This is a working overview of Retention time, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-08-01 and is reviewed periodically as new material appears.
HPLC testing separates dissolved compounds by passing a liquid sample through a column packed with stationary phase. A pump delivers mobile phase at controlled flow, and the sample components interact differently with stationary and mobile phases. Compounds that spend more time in mobile phase elute earlier; those retained by stationary phase elute later. Detectors record elution as peaks, and peak area or height relates to amount. This mechanism underpins quantitative analysis of mixtures.
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.
Developing an HPLC method begins with defining the purpose, such as quantifying a main component, measuring impurities, or confirming identity. Analysts select separation mode, column, mobile phase, detection, and sample preparation based on analyte properties and matrix. Experiments vary solvent strength, pH, buffer type, and temperature to achieve resolution between critical peaks. The goal is a robust method that produces reliable results across instruments and operators. Method development often involves trial runs and statistical optimization.
Validation demonstrates that a method is suitable for its intended use. Typical performance characteristics include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Regulators and standards organizations provide frameworks, but specific requirements depend on the application and jurisdiction. System suitability tests are run before sample analysis to confirm resolution, peak symmetry, retention time repeatability, and sensitivity. A validated method is not permanently fixed; changes may require partial or full revalidation.
Routine HPLC testing depends on controlled reagents, calibrated instruments, and documented procedures. Columns degrade over time, so retention times and peak shapes are monitored for drift. Mobile phases are filtered and degassed to prevent pump damage and detector noise. Reference standards must be traceable and stored under suitable conditions. Data handling systems record injections, calculations, and audit trails. Quality control samples interspersed with unknowns help detect errors during a run.
| Property | Value | Notes |
|---|---|---|
| Separation mode | Reversed-phase | Nonpolar stationary phase with polar mobile phase |
| Typical column particle size | 3–5 µm | Smaller particles improve resolution but raise pressure |
| Typical flow rate | 0.5–2.0 mL/min | Depends on column dimensions and pressure limits |
| Common detection | UV-Vis absorbance | Requires analytes with chromophores |
| Typical run time | 5–30 min | Varies with method, gradient, and sample complexity |
Laboratories apply HPLC testing across pharmaceutical, food, environmental, and industrial chemistry. The method can measure active ingredients, impurities, additives, preservatives, and degradation products. Sample preparation often includes dilution, filtration, and sometimes extraction or derivatization. The choice of column, mobile phase, pH, temperature, and detector depends on the analytes and matrix. Results are compared with reference standards to assign identity and concentration. Method suitability is judged by resolution, precision, and accuracy.
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.
Developing an HPLC test begins with defining the analytes, matrix, and required reporting limits. Chemists select a separation mode, column chemistry, mobile phase composition, flow rate, and detection wavelength or mass transition. Experiments then adjust these variables to achieve adequate retention, resolution, and peak shape. System suitability tests confirm that the instrument and method perform consistently before sample analysis. Without suitable resolution, quantitative results may be unreliable. Preliminary runs often use scouting gradients to locate retention windows.
Validation establishes that a method is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, robustness, and stability of standards and samples. Acceptance criteria are defined in advance, and results are documented in a validation report. Regulatory guidance for pharmaceuticals, foods, and environmental testing differs, so the applicable framework must be identified. Ongoing verification uses control samples and trend charts after validation. Method transfer to another laboratory may require partial revalidation.
Routine quality control includes blanks, duplicates, spiked samples, and certified reference materials. Calibration curves are prepared with standards at several concentrations, and the detector response is checked for linearity. Carryover, column aging, mobile phase evaporation, and temperature drift can shift retention times or peak areas. Maintenance such as replacing seals, filters, and columns helps prevent failures. Records of injections, integration, and deviations support traceability. Audits may request raw data and instrument logs for each batch.
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.
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.
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.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Typical checks include retention time, peak area precision, resolution between critical pairs, tailing factor, and theoretical plate count. Acceptance criteria are set in the method or pharmacopeial monograph. If a suitability check fails, the run may be rejected and the instrument or sample preparation may need investigation. This practice helps prevent release of data from a system that has drifted out of control.
