Retention time 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.
Updated 2025-11-30. Numbers and descriptions here follow the published literature rather than marketing material.
Laboratories apply HPLC testing across pharmaceutical, food, environmental, and industrial chemistry. The method can measure active ingredients, impurities, additives, preservatives, and degradation products. Sample preparation often includes dilution, filtration, and sometimes extraction or derivatization. The choice of column, mobile phase, pH, temperature, and detector depends on the analytes and matrix. Results are compared with reference standards to assign identity and concentration. Method suitability is judged by resolution, precision, and accuracy.
HPLC testing is not a single fixed procedure; it is a family of separation modes. Reversed-phase, normal-phase, ion-exchange, size-exclusion, and affinity chromatography each suit different analyte properties. Reversed-phase methods dominate because they handle many neutral and moderately polar compounds. Detection can be optical, electrochemical, or mass spectrometric, and the detector dictates what information is available. Coupling with mass spectrometry increases selectivity and enables identification when standards are unavailable. The technique cannot separate every mixture without adjustment.
HPLC testing is an analytical technique used to separate, identify, and quantify components in a liquid sample. It relies on a pressurized mobile phase that carries the sample through a column packed with stationary phase. Different compounds travel at different rates because of interactions with the stationary and mobile phases. The resulting signal versus time is a chromatogram. Peak position indicates identity under specified conditions, while peak area or height relates to amount.
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.
| Property | Value | Notes |
|---|---|---|
| Abbreviation | HPLC | Also called high-performance liquid chromatography |
| Separation mechanism | Differential partitioning | Compounds distribute between mobile and stationary phases |
| Typical column chemistry | C18 (octadecylsilane) | Used in reversed-phase separations |
| Typical detector | UV-Vis or photodiode array | Mass spectrometry is common for trace and confirmatory work |
| Typical particle size | 1.8–5 µm | Smaller particles require higher pressure and can improve speed |
Several separation modes exist, including reversed-phase, normal-phase, ion-exchange, size-exclusion, and hydrophilic interaction liquid chromatography. Reversed-phase uses a nonpolar stationary phase with a polar mobile phase and is widely applied to small organic molecules. Gradient elution changes mobile phase composition during the run, while isocratic elution keeps it constant. Column chemistry, particle size, temperature, flow rate, and mobile phase pH all influence retention and resolution. Method development selects conditions that separate analytes from matrix components and from each other.
Detection commonly uses ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. Ultraviolet detection depends on molecular chromophores that absorb light at specific wavelengths. Mass spectrometry provides mass information and sensitive quantification, often after electrospray ionization. Before sample batches, performance checks examine resolution, elution time repeatability, peak symmetry, and plate count. Matrix effects and co-elution remain recognized uncertainties; formal validation studies and orthogonal detection help address them. Detector choice depends on analyte properties and required sensitivity.
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.
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.
Ellen McLain (born 1952 or 1953) is an American voice actress. She is best known for providing the voice of GLaDOS, the primary antagonist of the Portal video game series, the Combine Overwatch AI in Half-Life 2, and the Administrator, the announcer in Team Fortress 2. Her voice roles also include the Jaeger A.I. in Pacific Rim and The Witch in Left 4 Dead 2.
== The use of "Intracrine" == As described above, intracrine signaling, also called intracrine action, is a process in which a cell produces a hormone that acts within the same cell that synthesized it. However, the term "intracrines" can be used more broadly to refer to all hormones that act on receptors within the cell, regardless of whether they act on their cell of origin. This means that while some intracrines function in a strictly intracrine manner, others may be secreted to influence neighboring cells. In such cases, an intracrine can function in a paracrine manner while still exerting its effects within the original cell through intracellular signaling.
The thyroid hormone is critical to the normal function of cells. In excess, it both overstimulates metabolism and disrupts the normal functioning of the sympathetic nervous system, causing speeding up of various body systems and symptoms resembling an overdose of epinephrine (adrenaline). These include fast heartbeat and symptoms of palpitations, nervous system tremor such as of the hands and anxiety symptoms, digestive system hypermotility, unintended weight loss, and, in lipid panel blood tests, a lower and sometimes unusually low serum cholesterol. Major clinical signs of hyperthyroidism include weight loss (often accompanied by an increased appetite), anxiety, heat intolerance, hair loss, muscle aches, weakness, fatigue, hyperactivity, irritability, high blood sugar, excessive urination, excessive thirst, delirium, tremor, pretibial myxedema (in Graves' disease), emotional lability, and sweating. Panic attacks, inability to concentrate, and memory problems may also occur. Psychosis and paranoia, common during thyroid storm, are rare with milder hyperthyroidism. Many persons will experience complete remission of symptoms 1 to 2 months after a euthyroid state is obtained, with a marked reduction in anxiety, sense of exhaustion, irritability, and depression. Some individuals may have an increased rate of anxiety or persistence of affective and cognitive symptoms for several months to up to 10 years after a euthyroid state is established.
