post-presidency in October 2023, he admitted on his talk show program Gikan sa Masa, para sa Masa to using intelligence funds to finance the extrajudicial killings done during his time as mayor.
==== Climbing Chimborazo ==== Humboldt and Bonpland began their ascent of Chimborazo from the plain of Tapia, situated at 3,163 yards (2,892 m) above sea level. The route led through a high plateau between the eastern and western chains of the Andes, passing sparse vegetation such as cacti and Schinus molle, as well as herds of llamas. The altitude caused agricultural difficulties, since nocturnal cooling often resulted in frozen crops. Before reaching Calpi, they visited Lican, once an important settlement before the Spanish conquest, but now reduced to a small village. Indigenous people believed that wild llamas on Chimborazo descended from domesticated herds scattered after the destruction of Lican. The travelers spent the night in Calpi, which Humboldt measured at 3,452 yards (3,157 m) meters above sea level. On June 23, they began the main phase of their Chimborazo expedition, choosing a south-southeast route favored by their Indigenous guides, though only a few guides had reached the limits of the perpetual snow. Humboldt observed that Chimborazo was surrounded by step-like, grass-covered plateaus, which he compared to former lake beds and similar terrace formations in the Alps. The flora of these grasslands was dominated by grass species common in northern Europe, with few dicotyledonous herbs and limited floral diversity compared to other Andean peaks. Temperatures in the region varied strongly between day and night, and the mean annual temperature at this elevation was approximately nine degrees Celsius.
=== Obesity === It has been observed that increased number of pro-inflammatory macrophages within obese adipose tissue contributes to obesity complications including insulin resistance and diabetes type 2. The modulation of the inflammatory state of adipose tissue macrophages has therefore been considered a possible therapeutic target to treat obesity-related diseases. Although adipose tissue macrophages are subject to anti-inflammatory homeostatic control by sympathetic innervation, experiments using ADRB2 gene knockout mice indicate that this effect is indirectly exerted through the modulation of adipocyte function, and not through direct Beta-2 adrenergic receptor activation, suggesting that adrenergic stimulation of macrophages may be insufficient to impact adipose tissue inflammation or function in obesity.
=== Under physiological conditions === Under physiological conditions, ptaquiloside readily liberates glucose to produce the ptaquilodienone. The alkylation of amino acids with the dienone mostly takes place at the thiol group in cysteine, glutathione and methionine. The alkylation at the carboxylate group of each amino acid, forming the corresponding ester, is also observed to a small extent based on the previously reported literature. The dienone reacts with both adenine (majorly at N-3) and guanine (majorly at N-7) residues of DNA to form the DNA adducts. The alkylation induces spontaneous depurination and cleavage of DNA at adenine base site. In a model reaction with a deoxytetranucleotide (as shown on the right), a covalent adduct is found at a guanine residue and the N-glycosidic bond breaks to release the adduct. In 1998, Prakash, Smith and co-workers showed that the alkylation of adenine by ptaquiloside in codon 61 followed by depurination and error in the DNA synthesis resulted in the activation of H-ras proto-oncogene in the ileum of calves fed bracken.
α-ketoglutarate + NH+4 ⇄ glutamate The α-ketoglutarate family of amino acid synthesis (synthesis of glutamate, glutamine, proline and arginine) begins with α-ketoglutarate, an intermediate in the Citric Acid Cycle. The concentration of α-ketoglutarate is dependent on the activity and metabolism within the cell along with the regulation of enzymatic activity. In E. coli citrate synthase, the enzyme involved in the condensation reaction initiating the Citric Acid Cycle is strongly inhibited by α-ketoglutarate feedback inhibition and can be inhibited by DPNH as well high concentrations of ATP. This is one of the initial regulations of the α-ketoglutarate family of amino acid synthesis. The regulation of the synthesis of glutamate from α-ketoglutarate is subject to regulatory control of the Citric Acid Cycle as well as mass action dependent on the concentrations of reactants involved due to the reversible nature of the transamination and glutamate dehydrogenase reactions. The conversion of glutamate to glutamine is regulated by glutamine synthetase (GS) and is a key step in nitrogen metabolism. This enzyme is regulated by at least four different mechanisms: 1. Repression and depression due to nitrogen levels; 2. Activation and inactivation due to enzymatic forms (taut and relaxed); 3. Cumulative feedback inhibition through end product metabolites; and 4. Alterations of the enzyme due to adenylation and deadenylation.
