stationary phase is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Last reviewed on 2026-03-26. Where a claim depends on a specific study, the study is described rather than over-claimed.
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. 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.
Routine HPLC testing compares a sample result with a calibration curve prepared from known reference standards. Peak area or peak height is plotted against concentration, and the curve is used to estimate unknown amounts. Retention time supports tentative identification when compared with a standard, though mass spectrometry or another confirmatory method may be needed for definitive identification. Pre-run checks verify repeatability, resolution, and peak symmetry before sample analysis. Limits of detection and quantification describe the smallest amounts that can be reliably observed or measured. Sample preparation, filtration, and degassing help prevent column damage and inconsistent results.
| Property | Value | Notes |
|---|---|---|
| Accuracy | Closeness to true value | Often assessed by recovery of spiked samples |
| Precision | Agreement among repeated measurements | Often reported as relative standard deviation |
| Specificity | Ability to measure analyte without interference | Must separate analyte from impurities and matrix |
| Linearity | Proportional detector response | Evaluated across a defined concentration range |
| Robustness | Resistance to small method changes | Tests flow rate, pH, temperature, and mobile phase composition |
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.
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.
=== Correcting for GPS signal errors === In the 1990s, NASA scientists at JPL developed software capable of correcting for GPS signal errors, enabling accuracy within inches; it is called Real-Time GIPSY (RTG). John Deere licensed the software and used it to develop self-driving farm equipment. As of 2016, as nearly 70% of North American farmland is cultivated by self-driving tractors, which rely on RTG that was developed at NASA. Another user of RTG is Comtech Telecommunications, which is a major provider of location-based services. This technology is used in cell phones so that 9-1-1 emergency callers can be located.
Travellers require a biometric passport to use SmartGate as it uses information from the passport (such as photograph, name and date of birth) and in the respective countries' databases (i.e. banned travellers database) to decide whether to grant entry or departure from Australia or to generate a referral to a customs agent. These checks would otherwise require manual processing by a human, which is time-consuming, costly, and potentially error-prone. UK and Ireland: ePassport gates in the UK and Ireland are operated by the UK Border Force and the Irish Naturalisation and Immigration Service, and are located at immigration checkpoints in the arrival halls of some airports across both countries, offering an alternative to using desks staffed by immigration officers. The gates use a facial recognition system to verify the user's identity by comparing their facial features to those recorded in the photograph stored on the chip of their biometric passport. British citizens, European Economic Area citizens and citizens of Australia, Canada, Japan, New Zealand, Singapore, South Korea, Taiwan and the United States as well as Chinese citizens of Hong Kong who are enrolled in the Registered Traveller Service, can use ePassport gates at 14 ports of entry in the United Kingdom provided that they are aged either 18 and over or 12 and over, travelling with an adult and holding valid biometric passports.
=== Structure Stabilization Improvements === DNA brick structures can be used to synthesize various and specific geometries that serve as tools in biological studies. Due to their nucleotide nature, they can quickly dissociate under environmental fluctuations during assembly, in the presence of low concentrations of divalent cations, and in the presence of nucleases. Various methods have been developed to protect and stabilize the DNA structures. However, such methods require the encapsulation of the nanostructure making accessing DNA strands difficult and leading to covalent crosslinking. Kim and Yi presented a stabilization method involving the synthesis of DNA brick nanostructure with dendritic oligonucleotides attached to the outer surface which maintain the DNA accessibility and prevent nuclease digestion. Certain DNA brick motifs remain structurally stable at low divalent salt concentrations and in the presence of nucleases. They demonstrated that neither chemical protectants nor covalent base pair interlocking was necessary to maintain the DNA brick structure stability, especially structures with binding domain lengths of 13 nucleotides or longer. Likewise, coating their surfaces with dendritic oligonucleotides prevented the usage of chemical base-pair interlocking techniques and encapsulation methods as they could still display structural stability in cellular media and made it possible to access the DNA sequences at the surface.
Sources: en.wikipedia.org
=== Trump administration === After Harris was defeated by former president Donald Trump in the general election on November 5, 2024, Moore pledged to work with the Trump administration, but said he would push back when necessary. He also pledged to defend Marylanders' constitutional rights, and restore faith in public institutions and democracy during Trump's second presidency. By February 2025, Moore maintained that he would still be open to working with anyone to advance Maryland's interests, but expressed pessimism toward being able to partner with the Trump administration, adding that he planned to use the power of his office to counter Trump—including executive orders and backing federal litigation filed by Maryland Attorney General Anthony Brown against several of Trump's actions—and criticizing the president for dismantling federal departments, furloughing thousands of federal workers, and starting tariff wars. Moore opposed the One Big Beautiful Bill Act, calling it "one of the worst bills for working families that our country has ever proposed" and predicting that it would result in one of the largest upward transfers of wealth from the poor to the rich in American history through cuts to federal assistance programs and tax cuts for wealthy individuals and big corporations.
Hyperpigmentation, also known as dark spots, is the darkening of an area of skin or nails caused by increased melanin. Many topical treatments disrupt the synthesis of melanin by inhibiting the enzyme tyrosine hydroxylase.
It has been described as a "second-generation" GnRH modulator due to its non-peptide and small-molecule nature and its oral activity. Unlike GnRH agonists and older GnRH antagonists, which are peptides and first-generation GnRH modulators, elagolix is not a GnRH analogue as it is not structurally related to GnRH. Elagolix was the first second-generation and orally active GnRH modulator to be introduced for medical use. The introduction of elagolix in the United States and Canada was followed by that of relugolix (brand name Relumina), the next second-generation GnRH antagonist, in Japan in January 2019. The U.S. Food and Drug Administration (FDA) considers it to be a first-in-class medication.
