Everything below concerns Quality control. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Last reviewed on 2026-07-18. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Common abbreviation | HPLC | High-performance liquid chromatography |
| Separation basis | Differential partitioning | Between liquid mobile phase and solid stationary phase |
| Common mode | Reverse phase | Nonpolar column, polar mobile phase |
| Typical detector | UV-Vis absorbance | Widely used for compounds with chromophores |
| Typical column particle size | 2–5 µm | Smaller particles can improve resolution |
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.
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.
The petroleum industry generally classifies crude oil by the geographic location it is produced in (e.g., West Texas Intermediate, Brent, or Oman), its API gravity (an oil industry measure of density), and its sulfur content. Crude oil may be considered light if it has low density, heavy if it has high density, or medium if it has a density between that of light and heavy. Additionally, it may be referred to as sweet if it contains relatively little sulfur or sour if it contains substantial amounts of sulfur. The geographic location is important because it affects transportation costs to the refinery. Light crude oil is more desirable than heavy oil since it produces a higher yield of gasoline, while sweet oil commands a higher price than sour oil because it has fewer environmental problems and requires less refining to meet sulfur standards imposed on fuels in consuming countries. Each crude oil has unique molecular characteristics which are revealed by the use of crude oil assay analysis in petroleum laboratories. Barrels from an area in which the crude oil's molecular characteristics have been determined and the oil has been classified are used as pricing references throughout the world. Some of the common reference crudes are:
The Cave of the High Place in the Small Valley (Cave 181), also called the "Highest Cave", is described extensively by Albert Grünwedel, as a particularly interesting cave of the small ravine. He explains that the cave is located high up on the right side of the ravine, which accounts for the fact that its murals have been preserved from the usual iconoclastic vandalism: the faces in particular are well preserved. Also, the murals did not use gold foils for decoration, which reduced the incentive for theft. In his plates, Grünwedel illustrates the murals of the cave, where he names the cave by its official name: Hochliegende Höhle der 2. Schlucht ("Cave of the High Place in the 2nd Valley"), which is the German name for cave 181. Grünwedel explains that the structure of the cave is extremely rare, as it is not a barrel-vaulted cave: instead, the ceiling has the shape of a tent. The flatness of the sides of the tent-like ceiling is the reason why Grünwedel was able to remove easily most of the ceiling paintings in large panels, something which is impossible with the strongly curved surface of a barrel-vaulted ceiling. The tent-like ceiling is bordered by a row of seven bejewelled princes on each side. The side wall depict rather tumultuous scenes of the sermon of the Buddha, no fewer than eight of them, with a multitude of attendants in various attitudes and clothing. The entrance wall had paintings of Tocharian donors and monks on both side. Above the entrance was the usual painting of Maitreya with surrounding Devaputras.
In molecular biology, the cyanobacterial clock proteins are the main circadian regulator in cyanobacteria. The cyanobacterial clock proteins comprise three proteins: KaiA, KaiB and KaiC. The kaiABC complex may act as a promoter-nonspecific transcription regulator that represses transcription, possibly by acting on the state of chromosome compaction. This complex is expressed from a KaiABC operon. In the complex, KaiA enhances the phosphorylation status of kaiC. In contrast, the presence of kaiB in the complex decreases the phosphorylation status of kaiC, suggesting that kaiB acts by antagonising the interaction between kaiA and kaiC. The activity of KaiA activates kaiBC expression, while KaiC represses it. Also in the KaiC family is RadA/Sms, a highly conserved eubacterial protein that shares sequence similarity with both RecA strand transferase and lon protease. The RadA/Sms family are probable ATP-dependent proteases involved in both DNA repair and degradation of proteins, peptides, glycopeptides. They are classified in as non-peptidase homologues and unassigned peptidases in MEROPS peptidase family S16 (lon protease family, clan SJ). RadA/Sms is involved in recombination and recombinational repair, most likely involving the stabilisation or processing of branched DNA molecules or blocked replication forks because of its genetic redundancy with RecG and RuvABC.