== External links == "Imipenem". Drug Information Portal. U.S. National Library of Medicine. Archived from the original on 10 July 2017. "Cilastatin". Drug Information Portal. U.S. National Library of Medicine. Archived from the original on 23 January 2017. "Relebactam". Drug Information Portal. U.S. National Library of Medicine. Archived from the original on 5 June 2020.
Naringenin is a flavanone from the flavonoid group of polyphenols. It is commonly found in citrus fruits, especially as the predominant flavonone in grapefruit. The fate and biological functions of naringenin in vivo are unknown, remaining under preliminary research, as of 2024. High consumption of dietary naringenin is generally regarded as safe, mainly due to its low bioavailability. Taking dietary supplements or consuming grapefruit excessively may impair the action of anticoagulants and increase the toxicity of various prescription drugs. Similar to furanocoumarins present in citrus fruits, naringenin may evoke CYP3A4 suppression in the liver and intestines, possibly resulting in adverse interactions with common medications.
Deupsilocin (INNTooltip International Nonproprietary Name, USANTooltip United States Adopted Name; former developmental code names HLP003 and CYB0003), also known as deuterated psilocin or as psilocin-d10, is a psychedelic drug of the tryptamine family related to psilocin which is under development for the treatment of major depressive disorder, alcoholism, and other psychiatric disorders. It is taken orally. The drug is a deuterated isotopologue of psilocin with altered pharmacokinetics.
Sources: en.wikipedia.org
The water cobras found in central and western Africa are an extremely venomous cobra species (Naja). These species were formerly under the genus Boulengerina. The banded water cobra (Naja annulata) and the Congo water cobra (Naja christyi) are dangerously venomous. The banded water cobra has one subspecies which is known as Storms water cobra (Naja annulata stormsi). Their venoms are extremely potent neurotoxins. A toxicological study listed the intraperitoneal (IP) LD50 of N. annulata at 0.143 mg/kg. Brown (1973) listed the intravenous LD50 for N. a. annulata at 0.2 mg/kg. The same study listed the intraperitoneal (IP) LD50 of N. christyi at 0.12 mg/kg. The venoms of these little-known elapids have the lowest intraperitoneal LD50 of any Naja species studied thus far and have high concentrations of potent postsynaptic neurotoxins. Serious and dangerous envenomation can result from a bite from either of these snakes. There is at least one case of human envenomation caused by the Congo water cobra (N. christyi). Symptoms of the envenomation were mild. There is no specific antivenom currently produced for either of these two species.
Low-carbohydrate diets restrict carbohydrate consumption relative to the average diet. Foods high in carbohydrates (e.g., sugar, bread, pasta) are limited, and replaced with foods containing a higher percentage of fat and protein (e.g., meat, poultry, fish, shellfish, eggs, cheese, nuts, and seeds), as well as low carbohydrate foods (e.g. spinach, kale, chard, collards, and other fibrous vegetables). There is a lack of standardization of how much carbohydrate low-carbohydrate diets must have, and this has complicated research. One definition, from the American Academy of Family Physicians, specifies low-carbohydrate diets as having less than 20% of calories from carbohydrates. There is no good evidence that low-carbohydrate dieting in general confers any particular health benefits apart from weight loss, where low-carbohydrate diets achieve outcomes similar to other diets, as weight loss is mainly determined by calorie restriction and adherence. One particular form of low-carbohydrate diet called the ketogenic diet was first established as a medical diet for treating epilepsy. It became a popular diet for weight loss through celebrity endorsement, but there is no evidence of any distinctive benefit for this purpose and the diet carries a risk of adverse effects, with the British Dietetic Association naming it one of the "top five worst celeb diets to avoid" in 2018.
At MIT, David Richardson was pursuing his doctorate in Al Cotton's lab using X-ray crystallography to study the structure of staphylococcal nuclease. Jane Richardson learned the necessary technical skills and scientific background in biochemistry and biophysics through work at the lab as she worked alongside her husband, whom she still works with today. Richardson later began drawing her eponymous diagrams as a method of interpreting the structures of protein molecules. Over the course of her career, Richardson has been recognized by many prestigious institutions of the scientific community. In July 1985 she was awarded a MacArthur Fellowship for her work in biochemistry. She was elected to the National Academy of Sciences and the American Academy of Arts and Sciences in 1991 and to the Institute of Medicine in 2006. As part of her role in the National Academy of Sciences, Richardson serves on panels that advise the White House and the Pentagon regarding nationally important scientific matters (e.g.,). For the 2012-2013 year, Richardson was elected president of the Biophysical Society for the 2012-2013 year, and she became a fellow of the American Crystallographic Association in 2012. Richardson is currently a James B. Duke Professor of Biochemistry at Duke University. The Richardsons continue to jointly head a research group at Duke University. Richardson is a contributor to Wikipedia, where she is a prominent member of WikiProject Biophysics.