=== Human intervention === Humans have semi-domesticated several species of honey bee by taking advantage of their swarming stage. Swarming is the means by which new colonies are established when there is no longer space for expansion in the colony's present hive. The old queen lays eggs that will develop into new queens and then leads as many as half the colony to a site for a new hive. Bees generally swarm before a suitable location for another hive has been discovered by scouts sent out for this purpose. Until such a location is found the swarm will simply conglomerate near the former hive, often from tree branches. These swarms are unusually docile and amenable to transport by humans. When provided with a suitable nesting site, such as a commercial Langstroth hive, the swarm will readily form a new colony in artificial surroundings. These semi-domesticated colonies are then looked after by humans practicing apiculture or meliponiculture. Captured bees are encouraged to forage, often in agricultural settings such as orchards, where pollinators are highly valued. The honey, pollen, wax and resins the bees produce are all harvested by humans for a variety of uses. The term "semi-domesticated" is preferred because all bee colonies, even those in very large agricultural apiculture operations, readily leave the protection of humans in swarms that can establish successful wild colonies. Much of the effort in commercial beekeeping is dedicated to persuading a hive that is ready to swarm to produce more honeycomb in its present location.
Sources: en.wikipedia.org
CORD provides a strong common voice to advocate for health policy and a healthcare system that works for those with rare disorders. NORD - National Organization for Rare Disorders (NORD) is an American national non-profit patient advocacy organization that is dedicated to individuals with rare diseases and the organizations that serve them. EURODIS - Rare Diseases Europe (EURODIS) is a unique, non-profit alliance of over 700 rare disease patient organizations across Europe that work together to improve the lives of the 30 million people living with a rare disease in Europe.
body tissues) If steady state is reached, context-sensitive half-life is equal to elimination half-life Only free drug that is in the plasma is metabolised Metabolism results in the concentration of free drug in the peripheral compartment to decrease Due to passive diffusion, free drug will leave the peripheral compartment (i.e. tissues) and enter the central compartment, replenishing any drug that was metabolised from the plasma If steady state is not reached, context-sensitive half-life is shorter than elimination half-life Only free drug that is in the plasma is metabolised Overall the entire body has less lipophilic drug. The infusion was stopped earlier. Not as much drug was able to enter the peripheral compartment. Because steady state is not reached, the peripheral compartment (i.e. tissues) has less free drug than the central compartment The drug continues to move into the peripheral compartment until equilibrium is reached. Remember the drug moves due to passive diffusion. It moves into the peripheral compartment because it has less free drug Once equilibrium is reached, the only other way the drug is able to leave the plasma is by elimination. This causes the free drug concentration in the central compartment to fall As the plasma concentration falls, the concentration gradient of drug reverses and drug moves from peripheral compartment (i.e. tissues) back into plasma, maintaining the plasma concentration of the drug Remifentanil is relatively context insensitive.
However those who drink 2–4 cups per day may be at a slightly increased risk. Caffeine increases intraocular pressure in those with glaucoma but does not appear to affect normal individuals. It may protect people from liver cirrhosis. There is no evidence that coffee stunts a child's growth. Caffeine may increase the effectiveness of some medications including ones used to treat headaches. Caffeine may lessen the severity of acute mountain sickness if taken a few hours prior to attaining a high altitude.
== Contraindications == Nicotine use for tobacco cessation has few contraindications. It is not known whether nicotine replacement therapy is effective for smoking cessation in adolescents, as of 2014. It is therefore not recommended to adolescents. It is not safe to use nicotine during pregnancy or breastfeeding, although it is safer than smoking. The desirability of NRT use in pregnancy is therefore debated. Randomized trials and observational studies of nicotine replacement therapy in cardiovascular patients show no increase in adverse cardiovascular events compared to those treated with placebo. Using nicotine products during cancer treatment may be contraindicated, as nicotine may promote tumour growth, but temporary use of NRTs to quit smoking may be advised for harm reduction. Nicotine gum is contraindicated in individuals with temporomandibular joint disease. People with chronic nasal disorders and severe reactive airway disease require additional precautions when using nicotine nasal sprays. Nicotine in any form is contraindicated in individuals with a known hypersensitivity to nicotine.
In 2015 fire and heat resulted in 67 million injuries. This resulted in about 2.9 million hospitalizations and 238,000 dying. This is down from 300,000 deaths in 1990. This makes it the fourth leading cause of injuries after motor vehicle collisions, falls, and violence. About 90% of burns occur in the developing world. This has been attributed partly to overcrowding and an unsafe cooking situation. Overall, nearly 60% of fatal burns occur in Southeast Asia with a rate of 11.6 per 100,000. The number of fatal burns has decreased from 280,000 in 1990 to 176,000 in 2015. In the developed world, adult males have twice the mortality as females from burns. This is most probably due to their higher risk occupations and greater risk-taking activities. In many countries in the developing world, however, females have twice the risk of males. This is often related to accidents in the kitchen or domestic violence. In children, deaths from burns occur at more than ten times the rate in the developing than the developed world. Overall, in children it is one of the top fifteen leading causes of death. From the 1980s to 2004, many countries have seen both a decrease in the rates of fatal burns and in burns generally.
Sources: en.wikipedia.org
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.
Validation demonstrates that a method produces reliable results for a defined purpose. It documents performance limits and acceptance criteria. Regulated industries require validation before routine testing of products or samples.
Retention time shifts can arise from changes in mobile phase composition, pH, temperature, column age, or flow rate. Contamination or worn seals may also alter pressure and delivery. Systematic checks of these factors help identify the cause.
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.