If you have been reading about LC-MS/MS and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2026-04-05. Numbers and descriptions here follow the published literature rather than marketing material.
Common analytical approaches include enzymatic recycling assays, high-performance liquid chromatography, and mass spectrometry. Enzymatic recycling measures total glutathione after converting GSSG back to GSH, while separation methods can quantify GSH and GSSG separately. Derivatization may be used to improve detection or stability during analysis. LC-MS/MS offers high specificity and can distinguish glutathione from related thiols and adducts. Each method has different sensitivity, throughput, and susceptibility to interference, so method selection depends on the study question and sample matrix.
For solid glutathione reagents, storage at low temperature and protection from moisture and light are typical precautions. Aqueous solutions can oxidize over time, and pH affects stability; alkaline conditions generally promote thiol oxidation. Some protocols prepare fresh solutions, while others use antioxidants or chelators to limit metal-catalyzed oxidation. Purity and counterion content can vary among commercial preparations, affecting concentration calculations. Certificates of analysis and validated assays help verify identity and purity.
Glutathione is a small tripeptide built from glutamate, cysteine, and glycine. The peptide bond between glutamate and cysteine uses the gamma-carboxyl group, a linkage that resists ordinary peptidases. Cells make it in two ATP-dependent steps: gamma-glutamylcysteine synthetase joins glutamate and cysteine, then glutathione synthetase adds glycine. The pathway is feedback-inhibited by glutathione itself, so intracellular levels tend to stay within a narrow range. Because cysteine is often limiting, sulfur amino acid supply influences how much glutathione a cell can produce.
In its reduced form, glutathione carries a sulfhydryl group that can donate electrons. This property lets it act as a major cellular antioxidant and redox buffer. Glutathione peroxidase uses it to reduce hydrogen peroxide and lipid peroxides, while glutathione reductase regenerates the reduced form using NADPH. The ratio of reduced glutathione to glutathione disulfide is widely used as an indicator of oxidative stress, though the ratio changes with compartment, cell type, and sample handling. Oxidized glutathione can also form mixed disulfides with proteins, affecting their activity.
| Property | Value | Notes |
|---|---|---|
| Typical analytical method | LC-MS/MS, HPLC, or enzymatic recycling | Choice depends on whether total, reduced, or oxidized glutathione is measured. |
| Sample stabilization | Acidification or thiol alkylation | Helps limit conversion of GSH to GSSG after collection. |
| Solution stability | Limited at room temperature | Oxidation and pH-dependent degradation can occur. |
| Storage of solid | -20 °C, desiccated, protected from light | Common for research reagents; follow supplier instructions. |
| Common interference | Other thiols and metal ions | Can affect separation or enzymatic detection. |
Samples for glutathione analysis require careful handling because the compound oxidizes readily and can be consumed by enzymes after collection. Blood is often treated with acid or thiol-blocking agents soon after draw, and plasma should be separated quickly from red blood cells. Tissues are usually snap-frozen or extracted immediately. Aqueous solutions of glutathione are less stable than dry powder and degrade faster at neutral or alkaline pH, in light, or with dissolved oxygen. Repeated freeze-thaw cycles also reduce reliability.
Quality control for glutathione materials checks identity, assay, purity, water content, and disulfide content. Commercial products vary from research-grade powder to dietary supplements, and labels may not distinguish reduced from oxidized forms. In the United States, oral glutathione is commonly sold as a dietary supplement rather than an approved drug, while injectable forms fall under different rules and may require a prescription. Regulatory status differs by country. Analytical certificates, when available, help verify what a material contains, but independent testing remains important for interpretation.
Laboratory measurement of glutathione typically starts with rapid acid extraction to prevent oxidation and enzymatic degradation. Common methods include enzymatic recycling assays, high-performance liquid chromatography, and liquid chromatography coupled with mass spectrometry. The recycling assay uses glutathione reductase and a thiol-reactive colorimetric or fluorescent reagent, measuring total glutathione after converting disulfide forms. Chromatographic methods can separate reduced and oxidized forms, which helps when the redox ratio is the target. Choice of method affects sensitivity, specificity, and the amount of sample needed.
Because GSH is central to redox balance, its status is studied in aging, liver disease, neurodegenerative conditions, and metabolic disorders. Observational studies often report lower GSH or higher GSSG in affected tissues, but such associations do not establish that raising glutathione changes disease outcomes. Oral glutathione is digested into amino acids, and whether intact absorption occurs remains debated; precursors such as N-acetylcysteine and cysteine donors are also investigated. Regulatory agencies generally treat glutathione as a dietary supplement, not an approved drug, and clinical claims require evidence from controlled trials.
