Retention time raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2026-01-31 and is reviewed periodically as new material appears.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Primary guidance | ICH Q2(R2) | Analytical procedure validation |
| Compendial chapter | USP <621> | Chromatography general chapter |
| Validation parameter | Accuracy | Closeness to accepted true value |
| System suitability check | Peak resolution | Ensures separation between adjacent peaks |
| Data record | Audit trail | Supports data integrity and traceability |
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.
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.
Greater Manchester Police confirm that, following their investigation, Labour deputy leader Angela Rayner will not face any further police action over her living arrangements before her time as an MP. Former Plaid Cymru MP Jonathan Edwards, who represents Carmarthen East and Dinefwr, announces he will not contest his seat at the election; Edwards was asked to leave Plaid in 2022 after accepting a police caution for assaulting his wife. Stormont passes the 2024 Northern Ireland budget, its first in three years, despite opposition from the Ulster Unionist Party, and the Assembly's official opposition, the Social Democratic and Labour Party. 29 May – MSPs vote 64–0 to exclude Scotland's former health secretary, Michael Matheson, from the Scottish Parliament for 27 sitting days, and to suspend his salary for 54 days, after he breached expenses rules by accumulating an £11,000 bill on his parliamentary iPad. The governing SNP abstains from voting, and calls for a review of the complaints procedure, suggesting it could be open to bias. The Welsh Conservatives table a motion of no confidence in First Minister Vaughan Gething following several weeks of controversy over donations to his leadership campaign. The motion is scheduled to face a Senedd vote on 5 June. Pat Cullen stands down as chief executive of the Royal College of Nursing in order to seek the nomination as Sinn Féin candidate for Fermanagh and South Tyrone in the general election.
Neutrons from the fission of uranium-235 are captured by uranium-238 nuclei to form uranium-239; a beta decay converts a neutron into a proton to form neptunium-239 (half-life 2.36 days) and another beta decay forms plutonium-239. Egon Bretscher working on the British Tube Alloys project predicted this reaction theoretically in 1940. Plutonium-238 is synthesized by bombarding uranium-238 with deuterons (D or 2H, the nuclei of heavy hydrogen) in the following reaction:
In 1916, Popielski described histamine as a gastric secretagogue of hydrochloric acid. William Beaumont was an army surgeon who in 1825, was able to observe digestion as it took place in the stomach. This was made possible by experiments on a man with a stomach wound that did not fully heal leaving an opening into the stomach. The churning motion of the stomach was described among other findings. In the 19th century, it was accepted that chemical processes were involved in the process of digestion. Physiological research into secretion and the gastrointestinal tract was pursued with experiments undertaken by Claude Bernard, Rudolph Heidenhain and Ivan Pavlov. The rest of the 20th century was dominated by research into enzymes. The first to be discovered was secretin by Ernest Starling in 1902, with ensuing results from John Edkins in 1905 who first suggested gastrin with its structure being determined in 1964. Andre Latarjet and Lester Dragstedt found a role for acetylcholine in the digestive system. In 1972, H2 receptor agonists were described by J. Black, that block the action of histamine and decrease the production of hydrochloric acid. In 1980, proton pump inhibitors were described by Sachs. In 1983, the role of Helicobacter pylori in the formation of ulcers was described by Barry Marshall, and Robin Warren. Art historians have often noted that banqueters on iconographic records of ancient Mediterranean societies almost always appear to be lying down on their left sides. One possible explanation could lie in the anatomy of the stomach and in the digestive mechanism.
Fever and Taking Your Child's Temperature US National Institute of Health factsheet Drugs most commonly associated with the adverse event Pyrexia (Fever) as reported the FDA Archived 9 March 2012 at the Wayback Machine Fever at MedlinePlus Why are We So Afraid of Fevers? at The New York Times
== Proposed benefits == AI agents have been proposed as a means of increasing personal and economic productivity, fostering greater innovation, and liberating users from monotonous tasks. However, Parmy Olson's Bloomberg opinion piece argued that agents are best suited for narrow, repetitive tasks with low risk. Conversely, researchers suggest that agents could be applied to web accessibility for people with disabilities, and researchers at Hugging Face propose that agents could be used for coordinating resources such as during disaster response. The R&D Advisory Team of the BBC views AI agents as being most useful when their assigned goal is uncertain. Erik Brynjolfsson suggests that AI agents are more valuable in enhancing, rather than replacing, humans.
Sources: en.wikipedia.org
== History == Cyclofenil was first introduced for medical use in 1970 under the brand name Ondogyne in France. Subsequently, it was introduced throughout the world under a variety of other brand names, including its most well-known brand name Sexovid.
All uranium fluorides are created using uranium tetrafluoride (UF4); UF4 itself is prepared by hydrofluorination of uranium dioxide. Reduction of UF4 with hydrogen at 1000 °C produces uranium trifluoride (UF3). Under the right conditions of temperature and pressure, the reaction of solid UF4 with gaseous uranium hexafluoride (UF6) can form the intermediate fluorides of U2F9, U4F17, and UF5. At room temperatures, UF6 has a high vapor pressure, making it useful in the gaseous diffusion process to separate the rare uranium-235 from the common uranium-238 isotope. This compound can be prepared from uranium dioxide and uranium hydride by the following process:
=== Space exploration === Synthetic biology raised NASA's interest as it could help to produce resources for astronauts from a restricted portfolio of compounds sent from Earth. On Mars, in particular, synthetic biology could lead to production processes based on local resources, making it a powerful tool in the development of occupied outposts with less dependence on Earth. Work has gone into developing plant strains that are able to cope with the harsh Martian environment, using similar techniques to those employed to increase resilience to certain environmental factors in agricultural crops.
