This is a working overview of Retention time, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-01-26. Anything still debated is marked as such rather than presented as settled.
HPLC testing is not a single fixed procedure; it is a family of separation modes. Reversed-phase, normal-phase, ion-exchange, size-exclusion, and affinity chromatography each suit different analyte properties. Reversed-phase methods dominate because they handle many neutral and moderately polar compounds. Detection can be optical, electrochemical, or mass spectrometric, and the detector dictates what information is available. Coupling with mass spectrometry increases selectivity and enables identification when standards are unavailable. The technique cannot separate every mixture without adjustment.
HPLC testing is an analytical technique used to separate, identify, and quantify components in a liquid sample. It relies on a pressurized mobile phase that carries the sample through a column packed with stationary phase. Different compounds travel at different rates because of interactions with the stationary and mobile phases. The resulting signal versus time is a chromatogram. Peak position indicates identity under specified conditions, while peak area or height relates to amount.
Key performance measures include retention time, peak area, peak height, resolution, tailing factor, and plate count. Retention time helps identify a peak under fixed conditions, but confirmation often requires a second method or detector. Peak area and height relate to concentration through calibration curves, which may be linear or nonlinear depending on the detector response. Resolution describes separation between adjacent peaks, while tailing factor and plate count describe peak shape and column efficiency. Performance checks verify these values before and during a run to confirm that the instrument is performing within limits.
High-performance liquid chromatography testing separates components of a liquid sample by forcing a mobile phase through a packed column. The stationary phase inside the column interacts with analytes to different degrees, so each compound exits at a characteristic retention time. A pump delivers solvent at controlled flow and pressure, while an injector introduces a precise sample volume. Detectors such as ultraviolet-visible, fluorescence, refractive index, or mass spectrometric instruments record the separated bands. The resulting chromatogram provides qualitative and quantitative information about the mixture.
| Property | Value | Notes |
|---|---|---|
| Abbreviation | HPLC | Also called high-performance liquid chromatography |
| Separation mechanism | Differential partitioning | Compounds distribute between mobile and stationary phases |
| Typical column chemistry | C18 (octadecylsilane) | Used in reversed-phase separations |
| Typical detector | UV-Vis or photodiode array | Mass spectrometry is common for trace and confirmatory work |
| Typical particle size | 1.8–5 µm | Smaller particles require higher pressure and can improve speed |
Method validation examines whether an HPLC procedure is suitable for its intended purpose. Common parameters include accuracy, precision, specificity, linearity, range, detection limit, quantification limit, and robustness. Accuracy describes closeness to a true or accepted value, while precision describes agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from related substances. Robustness tests small deliberate changes in flow, temperature, or solvent composition. Validation is not a one-time event; methods may need partial revalidation after changes to instruments, columns, sample handling, or specification limits. Regulatory guidance provides frameworks, but some details remain method-specific.
Regulatory and pharmacopeial texts shape how HPLC testing is performed and documented. The International Council for Harmonisation provides validation guidance, while pharmacopeias publish general chromatography chapters and monographs for specific materials. Accreditation standards such as ISO/IEC 17025 address laboratory competence and traceability. Inspectors may review instrument qualification, analyst training, reference material control, and electronic records. Open questions include how best to validate methods for new complex products and how to handle automated data processing. Laboratories generally resolve these issues through risk assessment, method lifecycle management, and documented scientific justification.
In quality control laboratories, HPLC testing supports batch release, raw material checks, stability studies, and impurity profiling. A validated method defines sample preparation, instrument settings, calibration, and acceptance criteria. Analysts compare results with specifications and investigate out-of-specification outcomes before a batch is approved. Documentation includes chromatograms, integration records, audit trails, and reagent details. Because results influence product decisions, laboratories follow formal quality systems and data integrity rules. The exact tests and limits depend on the material, its intended use, and the applicable regulatory framework.
Quality control samples are inserted at intervals to monitor accuracy and precision throughout a batch. Blank samples detect contamination, while spiked samples assess recovery from the sample matrix. Calibration standards establish the relationship between detector response and concentration, and control samples are prepared independently from them whenever possible. Laboratories also participate in proficiency testing and maintain audit trails, instrument logs, and reagent records. Ongoing review of control charts can reveal trends before they cause out-of-specification results.
Method validation demonstrates that an HPLC procedure is suitable for its intended purpose. Common validation parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, and robustness. Accuracy reflects agreement with a reference value, while precision describes repeatability under defined conditions. Specificity shows whether the method can measure the analyte in the presence of impurities or matrix components. Validation documents are reviewed before a method is used for routine testing or regulatory submissions.
