Stationary phase raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-01-09. Anything still debated is marked as such rather than presented as settled.
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 analytical procedure is suitable for its intended purpose. Typical validation characteristics include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Regulatory guidance from bodies such as the International Council for Harmonisation and the United States Pharmacopeia outlines expectations, though specific criteria depend on the product and method. System suitability tests are run before sample analysis to confirm resolution, peak symmetry, column efficiency, and injection repeatability. Failure of these checks can invalidate a batch of measurements.
Practical HPLC testing depends on careful sample preparation and instrument maintenance. Samples may require filtration, dilution, pH adjustment, or extraction to avoid column damage and matrix interference. Mobile phases are degassed and filtered, and columns are equilibrated before injection. Common problems include peak tailing, baseline drift, ghost peaks, carryover, and co-elution of analytes. Documentation of instrument logs, calibration records, and electronic audit trails supports data integrity and traceability. Ongoing training and routine maintenance help reduce variability between analysts and laboratories.
Quality control laboratories use HPLC to check identity, purity, concentration, and stability of raw materials and finished products. A validated method specifies the column, mobile phase, flow rate, detection wavelength, injection volume, and run time. Samples are prepared and compared against reference standards of known concentration. The resulting chromatogram provides quantitative data, such as assay values and impurity levels. This approach is common in pharmaceutical, food, environmental, and industrial testing where consistent measurements are required.
| 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. |
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.
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.
Method validation evaluates accuracy, precision, specificity, linearity, range, detection limit, quantitation limit, and robustness. Regulatory guidance for pharmaceuticals, foods, and environmental testing defines expected documentation and acceptance criteria. Verification confirms that a validated method works in a specific laboratory with its own instruments and reagents. Calibration curves use reference standards with known purity and traceability, while measurement uncertainty is estimated from validation data, control charts, and collaborative studies. The scope of validation depends on the method's intended use.
Routine quality control monitors retention time shifts, baseline noise, system pressure, and peak shape. Trends can reveal column aging, mobile phase preparation errors, detector drift, or sample degradation. Corrective actions may include replacing the column, preparing fresh mobile phase, or recalibrating the detector. Stability testing often uses HPLC to measure parent compound loss and degradation product formation. Open questions remain about how accelerated stability results extrapolate to long-term storage under varied conditions.
=== Values of spin angular momentum === Nuclear spin is an intrinsic angular momentum that is quantized. This means that the magnitude of this angular momentum is quantized (i.e. S can only take on a restricted range of values), and also that the x, y, and z-components of the angular momentum are quantized, being restricted to integer or half-integer multiples of ħ, the reduced Planck constant. The integer or half-integer quantum number associated with the spin component along the z-axis or the applied magnetic field is known as the magnetic quantum number, m, and can take values from +S to −S, in integer steps. Hence for any given nucleus, there are a total of 2S + 1 angular momentum states. The z-component of the angular momentum vector (
musculoskeletal pain neck pain muscle spasms extremity pain muscle fatigue anaphylaxis malignancy The most common adverse effect of reslizumab was oropharyngeal (mouth and throat) pain. According to the phase III clinical trials data, oropharyngeal pain occurred in ≥2% of individuals along with elevated baseline creatine phosphokinase (CPK), which was more common in patients treated with reslizumab versus placebo. Myalgia was also reported more in patients in the reslizumab 3 mg/kg group versus the placebo group as well as some musculoskeletal adverse reactions. Lastly, some serious adverse reactions that occurred in subjects treated with reslizumab but not in those treated with placebo included anaphylaxis and malignancy.
Vitamin D3 24-hydroxylase is an oxidoreductase that uses molecular oxygen in an oxidation reaction which requires adrenal ferredoxin to transfer electrons from nicotinamide adenine dinucleotide phosphate to its cytochrome P450 active site.
=== Structure === The plantar fascia is made up of predominantly longitudinally oriented collagen fibers. There are three distinct structural components: the medial component, the central component (plantar aponeurosis), and the lateral component (see diagram at right). The central component is the largest and most prominent.