NAD+ + ubiquinol This enzyme is a flavoprotein (FAD). It belongs to the family of oxidoreductases, specifically those acting on NADH or NADPH with other acceptors. The systematic name of this enzyme class is NADH:(quinone-acceptor) oxidoreductase. Other names in common use include reduced nicotinamide adenine dinucleotide (quinone) dehydrogenase, NADH-quinone oxidoreductase, NADH ubiquinone oxidoreductase, DPNH-menadione reductase, D-diaphorase, and NADH2 dehydrogenase (quinone), and mitochondrial (mt) complex I. This enzyme participates in oxidative phosphorylation. Several compounds are known to inhibit this enzyme, including AMP, and 2,4-dinitrophenol. NADH dehydrogenase is involved in the first step of the electron transport chain of oxidative phosphorylation (OXPHOS). Any change in the electron transport component caused by a mutation might effect the normal electron flow. This might be leading "an increase of bifurcation and generation of superoxidase radicals and increase oxidative stress in various types of cancer cells."
Fenthion is a common pesticide that is used to kill insects such as flies and gnats. It was also found that kestrels are highly susceptible to secondary fenthion poisoning. When 14 kestrels were presented with live sparrows who had come into contact with a fenthion solution, all 14 died within 3 days after consuming the sparrows. Diphacinone is another common pesticide that is often used to kill rodents and is thought to be related to secondary poisoning in birds of prey. When kestrels were orally dosed with diphacinone, blood clotting rates significantly decreases. Kestrels were also found to be 20 to 30 times more sensitive to secondary poisoning from diphacinone than other birds like Northern bobwhite and mallard ducks. The species has been used to monitor metals (Cd, Sn, Pb, Cu, Al, Hg) and metalloids (As) in western North American drylands using feathers as a suitable tool to measure environmental pollution. American kestrels can also be significantly influenced by air contaminants. When exposed to common gaseous pollutants such as benzene, toluene, nitrogen dioxide, and sulfur dioxide, significant changes to the thyroid systems were observed. Higher levels of thyroid activity indicate that exposure to these gases leads to a loss of inhibition of thyroid glands in kestrels. However, there were no changes to immune function or food consumption.
Sources: en.wikipedia.org
The kinetics of labeled derivatives of apamin were studied in vitro and in vivo in mice by Cheng-Raude et al. This shed some light on the kinetics of apamin itself. The key organ for excretion is likely to be the kidney, since enrichment of the labeled derivatives was found there. The peptide apamin is small enough to pass the glomerular barrier, facilitating renal excretion. The central nervous system, contrarily, was found to contain only very small amounts of apamin. This is unexpected, as this is the target organ for neurotoxicity caused by apamin. This low concentration thus appeared to be sufficient to cause the toxic effects. However, these results disagree with a study of Vincent et al. After injection of a supralethal dose of radioactive acetylated apamin in mice, enrichment was found in the spinal cord, which is part of the target organ. Some other organs, including kidney and brain, contained only small amounts of the apamin derivative. Symptoms following bee sting may include:
c7orf26 interacts uniquely with 11 different proteins, according to the Mentha interactome browser. In particular, c7orf26 interacts with the entire family of 'INTS' (Integrator Complex Subunit 1–7). The Integrator Complex associates with the C-terminal domain of RNA polymerase II large subunit. It is involved in the transcription and processing of their transcripts. INTS mediates recruitment of cytoplasmic dynein to the nuclear envelope. Outside of the INTS gene family, c7orf26 interacts with AK5, HDGF, and ASUN. According to Guirato et al. (2018), there may be some evidence that regions on chromosome 7 may be directly linked to a nuclear estrogen receptor (ESR2) that modulates cancer cell proliferation and tumor growth. In another journal article by Fu et al. (2014), there is further indication that regions along chromosome 7, located between open reading frames 20-30, directly correlate to cellular functions of a hepatoma-derived growth factor (HDGF), another way of expressing normal function in tumorigenesis.