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.
Although geneticists originally studied inheritance in a wide variety of organisms, the range of species studied has narrowed. One reason is that when significant research already exists for a given organism, new researchers are more likely to choose it for further study, and so eventually a few model organisms became the basis for most genetics research. Common research topics in model organism genetics include the study of gene regulation and the involvement of genes in development and cancer. Organisms were chosen, in part, for convenience—short generation times and easy genetic manipulation made some organisms popular genetics research tools. Widely used model organisms include the gut bacterium Escherichia coli, the plant Arabidopsis thaliana, baker's yeast (Saccharomyces cerevisiae), the nematode Caenorhabditis elegans, the common fruit fly (Drosophila melanogaster), the zebrafish (Danio rerio), and the common house mouse (Mus musculus).
At community gatherings, target shooting was a major sport; they practised shooting at targets, such as hens' eggs perched on posts 100 metres (110 yd) away. They made expert mounted infantry, using cover, from which they could pour in a destructive fire using modern, smokeless, Mauser rifles. In preparation for hostilities, the Boers had acquired around 100 of the latest Krupp field guns, all horse-drawn and dispersed among the Kommando groups and several Le Creusot "Long Tom" siege guns. The Boers' skill in adapting themselves to become first-rate artillerymen shows that they were a versatile adversary. The Transvaal had an intelligence service that stretched across South Africa, and of whose extent and efficiency the British were as yet unaware.
In the case of germline editing, there is no guarantee that treatment will provide an absolute cure throughout the patient's life and/or whether those genes can be passed onto their offspring. Although CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats), a technique that allows for genes to be edited with ease may present certain benefits, but it may also cause further risks to the human body. For example, there may be technical limitations to CRISPR editing. Until advancements are made to fully equip scientists with the knowledge to understand all potential benefits and risks associated with CRISPR editing, concerns regarding the safety of its applications remain. The possibility that editing could bring about an incomplete or inaccurate genetic sequence has been reported in several experiments related to both animal and human cell line studies. Since it is almost impossible to predict a favorable outcome with certainty, this technique makes germline editing all the more difficult to promote as a definite cure for anyone suffering from terminal illnesses.
===== North America ===== Canada - DMT is classified as a Schedule III drug under the Controlled Drugs and Substances Act, but is legal for religious groups to use. In 2017 the Santo Daime Church Céu do Montréal received religious exemption to use ayahuasca as a sacrament in their rituals. United States - DMT is classified in the United States as a Schedule I drug under the Controlled Substances Act of 1970. In 2019, it was decriminalized, along with other naturally derived psychedelics, in the city of Oakland after a campaign by Decriminalize Nature.
7 January Hunt for the Death Star, about lethal energy bursts across the universe; Ray Klebesadel; music from the opening of You Only Live Twice; Bohdan Paczyński of Princeton University and unknown gamma-ray bursts; Stan Woosley of the University of California, Santa Cruz; the Compton Gamma Ray Observatory was deployed from 1991; Canadian Dale Frail of the Very Large Array in Socorro, New Mexico, and the W. M. Keck Observatory; the High Energy Transient Explorer 1 (HETE), launched incorrectly by a Northrop Grumman Pegasus on 4 November 1996, due to a faulty battery; music from Moonraker- Flight Into Space; Dutch researchers from the Anton Pannekoek Institute for Astronomy; the Italian BeppoSAX satellite, launched in April 1996; HETE 2 was launched on 9 October 2000.
Sources: en.wikipedia.org
Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group -NH2 but is rather a secondary amine. The secondary amine nitrogen is in the protonated form (NH2+) under biological conditions, while the carboxyl group is in the deprotonated −COO− form. The "side chain" from the α carbon connects to the nitrogen forming a pyrrolidine loop, classifying it as a aliphatic amino acid. It is non-essential in humans, meaning the body can synthesize it from the non-essential amino acid L-glutamate. It is encoded by all the codons starting with CC (CCU, CCC, CCA, and CCG). Proline is the only proteinogenic amino acid which is a secondary amine, as the nitrogen atom is attached both to the α-carbon and to a chain of three carbons that together form a five-membered ring.
