retention time 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.
Updated 2025-10-16. Numbers and descriptions here follow the published literature rather than marketing material.
High-performance liquid chromatography is an analytical technique that separates components in a liquid sample by passing them through a packed column under pressure. A pump delivers a mobile phase at a controlled flow rate, and an injector introduces the sample into the stream. Differences in how analytes partition between the mobile phase and the stationary phase cause them to exit the column at different times. Detection then records a signal proportional to the amount of each separated substance. The resulting chromatogram provides retention times and peak areas for identification and quantification.
Instrumentation includes a solvent delivery system, an autosampler, a column oven, and one or more detectors. Reversed-phase columns with chemically modified silica are widely used, but normal-phase, ion-exchange, size-exclusion, and affinity modes exist for specific separations. Detectors may rely on ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry. Column temperature, mobile phase composition, and flow rate are adjusted to improve resolution. System pressure is monitored because rising pressure can indicate column blockage or deteriorating packing.
Most routine HPLC testing uses reversed-phase columns, where the stationary phase is nonpolar and the mobile phase is a polar mixture such as water with an organic solvent. Analytes partition between the two phases according to polarity, size, and charge. Gradients that change solvent composition over time can separate compounds with broad retention ranges. Isocratic conditions keep solvent composition constant and suit simpler mixtures. The choice of column chemistry, pH, and temperature affects selectivity and peak shape.
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. UV detection is widely used because many organic compounds absorb light, but it requires a chromophore. Mass spectrometry provides mass-based identification and high sensitivity for trace analytes. Each detector has trade-offs in selectivity, cost, and compatibility with mobile phases. Quantification typically uses calibration curves prepared from reference standards. Results are reported as concentration, purity, or presence above a limit.
| Property | Value | Notes |
|---|---|---|
| Separation principle | Differential partitioning | Analytes distribute between mobile and stationary phases. |
| Mobile phase | Liquid solvent mixture | Composition controls retention and selectivity. |
| Stationary phase | Packed column particles | Often chemically bonded silica. |
| Typical detector | UV-Vis or photodiode array | Mass spectrometry is also common. |
| Common synonym | High-performance liquid chromatography | Abbreviated as HPLC. |
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. A diode array detector records full spectra across a wavelength range, which helps identify co-eluting peaks. Mass spectrometry provides mass-to-charge ratios and can confirm molecular identity at low concentrations. The choice of detector depends on analyte structure, required sensitivity, and whether quantitation or identification is the goal. No single detector works for every compound, and method development often compares responses before selecting one.
High-performance liquid chromatography is an analytical technique that separates components of a liquid sample by passing it through a packed column under pressure. A pump delivers a mobile phase at a controlled flow rate, and an injector introduces the sample into the stream. Differences in interaction with the stationary phase cause analytes to migrate at different rates. Detectors record elution as peaks, and a data system converts signals into a chromatogram. The method is suited to compounds that dissolve in a liquid and are not volatile enough for gas chromatography.
Reversed-phase chromatography dominates modern HPLC testing, using a nonpolar stationary phase such as chemically bonded octadecyl groups and a polar mobile phase of water mixed with organic solvent. Analytes partition between the mobile and stationary phases according to hydrophobicity. Gradient elution changes the mobile phase composition over time to separate compounds with a wide range of retention. Isocratic elution keeps the composition constant and is simpler for routine assays. Column temperature, pH, and flow rate influence selectivity, peak shape, and retention time, so these parameters are controlled during a validated method.
Routine quality control monitors retention time shifts, baseline noise, system pressure, and peak shape. Trends can reveal column aging, mobile phase preparation errors, detector drift, or sample degradation. Corrective actions may include replacing the column, preparing fresh mobile phase, or recalibrating the detector. Stability testing often uses HPLC to measure parent compound loss and degradation product formation. Open questions remain about how accelerated stability results extrapolate to long-term storage under varied conditions.
