reversed-phase raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2025-09-15. 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.
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 separates dissolved compounds by passing a liquid sample through a column packed with stationary phase. A pump delivers mobile phase at controlled flow, and the sample components interact differently with stationary and mobile phases. Compounds that spend more time in mobile phase elute earlier; those retained by stationary phase elute later. Detectors record elution as peaks, and peak area or height relates to amount. This mechanism underpins quantitative analysis of mixtures.
| 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. |
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. A diode array detector records full spectra across a wavelength range, which helps identify co-eluting peaks. Mass spectrometry provides mass-to-charge ratios and can confirm molecular identity at low concentrations. The choice of detector depends on analyte structure, required sensitivity, and whether quantitation or identification is the goal. No single detector works for every compound, and method development often compares responses before selecting one.
High-performance liquid chromatography is an analytical technique that separates components of a liquid sample by passing it 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 interaction with the stationary phase cause analytes to migrate at different rates. Detectors record elution as peaks, and a data system converts signals into a chromatogram. The method is suited to compounds that dissolve in a liquid and are not volatile enough for gas chromatography.
Reversed-phase chromatography dominates modern HPLC testing, using a nonpolar stationary phase such as chemically bonded octadecyl groups and a polar mobile phase of water mixed with organic solvent. Analytes partition between the mobile and stationary phases according to hydrophobicity. Gradient elution changes the mobile phase composition over time to separate compounds with a wide range of retention. Isocratic elution keeps the composition constant and is simpler for routine assays. Column temperature, pH, and flow rate influence selectivity, peak shape, and retention time, so these parameters are controlled during a validated method.
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.
St. Francis of Assisi is widely considered the first recorded stigmatic in Christian history. In 1224, two years before his death, he embarked on a journey to Mount La Verna for a forty-day fast. The legend states that one morning, near the feast of the Exaltation of the Cross, a six-winged angel appeared to Francis while he prayed. As the angel approached, Francis could see that the angel was crucified. He was humbled by the sight, and his heart was filled with elation joined by pain and suffering. When the angel departed, Francis was left with wounds in his hands, feet, and side as if caused by the same lance that pierced Christ's side. The image of nails immediately appeared in his hands and feet, and the wound in his side often seeped blood. Pope Alexander IV and other witnesses declared that they had seen these marks both before and after his death. In traditional artistic depictions of the incident, Francis is accompanied by a Franciscan brother. St. Francis' first biographer, Thomas of Celano, reports the event in his 1230 First Life of St. Francis:
However, the biological effects of radiation due to radioactive substances were less easy to gauge. This gave the opportunity for many physicians and corporations to market radioactive substances as patent medicines. Examples were radium enema treatments, and radium-containing waters to be drunk as tonics. Marie Curie protested against this sort of treatment, warning that "radium is dangerous in untrained hands". Curie later died from aplastic anaemia, likely caused by exposure to ionizing radiation. By the 1930s, after a number of cases of bone necrosis and death of radium treatment enthusiasts, radium-containing medicinal products had been largely removed from the market (radioactive quackery).
For example, if it is undesirable or not possible to radiolabel the antigen or target molecule of interest, a RIA can be done if two different antibodies that recognize the target are available and the target is large enough (e.g., a protein) to present multiple epitopes to the antibodies. One antibody would be radiolabeled as above while the other would remain unmodified. The RIA would begin with the "cold" unlabeled antibody being allowed to interact and bind to the target molecule in solution. Preferably, this unlabeled antibody is immobilized in some way, such as coupled to an agarose bead, coated to a surface, etc. Next, the "hot" radiolabeled antibody is allowed to interact with the first antibody-target molecule complex. After extensive washing, the direct amount of radioactive antibody bound is measured and the amount of target molecule quantified by comparing it to a reference amount assayed at the same time. This method is similar in principle to the non-radioactive sandwich ELISA method.
