The short version of retention time fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-05-21. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
| 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 |
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.
Several separation modes exist, including reversed-phase, normal-phase, ion-exchange, size-exclusion, and hydrophilic interaction liquid chromatography. Reversed-phase uses a nonpolar stationary phase with a polar mobile phase and is widely applied to small organic molecules. Gradient elution changes mobile phase composition during the run, while isocratic elution keeps it constant. Column chemistry, particle size, temperature, flow rate, and mobile phase pH all influence retention and resolution. Method development selects conditions that separate analytes from matrix components and from each other.
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.
Collins was voted the show's "Most Iconic Cast Member" in the special anniversary episode TOWIE Turns 10: All Back to Essex in September 2020, for which she made a cameo appearance in a video acceptance message. In January 2016, she entered the Celebrity Big Brother house to participate as a housemate in the seventeenth series. Collins became known for her "diva outbursts" on the show, one of which saw her refuse to be locked inside a cage as part of a shopping task and proclaim to fellow housemate Darren Day that she was "claustrophobic", which would become one of her most well known memes. Her other notable moments in the house included gifting Tiffany Pollard a pair of Dolce & Gabbana shoes for her birthday, before taking them back, resulting in a confrontation, as well as confiding in the former that she believed she was pregnant, ultimately discovering she was not. Collins also struggled with being unable to maintain her hair within the house, exclaiming to Big Brother that her "hair was frazzled" and berated them for not providing heated rollers. She would later sacrifice the hot water in the house to receive a blow dry as part of an immunity prize. Collins received nine nominations from her housemates throughout the series, facing a total of three evictions, two of which she survived on days 11 and 18 respectively. She also won immunity from the fifth eviction after receiving a "gold mask" during the "Forgotten Theatre" task.
=== Other animals with wrinkles === Examples of wrinkles can be found in various animal species that grow loose, excess skin, particularly when they are young. Several breeds of dog, such as the Pug and the Shar Pei, have been bred to exaggerate this trait. In dogs bred for fighting, this is the result of selection for loose skin, which confers a protective advantage.
Indium has greater solubility in liquid mercury than any other metal (more than 50 mass percent of indium at 0 °C). Indium displays a ductile viscoplastic response, found to be size-independent in tension and compression. However it does have a size effect in bending and indentation, associated to a length-scale of order 50–100 μm, significantly large when compared with other metals.
Sources: en.wikipedia.org
Plants usually convert light into chemical energy with a photosynthetic efficiency of 3–6%. Absorbed light that is unconverted is dissipated primarily as heat, with a small fraction (1–2%) reemitted as chlorophyll fluorescence at longer (redder) wavelengths. This fact allows measurement of the light reaction of photosynthesis by using chlorophyll fluorometers. Actual plants' photosynthetic efficiency varies with the frequency of the light being converted, light intensity, temperature, and proportion of carbon dioxide in the atmosphere, and can vary from 0.1% to 8%. By comparison, solar panels convert light into electric energy at an efficiency of approximately 6–20% for mass-produced panels, and above 40% in laboratory devices. Scientists are studying photosynthesis in hopes of developing plants with increased yield. The efficiency of both light and dark reactions can be measured, but the relationship between the two can be complex. For example, the light reaction creates ATP and NADPH energy molecules, which C3 plants can use for carbon fixation or photorespiration. Electrons may also flow to other electron sinks. For this reason, it is not uncommon for authors to differentiate between work done under non-photorespiratory conditions and under photorespiratory conditions. Chlorophyll fluorescence of photosystem II can measure the light reaction, and infrared gas analyzers can measure the dark reaction. An integrated chlorophyll fluorometer and gas exchange system can investigate both light and dark reactions when researchers use the two separate systems together.
In 1966, Whirlpool dropped the RCA name, with the brand then being known as Whirlpool. The following year, the company introduced a 24-hour helpline. Also in 1966, Whirlpool purchased Warwick Electronics, a major television producer for Sears. The purchase also included the division Thomas Organ Company. Whirlpool exited the television market in 1976 by selling the operations to Japan's Sanyo Electronic Co., but retained the organ business for the electronic technology. By 1978, annual revenues exceeded $2 billion. In 1986, Whirlpool acquired KitchenAid, a division of the Hobart Corporation. It also announced that it would close most of its manufacturing facilities in the St. Joseph, Michigan area by the end of 1988.