Quality control for HPLC testing combines scheduled checks, documented procedures, and review of results. Before sample analysis, system suitability testing confirms that the instrument, column, and method meet predefined criteria. Common criteria include resolution between critical peaks, retention time precision, peak tailing, and theoretical plate count. Failure triggers investigation before results are reported. Records link raw data, calculations, instrument logs, and analyst identity to each batch, supporting audits and repeat analysis.
HCO2H → H2 + CO2 Soluble ruthenium catalysts are also effective for producing carbon monoxide-free hydrogen. It is used as a source of hydrogen in transfer hydrogenation, as in the Leuckart reaction to make amines and (in aqueous solution or in its azeotrope with triethylamine) for hydrogenation of ketones.
=== Casting === In February 2025, Jessica Lange, who starred in the first four seasons and briefly appeared in the eight season in 2018, answered a question about her potential return for the thirteenth season: "Oh Christ, no. I mean, I haven't done it for more than 10 years, 12 years, so, no, I'm not doing it." Murphy revealed that Lange was the first person he turned to about the return and she agreed under the condition she would have a musical number. Subsequently, he turned to Sarah Paulson and Evan Peters, who agreed instantly. They both last appeared in the tenth season in 2021. In October 2025, Lange, Paulson, Peters, Emma Roberts, Billie Lourd, Kathy Bates, Angela Bassett, Leslie Grossman, Jessica Lange, and Gabourey Sidibe were all confirmed to return for the thirteenth season, along with the newcomer Ariana Grande. Bates, Bassett and Sibide last appeared in the eight season in 2018. Bates revealed that she would have only one day of filming. In February 2026, John Waters joined the cast, while Joey Pollari joined in April, and Alex Consani and Paul Anthony Kelly joined in May. John Carroll Lynch and Matt Fraser were also confirmed to reprise their roles from Freak Show, with Mena Suvari and Berto Colón also joining the cast. In July, Frances Conroy was confirmed to reprise her role from Coven, with Avantika, Grace Dumdaw, Cara Delevingne, and Charlie Carver also joining the cast. In July 2026, it was reported that Grande dropped out due to scheduling conflicts with the season's production schedule and her Eternal Sunshine Tour.
== External links == Histocompatibility+Antigens+Class+II at the U.S. National Library of Medicine Medical Subject Headings (MeSH) MHC+Class+II+Genes at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
=== Heart === In the cardiovascular system, KOR activation produces negative inotropic and lusitropic effects in cardiac tissue through pertussis toxin-sensitive Gi/o protein signaling. KOR activation during myocardial infarction reperfusion reduces infarct size through ERK1/2-dependent mechanisms, suggesting cardioprotective effects. In cardiomyopathic hearts, KOR-mediated cardiac depression is augmented through increased inhibition of cAMP accumulation and decreased amplitude of systolic Ca2+ transients. Ventricular arrhythmias resulting from administration of certain antagonists are attributed to the presence of KORs in the heart. Cardiomyopathic hamster hearts show augmented negative inotropic responses to KOR agonists in heart failure.
Sources: en.wikipedia.org
== Pathophysiology == The primary characteristic of MASLD is the accumulation of lipids in the liver, largely in the form of triglycerides. However, the mechanisms by which triglycerides accumulate and the reasons that accumulation can lead to liver dysfunction are complex and incompletely understood. MASLD can include steatosis along with varied signs of liver injury: either lobular or portal inflammation (a form of liver injury) or ballooning degeneration. Similarly, MASH can include histological features such as portal inflammation, polymorphonuclear cell infiltrates, Mallory bodies, apoptotic bodies, clear vacuolated nuclei, microvesicular steatosis, megamitochondria, and perisinusoidal fibrosis. Hepatocyte death via apoptosis or necroptosis is increased in MASH compared with simple steatosis, and inflammation is a hallmark of MASH. The degree of inflammation can be correlated to the number of inflammatory foci. Various definitions exist for an inflammatory focus, but one defines it as the presence of more than four mononuclear cells in proximity within the hepatic parenchyma. One debated mechanism proposes that hepatic steatosis progresses to steatosis with inflammation following some further injury, or second hit. Oxidative stress, hormonal imbalances, and mitochondrial abnormalities are potential causes of this "second hit" phenomenon. A further nutrigenomics model named multiple hit extends the second hit model, suggesting that multiple disease biomarkers and factors such as genes and nutrition influence MASLD and MASH progression.
