The short version of Retention time fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-03-27. Anything still debated is marked as such rather than presented as settled.
Separation modes differ by the chemistry of the stationary phase and the composition of the mobile phase. Reversed-phase testing uses a nonpolar column and polar solvents, making it common for pharmaceutical, environmental, and food analytes. Normal-phase testing uses a polar column and nonpolar solvents for compounds that are poorly retained in reversed-phase systems. Ion-exchange and ion-pair methods separate charged species, while size-exclusion methods sort molecules by hydrodynamic volume. Gradient elution changes solvent strength over time to resolve complex mixtures, and isocratic elution holds solvent composition constant for simpler assays.
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.
Detection commonly uses ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. Ultraviolet detection depends on molecular chromophores that absorb light at specific wavelengths. Mass spectrometry provides mass information and sensitive quantification, often after electrospray ionization. Before sample batches, performance checks examine resolution, elution time repeatability, peak symmetry, and plate count. Matrix effects and co-elution remain recognized uncertainties; formal validation studies and orthogonal detection help address them. Detector choice depends on analyte properties and required sensitivity.
High-performance liquid chromatography, or HPLC, separates dissolved compounds by passing a liquid mobile phase through a packed column. Components distribute differently between the stationary phase and the moving liquid, so they travel at different speeds and exit at different times. A detector records these eluting bands as peaks, and peak area or height relates to amount. The technique supports testing in pharmaceuticals, foods, environmental samples, and industrial chemicals. Quantification usually depends on calibration with known standards.
| Property | Value | Notes |
|---|---|---|
| Separation mode | Reversed-phase | Common for polar and moderately polar analytes |
| Typical column length | 100-250 mm | Shorter columns can reduce run time |
| Particle size | 3-5 micrometers | Smaller particles improve efficiency but raise pressure |
| Flow rate | 0.5-2.0 mL/min | Depends on column dimensions and pressure limits |
| Detection | UV-Vis absorbance | Widely used for compounds with chromophores |
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.
Separation performance depends on particle size, pore size, column length, and the chemistry of the stationary phase. Smaller particles generally improve efficiency but require higher pressure and suitable instrumentation. The mobile phase often contains buffers and organic solvents that influence retention and selectivity. Testing labs select conditions based on the analytes, sample matrix, and required sensitivity. Method development frequently involves screening several columns and solvent mixtures before a final set of conditions is chosen.
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.
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.
High-performance liquid chromatography is an analytical technique that separates components in a liquid sample. A pump moves a liquid mobile phase through a column packed with a solid stationary phase. Compounds interact differently with both phases and travel at different rates, leaving the column at distinct retention times. A detector records these arrivals as peaks on a chromatogram. The resulting pattern supports identification and quantification of substances in mixtures. Modern instruments use high pressure to force solvent through small particles, which improves speed and resolution compared with older low-pressure liquid chromatography methods.
Separation in HPLC depends on the chemistry of the stationary phase, the composition of the mobile phase, and the physical properties of the column. Reverse-phase separations use a nonpolar stationary phase and a polar mobile phase, and they are common for many organic compounds. Ion-exchange, size-exclusion, and normal-phase modes serve other classes of analytes. Gradient elution changes solvent strength over time, while isocratic elution holds it constant. Flow rate, temperature, particle size, and column length all influence peak shape and resolution. Detection may use ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry, depending on the analyte and the required sensitivity.
UPS has been criticized for its treatment of its workforce, including providing inadequate protections and sick leave during the COVID-19 pandemic. The company has also been subject to perennial criticism for damaged, late, or otherwise mishandled packages. Safe streets activists have attacked UPS, along with other parcel delivery services, for frequently illegally parking their vehicles in bike lanes while making deliveries, a practice that endangers cyclists. They were sued over it in New York in 2015, and criticized alongside peers in a letter from Washington, D.C.'s transportation agency in 2018.
==== Sun drying ==== This preservation method is most economical out of all methods. The tempeh can be blanched prior to dehydration to preserve flavor and prolong shelf life. Tempeh is exposed to internal solar dryer temperature of 80–90 °C (180–200 °F) in this method. A disadvantage of this method is that sunlight can destroy some of the vitamin B12 of tempeh.