== Clinical evidence == In a six-month randomized trial published in The New England Journal of Medicine in 2019, 168 people with type 1 diabetes were assigned either Control-IQ with a t:slim X2 and Dexcom G6 or a sensor-augmented pump. Mean time with glucose in the target range of 70–180 mg/dL rose from 61% to 71% in the Control-IQ group and remained about 59% in the control group, an adjusted difference of 11 percentage points, or 2.6 hours per day. No severe hypoglycemic events occurred; one participant using the closed-loop system developed diabetic ketoacidosis after an infusion-set failure. The trial was funded by the National Institute of Diabetes and Digestive and Kidney Diseases; Tandem supplied systems and technical support but, according to the publication, did not control the study design, conduct or analysis. A 13-week randomized trial published in the same journal in 2025 enrolled 319 adults with insulin-treated type 2 diabetes. Time in the target range increased from 48% to 64% with Control-IQ, compared with 51% to 52% in a control group that continued its previous insulin method; the adjusted difference was 14 percentage points. Glycated hemoglobin fell by 0.9 percentage points in the automated-delivery group and by 0.4 points in the control group. One severe hypoglycemic event occurred in the automated-delivery group. The study was funded by Tandem.
Sources: en.wikipedia.org
== Cell cycle control == Cell cycle progression is controlled by ordered action of cyclin-dependent kinases (CDKs), activated by specific cyclins that demarcate phases of the cell cycle. Mitotic cyclins, which persist in the cell for only a few minutes, have one of the shortest life spans of all intracellular proteins. After a CDK-cyclin complex has performed its function, the associated cyclin is polyubiquitinated and destroyed by the proteasome, which provides directionality for the cell cycle. In particular, exit from mitosis requires the proteasome-dependent dissociation of the regulatory component cyclin B from the mitosis promoting factor complex. In vertebrate cells, "slippage" through the mitotic checkpoint leading to premature M phase exit can occur despite the delay of this exit by the spindle checkpoint. Earlier cell cycle checkpoints such as post-restriction point check between G1 phase and S phase similarly involve proteasomal degradation of cyclin A, whose ubiquitination is promoted by the anaphase promoting complex (APC), an E3 ubiquitin ligase. The APC and the Skp1/Cul1/F-box protein complex (SCF complex) are the two key regulators of cyclin degradation and checkpoint control; the SCF itself is regulated by the APC via ubiquitination of the adaptor protein, Skp2, which prevents SCF activity before the G1-S transition. Individual components of the 19S particle have their own regulatory roles.
=== Vitamin B12 structure === In 1948, Hodgkin first encountered vitamin B12, one of the most structurally complex vitamins known, and created new crystals. Vitamin B12 had first been discovered at Merck earlier that year. It had a structure at the time that was almost completely unknown, and when Hodgkin discovered it contained cobalt, she realized the structure actualization could be determined by X-ray crystallography analysis. The large size of the molecule, and the fact that the atoms were largely unaccounted for—aside from cobalt—posed a challenge in structure analysis that had not been previously explored. From these crystals, she deduced the presence of a ring structure because the crystals were pleochroic, a finding which she later confirmed using X-ray crystallography. The B12 study published by Hodgkin was described by Lawrence Bragg as being as significant "as breaking the sound barrier". Scientists from Merck had previously crystallised B12, but had published only refractive indices of the substance. The final structure of B12, for which Hodgkin was later awarded the Nobel Prize, was published in 1955 and 1956.
== History after 1936 == Moniz rapidly disseminated his results through articles in the medical press and a monograph in 1936. Initially, however, the medical community appeared hostile to the new procedure. On 26 July 1936, one of his assistants, Diogo Furtado, gave a presentation at the Parisian meeting of the Société Médico-Psychologique on the results of the second cohort of patients leucotomised by Lima. Sobral Cid, who had supplied Moniz with the first set of patients for leucotomy from his own hospital in Lisbon, attended the meeting and denounced the technique, declaring that the patients who had been returned to his care post-operatively were "diminished" and had experienced a "degradation of personality". He also claimed that the changes Moniz observed in patients were more properly attributed to shock and brain trauma, and he derided the theoretical architecture that Moniz had constructed to support the new procedure as "cerebral mythology." At the same meeting the Parisian psychiatrist, Paul Courbon, stated he could not endorse a surgical technique that was solely supported by theoretical considerations rather than clinical observations. He also opined that the mutilation of an organ could not improve its function and that such cerebral wounds as were occasioned by leucotomy risked the later development of meningitis, epilepsy and brain abscesses.
While most causes of sudden cardiac death relate to congenital or acquired cardiovascular disease, an exception is commotio cordis, in which the heart is structurally normal but a potentially fatal loss of rhythm occurs because of the accident of timing of a blow to the chest. Its fatality rate is about 65% even with prompt CPR and defibrillation, and more than 80% without.
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 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.