A practical reference on stationary phase: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-08-01 and is reviewed periodically as new material appears.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Common abbreviation | HPLC | High-performance liquid chromatography |
| Separation basis | Differential partitioning | Between liquid mobile phase and solid stationary phase |
| Common mode | Reverse phase | Nonpolar column, polar mobile phase |
| Typical detector | UV-Vis absorbance | Widely used for compounds with chromophores |
| Typical column particle size | 2–5 µm | Smaller particles can improve resolution |
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.
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.
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, or HPLC, separates dissolved compounds by passing a liquid mobile phase through a packed column. Components distribute differently between the stationary phase and the moving liquid, so they travel at different speeds and exit at different times. A detector records these eluting bands as peaks, and peak area or height relates to amount. The technique supports testing in pharmaceuticals, foods, environmental samples, and industrial chemicals. Quantification usually depends on calibration with known standards.
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.
==== Matrix-assisted laser desorption/ionization ==== MALDI is typified by the use of an ultraviolet (UV) laser to trigger ablation of analyte species that are mixed with a matrix of crystallized molecules with high optical absorption. The ions within the resulting ablated gasses are then protonated or deprotonated before acceleration into a mass spectrometer. The primary advantages of MALDI detection over ESI in microfluidic devices are that MALDI allows for much easier multiplexing, which even further increases the device's overall throughput, as well as less reliance on moving parts, and the absence of Taylor cone stability problems posed by microfluidic-scale flow rates. The speed of MALDI detection, along with the scale of microfluidic droplets, allows for improvements upon macro-scale techniques in both throughput and time-of-flight (TOF) resolution. Where typical MS detection setups often utilize separation techniques such as chromatography, MALDI setups require a sufficiently purified sample to be mixed with pre-determined organic matrices, suited for the specific sample, prior to detection. MALDI matrix composition must be tuned to produce appropriate fragmentation and ablation of analytes. One method to obtain a purified sample from droplet-based microfluidics is to end the microfluidic channel onto a MALDI plate, with aqueous droplets forming on hydrophilic regions on the plate. Solvent and carrier fluid are then allowed to evaporate, leaving behind only the dried droplets of the sample of interest, after which the MALDI matrix is applied to the dried droplets.
S-Adenosyl methionine (SAM), also known under the commercial names of SAMe, SAM-e, or Adonat, is a common cosubstrate involved in methyl group transfers, transsulfuration, and aminopropylation. Although these anabolic reactions occur throughout the body, most SAM is produced and consumed in the liver. More than 40 methyl transfers from SAM are known, to various substrates such as nucleic acids, proteins, lipids and secondary metabolites. It is made from adenosine triphosphate (ATP) and methionine by methionine adenosyltransferase. SAM was first discovered by Giulio Cantoni in 1952. In bacteria, SAM is bound by the SAM riboswitch, which regulates genes involved in methionine or cysteine biosynthesis. In eukaryotic cells, SAM serves as a regulator of a variety of processes including DNA, tRNA, and rRNA methylation; immune response; amino acid metabolism; transsulfuration; and more. In plants, SAM is crucial to the biosynthesis of ethylene, an important plant hormone and signaling molecule. SAM has been studied for depression, osteoarthritis, and liver diseases with inconclusive results, and while generally considered safe short-term, its long-term safety, use during pregnancy, and risks for people with bipolar disorder or compromised immune systems remain unclear.
He then attempted to assuage fears that economic sanctions might destroy the economy, and asked Rhodesians to stand firm: "The mantle of the pioneers has fallen on our shoulders ... In the lives of most nations there comes a moment when a stand has to be made for principles, whatever the consequences. This moment has come to Rhodesia ... the first Western nation in the last two decades to say 'so far and no further'." He concluded with an assertion that the declaration of independence was "a blow for the preservation of justice, civilisation and Christianity".