Sources: en.wikipedia.org
=== Pricing and Profits === Throughout B.P.C. control, significant profits were made. In 1948, revenues from the island's phosphate reached $745,000. As the B.P.C. was controlled by its partner governments and was a major supplier of phosphate, it had an effective monopoly over the supply of phosphate to the markets in Australia and New Zealand, and could determine the price of phosphate delivered to those markets. The B.P.C. tied the pice for Ocean Island phosphate to the price paid for Nauru phosphate, however, the BPC would vary the price paid for phosphate. For example, around 1970, Nauru phosphate was sold to Japan at $14 and $15 a ton, but sold into the markets in Australia and New Zealand at $12.30.
=== Peptide subunit === A peptide-based subunit vaccine employs a peptide instead of a full protein. Peptide-based subunit vaccine mostly used due to many reasons,such as, it is easy and affordable for massive production. Adding to that, its greatest stability, purity and exposed composition. Three steps occur leading to creation of peptide subunit vaccine;
Revenues in the world liquid chromatography market, specifically, are expected to grow from $3.4 billion in 2007 to $4.7 billion in 2013, with a slight decrease in spending expected in 2008 and 2009 from the worldwide economic slump and decreased or stagnant spending. The pharmaceutical industry alone accounts for 35% of all the HPLC instruments in use. The main source of growth in LC stems from biosciences and pharmaceutical companies.
=== 1993 === 18 July The Real Jurassic Park, an Equinox Special and also called Jurassic Park Revisited, it looked at whether the film could happen, with American geologist Jim Kirkland of Colorado Mesa University, and Jack Horner, the scientific advisor for the film; Dale Marcellini of Washington Zoo; Ward Wheeler of the American Museum of Natural History and extracting DNA from insects encased in amber, by the PCR method; the work of Raul Cano with Hendrik Poinar at the Department of Entomology at the University of California, Berkeley; Noreen Tuross; Mary Higby Schweitzer and Jack Horner of Montana State University; Robert T. Bakker; geneticist Stephen J. O'Brien of the National Cancer Institute in Virginia; development biologist Peter Anthony Lawrence of the MRC Laboratory of Molecular Biology in Cambridge, with French biologist Jean-Paul Vincent and biochemist Rob Kay; conservation biologist Bill Toone of the California Condor Recovery Program.; Bruce H. Tiffney of University of California, Santa Barbara with Karen Chin; geologist Jim Kirkland. Narrated by Andrew Sachs, produced by Oliver Morse, jointly made with the WGBH Educational Foundation, directed by David Dugan, made by Windfall Films 15 August Bridging the Future, about the science, engineering and technology of bridge-building; the programme examines why bridges sometimes spectacularly fail, and how ever-longer and higher spans are achievable; the programme is introduced by Spike Milligan who recites the poems of William McGonagall, extolling the virtues and sorrows of the legendary Tay Bridge.
== Class A peptidomimetics == This group includes modified peptides that are mainly composed of proteogenic amino acids thereby closely resembling a natural peptide binding epitope. Introduced modifications usually aim to increase the stability of the peptide, its affinity for a desired binding partner, oral availability or cell permeability. The design of class A peptidomimetics often involves macrocyclization strategies as for example in stapled peptides.
Sources: en.wikipedia.org
He later developed the idea that humans possess a mutated form of the l-gulonolactone oxidase coding gene. Stone introduced Linus Pauling to the theory that humans needed to consume vitamin C in quantities far higher than what was considered a recommended daily intake in order to optimize health. In 2008, researchers discovered that in humans and other primates the red blood cells have evolved a mechanism to more efficiently use the vitamin C present in the body by recycling oxidized l-dehydroascorbic acid (DHA) back into ascorbic acid for reuse by the body. The mechanism was not found to be present in mammals that synthesize their own vitamin C.
=== Pharmacogenetics === Since doxepin is mainly metabolized by CYP2D6, CYP2C9, and CYP2C19, genetic variations within the genes coding for these enzymes can affect its metabolism, leading to changes in the concentrations of the drug in the body. Increased concentrations of doxepin may increase the risk for side effects, including anticholinergic and nervous system adverse effects, while decreased concentrations may reduce the drug's efficacy. Individuals can be categorized into different types of cytochrome P450 metabolizers depending on which genetic variations they carry. These metabolizer types include poor, intermediate, extensive, and ultrarapid metabolizers. Most people are extensive metabolizers, and have "normal" metabolism of doxepin. Poor and intermediate metabolizers have reduced metabolism of the drug as compared to extensive metabolizers; patients with these metabolizer types may have an increased probability of experiencing side effects. Ultrarapid metabolizers break down doxepin much faster than extensive metabolizers; patients with this metabolizer type may have a greater chance of experiencing pharmacological failure. A study assessed the metabolism of a single 75 mg oral dose of doxepin in healthy volunteers with genetic polymorphisms in CYP2D6, CYP2C9, and CYP2C19 enzymes. In CYP2D6 extensive, intermediate, and poor metabolizers, the mean clearance rates of (E)-doxepin were 406, 247, and 127 L/hour, respectively (~3-fold difference between extensive and poor).