Laboratory research suggests AHCC may have immunostimulatory effects. AHCC has been proposed as a treatment for cancer, but research into its effectiveness has produced only uncertain and inconclusive evidence. Detailed research is needed into the pharmacology of AHCC before any recommendation of its use as an adjuvant therapy can be made. Studies have suggested that AHCC supplementation may affect immune outcomes and immune cell populations, suggesting that it has anti-inflammatory effects. Moreover, available data have demonstrated that AHCC may possibly reduce symptoms, improve survival, and shorten recovery time in animal models infected with viruses, bacteria, and fungal infections. AHCC was shown in a double-blind clinical study to completely clear HPV viral load in women chronically affected with the virus, and increase their CD4 counts by 25% to 50% after taking 3 grams after six months. Alternative cancer treatments Agaricus blazei mushroom Medicinal mushrooms Shiitake
miR-324-5p likely regulates cell growth and survival through interaction with multiple pathways. Published research demonstrates that this miRNA interacts with the Hedgehog (HH) signaling pathway via interactions with HH transcription factor Gli1 and HH protein receptor Smo, often contributing to tumorigenesis. miR-324-5p's activating interaction with the protein NfkB also regulates numerous components of cell survival, including cell cycle control, enzyme synthesis, and cell adhesion. In addition, miR-324-5p regulates components of the MAPK pathway, influencing cell growth, proliferation, and survival. Specifically, miR-324-5p downregulates RAF and ERK and is necessary for normal levels of cell growth. Reduced expression leads to increased cell growth and proliferation, and overexpression limits growth, leading to its role in oncogenesis.
Sources: en.wikipedia.org
Each Equip issue discussed the state of a particular games platform, looking back on significant releases with the benefit of hindsight and outlining future developments. For example, the GameCube issue featured lengthy retrospectives on The Legend of Zelda: The Wind Waker and Animal Crossing, plus a feature on upcoming titles that would use the GameCube – Game Boy Advance link cable. 'Specials issue ten: "Retro: The Collector's Series" This final edition in the Retro series reprinted all of the "Collector's Series" of articles from the main magazine. Each feature focused on a specific video game console of yesteryear and examined its history and the collectors market surrounding its rare or collectable games. Unusually for Edge, the majority of these articles were written by one video games journalist: Simon Parkin, a long-time freelance contributor to the magazine. "Edge presents FILE Volume 1 - Issues 1-12: The birth of a new generation" (2006) "Edge presents FILE Volume 2 - Issues 13-24: The new generation shows its strength" (2007) "Edge presents FILE Volume 3 - Issues 25-36: Videogame culture enters a new era" (2007)
== Related compounds == A dual DOR and κ-opioid receptor (KOR) PAM, BMS-986187, derived from BMS-986122, has been developed and is selective for these receptors over the MOR. Another MOR PAM with a simpler synthesis, MS1, was subsequently developed and has shown similar effects to those of BMS-986122. Additionally, ignavine, a natural MOR PAM found in Aconitum, has also been identified. In 2024, ketamine and its metabolites norketamine and hydroxynorketamine (HNK) were identified as highly potent MOR, DOR, and KOR PAMs (active at a concentration of as low as 1 nM). These actions were implicated in their potential antidepressant and analgesic effects.
Evidence indicating that Early to Middle Pleistocene hominins from the northern Indian Subcontinent lived in a mosaic environment dominated by savannas is presented by Kaur et al. (2026). Tu et al. (2026) determine the three crania of Homo erectus from the Yunxian site (Hubei, China) to be approximately 1.77 million years old, representing the oldest securely dated hominin fossils from eastern Asia reported to date. Gousset et al. (2026) study the phylogenetic relationships of Homo luzonensis, and interpret the studied hominin as most likely originating from an Asian population of Homo erectus, resulting in evolutionary reversals in an insular context and likely caused by living in tropical environment. A study on the technological characteristics of the stone tools from the Rizal Archaeological Site (Philippines) is published by Guibert et al. (2026). Li et al. (2026) report a new Lower Paleolithic site with stone tools and animal remains (the Daanmiao site) in the Bailong River valley (Gansu, China) providing evidence of hominin occupation of western Qinling Mountain Ranges approximately 900,000 years ago, and evidence of more favorable habitat for early hominins in the studied area than in other parts of North China during the Mid-Pleistocene Transition. Shao et al. (2026) determine two hominin crania from the Hulu Cave (China) to likely fall within a similar chronological range and date them to Marine Isotope Stage 16. Fu et al.
Sources: en.wikipedia.org
It measures the presence and amount of one or more compounds in a liquid sample. Separation occurs in a column, and detection produces a signal proportional to concentration. Identification usually requires comparison with a known reference standard under the same conditions.
In most cases the sample is consumed or altered during analysis, though some detectors are non-destructive. Fractions can be collected after separation for further study. Repeated testing therefore requires additional sample.
Run times range from under a minute for fast methods to over an hour for complex separations. Sample preparation, equilibration, and data review add time. Throughput depends on instrument configuration and method requirements.
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.