LC-MS/MS 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 2025-08-22. Where a claim depends on a specific study, the study is described rather than over-claimed.
Measuring glutathione in biological samples requires attention to oxidation and matrix effects. High-performance liquid chromatography with ultraviolet or fluorescence detection can separate reduced and oxidized forms after derivatization. Liquid chromatography with tandem mass spectrometry offers higher specificity and can quantify glutathione alongside related thiols. Because glutathione can oxidize during sample handling, many protocols use rapid acidification with metaphosphoric acid or sulfosalicylic acid. Internal standards help correct for losses during extraction and analysis.
Enzymatic recycling assays provide a complementary approach for total glutathione. In these methods, glutathione reductase reduces oxidized glutathione while a thiol-reactive reagent, such as 5,5'-dithiobis(2-nitrobenzoic acid), produces a colored product. The reaction cycles between reduced and oxidized forms, amplifying the signal. Spectrophotometric or fluorometric detection can then estimate concentration. Distinguishing reduced glutathione from glutathione disulfide often requires separate aliquots, masking agents, or chromatographic separation, and the choice affects reported values.
Storage conditions strongly influence glutathione stability. The solid reduced form is commonly kept desiccated at or below minus twenty degrees Celsius, protected from light and moisture. Aqueous solutions are less stable because the thiol group reacts with dissolved oxygen, and oxidation accelerates at neutral or alkaline pH. Acidic solutions and oxygen-free handling can slow degradation, but repeated freeze-thaw cycles should be avoided. Researchers often verify concentration before use, because apparent losses can arise from oxidation or water uptake.
Glutathione is most stable as a dry powder stored cool and dry, but its thiol group is readily oxidized in solution. Aqueous preparations at neutral or alkaline pH lose GSH faster because the thiolate form reacts with dissolved oxygen and metal ions. Acidic conditions, chelating agents, and oxygen exclusion can slow oxidation, while repeated freeze-thaw cycles promote degradation. Light exposure and trace metals also contribute to loss. Laboratories typically validate stability for their own matrices because degradation rates depend on pH, temperature, concentration, and container materials.
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.
| Property | Value | Notes |
|---|---|---|
| Solid storage temperature | -20 °C | Desiccated, protected from light |
| Solution stability | Hours to days at neutral pH | Acidic pH and low oxygen slow oxidation |
| Oxidized form | Glutathione disulfide (GSSG) | Formed by thiol oxidation |
| Typical analytical method | LC-MS/MS or enzymatic recycling | Choice depends on matrix and specificity |
| Thiol pKa | Approximately 9.2 | Influences reactivity at physiological pH |
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.
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.
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.
Measuring glutathione in biological samples requires attention to oxidation, because GSH can convert to GSSG after sample collection. Blood and plasma samples are often treated with acid or alkylating agents to preserve the reduced form. Without stabilization, apparent GSH concentrations can fall while GSSG rises. Differences in sample type, handling delay, and deproteinization method can produce results that are not comparable across studies. Reporting preanalytical details is therefore important for interpreting findings.
Expectations diminished as a result of numerous failed replications, the retraction of several previously reported positive replications, and the identification of methodological flaws and experimental errors in the original study. By late 1989, most scientists considered cold fusion claims dead, and cold fusion subsequently gained a reputation as pathological science. In 1989 the United States Department of Energy (DOE) concluded that the reported results of excess heat did not present convincing evidence of a useful source of energy and decided against allocating funding specifically for cold fusion. A second DOE review in 2004, which looked at new research, reached similar conclusions and did not result in DOE funding of cold fusion. Presently, since articles about cold fusion are rarely published in peer-reviewed mainstream scientific journals, they do not attract the level of scrutiny expected for mainstream scientific publications. Some interest in cold fusion has continued through the decades—for example, a Google-funded failed replication attempt was published in a 2019 issue of Nature. A small community of researchers continues to investigate it, often under the alternative designations low-energy nuclear reactions (LENR) or condensed matter nuclear science (CMNS).