Starmer says he has taken account of whether it would be right "to impose a further burden on the taxpayer". MSPs vote unanimously in favour of plans to ban dual mandates. Following an external review into the use of messaging services, Scotland's Deputy First Minister, Kate Forbes announces that Scottish Government ministers and staff will be banned from using WhatsApp for official business. Former First Minister of Scotland Humza Yousaf announces he will step down as an MSP at the 2026 Scottish Parliament election. Democracy and Boundary Commission Cymru unveils the names of the 16 constituencies that will make up the enlarged Senedd from 2026, with all but four of them known by exclusively Welsh language names. The Welsh Conservatives reaffirm their commitment to devolution following a social media post by MS Joel James, who said he wanted to get "rid" of the Senedd; the post, in response to the announcement of the constituencies for the 2026 election, was swiftly deleted. Nigel Farage says that Reform UK are in "open negotiations" with US billionaire Elon Musk about him donating to the party after the pair met at Donald Trump's Mar-a-Lago estate in Florida. 18 December – Reform UK confirms that Craig Campbell, a party official in Scotland, has been removed from his post after revelations his family has links to Ulster Loyalists and has a relatives who was convicted of murdering a Celtic fan. Police are called to what is described as a heated meeting of Oldham Council.
Sources: en.wikipedia.org
GLP-1 is effective at reducing blood glucose levels. GLP-1 analogs have a significant therapeutic effect and high efficacy on diabetes treatments and hypoglycemia prevention. Proliferation effect and trophic effect on the small intestine, GLP-2 is used as a therapy to support patients with short-bowel syndrome and other underlying intestinal conditions. Proglucagon Overview at colostate.edu Nosek, Thomas M. "Section 6/6ch2/s6ch2_27". Essentials of Human Physiology. Archived from the original on 2016-03-24. Enteroglucagon at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
The marine sulfur cycle is driven by sulfate reduction because hydrogen sulfide is oxidized by microbes for energy or is oxidized abiotically. Dissimilatory sulfate reduction is driven by the degradation of buried organic matter and anaerobic oxidation of methane (AOM) both of which produce carbon dioxide. At depths where sulfate is depleted, methanogenesis is prevalent. At the sulfate-methane transition zone (SMTZ), the upwelling of methane produced by the methanogens is met by the anaerobic methanotrophic archaea in the SMTZ which oxidize it using sulfate as an electron acceptor. More sulfate is present at the SMTZ than methane. A 4:1 ratio of sulfate: methane is observed and the excess sulfate is directed towards organic matter degradation. Syntrophic aggregates of sulfate reducers and methanotrophs have been discovered and the underlying mechanisms observed include direct interspecies electron transfer using large multi heme complexes.
Barium is formed in large amounts by the fission process. A short-lived barium isotope was confused with radium by some early workers. They were bombarding uranium with neutrons in an attempt to form a new element. But instead they caused fission which generated a large amount of radioactivity in the target. Because the chemistry of barium and radium the two elements could be coseparated by for instance a precipitation with sulfate anions. Because of this similarity of their chemistry the early workers thought that the very radioactive fraction which was separated into the "radium" fraction contained a new isotope of radium. Some of this early work was done by Otto Hahn and Fritz Strassmann.
Sources: en.wikipedia.org
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.
It offers high resolution, reproducibility, and compatibility with many sample types. A single run can separate and quantify multiple analytes. It is common in pharmaceutical, food, environmental, and industrial laboratories.
Samples must be soluble in a suitable mobile phase and free of particles that can block the column. Detector response depends on analyte structure, so some compounds need derivatization or alternative detection. Complex matrices may require extensive sample preparation.
It is a set of checks performed before or during an HPLC run to confirm the system works as expected. Parameters may include resolution, tailing factor, theoretical plates, and retention time precision. Failure can trigger maintenance, method adjustment, or repeat analysis.