=== Dyeing === Xanthoria parietina has been used as a natural dye source for centuries. Historical evidence indicates that ancient civilizations recognized this lichen's dyeing properties. In a 1934 publication, Reginald Campbell Thompson analyzed ancient Assyrian texts that mention lichens and dyeing. Thompson noted that the "yellow wall lichen" was "affirmed to give a good yellow or orange colour, if fixed with alum". Thompson's analysis of these ancient tablets suggests that knowledge of using lichens with alum as a mordant existed in ancient Mesopotamia. Alum (a naturally occurring mineral containing aluminium sulfate) was a mordant used with this lichen primarily to fix the dye to fabrics. Thompson notes that "the discovery of alum was one of the most important events in the history of dyeing." X. parietina was valued for its accessibility, growing readily on tree trunks and walls, and its ability to produce consistent yellow to orange hues when properly processed with mordants. Parietin is responsible for the lichen's dyeing properties, and pure isolated parietin produces the same color characteristics as whole lichen extracts. When processed using different extraction methods and mordants, this lichen yields a diverse range of colors. Extractions in boiling water produce golden-brown, yellow, and caramel hues, whereas 10% ammonia fermentation processes yield purplish-pink, orange, and pink shades. The POD (photo-oxidized) method, which involves exposing the lichen material to sunlight in an alkaline solution over time, can extract blue or purple dyes from X.
Sources: en.wikipedia.org
In Piazza Castello converge some of the main streets of the city centre. Among them, one of the most significant is the arcaded Via Po, built by Amedeo di Castellamonte in 1674 and featuring some interesting buildings, such as the first and original building of the University of Turin and the historical Caffè Fiorio, which was the favourite café of the 19th-century politicians. Via Po ends in Piazza Vittorio Veneto (simply called Piazza Vittorio locally), the largest Baroque square in Europe and today heart of Turin nightlife. Piazza Vittorio features the most fashionable bars and not far from here, along the Po riverfront, the Murazzi quays used to host several bars and nightclubs open until the morning until a few years ago.
Sanger then turned to sequencing DNA, which would require an entirely different approach. He looked at different ways of using DNA polymerase I from E. coli to copy single-stranded DNA. In 1975, together with Alan Coulson, he published a sequencing procedure using DNA polymerase with radiolabelled nucleotides that he called the "Plus and Minus" technique. This involved two closely related methods that generated short oligonucleotides with defined 3' termini. These could be fractionated by electrophoresis on a polyacrylamide gel and visualised using autoradiography. The procedure could sequence up to 80 nucleotides in one go and was a big improvement on what had gone before, but was still very laborious. Nevertheless, his group were able to sequence most of the 5,386 nucleotides of the single-stranded bacteriophage φX174. This was the first fully sequenced DNA-based genome. To their surprise they discovered that the coding regions of some of the genes overlapped with one another. In 1977 Sanger and colleagues introduced the "dideoxy" chain-termination method for sequencing DNA molecules, also known as the "Sanger method". This was a major breakthrough and allowed long stretches of DNA to be rapidly and accurately sequenced. It earned him his second Nobel prize in Chemistry in 1980, which he shared with Walter Gilbert and Paul Berg. The new method was used by Sanger and colleagues to sequence human mitochondrial DNA (16,569 base pairs) and bacteriophage λ (48,502 base pairs). The dideoxy method was eventually used to sequence the entire human genome.
In June 2015, the United States Office of Personnel Management (OPM) announced that it had been the target of a data breach targeting the records of as many as four million people. Later, FBI Director James Comey put the number at 18 million. The Washington Post has reported that the attack originated in China, citing unnamed government officials. Operation Shady RAT is a series of cyber attacks starting mid-2006, reported by Internet security company McAfee in August 2011. China is widely believed to be the state actor behind these attacks which hit at least 72 organizations including governments and defense contractors. The 2018 cyberattack on the Marriott hotel chain that collected personal details of roughly 500 million guests is now known to be a part of a Chinese intelligence-gathering effort that also hacked health insurers and the security clearance files of millions more Americans, The hackers, are suspected of working on behalf of the Ministry of State Security (MSS), the country's Communist-controlled civilian spy agency. On 14 September 2020, a database showing personal details of about 2.4 million people around the world was leaked and published. A Chinese company, Zhenhua Data compiled the database. According to the information from "National Enterprise Credit Information Publicity System", which is run by State Administration for Market Regulation in China, the shareholders of Zhenhua Data Information Technology Co., Ltd. are two natural persons and one general partnership enterprise whose partners are natural persons.