== History == In March 1963 the Danish pharmaceutical company Lundbeck began research into further agents for schizophrenia, having already developed the thioxanthene derivatives clopenthixol and chlorprothixene. By 1965 the promising agent flupenthixol had been developed and trialled in two hospitals in Vienna by Austrian psychiatrist Heinrich Gross. The long- acting decanoate preparation was synthesised in 1967 and introduced into hospital practice in Sweden in 1968, with a reduction in relapses among patients who were put on the depot.
3-Allylfentanyl is an opioid analgesic that is an analogue of fentanyl. 3-Allylfentanyl has effects similar to fentanyl, although it is only 0.13x-0.14x as potent by weight. The decreased potency of this analogue caused by the addition of the allyl group makes it somewhat less dangerous than fentanyl itself (ED50(rat) of 80μg/kg vs 11μg/kg for fentanyl), although this is relative. For comparison, carfentanil is at least 20-30x as potent as fentanyl.
== History == 1993-2000 In 1994, Hetero began operating their first API manufacturing unit in Hyderabad, and by 1995 Hetero formalized its commitment to scientific research with the establishment of the Hetero Research Foundation (HRF). HRF is a dedicated research institution that serves as the engine of the company’s new medicine development and molecule work. By 1997, four years after its founding, Hetero emerged as one of the leading companies globally offering affordable antiretroviral APIs, having independently developed generic processes for more than 20 molecules. This placed Hetero at the forefront of the global effort to improve access to HIV/AIDS treatment in low income countries at a time when branded ARVs were incredibly expensive for the majority of patients. 2001-2005 Three years later, in 2001, Hetero received its first USFDA approval for an API facility in Hyderabad, marking the company’s formal entry into regulatory environments and laying the foundation for its subsequent US businesses. By 2005, Hetero broadened its capabilities beyond antiretrovirals and gained recognition as one of the first companies in India to develop and market the antiviral medication Oseltamivir, for the treatment of bird flu and swine flu. 2006-2009 In 2006, Hetero received USFDA approval for a finished dosage manufacturing facility in Hyderabad, an important development that enabled the company to supply generic formulations directly to the US market. This marked Hetero’s vertical integration from raw material production to patient ready medicines.
Sources: en.wikipedia.org
Andy Street, the Mayor of the West Midlands, announces that he and his Manchester counterpart, Andy Burnham, are to meet Mark Harper, the Secretary of State for Transport, to discuss proposals for a privately funded alternative to the abandoned Manchester leg of HS2. The UK is to lend several pieces of the Ghana crown jewels back to Ghana 150 years after looting them from the court of the Asante king. 25 January The UK government announces fresh plans to ban the sale of zombie knives, with legislation taking effect from the autumn. Lloyds Banking Group announces plans to cut around 1,600 positions from its branch staff in a reorganisation that it says is because more customers are banking online. 26 January Buckingham Palace confirms that King Charles III has been admitted to hospital for treatment for an enlarged prostate. Jürgen Klopp, currently the longest-serving manager in the Premier League, announces he is departing as manager of Liverpool F.C. after the conclusion of the 2023–24 season, and taking a break from football management. 27 January The UK government suspends funding for the UN agency for Palestinian refugees, UNRWA, after the organisation sacked several officials reported to have been involved in the 7 October attacks on Israel. Kemi Badenoch, the business secretary, asks Henry Staunton to step down as chair of Post Office Limited after 13 months in the role, as the government moves to strengthen governance at the Post Office in the wake of the long-running Horizon IT scandal.
== Education and academic career == Bhushan began his education in his native India, completing his undergraduate and master's degrees from the University of Jodhpur. He received his Ph.D. in chemistry (working on structure elucidation of natural products isolated from certain desert plants) in 1978 at the University of Jodhpur. Bhushan joined as a lecturer at the University of Roorkee (now Indian Institute of Technology Roorkee, India) in 1979 and was later selected for the position of full professor of chemistry in 1996 and served there till retirement in 2018.
MG132 is a potent, reversible, and cell-permeable proteasome inhibitor (Ki = 4 nM). It belongs to the class of synthetic peptide aldehydes. It reduces the degradation of ubiquitin-conjugated proteins in mammalian cells and permeable strains of yeast by the 26S complex without affecting its ATPase or isopeptidase activities. MG132 activates c-Jun N-terminal kinase (JNK1), which initiates apoptosis. MG132 also inhibits NF-κB activation with an IC50 of 3 μM and prevents β-secretase cleavage.