Glutathione is a small tripeptide composed of glutamate, cysteine, and glycine, with the unusual gamma-glutamyl linkage between glutamate and cysteine. Its cysteine thiol group makes it a major non-enzymatic antioxidant in cells. The reduced form, GSH, predominates in most intracellular compartments, while the oxidized disulfide form, GSSG, is produced when GSH reduces reactive oxygen species. Intracellular concentrations often reach millimolar levels, whereas plasma concentrations are much lower, typically in the low micromolar range. This gradient reflects active synthesis, transport, and consumption rather than passive distribution.
Synthesis occurs in two ATP-dependent steps: glutamate-cysteine ligase joins glutamate and cysteine to form gamma-glutamylcysteine, and glutathione synthetase adds glycine to complete the tripeptide. The pathway is feedback-inhibited by GSH and limited by cysteine availability, so cysteine supply often constrains production. Once formed, GSH participates in redox buffering, xenobiotic conjugation, and protein glutathionylation. Glutathione peroxidase uses GSH to reduce hydrogen peroxide and lipid peroxides, yielding GSSG, while glutathione reductase regenerates GSH using NADPH. Glutathione S-transferases conjugate electrophiles to GSH, supporting detoxification and excretion.
Commercial glutathione is available in research-grade, food-grade, and supplement-grade forms, and purity specifications differ accordingly. Certificates of analysis commonly report identity by nuclear magnetic resonance or mass spectrometry, purity by HPLC, residual solvents, and heavy metals. Reference standards with assigned purity support calibration, while isotopically labeled glutathione can serve as an internal standard for mass spectrometry. For supplements, label claims may not be independently verified, and regulatory oversight varies by country. Verification often involves third-party testing for identity, potency, and contaminants.
Quantifying glutathione requires distinguishing GSH from GSSG and preventing oxidation during sample preparation. Common approaches include the enzymatic recycling assay, often called the Tietze method, which measures total glutathione after converting GSSG to GSH. HPLC with ultraviolet or fluorescence detection and LC-MS/MS can separate and quantify both forms, sometimes after derivatization of the thiol group. Blood, plasma, and tissue samples differ in matrix and baseline concentrations, so method validation must account for recovery, linearity, and interference. No single assay is universally standard.
(2026) report evidence from the study of carbon and oxygen stable isotope compositions of mammal fossils from the Pinturas Formation (Argentina) indicative of presence of a diverse range of habitats in Patagonia during the Miocene, and interpret the diversity of the primate assemblage from the studied formation as likely linked to habitat diversity. Cooke et al. (2026) report the first discovery of mandibular remains of Stirtonia victoriae from the La Victoria Formation (Colombia), and interpret their anatomy as indicative of leaf-eating adaptations of the studied monkey. Urciuoli et al. (2026) determine the phylogenetic relationships of early members of Catarrhini on the basis of the study of the semicircular canal and vestibule shape in Saadanius, Pliobates, Ekembo and Victoriapithecus, interpret Saadanius as most likely to be a stem catarrhine that evolved ossified tubular ectotympanic independently from crown catarrhines, and interpret pliopithecoids as most likely to be stem catarrhines closer to the crown group than Saadanius. Arias-Martorell et al. (2026) report evidence of similarities of shape of the radial head of Pliobates cataloniae and extant apes, and interpret Pliobates as better adapted to climbing than to behaviors involving forelimb-dominated suspension. Arias-Martorell et al. (2026) compare the shape of the distal part of the humerus of Pliobates cataloniae and other extinct and extant simians, and interpret Pliobates as unlikely to perform acrobatic suspensory behaviors seen in extant gibbons.
== See also == Alexis St. Martin – Canadian subject of digestion experiments (1802–1880) Fistulated cow M. Ijaiya's technique – Surgical procedure to close juxtacervical vesicovaginal fistulae Obstetric fistula Stoma (medicine)
Viscosity is measured with various types of viscometers and rheometers. Close temperature control of the fluid is essential to obtain accurate measurements, particularly in materials like lubricants, whose viscosity can double with a change of only 5 °C. A rheometer is used for fluids that cannot be defined by a single value of viscosity and therefore require more parameters to be set and measured than is the case for a viscometer. For some fluids, the viscosity is constant over a wide range of shear rates (Newtonian fluids). The fluids without a constant viscosity (non-Newtonian fluids) cannot be described by a single number. Non-Newtonian fluids exhibit a variety of different correlations between shear stress and shear rate. One of the most common instruments for measuring kinematic viscosity is the glass capillary viscometer. In coating industries, viscosity may be measured with a cup in which the efflux time is measured. There are several sorts of cup—such as the Zahn cup and the Ford viscosity cup—with the usage of each type varying mainly according to the industry. Also used in coatings, a Stormer viscometer employs load-based rotation to determine viscosity. The viscosity is reported in Krebs units (KU), which are unique to Stormer viscometers. Vibrating viscometers can also be used to measure viscosity. Resonant, or vibrational viscometers work by creating shear waves within the liquid. In this method, the sensor is submerged in the fluid and is made to resonate at a specific frequency.