== Definition == The word Wagyu literally means "Japanese cattle" and does not denote a single breed. Before the modern breeds were established, Japan had regional populations of native cattle. After the Meiji Restoration in 1868, most were crossed for several generations with imported breeds, mainly British and continental European cattle. Two uncrossed native populations, the Mishima and Kuchinoshima cattle, survive and are considered to have remained free from European genetic influence. In modern Japanese breed and meat classifications, Wagyu usually means four breeds: the Japanese Black, Japanese Brown, Japanese Polled, and Japanese Shorthorn. Beginning in the late nineteenth century, these breeds developed from regional native cattle crossed with imported stock. The imported breeds used differed by breed and region. The resulting cattle were later established as distinct breeds through selection and closed breeding. After bovine spongiform encephalopathy (BSE) was first confirmed in Japan in 2001, the Beef Traceability Law was enacted in 2003. The system assigns each animal a ten-digit identification number and records its birth and movements; it applies to all cattle in Japan, not only Wagyu. This system is also used to verify the labeling requirements introduced for Wagyu beef in 2007. Under guidelines issued by the Ministry of Agriculture, Forestry and Fisheries, the designation Wagyu is recommended only for beef from cattle documented as one of the four breeds or specified crosses between them and confirmed as having been born and raised in Japan.
Luteinizing hormone is available mixed with FSH in the form of menotropin, and other forms of urinary gonadotropins. More purified forms of urinary gonadotropins may reduce the LH portion in relation to FSH. Recombinant luteinizing hormone is available as lutropin alfa (Luveris).
Heroin, also known as diacetylmorphine and diamorphine among other names, is a morphinan opioid substance synthesized from the dried latex of the opium poppy; it is mainly used as a recreational drug for its euphoric effects. Heroin is used medically in several countries to relieve pain, such as during childbirth or a heart attack. Medical-grade diamorphine is used as a pure hydrochloride salt. Various white and brown powders sold illegally around the world as heroin are routinely diluted with cutting agents. Black tar heroin is a variable admixture of morphine derivatives—predominantly 6-MAM (6-monoacetylmorphine), which is the result of crude acetylation during clandestine production of street heroin. Heroin is typically injected, usually into a vein, but it can also be snorted, smoked, or inhaled. In a clinical context, the route of administration is most commonly intravenous injection; it may also be given by intramuscular or subcutaneous injection, as well as orally in the form of tablets. The onset of effects is usually rapid and lasts for a few hours. Common side effects include respiratory depression (decreased breathing), dry mouth, drowsiness, impaired mental function, constipation, and addiction. Use by injection can also result in abscesses, infected heart valves, blood-borne infections, and pneumonia. After a history of long-term use, opioid withdrawal symptoms can begin within hours of the last use. When given by injection into a vein, heroin has two to three times the effect of a similar dose of morphine.
Sources: en.wikipedia.org
Detrital monazite grains are produced by the weathering and erosion of pre-existing rocks and then transported into sedimentary basins. The detrital monazite contains zonation patterns which preserve the geological history of the source region. Investigating detrital monazite in the basin not only helps in reconstructing the metamorphic, tectonic and hydrothermal history of the source region, but also finding the depositional age, structural evolution and sediment sources of the basin. For example, the domain with youngest age may represent exhumation of source rock, which is followed by immediate erosion and deposition.
== Production == Thebacon is generated by the esterification product of the enol tautomer of hydrocodone (dihydrocodeineone) with acetic anhydride. Although modification of thebaine is the most common way of making thebacon, preparation by refluxing hydrocodone with acetic anhydride is not uncommon, generally similar to how diacetylmorphine is produced. It is also a product of the metabolism of hydrocodone by Pseudomonas putida M10, the bacterium used for oil spill remediation. This also produces a morphinone reductase, which can turn morphine into hydromorphone in a process which produces other active opioids, such as oxymorphone, oxymorphol, or hydromorphinol as intermediates.
In addition, they announced plans to conduct a phase 2b study of enobosarm at doses of 3 to 6 mg/day for this purpose in sarcopenic obese or overweight elderly individuals receiving GLP-1 receptor agonists. Enobosarm was developed by GTx, Inc., and is now being developed by Veru, Inc.
Other compounds other than radiolabelled somatostatin receptor antagonists have also been studied. Cyclosomatostatin is one such compound. Contrary to previously discussed compounds, cyclosomatostatin does not contain a radionuclide. It is a non-selective somatostatin receptor antagonist, inhibiting the effects of somatostatin on target cells in the gastrointestinal tract, pancreas, hypothalamus, and central nervous system. Cyclosomatostatin is used as a research chemical to investigate the effects of somatostatin on different cell types by antagonizing its receptors. However it acts as an agonist in SH-SY5Y neuroblastoma cells. Cyclosomatostatin is also known by the following names:
Sources: en.wikipedia.org
The LSD molecule has two chiral centers at carbons 5 and 8 of the ergoline ring system and hence there are four possible enantiomeric stereoisomers of LSD. Iso-LSD, also known as d-iso-LSD, (+)-iso-LSD, or (5R-8S)-LSD, is one of four possible stereoisomers. The other isomers are LSD (d-LSD, (+)-LSD, or (5R,8R)-LSD), l-iso-LSD ((–)-iso-LSD or (5S,8R)-iso-LSD), and l-LSD ((–)-LSD or (5S,8S)-LSD). None of them are known to have significant psychoactivity in humans besides LSD. LSD is easily epimerized into iso-LSD with base. Consequently, iso-LSD is a common synthetic contaminant in chemical synthesis of LSD. Iso-LSD can be easily epimerized back into LSD. LSD can degrade into iso-LSD depending on temperature, solvent and pH, among other factors. In clinical studies, up to 30% of LSD administered in capsules has been found to isomerize into iso-LSD. Iso-LSD is said to be a metabolite of LSD in animals and humans. However, according to other sources, iso-LSD not a metabolite of LSD but is instead only a contaminant.
