The short version of Tietze assay fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-08-01. Anything still debated is marked as such rather than presented as settled.
Common analytical approaches include enzymatic recycling assays, high-performance liquid chromatography, and mass spectrometry. The enzymatic recycling assay uses glutathione reductase and a colorimetric or fluorometric reagent to amplify signal, which gives good sensitivity for total glutathione. Chromatographic methods can separate GSH from GSSG and related thiols, while mass spectrometry offers structural confirmation and multiplexing. Each approach has different requirements for calibration, internal standards, and validation. No single method captures every form of glutathione in every matrix.
Storage recommendations for glutathione reagents usually specify a cool, dry, dark environment because the thiol oxidizes in air and light. Solid material is often kept desiccated at low temperature, while solutions are prepared fresh or stored frozen in aliquots. Repeated freeze-thaw cycles can accelerate degradation, and metal ions can catalyze oxidation. Quality control may include purity assays, water content, and identity confirmation. Stability limits are method-specific, so a stated shelf life applies only to defined conditions and packaging.
Laboratory measurement of glutathione requires attention to oxidation before analysis. Blood, tissue, or cell samples can lose reduced glutathione as it converts to GSSG or forms mixed disulfides with proteins. Acid extraction, rapid freezing, and thiol-blocking reagents are common strategies to preserve the original distribution. Reported concentrations therefore depend on collection protocol, extraction method, and the time between sampling and analysis. Comparisons across studies are most reliable when these pre-analytical variables are described.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Typical storage temperature | -20 °C or below | For solid reagent and frozen aliquots; protect from moisture and light. |
| Common analytical method | HPLC with UV or fluorescence detection | Separates GSH and GSSG after derivatization or direct detection. |
| Alternative method | LC-MS/MS | Provides high specificity and can quantify multiple thiols. |
| Total glutathione assay | Enzymatic recycling | Uses glutathione reductase and a chromogen or fluorogen. |
| Key stability risk | Oxidation to GSSG | Air, light, and trace metals promote conversion. |
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.
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.
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.
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.
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.
== Public awareness and solutions == Third-hand smoke is a relatively newly postulated and initially controversial concept, and public awareness of it is lower than that of passive smoke. A 2013 study with six focus groups in metro and rural Georgia (USA) asked participants whether they had heard of THS, most of the participants had not heard about it and did not know what third-hand smoke was. Research on THS is growing, but it does not compare to the 40 years of research on the effects of passive smoke. Yet, it is estimated that 5%-60% of passive smoke-related harm may be attributable to third-hand smoke exposure. THS poses such a risk because its exposure can linger much longer than passive smoke. Third-hand smoke-contaminated surfaces like carpet, walls, and car interiors are also especially hard to clean, whereas passive smoke can be removed with ventilation. Smoking rates in the United States have fallen considerably from 42.4% in 1965 to 17.8% in 2016. However, the downward trend is slowing, and it is estimated that 23% to 42% of adults in America with low education or living in poverty still smoke. This exposes millions of nonsmokers, many of whom are children. THS awareness campaigns are growing and primarily focus on the health risks for young children. A 2014 study published in Pediatrics demonstrated that parents are more likely to attempt to quit smoking if they become convinced that third-hand smoke is harmful to children and are more likely to have smoke-free home and car policies if they are aware of the dangers of third-hand smoke.