Sources: en.wikipedia.org
== UK appliance safety recalls == Following its 2014 acquisition of Indesit, Whirlpool identified a fire risk affecting certain vented and condensing tumble dryers sold in the United Kingdom under the Hotpoint, Indesit, Creda, Swan and Proline brands. The affected models had been manufactured between April 2004 and September 2015; lint could accumulate and come into contact with a heating element, creating a fire risk. Whirlpool told the House of Commons Business, Energy and Industrial Strategy Committee that 5.3 million affected machines had been manufactured for the UK market. Whirlpool began a modification programme in November 2015 rather than a full recall. Owners were initially advised that affected dryers could continue to be used under specified precautions, but the advice was changed in early 2017 to tell consumers not to use unmodified machines. In August 2016, a fire at Shepherds Court in Shepherd's Bush was attributed by the London Fire Brigade to an Indesit tumble dryer covered by Whirlpool's corrective-action programme. A House of Commons committee later criticised the decision not to initiate a full recall and the pace of the modification programme. In April 2019, the Office for Product Safety and Standards (OPSS) concluded that the risk of harm or injury from lint fires in dryers that had been modified was low, but required Whirlpool to improve aspects of its risk management and communication with consumers. Following further intervention by OPSS, Whirlpool agreed in July 2019 to recall remaining unmodified affected tumble dryers.
== Recalls and safety corrections == In 2014, Tandem recalled selected lots of t:slim cartridges because leaks could cause too much or too little insulin to be delivered. In 2024, the FDA classified a correction of version 2.7 of the iOS t:connect app as a Class I recall. Repeated app crashes and automatic relaunches could increase Bluetooth communication, drain a connected t:slim X2 battery and interrupt insulin delivery. The action covered 85,863 distributed app installations; the FDA reported 224 injuries and no deaths as of April 15, 2024. Tandem released updated app versions and advised users to monitor pump batteries. In April 2025, the FDA classified a correction of Control-IQ+ software version 7.9 as a Class I recall. A defect affecting 85 pumps could incorrectly interpolate glucose values after gaps in CGM data and cause too much or too little insulin to be delivered. Tandem instructed affected users to turn off Control-IQ+ until the software was corrected. Later in 2025, Tandem issued two further corrections that the FDA classified as Class I recalls. One covered 171,750 t:slim X2 pumps whose speakers could fail and stop insulin delivery; the company reported 59 injuries and no deaths. The other covered 17,745 Mobi pumps that could falsely detect vibration-motor failure and enter a non-operational state, stopping insulin delivery and CGM sessions. Tandem directed users to install corrected pump software.
== External links == Actin Staining Techniques (Live and Fixed Cell Staining) Eukaryotic Linear Motif resource motif class LIG_Actin_RPEL_3 Eukaryotic Linear Motif resource motif class LIG_Actin_WH2_1 Eukaryotic Linear Motif resource motif class LIG_Actin_WH2_2 3D macromolecular structures of actin filaments from the EM Data Bank(EMDB)
=== Cathinones === Cathinones include some stimulants and entactogens, which are derivatives of cathinone. They feature a phenethylamine core with an alkyl group attached to the alpha carbon, and a ketone group attached to the beta carbon, along with additional substitutions.
Sources: en.wikipedia.org
It was suggested by Nichols as a more economical and accessible alternative to psilocybin for use in scientific research, as the synthesis of psilocybin is more challenging and as psilocybin is a controlled substance. 4-AcO-DMT was first detected as a designer drug in Europe in 2009. It became increasingly prevalent as a recreational drug in the 2010s and has been the most commonly used novel tryptamine. In the 2020s, 4-AcO-DMT became widely encountered in the form of mushroom edibles in the United States as an alternative to psilocybin. Relatedly, it has sometimes been referred to as "synthetic shrooms". So-called "mushroom edibles" sold at places such as gas stations and headshops may contain 4-AcO-DMT, Amanita muscaria mushroom extract, or unrelated drugs such as bath salts, and have been linked to severe and potentially deadly adverse effects. 4-AcO-DMT is not scheduled under United States law or any international drug schedules, including the United Nations 1971 Convention on Psychotropic Substances, making it a potentially more accessible alternative to psilocybin for research. It can be imported and possessed for research in the United States if labeled "for research purposes only not approved by the FDA for human consumption,", however marketing or distributing it to humans as psilocybin, a schedule 1 narcotic carries the same penalties of intent.