=== Doug Rattmann === Doug Rattmann, often referred to as the "Ratman" is a character in both Portal and Portal 2. He was a former scientist working at Aperture and one of the few who survived when GLaDOS flooded the facility with neurotoxin. In the two games there are various "Ratman dens", where Doug Rattmann has left scribblings and paintings on walls in hidden rooms. Ratman's full appearance is only seen in the Portal 2: Lab Rat webcomic released by Valve prior to Portal 2's release to tie the story of the two games together. Ratman is the comic's main character. Prior to GLaDOS' rampancy and the neurotoxin release, Doug Rattmann was once an Aperture scientist. Already skeptical of the computer, the man fled from the gas and kept himself hidden from GLaDOS' view, slowly becoming more insane over an unknown stretch of time. Among the wall scribblings in the Portal dens is the sentence "The cake is a lie", which became an internet meme. The Lab Rat comic reveals that, despite his madness, Doug Rattmann identified Chell as a rejected test subject due to her high tenacity, and moved her to the top of the queue for testing. During events in Portal, he worked behind the scenes to scribble messages and warnings to Chell on the walls, leading her out of the testing chambers and towards GLaDOS. After watching her defeat the computer, he managed to escape the facility, but returned to assure Chell would be put in indefinite cryogenic storage animation after she was dragged back inside, suffering a serious injury (a shot in the leg from a turret) to complete this.
Sources: en.wikipedia.org
Bromley is a large town in Greater London, England, within the London Borough of Bromley. It is 9+1⁄2 miles (15 kilometres) southeast of Charing Cross, and had an estimated population of 97,540 as of 2021. Originally part of Kent, Bromley became a market town, chartered in 1158. Its location on a coaching route and the opening of a railway station in 1858 were key to its development and the shift from an agrarian village to an urban town. As part of the growth of London's conurbation in the 20th century, Bromley Town significantly increased in population and was incorporated as a municipal borough in 1903 and became part of the London Borough of Bromley in 1965. Bromley today forms a major retail and commercial centre. It is identified in the London Plan as one of the 13 metropolitan centres of Greater London.
== Biology of hydrothermal vents == Life has traditionally been seen as driven by energy from the sun, but deep-sea organisms have no access to sunlight, so biological communities around hydrothermal vents must depend on nutrients found in the dusty chemical deposits and hydrothermal fluids in which they live. Previously, benthic oceanographers assumed that vent organisms were dependent on marine snow, as deep-sea organisms are. This would leave them dependent on plant life and thus the sun. Some hydrothermal vent organisms do consume this "rain", but with only such a system, life forms would be sparse. Compared to the surrounding sea floor, however, hydrothermal vent zones have a density of organisms 10,000 to 100,000 times greater. The hydrothermal vents are recognized as a type of chemosynthetic based ecosystems (CBE) where primary productivity is fuelled by chemical compounds as energy sources instead of light (chemoautotrophy). Hydrothermal vent communities are able to sustain such vast amounts of life because vent organisms depend on chemosynthetic bacteria for food. The water from the hydrothermal vent is rich in dissolved minerals and supports a large population of chemoautotrophic bacteria. These bacteria use sulfur compounds, particularly hydrogen sulfide, a chemical highly toxic to most known organisms, to produce organic material through the process of chemosynthesis. The vents' impact on the living environment goes beyond the organisms that lives around them, as they act as a significant source of iron in the oceans, providing iron for the phytoplankton.
=== Barrow's microdimensional mastering === The astronomer John D. Barrow of the University of Sussex has hypothesized that there are other stages beyond Type III. These Type IV, V, or even VI civilizations would be able to manipulate cosmic structures (galaxies, galactic clusters, superclusters) and even escape the Big Crunch through holes in space. Barrow also proposes an "anti-Kardashev scale": he observes that humans have found it more cost effective to extend their ability to manipulate their environment to smaller and smaller scales rather than to larger and larger ones. He, therefore, proposes a reverse classification, from Type I-minus to Type Omega-minus:
Sources: en.wikipedia.org
HPLC testing measures the presence and amount of one or more compounds in a liquid sample. It separates mixture components and records detector responses as peaks, which are compared with reference standards. Results are usually reported as concentrations or relative percentages.
Retention time is the interval between sample injection and the detector response for a given compound. It depends on the compound's interactions with the stationary and mobile phases under set conditions. Matching a retention time to a standard supports tentative identification but is not always unique.
HPLC alone can separate unknown compounds and provide retention times, but it often cannot identify them with certainty. Coupling HPLC to mass spectrometry gives mass information that improves identification. Confirmation usually requires comparison with reference standards or complementary techniques.
System suitability is a set of checks performed before and during a run to confirm that the instrument, column, and method work as expected. Common checks include resolution, tailing factor, theoretical plates, and relative standard deviation of replicate injections. Failure triggers troubleshooting or method adjustment.