Sources: en.wikipedia.org
=== Valve Corporation v. Vivendi Universal Games === Between 2002 and 2005, Valve was involved in a complex legal dispute with its publisher, Vivendi Universal Games (under Vivendi's brand Sierra Entertainment). Valve had entered into a publishing agreement with Sierra to release Half-Life and subsequent games in 1997, with the contract giving Sierra some intellectual property (IP) rights to Valve's games. After Valve began development of Half-Life 2, it agreed a new contract with Sierra in 2001, removing these rights from Sierra and giving Valve some rights for digital distribution. Internally, Valve started work on Steam as a means to digitally distribute these games, and first revealed this project at the March 2002 Game Developers Conference. By August 2002, Valve had found that Sierra was distributing copies of their games to Internet cafes against the terms of their contracts and filed a lawsuit against Sierra and Vivendi. In addition to claims of copyright infringement, Valve asserted that Sierra breached contract by withholding royalties and delaying the release of Counter-Strike: Condition Zero until after the holiday season. Vivendi and Sierra countersued, stating that Valve had misrepresented their position in the revised 2001 contract since they had been working on Steam at that point as a means to circumvent the publishing agreement. Vivendi sought intellectual property rights to Half-Life and a ruling preventing Valve from using Steam to distribute Half-Life 2. The countersuits, if successful, likely would have bankrupted Valve, according to COO Scott Lynch.
=== TSI slant === The triple sugar iron (TSI) test is a differential media used to tell whether an organism can ferment glucose, sucrose, and/or lactose and whether an organism can produce hydrogen sulfide gas.
The widespread perception about the economic management of Rodríguez Zapatero's government during the "legislature of crisis" was that it had failed, despite having managed to avoid the European bailout. That perception was key to the People's Party's landslide victory in the general election of November 2011. The deep economic crisis translated into a political crisis from the moment that the lack of confidence in the government's ability to deal with it was transferred to the entire "political class" and the system as a whole. To this was added the proliferation of corruption scandals involving the two main parties — Gürtel affair, Palma Arena case, Andalucian ERE affair — and even the Royal House when the King's son-in-law Iñaki Urdangarín was indicted in 2011, an affair that had a huge media repercussion and deteriorated the image of the monarchy. The rating of the government, its president and the PSOE were falling in the polls and in the Galician regional election of 2009 and in the European Parliament elections of the same year, the Socialists were defeated. The fall was accentuated after the economic policy turnaround of May 2010. The first confirmation of the Socialist slump came in the Catalan elections of November 2010 in which the Socialists' Party of Catalonia lost nine deputies, and the "three party" was ousted from power by CiU – the "convergent" Artur Mas replaced the socialist José Montilla at the head of the Generalitat.
=== Breast cancer === Pregnancy has a positive effect on the prognosis of breast cancer according to several studies and it apparently increases the chance of survival after diagnosis of breast cancer. Possible positive effects of pregnancy could be explained by the persistence of fetal cells in the blood and maternal tissues. Fetal cells are probably actively migrating from peripheral blood into the tumor tissue where they are preferentially settled in the tumor stroma and one their concentration decreases as they get closer to the healthy breast tissue. There are two suggested mechanisms by which the fetal cells could have the positive effect on the breast cancer prognosis. The first mechanism suggests that fetal cells only oversee cancer cells and they attract components of the immune system if needed. The second option is that the down-regulation of the immune system induced by the presence of fetal cells could ultimately lead to cancer prevention, because women in whom FMC is present produce lower concentrations of inflammatory mediators, which may lead to the development of neoplastic tissue. The effect also depends on the level of microchimerism: Hyperchimerism (a high rate of microchimerism) and hypochimerism (a low rate of microchimerism) can be related to the negative effect of FMC and thus can promote a worse prognosis of breast cancer. Apparently, women with breast cancer may fail in the process of obtaining and maintaining allogeneic fetal cells.
In their model, it is assumed that the infected individuals can develop active TB by either direct progression (the disease develops immediately after infection) considered above as FAST tuberculosis or endogenous reactivation (the disease develops years after the infection) considered above as SLOW tuberculosis.