== Pharmacodynamics == In addition to its oxytocin receptor agonism, oxytocin has been found to act as a positive allosteric modulator (PAM) of the μ- and κ-opioid receptors and this may be involved in its analgesic effects.
== Hormonal regulation == Insulin is a peptide hormone that is critical for managing the body's metabolism. Insulin is released by the pancreas when blood sugar levels rise, and it has many effects that broadly promote the absorption and storage of sugars, including lipogenesis. Insulin stimulates lipogenesis primarily by activating two enzymatic pathways. Pyruvate dehydrogenase (PDH), converts pyruvate into acetyl-CoA. Acetyl-CoA carboxylase (ACC), converts acetyl-CoA produced by PDH into malonyl-CoA. Malonyl-CoA provides the two-carbon building blocks that are used to create larger fatty acids. Insulin stimulation of lipogenesis also occurs through the promotion of glucose uptake by adipose tissue. The increase in the uptake of glucose can occur through the use of glucose transporters directed to the plasma membrane or through the activation of lipogenic and glycolytic enzymes via covalent modification. The hormone has also been found to have long term effects on lipogenic gene expression. It is hypothesized that this effect occurs through the transcription factor SREBP-1, where the association of insulin and SREBP-1 lead to the gene expression of glucokinase. The interaction of glucose and lipogenic gene expression is assumed to be managed by the increasing concentration of an unknown glucose metabolite through the activity of glucokinase. Another hormone that may affect lipogenesis through the SREBP-1 pathway is leptin. It is involved in the process by limiting fat storage through inhibition of glucose intake and interfering with other adipose metabolic pathways.
=== Certification === Several bodies independently certify the production of tea, such as Rainforest Alliance, Fairtrade, UTZ Certified, and Organic. From 2008 to 2016, sustainability standards-certified tea production experienced a compound annual growth rate of about 35%, accounting for at least 19% of overall tea production. In 2016, at least 1.15 million tonnes of sustainably certified tea was produced, valued at US$2 billion. Rainforest Alliance certified tea is sold by Unilever brands Lipton and PG Tips in Western Europe, Australia and the U.S. Fairtrade certified tea is sold by a large number of suppliers around the world. UTZ Certified tea is sold by Pickwick tea.
=== Antibiotic function === The β-lactam family of antibiotic molecules consists of four groups: penicillins, cephalosporins, carbapenems (such as imipenem, ertapenem, meropenem and doripenem) and monobactams. These antibiotics share common structure and mechanism of action. They enter the periplasmic space through porins, where they then inhibit transpeptidases (which are also known as penicillin-binding proteins (PBPs)), enzymes that facilitate peptide cross-links during cell wall synthesis. Their binding to the PBP active site is facilitated in part by their common structure, which is similar to that of D-alanyl-D-alanine. D-Alanyl-D-alanine is a residue on the NAM peptide subunit involved in building peptidoglycan. Carbapenem covalently binds to PBPs, which causes transpeptidases to irreversibly lose their catalytic activity. Inhibition of transpeptidases prevents the formation of cross-links between peptidoglycan polymers and causes a build-up of peptidoglycan precursors. Newly formed peptidoglycan is weakened from the absence of cross-linkages. The continued activity of autolysins, that function like lysozymes and cleave glycosidic and peptide bonds of peptidoglycan in periplasm, weakens the cell wall and leads to osmotic bursting of the bacterial cell. One notable property of carbapenems is their resistance to hydrolysis by bacterial plasmid and chromosomally mediated extended-spectrum β-lactamases (ESBL).
Sources: en.wikipedia.org
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.
Performance checks confirm that the chromatographic system works within preset limits before results are accepted. They examine factors such as peak resolution, tailing, and repeatability. If criteria fail, the run may need correction or repetition.
Retention time alone is not definitive proof because other compounds can elute at similar times. Confirmation usually uses a second method, a different column, or a detector such as mass spectrometry. Authentic standards strengthen identification.
HPLC separates and quantifies compounds in a liquid sample. Detectors produce a response proportional to the amount of a compound passing through the flow cell. Identification by retention time requires comparison with a known standard.