This is a working overview of Stationary phase, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-05-13 and is reviewed periodically as new material appears.
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.
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.
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.
In quality control laboratories, HPLC testing supports batch release, raw material checks, stability studies, and impurity profiling. A validated method defines sample preparation, instrument settings, calibration, and acceptance criteria. Analysts compare results with specifications and investigate out-of-specification outcomes before a batch is approved. Documentation includes chromatograms, integration records, audit trails, and reagent details. Because results influence product decisions, laboratories follow formal quality systems and data integrity rules. The exact tests and limits depend on the material, its intended use, and the applicable regulatory framework.
| Property | Value | Notes |
|---|---|---|
| Separation principle | Differential partitioning | Analytes distribute between mobile and stationary phases. |
| Mobile phase | Liquid solvent mixture | Composition controls retention and selectivity. |
| Stationary phase | Packed column particles | Often chemically bonded silica. |
| Typical detector | UV-Vis or photodiode array | Mass spectrometry is also common. |
| Common synonym | High-performance liquid chromatography | Abbreviated as HPLC. |
Documentation and traceability are central to regulated HPLC testing. Records typically include instrument logs, column history, mobile-phase preparation, sample preparation, injection sequences, raw chromatograms, and audit trails. Electronic systems may require user access controls, time-stamped changes, and backup procedures. Training records show that analysts are qualified for assigned methods. Audits and inspections check whether written procedures match actual practice and whether deviations are documented. These controls support reproducibility and allow results to be reconstructed if questions arise later.
Method validation establishes that an HPLC procedure is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, robustness, and solution stability. Accuracy reflects closeness to a reference value, while precision reflects agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from matrix components. Validation is documented through protocols and reports, and the required extent depends on the method's use and regulatory context.
The use of old technologies plays a large factor in how hazardous wastewater results in contaminating the environment. This is especially prominent in small and medium-sized tanneries in developing countries. The UN Leather Working Group (LWG) "provides an environmental audit protocol, designed to assess the facilities of leather manufacturers," for "traceability, energy conservation, [and] responsible management of waste products."
Macrophages and inflammatory components (within 1–2 days) Epithelial-mesenchymal interaction: re-epithelialization (phenotype change within hours, migration begins on day 1 or 2) Fibroblasts and myofibroblasts: progressive alignment, collagen production, and matrix contraction (between day 4 and day 14) Endothelial cells and angiogenesis (begins on day 4) Dermal matrix: elements of fabrication (begins on day 4, lasting 2 weeks) and alteration/remodeling (begins after week 2, lasting weeks to months—depending on wound size).
=== Disadvantages === The used fuel is difficult and dangerous to reprocess because many of the daughters of 232Th and 233U are strong gamma emitters. All 233U production methods result in impurities of 232U, either from parasitic knock-out (n,2n) reactions on 232Th, 233Pa, or 233U that result in the loss of a neutron, or from double neutron capture of 230Th, an impurity in natural 232Th:
=== Economics === In the United States, the price of for a vial of Humalog increased from US$35 in 2001 to $234 in 2015, or $10.06 and $29.36 per 100 units. In April 2019, Eli Lilly and Company announced they would produce a version selling for $137.35 per vial. The chief executive said that this was a contribution "to fix the problem of high out-of-pocket costs for Americans living with chronic conditions", but Patients for Affordable Drugs Now said it was just a public relations move, as "other countries pay $20 for a vial of insulin." In March 2023, Lilly announced a program capping their insulin prices at $35 per month.
Sources: en.wikipedia.org
Planar cell polarity was first described in insects and then further defined in fruit flies (Drosophila melanogaster). Some of the earlier work on gene controlled polarity of fly wings was published by D. Gubb and A. García-Bellido in 1982 describing how the mutation of some genes resulted in a morphology change in the cuticle orientation on the fly body. The history of the PCP pathway as it was expanded by fly genetics work, which lead to the interesting names for PCP components like Frizzled, Van Gogh, and Dishevelled. These are typical nomenclature for new genes discovered in flies, which are often based on the description of the visual presentation of the mutant flies for each gene. Early PCP research focused on its role in embryology and genetics, but the discovery that PCP proteins were localized asymmetrically within the cell pushed the topic into the world of cell biology. There was a surge in interest in the Planar Cell Polarity pathway after conserved PCP genes were found to be involved in important vertebrate processes vertebrate gastrulation, mammalian ear patterning and hearing, and neural tube closure. Discoveries from this popular wave of PCP research has found its involvement in polarized ciliary beating in the trachea and brain ventricles, oriented cell divisions, lung branching, and hair follicle alignment. A major challenge to studying PCP is that the in vivo protein and cell contact signaling required to facilitate it are difficult to recapitulate in a cell culture dish.
== External links == Video of the Daisy ad, from the PBS website A Historical Look at Campaign Commercials The Emergence of the Maimed Hero Spy vs Spy Gallery Missile Command at the Killer List of Videogames
On October 31, a federal judge in Rhode Island cited the Administrative Procedure Act and temporarily ordered the Trump administration to continue SNAP funding. A second federal judge in Boston said the Trump administration's plan to stop SNAP funding during the shutdown was against the law, but did not order payments to resume. On November 7, Justice Ketanji Brown Jackson temporarily froze the lower court order requiring full payment of SNAP. ABC News stated, "at least nine states had already begun issuing SNAP benefits under the direction of the federal agency that operates SNAP," reportedly including California, Wisconsin, Kansas, Pennsylvania, New York, New Jersey, and Vermont. In early November, Trump called for ending the Senate's rule and tradition of the filibuster. On November 6, some Republican senators talked about making a "clean" Continuing Resolution one of the exceptions to the filibuster rule, but it's estimated that this change is unlikely. On November 9, the Senate achieved a 60-vote compromise of a "mini-bus" which will fund certain departments through next September and the rest of government through January 30. SNAP would be funded through September 2026. Senate Republicans agreed to have a vote on the Obamacare funding by the 2nd week of December. Eight Democrats voted with Republicans to end the shutdown. On November 12, the House passed the bill, 222 to 209. Trump then signed it into law.