== Application == Microtox has a variety of environmental and industrial applications. Common applications are for testing the toxicity of both marine and freshwater, as well as sediments for pesticides and other inorganic and organic chemicals. Drinking water: Microtox is used to test drinking water sources in many areas where either accidental or deliberate contamination is possible. Toxic contaminants in drinking water are indicated by a change in the color or intensity of light, or by a change in the rate of oxygen use. Lakes and rivers: Microtox is used to test the toxicity of lake and river sediments contaminated by metals or nonspecific contaminants. The Solid-Phase test is used for sediments, while either the Basic test or the 100% test is used for pore water. Sediment testing: Microtox is used to test and evaluate the toxicity of various marine and freshwater sediments contaminated by metals and organics. Aqueous extracts of contaminated soils, drilling muds, and sludge. Microtox data may be used to establish apparent effects threshold (AET), sediment quality standards and used for NPDES permits, as well as Superfund cleanup levels. Industrial: This bioassay is used in the assessment of the toxicity of complex industrial effluent sources. It is a cost-effective way for monitoring and testing large numbers of samples. Microtox can also be applied as an early warning system (EWS) and aid in detecting the presence of toxic materials, as well as predict the outcomes of other bioassays and tests.
Sources: en.wikipedia.org
== Efficacy and susceptibility == Cefodizime demonstrated superior clinical efficacy that what could be predicted from its in vitro experimental results. Certain immunomodulatory properties of the drug might account for its increased in vivo activity against specific bacterial species. These immunomodulatory properties stimulate some phagocyte and lymphocyte cellular functions when they have been impaired. It was shown in a 2004 study that cefodizime increased expression of toll-like receptor 4 (TLR-4) in neutrophils stimulated by Klebsiella pneumoniae infection which then affected the production of cytokines in the stimulated cells. A 1992 study conducted in vitro susceptibility studies for cefodizime and found that gram negative bacteria with consistent susceptibility include: Enterobacteriaceae including E. coli, K. pneumoniae, Morganella morganii, Proteus mirabilis, P. vulgaris, Shigella sonnei, Yersinia enterocolitica, Salmonella, Haemophilus influenzae, Moraxella catarrhalis, Neisseria gonorrhoeae, and Neisseria meningitidis. In vitro susceptible gram positive bacteria include: methicillin-sensitive Staphylococcus aureus, and Streptococcus agalactiae, S. pneumoniae and S. pyogenes. Cefodizime was shown to be ineffective in vitro against Enterobacter spp., Pseudomonas aeruginosa, and Xanthomonas maltophilia. Gram positive bacteria it was inactive against include Staphylococcus epidermidis and methicillin-resistant Streptococcus aureus.
CGRP antagonists can be used for both acute migraine treatment as well as prophylactically. CGRP is a neuropeptide which is thought to induce migraines via vasodilation of cranial arteries. CGRP can also release inflammatory agents and cause nervous system sensitization. It is theorized that by antagonizing the CGRP receptor of the trigeminal ganglia, lowered CGRP is released and less migraine occurs. Erenumab is a highly selective human monoclonal antibody which is a promising new development in migraine treatment. It has low risk of hepatoxicity like gepants can have, due to being mostly eliminated via proteolysis. There have been some studies suggesting the benefit of using melatonin for prophylaxis of migraine, however, there is a lack of strength of evidence due to a low number of studies as well as conflicting results. Melatonin has a good safety profile but there have been rare instances of serious side effects. More studies are needed in order to suggest the therapeutic use of melatonin for prophylaxis of migraine.
Since 1991, the year the Gulf War ended, veterans and their families voiced concern about subsequent health problems. In 1999, an assessment of the first 1,000 veterans involved in the Ministry of Defence's Gulf War medical assessment programme found "no evidence" of a single illness, physical or mental, that would explain the pattern of symptoms observed in the group. In 1999, MEDACT petitioned for the WHO to conduct an investigation into illnesses in veterans and Iraqi civilians. A major 2006 review of peer-reviewed literature by a US Institute of Medicine (IOM) committee concluded that, "[b]ecause the symptoms vary greatly among individuals", they do not point to a syndrome unique to Gulf War veterans, though their report conceded that the lack of objective pre-deployment health data meant definitive conclusions were effectively impossible. Simon Wessely praised the IOM's review, and noted that, despite its central conclusion that no novel syndrome existed, its other findings made it "equally clear that service in the Gulf war did adversely affect health in some personnel". Aside from the lack of baseline data to guide analysis of the veterans' postwar health, because no detailed health screening was carried out when the veterans entered service, another major stumbling block with some studies, like the thousand-veteran one, is that the subjects are self-selected, rather than a random sample, making general conclusions impossible.