Successful bead beating is dependent not only on design features of the shaking machine (which take into consideration shaking oscillations frequency, shaking throw or distance, shaking orientation and vial orientation), but also the selection of correct bead size (0.1–6 mm (0.004–0.2 in) diameter), bead composition (glass, ceramic, steel) and bead load in the vial. In most laboratories, bead beating is done in batch sizes of one to twenty-four sealed, plastic vials or centrifuge tubes. The sample and tiny beads are agitated at about 2000 oscillations per minute in specially designed reciprocating shakers driven by high power electric motors. Cell disruption is complete in 1–3 minutes of shaking. Significantly faster rates of cell disruption are achieved with a bead beater variation called SoniBeast. Differing from conventional machines, it agitates the beads using a vortex motion at 20,000 oscillations per minute. Larger bead beater machines that hold deep-well microtiter plates also shorten process times, as do Bead Dispensers designed to quickly load beads into multiple vials or microplates. Pre-loaded vials and microplates are also available. All high energy bead beating machines warm the sample about 10 degrees per minute. This is due to frictional collisions of the beads during homogenization. Cooling of the sample during or after bead beating may be necessary to prevent damage to heat-sensitive proteins such as enzymes.
Maurice "Moe" Granat (84) (2007) Gladys Millard (87) (2011) Helen Matheson (95) (2011) Mary Zurawinski (96) (2011) Helen Young (90) (2013) Maureen Pickering (79) (2014) While at Caressant Care, Wettlaufer also injected Michael Priddle (63) and Wayne Hedges (57) "with intent to murder". She confessed to two counts of attempted murder in these cases. She left employment at Caressant Care in 2014, but in part-time work at other facilities and at patients' homes, she injected three more people with insulin:
Sources: en.wikipedia.org
Hylomorphism is a philosophical doctrine developed by the Ancient Greek philosopher Aristotle, which conceives every physical entity or being (ousia) as a compound of matter (potency) and substantial form (act), with the generic form as immanently real within the individual. The word is a 19th-century term formed from the Greek words ὕλη (hyle: "wood, matter") and μορφή (morphē: "form"). Hylomorphic theories of physical entities have been undergoing a revival in contemporary philosophy, especially since the 2000s.
At certain times in the geological past, reef-building organisms similar to corals were very abundant. Like modern corals, these ancient organisms built reefs, some of which ended as great structures in sedimentary rocks. Fossils of fellow reef-dwellers algae, sponges, and the remains of many echinoids, brachiopods, bivalves, gastropods, and trilobites appear along with coral fossils. This makes some corals useful index fossils. Coral fossils are not restricted to reef remnants, and many solitary fossils are found elsewhere, such as Cyclocyathus, which occurs in England's Gault clay formation.
== Research == In an in vitro analysis by the University of Rhode Island on cannabinoids it was found that 11-OH-Δ9-THC had the 3rd highest 3C-like protease inhibitor activity against COVID-19 out of all the cannabinoids tested within that study but not as high as the antiviral drug GC376 (56% for 11-OH-Δ9-THC vs. 100% for GC376).
== Structure == Epithelial tissue cells can adopt shapes of varying complexity from polyhedral to scutoidal to punakoidal. They are tightly packed and form a continuous sheet with almost no intercellular spaces. All epithelia is usually separated from underlying tissues by an extracellular fibrous basement membrane. The lining of the mouth, lung alveoli and kidney tubules are all made of epithelial tissue. The lining of the blood and lymphatic vessels are of a specialised form of epithelium called endothelium.
Sources: en.wikipedia.org
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.
Retention time is the interval between sample injection and the detector response for a given compound. It depends on the compound's interactions with the stationary and mobile phases under set conditions. Matching a retention time to a standard supports tentative identification but is not always unique.
HPLC alone can separate unknown compounds and provide retention times, but it often cannot identify them with certainty. Coupling HPLC to mass spectrometry gives mass information that improves identification. Confirmation usually requires comparison with reference standards or complementary techniques.
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.