== Deaths == 28 March – Paul O'Grady, comedian, actor and drag queen (born 1955) 22 April – Len Goodman, ballroom dancer and television personality (born 1944) 26 November – Terry Venables, football player and manager (born 1943)
=== Protein-type CSP === Proteins are complex, high-molecular weight biopolymers. They are inherently chiral being composed of L-amino acids and possess ordered 3D-structure. They are known to bind/interact stereoselectively with small molecules reversibly, making them extremely versatile CSPs for chiral separation of drug molecules. Hermansson made use of this property to develop number of CSPs by immobilizing proteins on to silica surface. They operate under reverse phase mode (phosphate buffer and organic modifiers). Protein polymer remains in twisted form because of the different intramolecular bonding. These bonding create different type of chiral loops/grooves present in the protein molecule. Separation mechanism of proteins depends on unique combination of hydrophobic and polar interactions by which the analytes are oriented to chiral surfaces. H-bonding and charge transfer may also contribute to enantioselectivity. The mechanism of chiral distinction by proteins is mostly not well established due to their complex nature. Several proteins based CSP have been employed for chiral drug analysis including α-acid glycoprotein (enantiopac; chiral-AGP), ovomucoid protein (Ultron ES DVM), human serum albumin (HSA). α-AGP CSP (chiral AGP), has been employed for the quantification of atenolol enantiomers in biological matrices, for pharmacokinetic investigation of racemic metoprolol. The major weakness of protein based CSPs include low loading capacity, protein phases are expensive, extremely fragile, delicate to handle, very low column efficiency, cannot invert elution order.
Aspartic acid (symbol Asp or D; known as aspartate in its anionic form), is an α-amino acid that is used in the biosynthesis of proteins. The L-isomer of aspartic acid is one of the 22 proteinogenic amino acids, i.e., the building blocks of proteins. D-aspartic acid is one of two D-amino acids commonly found in mammals. Apart from a few rare exceptions, D-aspartic acid is not used for protein synthesis but is incorporated into some peptides and plays a role as a neurotransmitter/neuromodulator. Like all other amino acids, aspartic acid contains an amino group and a carboxylic acid. Its α-amino group is in the protonated –NH+3 form under physiological conditions, while its α-carboxylic acid group is deprotonated −COO− under physiological conditions. Aspartic acid has an acidic side chain (CH2COOH) which reacts with other amino acids, enzymes and proteins in the body. Under physiological conditions (pH 7.4) in proteins the side chain usually occurs as the negatively charged aspartate form, −COO−. It is a non-essential amino acid in humans, meaning the body can synthesize it as needed. It is encoded by the codons GAU and GAC. In proteins aspartate sidechains are often hydrogen bonded to form asx turns or asx motifs, which frequently occur at the N-termini of alpha helices. Aspartic acid, like glutamic acid, is classified as an acidic amino acid, with a pKa of 3.9; however, in a peptide this is highly dependent on the local environment, and could be as high as 14. The one-letter code D for aspartate was assigned arbitrarily, with the proposed mnemonic asparDic acid.
These conditions are valid in a general way. The mathematical formulation of the gap depends upon the kinematics of the underlying theory of the solid (e.g., linear or nonlinear solid in two- or three dimensions, beam or shell model). By restating the normal stress
Sources: en.wikipedia.org
=== The discovery of copper-histidine in human blood and invention of Menkes disease treatment === Sarkar discovered copper-histidine in human blood in 1966 and recognized it as a biological form by which copper, an essential element to sustain life, is transported in blood. In 1976, Sarkar proposed that a baby with Menkes disease receive copper-histidine via subcutaneous injection. This was the world's first Menkes patient to receive copper-histidine therapy. Children with this disease are now living longer and reaching adulthood with copper-histidine treatment. Sarkar did not patent copper-histidine; he intended that it be readily available to Menkes patients at a reasonable cost. The formulation and detailed compounding procedure for the preparation of copper-histidine is freely available by SickKids Pharmacy to physicians and hospital pharmacies around the world upon request. Sarkar also helped make copper-histidine formulation for Menkes disease in other countries, including the NIH Clinical Center, Bethesda, Maryland, USA, India, and Mexico.