Sources: en.wikipedia.org
=== November === 1 November – A Wellington College student is diagnosed with measles, bringing the total number of measles cases nationwide to 14. 2 November – A new measles case is reported in Auckland, bringing the total number of cases nationwide to 17. 3 November – The New Zealand Government launches a three-month visa waiver trial for Chinese citizens with valid Australian visitor, work, family or student visas. 4 November – 400 protesters gather on the grounds of the New Zealand Parliament to protest against the Government's proposed legislation easing restrictions of gene technology. New Zealand First leader Winston Peters and Green Party MP Scott Willis address the crowd, reiterating their opposition to the legislation. 5 November: 20,000 secondary school teachers affiliated with the Post Primary Teachers' Association hold a half-day strike to demand better pay and work conditions. Australian mining company Santana Minerals secures a 30-year permit from the New Zealand Government to mine gold from the Bendigo-Ophir goldfields. The New Zealand Parliament passes legislation formalizing a Treaty of Waitangi settlement with Ngāti Pāoa. The settlement includes NZ$23.5 million in financial compensation, recognising 12 "culturally significant" sites, and a formal Crown apology for historical land alienation. 6 November: Former Deputy Police Commissioner Jevon McSkimming pleads guilty to three charges of possessing child sexual exploitation and bestiality material.
==== Reoxygenation of intolerant animals ==== When oxygen re-enters the system, animals are faced with a different set of problems. Since ATP was used up during the anoxic period, it leads to a lack of ADP within the system. This is due to ADP's natural degradation into AMP, resulting in ADP being drained from the system. With no ADP in the system, Complex V is unable to start, meaning the protons will not flow through it to enter the matrix. Due to Complex V's reversal during anoxia, the proton gradient has become hyperpolarized (where the proton gradient is highly positively charged). Another factor in this problem is that succinate built up during anoxia, so when oxygen is reintroduced, succinate donates electrons to Complex II. The hyperpolarized gradient and succinate buildup leads to reverse electron transport, causing oxidative stress, which can lead to cellular damage and diseases.
The Space Race (Russian: космическая гонка, romanized: kosmicheskaya gonka, IPA: [kɐsˈmʲitɕɪskəjə ˈɡonkə]) was a 20th-century competition between the Cold War rivals, the United States and the Soviet Union, to achieve superior spaceflight capability. It had its origins in the ballistic missile-based nuclear arms race between the two nations that followed World War II and the onset of the Cold War. The technological advantage demonstrated by spaceflight achievement was seen as necessary for national security, particularly in regard to intercontinental ballistic missile and satellite reconnaissance capability, but also became part of the cultural symbolism and ideology of the time. The Space Race brought pioneering launches of artificial satellites, robotic landers to the Moon, Venus, and Mars, and human spaceflight in low Earth orbit and ultimately to the Moon. Public interest in space travel originated in the 1951 publication of a Soviet youth magazine and was promptly picked up by US magazines. The competition began on July 29, 1955, when the United States announced its intent to launch artificial satellites for the International Geophysical Year. Five days later, the Soviet Union responded by declaring they would also launch a satellite "in the near future". The launching of satellites was enabled by developments in ballistic missile capabilities since the end of World War II. The competition gained Western public attention with the "Sputnik crisis", when the USSR achieved the first successful satellite launch, Sputnik 1, on October 4, 1957.
Girls married through this practice are often treated as compensation for a dispute, which places them in a vulnerable social position within the family they marry into. In 2021, the Federal Shariat Court declared the practice un-Islamic and unconstitutional, reaffirming earlier Supreme Court jurisprudence. UN Women reported in 2024 that around one in six girls in Pakistan are married during childhood, with the country home to nearly 19 million child brides. In 2025, Pakistan enacted a law setting the minimum legal age for marriage at 18 and introducing penalties for arranging underage marriages; the law is limited to the Islamabad Capital Territory and does not apply nationwide.
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.
Method validation is the documented process of confirming that an HPLC procedure is suitable for its intended use. It evaluates accuracy, precision, specificity, linearity, range, detection limits, and robustness. Validation criteria depend on the regulatory context and the sample type.