Extended breastfeeding usually means breastfeeding beyond the age of 12 to 24 months, depending on the culture. The American Academy of Family Physicians states that "health outcomes for mothers and babies are best when breastfeeding continues for at least two years. The American Academy of Pediatrics recommends that mothers nurse for the first 12 months and "thereafter for as long as mother and baby desire." The World Health Organization recommends breastfeeding up to age 2 "or beyond." Breast milk is known to contain lactoferrin (Lf), which protects the infant from infection caused by a wide range of pathogens. The amount of Lf in breast milk is lactation-stage related. One study evaluated Lf concentration in prolonged lactation from the first to the 48th month postpartum. It was found to be at the highest level in colostrum, dropped to the lowest level during 1 – 12 months of lactation, and then increased significantly during the 13–24 months of lactation, close to the Lf concentration in colostrum. At over 24 months, the level dropped, though not significantly.
Charcot–Marie–Tooth disease was first discovered in 1886 by three scientists: Jean-Martin Charcot (1825–1893) and his assistant Pierre Marie (1853–1940), along with the English doctor Howard Henry Tooth (1856–1925). In their original publication, titled “Concerning a Special Form of Progressive Muscular Atrophy,” Charcot and Marie acknowledged that similar cases had been previously published in medical literature. Their findings described hereditary neuropathy, marked by gradual muscle wasting and diminished sensation in the extremities. This crucial discovery helped establish CMT as a distinct clinical entity, differentiating it from other neuromuscular conditions such as muscular dystrophies. Over the years, advancements in neurogenetics have led to the identification of various genetic mutations responsible for the disease, significantly enhancing our understanding of its pathogenesis and classification. Charcot also noted that prior descriptions of the disease were neither objective nor thorough. Most of the earlier accounts merely mentioned that CMT was hereditary. As a result, Charcot felt it was essential to provide a comprehensive description of the disease, ensuring that it received the attention it deserved. In 2010, Charcot–Marie–Tooth (CMT) disease became one of the first conditions in which the precise genetic cause was identified in an individual patient using whole-genome sequencing. This groundbreaking discovery was made by scientists affiliated with the Charcot–Marie–Tooth Association (CMTA).
== Further reading == Biochemistry textbook reference, from the NCBI bookshelf – Jeremy M. Berg; John L. Tymoczko; Lubert Stryer (eds.). "18.4. A Proton Gradient Powers the Synthesis of ATP". Biochemistry (5th ed.). W. H. Freeman. Archived from the original on August 3, 2007. A set of experiments aiming to test some tenets of the chemiosmotic theory – Ogawa S, Lee TM (August 1984). "The relation between the internal phosphorylation potential and the proton motive force in mitochondria during ATP synthesis and hydrolysis". The Journal of Biological Chemistry. 259 (16): 10004–10011. doi:10.1016/S0021-9258(18)90918-X. PMID 6469951.
The study Fat Grafting to the Breast Revisited: Safety and Efficacy (2007) indicates that the autologous fat was harvested by liposuction with a 10-ml. syringe attached to a two-hole Coleman harvesting cannula; after centrifugation, the refined breast filler-fat was transferred to 3-ml. syringes. Blunt infiltration cannulas were used to inject the body-fat through 2-mm. incisions; the blunt cannula injection method allowed greater dispersion of small aliquots (equal measures) of body-fat, and reduced the possibility of intravascular fat injection. The 2-mm. incisions were positioned to allow the injection of the fat-grafts from two injection sites; a 0.2 ml fat volume was injected with each withdrawal of the cannula. The breast-contours were realized by layering the fat-grafts at different levels within the breast hemisphere. The fat-graft injection technique allows the plastic surgeon to accurately define the contour of the breast — from the chest wall to the breast-skin envelope— with subcutaneous fat-grafts to the superficial planes of the breast. The greater control in sculpting the contour of the breast is unlike the global augmentation realised with an implant below the breast or below the pectoralis major muscle, respectively expanding the retromammary space and the retropectoral space. The greatest proportion of the grafted fat usually is infiltrated to the pectoralis major muscle, then to the retropectoral space, and to the prepectoral space (before and behind the pectoralis major muscle).
Sources: en.wikipedia.org
Preanalytical factors such as sample type, time to processing, and stabilization method can change GSH and GSSG amounts. Analytical method and calibration also contribute to variation. Comparing absolute values across studies requires caution.
These assays typically measure total glutathione after oxidizing or reducing steps convert GSSG to GSH. A colorimetric or fluorometric signal is proportional to the recycling reaction. They generally do not report GSH and GSSG separately unless additional steps are used.
Solutions are often prepared fresh and kept cold, with protection from light and oxygen exposure. Chelating agents may reduce metal-catalyzed oxidation. Storage recommendations vary by buffer, pH, and concentration, so protocol-specific guidance should be followed.
It is a tripeptide of glutamate, cysteine, and glycine. The glutamate-cysteine bond is unusual because it forms through the gamma-carboxyl group.