== Classification == In the third edition of the International Classification of Sleep Disorders (ICSD-3), obstructive sleep apnea is classified amongst the sleep-related breathing disorders and is divided in two categories, namely adult OSA and pediatric OSA. Obstructive sleep apnea is differentiated from central sleep apnea (CSA), which is characterized by episodes of reduction or cessation in breathing attributable to decreased effort, rather than upper airway obstruction. The respiratory effort must then be assessed in order to correctly classify the apnea as obstructive given the specificity of the diaphragmatic activity in this condition: the inspiratory effort is continued or increased through the entire episode of absent airflow. When hypopneas are present alongside apneas, the term obstructive sleep apnea-hypopnea is used. If it is associated with daytime sleepiness and other daytime symptoms, it is known as obstructive sleep apnea-hypopnea syndrome. To be categorized as obstructive, the hypopnea must meet one or more of the following symptoms: (1) snoring during the event, (2) increased oronasal flow flattening, or (3) thoraco-abdominal paradoxical respiration during the event. If none of them are present during the event, then it is categorized as central hypopnea.
Certain other inherited diseases are associated with an increased risk of developing soft-tissue sarcomas. For example, people with neurofibromatosis type I (also called von Recklinghausen disease, associated with alterations in the NF1 gene) are at an increased risk of developing soft-tissue sarcomas known as malignant peripheral nerve-sheath tumors. Patients with inherited retinoblastoma have alterations in the RB1 gene, a tumor-suppressor gene, and are likely to develop soft-tissue sarcomas as they mature into adulthood.
Throughout his managerial career, Wenger has trusted his players to perform and learn from their own mistakes, a quality Vieira regards as his biggest strength and weakness. Wenger encourages sportsmen to show intuition, and makes observations rather than explicitly giving orders. Campbell reflected that his former manager "puts a lot of onus on players to change the game" and "he wants certain players – especially in the last third – to be able to produce it and give something different". When Wenger joined Arsenal, he spoke of his desire to see "real, modern football. That means compact lines, of zones, of quick, coordinated movements with a good technique." He characteristically focuses on the strengths of his teams, rather than looking for areas to exploit the opposition.
=== Donald Trump's first presidency === Since late 2018, Trump repeatedly privately and publicly discussed buying Greenland. The Trump administration "courted Greenlandic politicians with promises of American business investment, educational opportunities, and development aid". According to a report in the New Yorker, a 2019 delegation of American diplomats and national-security officials, dispatched to discuss mining of mineral and particularly rare-earth mineral resources, included members of the Greenland Policy Coordination Committee, a committee within the National Security Council "working to subvert the Kingdom of Denmark".
Sources: en.wikipedia.org
This difference is reflected in their metabolism; M1 macrophages have the unique ability to metabolize arginine to the "killer" molecule nitric oxide, whereas M2 macrophages have the unique ability to metabolize arginine to the "repair" molecule ornithine. However, this dichotomy has been recently questioned as further complexity has been discovered. Macrophages are widely thought of as highly plastic and fluid cells, with a fluctuating phenotype. Human macrophages are about 21 micrometres (0.00083 in) in diameter and are produced by the differentiation of monocytes in tissues. They can be identified using flow cytometry or immunohistochemical staining by their specific expression of proteins such as CD14, CD40, CD11b, CD64, F4/80 (mice)/EMR1 (human), lysozyme M, MAC-1/MAC-3 and CD68. Macrophages were first discovered and named by Élie Metchnikoff, a Russian Empire zoologist, in 1884.
== Control and detection == The use of bracken fern as human food is mainly a historical question. The rhizomes of these plants served as human food in Scotland during the First World War. In America (USA, Canada), Russia, China and Japan, fern is grown commercially for human use. The usual procedure that is performed before eating the plant is to pre-treat the fern with boiling water in the presence of different chemicals, such as sodium bicarbonate and wood ash, to degrade or inactivate ptaquiloside and other toxic agents. Nevertheless, some carcinogenic activity persists even after the treatment. As shown by Kamon and Hirayama, the risk of oesophageal cancer was increased approximately by 2.1 in men and 3.7 in women who regularly consume bracken in Japan. Recent researches have suggested that sulfur-containing amino acids can potentially be used under appropriate conditions as detoxifying agents for ptaquiloside and selenium supplementation can prevent as well as reverse the immunotoxic effects induced by ptaquiloside. Ptaquiloside in the aqueous extract of bracken can be detected using different instrumental methods: thin-layer chromatography–densitometry (TLC-densitometry), high-performance liquid chromatography (HPLC), gas chromatography–mass spectrometry (GCMS), and liquid chromatography–mass spectrometry (LC-MS).