=== Available forms === Trazodone is provided as the hydrochloride salt and is available in the form of 50 mg, 100 mg, 150 mg, and 300 mg oral tablets. In Italy, it is also available as an oral solution (Trittico 60 mg/mL) with a dosing pipette marked at 25 mg and 50 mg. An extended-release oral tablet formulation at doses of 150 mg and 300 mg is also available.
On May 5, 2026, Rubio held a meeting with SOUTHCOM commander General Francis L. Donovan regarding Operation Southern Spear with a map of Cuba on the background. When asked about why he posed a picture with the map of Cuba, he had clarified saying "Cuba is under the Southern Command, you know it's the closest part. Our ambassadors were all over the Western Hemisphere. I met with the general who just took command of SOUTHCOM, and there was a map of Cuba behind us. I thought it would be fitting to take a picture in front of it because it's the closest to the United States within SOUTHCOM.". On May 20, 2026, USS Nimitz (CVN-68) and her Carrier Strike Group along with USS Gridley (DDG-101) and USNS Patuxent had arrived in the Caribbean.
== Society == Mass Party, a political party in Thailand (2006–2009?) Mass society, a society based on relations between huge numbers of people, whose prototypical denizen is the "mass man" Mass politics, politics in the mass society, featuring especially the modern political party
== Veterinary use == Meloxicam is used in veterinary medicine mainly to treat dogs, but also sees off-label use in other animals such as cattle and exotics. In the European Union and other countries it is not considered off-label and can be used in cattle, pigs, horses, dogs, cats and guinea pigs. It has also been investigated as an alternative to diclofenac by the Royal Society for the Protection of Birds (RSPB) to prevent deaths of vultures. Depending on the animal species, each country or union of countries applies different guidelines or legal frameworks for the use of the drug, as well as different recorded side effects. The most common side effects in dogs include gastrointestinal irritation (vomiting, diarrhea, and ulceration). As far as the perioperative administration is concerned, in healthy dogs given meloxicam, no perioperative adverse effects on the cardiovascular system have been reported at recommended dosages. Perioperative administration of meloxicam to cats did not affect postoperative respiratory rate nor heart rate.
Sources: en.wikipedia.org
12 April The Scottish Government announces it will mount a legal challenge against the UK government's decision to block the Gender Recognition Reform (Scotland) Bill. SNP leader Humza Yousaf confirms that his party will not pay any legal fees for former chief executive Peter Murrell, but that he will not be suspended from the party because he is "innocent until proven guilty". 13 April – Representatives from BBC Scotland, STV, Viaplay and the Scottish FA meet to discuss the broadcasting of men's football in Scotland, the rights of which are owned by Viaplay until 2028. The meeting, to discuss showing free-to-air matches, ends without resolution, but is described by Gavin Newlands MP as encouraging. 15 April – The SNP's National Executive Committee orders a review of the party's transparency and governance. Corach Rambler, trained in Scotland at Milnathort by Lucinda Russell, wins the 2023 Grand National. 16 April The Sunday Mail publishes leaked video purporting to show Nicola Sturgeon playing down concerns about the SNP's finances. The SNP says that its finances are "in balance" following reports the party is facing a financial crisis. 18 April – SNP treasurer Colin Beattie is arrested and questioned by Police Scotland in connection with their ongoing investigation into the party's finances. 19 April – Colin Beattie resigns as SNP treasurer with immediate effect. 22 April – Police Scotland make several arrests at Ayr Racecourse as the protest group Animal Rising attempts to disrupt the Scottish Grand National by invading the course.