=== Early life === Logan Roy's early life is elaborated in an animation made for the episode "Dundee" that was eventually cut and replaced by a scene where Kendall performs a rap song exalting his father. Roy was born on 29 October in Dundee, Scotland, United Kingdom in 1938, in a working-class family. His father died from a brain hemorrhage several years later. During World War II, he was sent with his older brother Ewan to live with his uncle Noah in Quebec, Canada. In the episode "Church and State," Ewan recalls in a eulogy that during the journey, the two brothers were stranded at sea after their ship's engines had failed. Fearing attacks by German submarines, the two did not speak or move for three days. While Logan was enrolled at a boarding school, his baby sister, Rose, arrived to Canada. After falling ill and returning home, Rose died of polio, which would cause immense guilt for the rest of Logan's life as he believed he was responsible. In the episode "Austerlitz," he claims that Noah was physically abusive towards him throughout his childhood, which is indicated by scars across Logan's back.
== Function == Epiplakin's role in maintaining keratin intermediate filament organization suggests that dysregulation of epiplakin expression or function may contribute to epithelial fragility or altered wound-healing responses, as indicated by accelerated wound closure observed in epiplakin-depleted corneal epithelial cells.
=== Identification of the chain === The length, gauge and number of drive links is punched on the side of the saw bar. This information can be found near the saw head. Since the saw bar should be turned 180 degrees between sharpenings, the punched information can be towards the saw power head or outside. It is also often found on an identification label under the handle depending on your brand of chainsaw.
Sources: en.wikipedia.org
63Ni, with a half-life of 100.1 years, is useful in krytron devices as a beta particle (high-speed electron) emitter to make ionization by the keep-alive electrode more reliable. It is being investigated as a power source for betavoltaic batteries. Around 27% of all nickel production is used for engineering, 10% for building and construction, 14% for tubular products, 20% for metal goods, 14% for transport, 11% for electronic goods, and 5% for other uses. In 2025, QuesTek Innovations and Stoke Space developed a nickel-based superalloy for additive manufacturing and extreme high-pressure, high-temperature oxygen environments. Its characteristics allow the material to be used for fully reusable spacecraft launch systems, it can withstand the full-flow staged combustion rocket engine Zenith. Raney nickel is widely used for hydrogenation of unsaturated oils to make margarine, and substandard margarine and leftover oil may contain nickel as a contaminant. Forte et al. found that type 2 diabetic patients have 0.89 ng/mL of Ni in the blood relative to 0.77 ng/mL in control subjects. Nickel titanium is an alloy of roughly equal atomic percentages of its constituent metals which exhibits two closely related and unique properties: the shape memory effect and superelasticity.
== External links == Fankhauser's Page on Rennet history and use Appendix D - Assessment of filamentous fungi - Qualified Presumption of Safety FDA-registration of recombinant chymosin Recombinant Chymosin Cheese Yield Experiments and Proteolysis by Milk-Clotting Enzymes Validation of recombinant and bovine chymosin by mass spectrometry Native and Biotechnologically Engineered Plant Proteases with Industrial Applications
D* → D + hν For example, A could be luminol and B could be hydrogen peroxide. D would be 3-aminophthalate (3-APA). In theory, one photon of light should be given off for each molecule of reactant. In practice, the yield ("quantum efficiency") is often low owing to side reactions. Chemiluminescence differs from fluorescence or phosphorescence in that the electronic excited state is the product of a chemical reaction rather than of the absorption of a photon. It is the antithesis of a photochemical reaction, in which light is used to drive an endothermic chemical reaction. Instead, here light is generated from a chemically exothermic reaction. The chemiluminescence might be also induced by an electrochemical stimulus and in that case, it is called electrochemiluminescence.
Sources: en.wikipedia.org
In response to these developments, the United States has begun a re-balancing of strategic forces out of Europe and into the Asia–Pacific. Major events of the period are generally agreed to have included the September 11 attacks and ensuing war on terror, the militarization of the war on drugs, the Great Recession, the China–United States trade war, the COVID-19 pandemic, hybrid warfare predominantly using the Internet, and growing concerns surrounding the AI boom, climate change, misinformation, information overload, and wealth inequality. Major conflicts generally associated with the post–Cold War era include the United States invasion of Panama, the Gulf War, the Yugoslav Wars, the First and Second Congo Wars, the First and Second Chechen Wars, the War in Afghanistan and the Iraq War, the Mexican drug war, the Arab Spring, the Russo-Georgian War, the Syrian civil war, the North Korea crisis, the Russo-Ukrainian War, the Gaza War and associated Middle Eastern crisis and Red Sea crisis, Operation Southern Spear, the 2026 United States intervention in Venezuela, and the 2026 Iran war.