The Conspiracy of 1810 was instigated by three members of Temple of the Theologic Virtues. This was one of the first coordinated attempts at rebellion against Spanish rule to create an independent state in Cuba, and also saw the creation of the first constitution ever written on Cuban soil for the governing of an independent Cuba. The three ringleaders of this revolution were Román de la Luz, Luis F. Bassave, and Joaquín Infante. The constitution written by Joaquín Infante was completed in the same year that the Spanish Constitution of 1812 was completed in Cádiz. De la Luz was discovered when his wife informed her priest of her and her husband's involvement in the revolution during confession. The priest absolved her of her sins, but used the information to launch an investigation against De la Luz. De la Luz was arrested as a heretic and a traitor and deported to Spain. Despite the fact that his wife had sent him money each month while he was in prison, the church intercepted the payments and withheld them. Román de la Luz died in prison. On July 17, 1814, Don Manuel Ramirez was jailed without a trial in Cuba, charged with being a Freemason.
=== India === In India, after completing MBBS degree and one year of integrated internship, doctors can enroll in several types of postgraduate training programs: M.D. (DOCTOR OF MEDICINE) in: Anesthesiology, Anatomy, Biochemistry, Community Medicine, Dermatology Venereology and Leprosy, General Medicine, Forensic Medicine, Microbiology, Pathology, Paediatrics, Pharmacology, Physical medicine and rehabilitation, Physiology, Psychiatry, Radio diagnosis, Radiotherapy, Tropical Medicine, and, Tuberculosis & Respiratory Medicine. M.S. (MASTER OF SURGERY) in: Otorhinolaryngology, General Surgery, Ophthalmology, Orthopaedics, Obstetrics & Gynecology. D.M. (DOCTOR OF MEDICINE) in: Cardiology, Endocrinology, Medical Gastroenterology, Nephrology, and Neurology. M.Ch. (MASTER OF CHIRURGIE) in: Cardio vascular & Thoracic Surgery, Urology, Neurosurgery, Paediatric Surgery, Plastic Surgery. Or diploma in: Anesthesiology (D.A.), Clinical Pathology (D.C.P.), Dermatology Venereology and Leprosy (DDVL), Forensic Medicine (D.F.M.), Obstetrics & Gynaecology (D.G.O.), Ophthalmology (D.O.), Orthopedics (D.Ortho.), Otorhinolaryngology (D.L.O.), Paediatrics (D.C.H.) Psychiatry (D.P.M.), Public health (D.P.H.), Radio-diagnosis (D.M.R.D.), Radiotherapy (D.M.R.T.)., Tropical Medicine & Health (D.T.M. & H.), Tuberculosis & Chest Diseases (D.T.C.D.), Industrial Health (D.I.H.), Maternity & Child Welfare (D. M. C. W.)
=== Alcohols === Alcohols generally have weak molecular ion peaks due to the strong electronegativity of oxygen. “Alpha” cleavage is common due to the resonance stabilization. The largest alkyl group will be lost.
Sources: en.wikipedia.org
Pre-analytical handling, extraction chemistry, and detection method all influence reported glutathione values. Oxidation during sample processing can shift the measured GSH/GSSG ratio. Standardized protocols and reference materials help reduce, but do not eliminate, these differences.
Total glutathione typically refers to the combined amount of reduced glutathione and glutathione disulfide, expressed in glutathione equivalents. Assays that measure total glutathione do not distinguish GSH from GSSG unless a separation step is included. Researchers often pair a total assay with a specific GSSG measurement to estimate the redox ratio.
Glutathione reference standards are generally stored cold, dry, and protected from light. Weighed portions should be prepared promptly and used within validated stability windows. Purity and water content can affect the accuracy of calibration curves.
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.