== Sex identification == The 2002 report on the grave had reported that "This is the only known Iron Age grave to contain both a sword and mirror, raising interesting questions as to the gender significance of both these grave goods", but that "preservation of bone and DNA was too poor to determine the person's sex". A 2016 paper said that "Their combined presence within the burial of a single individual represents a touchstone within the ongoing unraveling of a long-held, interconnected set of reified sex and gender assumptions that have permeated discussions of British Iron Age mortuary contexts" and that "Hillside Farm as a starting point highlights the need to keep in mind the potential significance of any aspect of the burial, not to deny that men and women may have existed, or that certain artifacts may have conveyed a gendered meaning, but to refrain from excluding other routes to identity, personhood, or significance before analysis begins." In 2023, American scientists used new techniques of analysis of dental peptides, which indicated that, with 96% probability, the person in the grave was female.
=== Home sleep test (HST) / home sleep apnea test (HSAT) === Sleep apnea can also be diagnosed using an in-home testing kit. The main advantage is that these record in the usual sleep environment and thus are more representative of their natural sleep than staying overnight at a lab. Home sleep testing is more accessible and less expensive than polysomnography due to long waiting periods for in-lab tests.
Systemic lupus erythematosus (SLE) Systemic sclerosis Polymyositis Dermatomyositis Rheumatoid arthritis (RA) Sjögren's syndrome Eosinophilic granulomatosis with polyangiitis (EGPA) Autoimmune thyroiditis Antiphospholipid antibody syndrome The treatment of overlapping connective tissue disorders is mainly based on the use of corticosteroids and immunosuppressants. Biologic drugs, i.e. anti-TNFα or anti-CD20 monoclonal antibodies, have been recently introduced as alternative treatments in refractory cases. There are some concerns with the use of anti-TNF agents in patients with systemic autoimmune diseases due to the risk of triggering disease exacerbations. The term polyangiitis overlap syndrome refers to a systemic vasculitis that shares features with two or more distinct vasculitis syndromes. The most common type of polyangiitis overlap syndrome is microscopic polyangiitis (MPA), which shares features with EGPA, granulomatosis with polyangiitis and panarteritis nodosa. Sometimes polyangiitis overlap syndrome is used as a synonym for MPA.
=== Kinetically frozen micelles === When block copolymer micelles do not display the characteristic relaxation processes of surfactant micelles, these are called kinetically frozen micelles. These can be achieved in two ways: when the unimers forming the micelles are not soluble in the solvent of the micelle solution, or if the core forming blocks are glassy at the temperature in which the micelles are found. Kinetically frozen micelles are formed when either of these conditions is met. A special example in which both of these conditions are valid is that of polystyrene-b-poly(ethylene oxide). This block copolymer is characterized by the high hydrophobicity of the core forming block, PS, which causes the unimers to be insoluble in water. Moreover, PS has a high glass transition temperature which is, depending on the molecular weight, higher than room temperature. Thanks to these two characteristics, a water solution of PS-PEO micelles of sufficiently high molecular weight can be considered kinetically frozen. This means that none of the relaxation processes, which would drive the micelle solution towards thermodynamic equilibrium, are possible. Pioneering work on these micelles was done by Adi Eisenberg. It was also shown how the lack of relaxation processes allowed great freedom in the possible morphologies formed. Moreover, the stability against dilution and vast range of morphologies of kinetically frozen micelles make them particularly interesting, for example, for the development of long circulating drug delivery nanoparticles.
Sources: en.wikipedia.org
HPLC separates and detects individual compounds in a liquid sample, producing peaks at characteristic retention times. Peak area or height can be used to estimate concentration when calibrated with known standards. It does not identify unknown compounds with certainty unless additional detectors or reference materials are used.
Pressure drives the liquid mobile phase through a column packed with small particles. Without pressure, flow would be very slow or stop because the packed bed resists liquid movement. Modern pumps maintain a steady flow despite the resistance.
A chromatogram is a plot of detector signal against time after sample injection. Each peak represents a compound or group of compounds eluting from the column. Retention time and peak area are the main measurements read from the plot.
It separates components in a liquid sample and measures their amounts using a detector. Results can indicate concentration, purity, or identity based on retention time and detector response. The technique works for mixtures that can be dissolved and filtered.