Collective cell migration describes the movements of group of cells and the emergence of collective behavior from cell-environment interactions and cell-cell communication. Collective cell migration is an essential process in the lives of multicellular organisms, e.g. embryonic development, wound healing and cancer spreading (metastasis). Cells can migrate as a cohesive group (e.g. epithelial cells) or have transient cell-cell adhesion sites (e.g. mesenchymal cells). They can also migrate in different modes like sheets, strands, tubes, and clusters. While single-cell migration has been extensively studied, collective cell migration is a relatively new field with applications in preventing birth defects or dysfunction of embryos. It may improve cancer treatment by enabling doctors to prevent tumors from spreading and forming new tumors.
== Mechanism == NADK phosphorylates NAD+ at the 2’ position of the ribose ring that carries the adenine moiety. It is highly selective for its substrates, NAD and ATP, and does not tolerate modifications either to the phosphoryl acceptor, NAD, or the pyridine moiety of the phosphoryl donor, ATP. NADK also uses metal ions to coordinate the ATP in the active site. In vitro studies with various divalent metal ions have shown that zinc and manganese are preferred over magnesium, while copper and nickel are not accepted by the enzyme at all. A proposed mechanism involves the 2' alcohol oxygen acting as a nucleophile to attack the gamma-phosphoryl of ATP, releasing ADP.
Sources: en.wikipedia.org
=== Enzymes === Peripheral enzymes participate in metabolism of different membrane components, such as lipids (phospholipases and cholesterol oxidases), cell wall oligosaccharides (glycosyltransferase and transglycosidases), or proteins (signal peptidase and palmitoyl protein thioesterases). Lipases can also digest lipids that form micelles or nonpolar droplets in water.
=== Miscellaneous === Liquids are sometimes used in measuring devices. A thermometer often uses the thermal expansion of liquids, such as mercury, combined with their ability to flow to indicate temperature. A manometer uses the weight of the liquid to indicate air pressure. The free surface of a rotating liquid forms a circular paraboloid and can therefore be used as a telescope. These are known as liquid-mirror telescopes. They are significantly cheaper than conventional telescopes, but can only point straight upward (zenith telescope). A common choice for the liquid is mercury.
In a 3 January 2026 editorial, The New York Times editorial board condemned the attack as "dangerous and illegal", describing it as an act of "latter-day imperialism" which lacked "any semblance of international legitimacy, valid legal authority or domestic endorsement". Comparing the attack to interventions in Libya, the war in Afghanistan, and US involvement in Nicaragua, it warned of the "potential for chaos in Venezuela", including violence from paramilitary groups such as the Venezuelan colectivos or the Colombian National Liberation Army (ELN), which operates in western Venezuela. The AFL-CIO condemned the attack, calling it unconstitutional. Many analysts liken the operation in Venezuela to prior operations, such as Operation Nifty Package which led to the capture of Panamanian military leader, Manuel Noriega, as well as Operation Red Dawn, which led to the capture of former Iraqi president, Saddam Hussein.
Russia leather is a water-resistant leather, oiled with birch bark oil after tanning. This leather was a major export good from seventeenth- and eighteenth-century Russia, as the availability of birch bark oil limited its geographical production. The oil impregnation also deterred insect attack and gave a distinctive and pleasant aroma that was seen as a mark of quality in leather. Birch bark tar is also one of the components of Vishnevsky liniment. Birch bark tar oil is an effective repellent of gastropods. The repellent effect lasts about two weeks. The repellent effect of birch bark tar oil mixed with petroleum jelly and applied to a fence can last up to several months. Birch bark tar oil has strong antiseptic properties, owing to a large amount of phenol derivatives and terpenoid derivatives. Birch bark tar oil was used in the eighteenth century alongside civet and castoreum and many other aromatic substances to scent the fine Spanish leather Peau d'Espagne. At the turn of the twentieth century, birch bark tar had become a specialty fragrance material in perfumery as a base note to impart a leathery, smoky note in fragrances, especially from the leather and tobacco genre, and to a lesser extent in Chypres, especially Cuir de Russie perfumes and fragrance bases, typically together with castoreum and isobutyl quinoline. It is used as an ingredient in some soaps, e.g. the scent of Imperial Leather soap, though other tars (i.e. from pine, coal) with an equally phenolic and smoky odour are more commonly used in soaps as a medicating agent.
Sources: en.wikipedia.org
HPLC separates and detects individual compounds in a liquid sample, producing peaks at characteristic retention times. Peak area or height can be used to estimate concentration when calibrated with known standards. It does not identify unknown compounds with certainty unless additional detectors or reference materials are used.
Pressure drives the liquid mobile phase through a column packed with small particles. Without pressure, flow would be very slow or stop because the packed bed resists liquid movement. Modern pumps maintain a steady flow despite the resistance.
A chromatogram is a plot of detector signal against time after sample injection. Each peak represents a compound or group of compounds eluting from the column. Retention time and peak area are the main measurements read from the plot.
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.