== Medical uses == Datopotamab deruxtecan is indicated for the treatment of adults with unresectable or metastatic, hormone receptor positive, human epidermal growth factor receptor 2-negative (IHC 0, IHC1+ or IHC2+/ISH-) breast cancer who have received prior endocrine-based therapy and chemotherapy for unresectable or metastatic disease. In June 2025, the US Food and Drug Administration (FDA) expanded the indication to include the treatment of adults with locally advanced or metastatic epidermal growth factor receptor-mutated non-small cell lung cancer who have received prior epidermal growth factor receptor-directed therapy and platinum-based chemotherapy. In May 2026, the FDA expanded the indication to include the treatment of adults with unresectable or metastatic triple-negative breast cancer who are not candidates for PD-1/PD-L1 inhibitor therapy.
=== 1990s: Early development of AI and open-source software === The concept of AI dates back to the mid-20th century, when computer scientists like Alan Turing and John McCarthy laid the groundwork for modern AI theories and algorithms. An early form of AI, the natural language processing "doctor" ELIZA, was re-implemented and shared in 1977 by Jeff Shrager as a BASIC program, and soon translated to many other languages. Early AI research focused on developing symbolic reasoning systems and rule-based expert systems. During this period, the idea of open-source software was beginning to take shape, with pioneers like Richard Stallman advocating for free software as a means to promote collaboration and innovation in programming. The Free Software Foundation, founded in 1985 by Stallman, was one of the first major organizations to promote the idea of software that could be freely used, modified, and distributed. The ideas from this movement eventually influenced the development of open-source AI, as more developers began to see the potential benefits of open collaboration in software creation, including AI models and algorithms. In the 1990s, open-source software began to gain more traction, the rise of machine learning and statistical methods also led to the development of more practical AI tools. In 1993, the CMU Artificial Intelligence Repository was initiated, with a variety of openly shared software.
== History == Pharmaceutical company Johnson & Johnson's Ortho Research Laboratory wrote that case histories of his therapy, "were quite remarkable and your concepts most intriguing" and ICN Pharmaceuticals replied, "The results you have obtained with this drug in the treatment of gangrene have been most spectacular", but DeMarco was never able to commercialize the therapy beyond his own medical practice. Swiss pharmaceutical company Debiopharm S.A. replied, "Drug induced cell regeneration appears to be a revolutionary new form of treatment which is bound to be perceived as highly controversial by several regulatory agencies. We are not in a position to take the considerable time and risk involved in convincing the bureaucrats." Thus although intrigued, the pharmaceutical companies never showed a serious interest in developing his product. Regenerative medicine was a new field at the time and DeMarco likened the companies' antipathy of his discovery to the history of penicillin; although discovered in 1928, penicillin was not mass-produced until 1941 when production became a top priority World War II project to reduce the infection casualty rate. DeMarco's clinical use of a drug not approved by the U.S. Food and Drug Administration came to the attention of regulators in both New Jersey and Pennsylvania, leading to the suspension of his license to practice and the seizure of his supply of procaine hydrochloride, which investigators later found to be contaminated and mislabeled. The New Jersey Department of Health traced 64 cases of infectious hepatitis to Dr. DeMarco.
Sources: en.wikipedia.org
Karl Fischer titration is widely used because it is specific for water and works at low levels. Loss on drying is simpler but less specific, since volatile solvents or decomposition products can also be lost.
Collapse can occur when the product temperature exceeds its critical formulation temperature during drying. The porous structure then melts or shrinks, reducing reconstitution speed and sometimes altering stability.
No. Low moisture slows many degradation pathways but does not stop oxidation, hydrolysis, or physical changes completely. Storage temperature, container closure, and formulation still influence shelf life.
Karl Fischer titration is a common method, using coulometric or volumetric detection. Thermogravimetric analysis can also measure weight loss on heating. Results depend on sample handling because the dried solid can absorb moisture quickly.