==== Resistance exercise and muscle atrophy ==== Resistance exercise is exercising a muscle or muscle group against external resistance (see strength training). Studies have found that: a) mice feeding on a high fat or normal diet and given the resistance exercise of repeatedly climbing up a 1 meter ladder for 40 minutes had higher levels of α-ketoglutarate in their blood and seven muscles than non-exercising mice feeding respectively on the high fat or normal diet; b) mice conducting ladder climbing for several weeks and eating a high fat diet developed lower fat tissue masses and higher lean tissue masses than non-exercising mice on this diet; c) mice not in exercise training fed α-ketoglutarate likewise developed lower fat tissue and higher lean tissue masses than α-ketoglutarate-unfed, non-exercising mice; d) OXGR1 was strongly expressed in the mouse adrenal gland inner medullas and either resistance training or oral α-ketoglutarate increased this tissue's levels of the mRNA that is responsible for the synthesis of OXGR1; e) α-ketoglutarate stimulated chromaffin cells isolated from mouse adrenal glands to release epinephrine but reduction of these cells' OXGR1 levels by small interfering RNA reduced this response; f) α-ketoglutarate increased the blood serum levels of epinephrine in mice expressing OXGR1 but not in Oxgr1 gene knockout mice (i.e., mice lacking the OXGR1 gene and protein); g) mice on the high fat diet challenged with α-ketoglutarate increased their blood serum levels of epinephrine and developed lower fat tissue masses and higher lean tissue masses but neither OXGR1 gene knockout mice nor mice that had only their adrenal glands' OXGR1 gene knocked out showed these responses; and h) OXGR1 gene knockout mice fed the high fat diet developed muscle protein degradation, muscle atrophy (i.e., wasting), and falls in body weight whereas control mice did not show these fat diet-induced changes. These findings indicate that in mice resistance exercise increases muscle production as well as serum levels of α-ketoglutarate which in turn suppresses diet-induced obesity (i.e., low body fat and high lean body masses) at least in part by stimulating the OXGR1 on adrenal gland chromaffin cells to release epinephrine. Additional mechanisms include inhibition of hepatic gluconeogenesis via serpina1e signaling (reducing hyperglycemia) and activation of the PHD3/ADRB2 pathway in muscle cells. Supplementation studies have shown that oral α-ketoglutarate increases serum levels of α-ketoglutarate, suppresses obesity and improves glucose tolerance in mice. See § Glucose tolerance below.
Iranians have one of the highest per capita rates of tea consumption in the world. Châikhânes (teahouses) are common in Iran. Iranian tea is typically served in traditional Iranian glasses with a traditional saucer and teaspoon. Tea is cultivated in northern Iran along the shores of the Caspian Sea. In Burma (Myanmar), tea is consumed not only as hot drinks, but also as sweet tea and green tea known locally as laphet-yay and laphet-yay-gyan, respectively. Pickled tea leaves, known locally as lahpet, are a national delicacy. Pickled tea is usually eaten with roasted sesame seeds, crispy fried beans, roasted peanuts and fried garlic chips. In Mali, gunpowder tea is served in series of three, starting with the highest oxidisation or strongest, unsweetened tea, locally referred to as "strong like death", followed by a second serving, where the same tea leaves are boiled again with some sugar added ("pleasant as life"), and a third one, where the same tea leaves are boiled for the third time with yet more sugar added ("sweet as love"). Green tea is the central ingredient of a distinctly Malian custom, the "grin", an informal social gathering that cuts across social and economic lines, starting in front of family compound gates in the afternoons and extending late into the night, and is widely consumed in Bamako and other large urban areas. In the United States, 80% of tea is consumed as iced tea. Sweet tea is native to the southeastern U.S. and is iconic in its cuisine due to its refreshing temperature and large amount of sweetener.
Sources: en.wikipedia.org
It measures the presence and amount of one or more compounds in a liquid sample. Separation occurs in a column, and detection produces a signal proportional to concentration. Identification usually requires comparison with a known reference standard under the same conditions.
In most cases the sample is consumed or altered during analysis, though some detectors are non-destructive. Fractions can be collected after separation for further study. Repeated testing therefore requires additional sample.
Run times range from under a minute for fast methods to over an hour for complex separations. Sample preparation, equilibration, and data review add time. Throughput depends on instrument configuration and method requirements.
It measures the amounts and identities of compounds in liquid samples by separation and detection. Depending on the detector and reference standards, results can be qualitative or quantitative. The technique is used in fields such as pharmaceutical analysis, food safety, and environmental monitoring.