== Counteraction == A 2015 study, reported in the journal Ergonomics, showed that, for twenty healthy subjects, exposure to blue-enriched light during the post-lunch dip period significantly reduced the EEG alpha activity, and increased task performance.
Anglo Boer War - Home The Boer War, A 2 part documentary series shown on British television (1999). Scrapbook of Boer War, MSS P 456 at L. Tom Perry Special Collections, Harold B. Lee Library, Brigham Young University The Concentration Camps 1899–1902 by Hennie Barnard Archived 23 March 2020 at the Wayback Machine British Commanders of the Boer War, Link
Sources: en.wikipedia.org
Similar to plant cells, the cell wall of some microorganisms such as algae and yeast contains indigestible components, such as cellulose. The cells of some kind of SCP should be broken up in order to liberate the cell interior and allow complete digestion. Some kind of SCP exhibits unpleasant color and flavors. Depending on the kind of SCP and the cultivation conditions, care must be taken to prevent and control contamination by other microorganisms because contaminants may produce toxins such as mycotoxins or cyanotoxins. An interesting approach to address this problem was proposed with the fungus Scytalidium acidophilum which grows at a pH as low as 1, outside the tolerance of most microorganisms. This allows it to grow on acid-hydrolysed paper waste at low-cost. Some yeast and fungal proteins are deficient in methionine.
=== Plasma ACTH concentration === This test may also be referred to as a ‘’resting ACTH’’, ’’endogenous ACTH’’, or ‘’basal ACTH’’. The majority of ACTH produced in normal horses comes from corticotrope cells in the pars distalis, with only 2% thought to come from melanotropes in the pars intermedia. In horses with PPID, melanotropes produce abnormally high concentrations of ACTH. Basal plasma ACTH concentrations, which measure the blood levels of circulating ACTH, can therefore be useful in diagnosing the disease. ACTH levels naturally fluctuate in healthy horses, with a significant rise occurring the in autumn (August through October) in North American horses. Horses with PPID have a similar, but much more significant, rise in the autumn. Therefore, a seasonally adjusted reference range must be used that correlates with the time of year the sample is taken. Failure to use a seasonally adjusted reference range may lead to false-positive results in normal horses if they are sampled in the fall. Autumnal testing was thought to be more sensitive and specific than testing at other times of the year; however, this concept has been recently challenged. Basal plasma ACTH levels may increase if the horse is severely ill or under great stress or pain, such as if it has laminitis. However, such events must be fairly significant to confound the results. Additionally, ACTH levels may not be significantly increased early on in the disease, leading to false negatives.
== Further reading == Kropotkin, Peter Alexeivitch; Bealby, John Thomas (1911). "Don Cossacks, Territory of the" . Encyclopædia Britannica. Vol. 8 (11th ed.). p. 412. Peter Holquist, "'Conduct Merciless Mass Terror': Decossackization on the Don, 1919," Cahiers du Monde russe, vol. 38, no. 1/2(Jan.-June 1997), pp. 127–162. In JSTOR Noël Bonneuil, Elena Fursa. 2020. "Nuptiality to regulate the commons? The case of the Don Cossacks (South Russia), 1867–1916." Oxford Economic Papers
Buthionine sulfoximine (BSO) is a sulfoximine derivative which reduces levels of glutathione and is being investigated as an adjunct with chemotherapy in the treatment of cancer. The compound inhibits gamma-glutamylcysteine synthetase, the enzyme required in the first step of glutathione synthesis. Buthionine sulfoximine may also be used to increase the sensitivity of parasites to oxidative antiparasitic drugs.
Drug development is the process of bringing a new pharmaceutical drug to the market once a lead compound has been identified through the process of drug discovery. It includes preclinical research on microorganisms and animals, filing for regulatory status, such as via the United States Food and Drug Administration for an investigational new drug to initiate clinical trials on humans, and may include the step of obtaining regulatory approval with a new drug application to market the drug. The entire process—from concept through preclinical testing in the laboratory to clinical trial development, including Phase I–III trials—to approved vaccine or drug typically takes more than a decade.
Sources: en.wikipedia.org
System suitability is a set of checks performed before and during an HPLC run to confirm that the instrument and method are working as expected. It may include retention time repeatability, resolution between peaks, peak symmetry, and signal intensity. Failing suitability criteria usually invalidates the run.
An HPLC method is typically validated before its routine use and revalidated in part when significant changes affect the method. Regulators do not set a universal calendar interval. The need for revalidation depends on the change, its risk, and the applicable guidance.
Validation establishes that a method is suitable for its intended purpose, often through a planned study. Verification confirms that a laboratory can reproduce a previously validated or compendial method under its own conditions. Verification is usually narrower than full validation.
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.