Inhibitors of dipeptidyl peptidase 4 (DPP-4 inhibitors or gliptins) are a class of oral hypoglycemics that block the enzyme dipeptidyl peptidase-4 (DPP-4). They can be used to treat diabetes mellitus type 2. The first agent of the class—sitagliptin—was approved for marketing by the US Food and Drug Administration (FDA) in 2006. Glucagon increases blood glucose levels, and DPP-4 inhibitors reduce glucagon and blood glucose levels. The mechanism of DPP-4 inhibitors is to increase incretin levels (GLP-1 and GIP), which inhibit glucagon release, which in turn increases insulin secretion, decreases gastric emptying, and decreases blood glucose levels. A 2018 meta-analysis found no favorable effect of DPP-4 inhibitors on all-cause mortality, cardiovascular mortality, myocardial infarction or stroke in patients with type 2 diabetes.
On 15 September 2008, RIA Novosti reported that Russian foreign minister Sergey Lavrov said: "There were excesses by all parties, but this was a war, and when you see on night, that you are being fired upon and you're on the move, while you're advancing to help Tskhinvali, then your response can not be precisely accurate and cannot avoid hurting anyone." On 21 September 2008, Russia-1 TV reported that the wife of Lieutenant Sergey Shevelev, intelligence officer of the peacemaking battalion who died in South Ossetia, said that her husband called her every day and they talked casually. However, on 1 August he sent her text message saying "Everything is normal ... Watch TV. That's all." Konstantin Timerman, the commander of the Russian peacekeeping battalion, said in 2017 that as soon as his combat buddy Sergey Shevelev arrived in Tskhinvali on 1 August 2008, the escalation of the conflict began.
Sources: en.wikipedia.org
== Cause == Burns are caused by a variety of external sources classified as thermal (heat-related), chemical, electrical, and radiation. In the United States, the most common causes of burns are: fire or flame (44%), scalds (33%), hot objects (9%), electricity (4%), and chemicals (3%). Most (69%) burn injuries occur at home or at work (9%), and most are accidental, with 2% due to assault by another, and 1–2% resulting from a suicide attempt. These sources can cause inhalation injury to the airway and/or lungs, occurring in about 6%. Burn injuries occur more commonly among the poor. Smoking and alcoholism are other risk factors. Fire-related burns are generally more common in colder climates. Specific risk factors in the developing world include cooking with open fires or on the floor as well as developmental disabilities in children and chronic diseases in adults.
Anne Hardy argues that widespread public education of food hygiene can be useful, particularly through media (TV cookery programmes) and advertisement. She points to the examples set by Scandinavian societies.
from the World Health Organization, the Paris Climate Accords, and UNESCO. The Trump administration has been criticized for its targeting of political opponents and civil society. Many of his administration's actions have been found by the judiciary to be illegal and unconstitutional, and have been criticized as authoritarian and fascistic. These actions have also been seen as contributing to democratic backsliding in the country, as well as incalculable damage to the country's international standing. Trump, his family, and his administration have faced unprecedented conflicts of interest, self-enrichment, and allegations of corruption. Trump is the first president with a felony conviction, having been convicted in 2024 for falsifying business records to conceal hush money payments. Having taken office at 78 years and seven months old, he is the oldest person to become U.S. president.
The company set up a ghostwriting programme called CASPPER, initially to produce articles about Paxil but which was extended to cover Avandia. As part of the settlement GSK signed a five-year corporate integrity agreement with the Department of Health and Human Services, which obliged the company to make major changes in the way it did business, including changing its compensation programmes for its sales force and executives, and to implement and maintain transparency in its research practices and publication policies. It announced in 2013, that it would no longer pay doctors to promote its drugs or attend medical conferences, and that its sales staff would no longer have prescription targets.
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.
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.