In the 12th and 13th centuries, crusades and conquest had subjugated Islamic territories in southern Italy, central Spain, and the Levant under European rule, and for the first time translations into Latin of the great works of Arabic and Greek scholars were made with the help of Jewish and Muslim scholars, especially in Toledo, which had fallen into Christian hands in 1085 and whose libraries had escaped destruction. Michael Scotus from Scotland made a Latin translation of Aristotle's work on animals from Arabic here around 1215, which was disseminated widely and was the first time in a millennium that this foundational text on zoology became available to Europeans. Falconry was popular in the Norman court in Sicily, and a number of works on the subject were written in Palermo. Emperor Frederick II of Hohenstaufen (1194–1250) learned about an falconry during his youth in Sicily and later built up a menagerie and sponsored translations of Arabic texts, among which the popular Arabic work known as the Liber Moaminus by an unknown author which was translated into Latin by Theodore of Antioch from Syria in 1240–1241 as the De Scientia Venandi per Aves, and also Michael Scotus (who had removed to Palermo) translated Ibn Sīnā's Kitāb al-Ḥayawān of 1027 for the Emperor, a commentary and scientific update of Aristotle's work which was part of Ibn Sīnā's massive Kitāb al-Šifāʾ.
Diabetes burden and access to care vary widely between and within countries. Between 1990 and 2022, diabetes prevalence rose faster in low and middle income countries than in high-income countries. In 2022, more than half of adults aged 30 and over with diabetes were not taking medication for it, and treatment coverage was lowest in low and middle income countries. A pooled analysis of 1,108 population-based studies estimated that in most countries, especially low and middle income ones, treatment had not increased enough to keep pace with rising prevalence, and that the gap in treatment coverage between the countries widened from 56 percentage points in women and 43 in men in 1990 to 78 and 71 respectively in 2022. WHO reported in 2021 that essential diabetes medicines were available in only about half of facilities in low and lower middle income countries, compared to about 80% of facilities globally. The International Diabetes Federation estimated that 252 million adults aged 20–79 were unaware they had diabetes in 2024. Risk also differs between ethnic groups. South Asian people tend to develop type 2 diabetes earlier in life and often at a normal body mass index. In a study of British Pakistani and British Bangladeshi participants, those with a high genetic risk of both insulin deficiency and unfavourable fat distribution were diagnosed about 8 years earlier, at a BMI about 3 kg/m² lower, than those at low genetic risk. Disparities are also documented for Indigenous peoples.
=== Associated conditions === Researchers have implicated estrogens in various estrogen-dependent conditions, such as ER-positive breast cancer, as well as a number of genetic conditions involving estrogen signaling or metabolism, such as estrogen insensitivity syndrome, aromatase deficiency, and aromatase excess syndrome. Estrogens promote salt and water retention, which can lead to facial swelling and edema. High estrogen can amplify stress-hormone responses in stressful situations.
Sources: en.wikipedia.org
Chromatographic methods can separate the two forms before detection. Enzymatic assays often measure total glutathione first and then use a separate procedure to estimate the oxidized fraction. The difference between total and oxidized amounts provides an indirect estimate of the reduced form.
Acidification lowers pH and slows thiol oxidation during handling. It also helps precipitate proteins that could interfere with detection. Typical choices include metaphosphoric acid and sulfosalicylic acid.
Dissolved oxygen reacts with the thiol group, forming glutathione disulfide. Neutral and alkaline conditions generally increase the oxidation rate. Light, metal ions, and repeated freezing and thawing can also reduce stability.
The ratio depends on rapid separation or blocking of GSH before oxidation occurs. GSSG can be formed ex vivo if samples are not processed quickly in cold, acidic conditions. Even small delays can shift the apparent ratio, making standardized protocols essential.