The short version of detector fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-08-01. Anything still debated is marked as such rather than presented as settled.
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.
Quality control for HPLC testing combines scheduled checks, documented procedures, and review of results. Before sample analysis, system suitability testing confirms that the instrument, column, and method meet predefined criteria. Common criteria include resolution between critical peaks, retention time precision, peak tailing, and theoretical plate count. Failure triggers investigation before results are reported. Records link raw data, calculations, instrument logs, and analyst identity to each batch, supporting audits and repeat analysis.
Routine quality control uses system suitability, blank injections, check standards, and control samples to detect drift or contamination. System suitability criteria may specify minimum resolution, maximum tailing factor, and a permitted range for repeated injections. Blank injections reveal carryover or solvent contamination, while check standards confirm calibration accuracy over a batch. Control samples with known analyte levels can show whether results remain within statistical limits. When a control result falls outside limits, the analyst investigates the cause and may invalidate affected results before repeating the batch.
Documentation and traceability are central to regulated HPLC testing. Records typically include instrument logs, column history, mobile-phase preparation, sample preparation, injection sequences, raw chromatograms, and audit trails. Electronic systems may require user access controls, time-stamped changes, and backup procedures. Training records show that analysts are qualified for assigned methods. Audits and inspections check whether written procedures match actual practice and whether deviations are documented. These controls support reproducibility and allow results to be reconstructed if questions arise later.
Method validation establishes that an HPLC procedure is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, robustness, and solution stability. Accuracy reflects closeness to a reference value, while precision reflects agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from matrix components. Validation is documented through protocols and reports, and the required extent depends on the method's use and regulatory context.
| Property | Value | Notes |
|---|---|---|
| Retention time RSD | ≤1% for five replicate injections | Typical criterion; method-specific limits apply. |
| Resolution | ≥1.5 between critical pair | Baseline separation is generally desired. |
| Tailing factor | ≤2.0 | Measures peak symmetry. |
| Theoretical plates | ≥2000 per column | Method-dependent; higher values indicate greater efficiency. |
| Peak area RSD | ≤2% for replicate injections | Reflects autosampler and detector precision. |
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.
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.
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.
Eric Carlin, a member of the ACMD and former chairman of the English Drug Education Forum, also resigned after the announcement. He said the decision by the Home Secretary was "unduly based on media and political pressure" and there was "little or no discussion about how our recommendation to classify this drug would be likely to impact on young people's behaviour." Some former members of the ACMD and various charity groups expressed concern over the banning of the drug, arguing it would inevitably criminalise users, particularly young people. Others expressed concern that the drug would be left in the hands of black market dealers, who will only compound the problem. Carlin's resignation was specifically linked to the criminalisation of mephedrone; he stated: "We need to review our entire approach to drugs, dumping the idea that legally-sanctioned punishments for drug users should constitute a main part of the armoury in helping to solve our country's drug problems. We need to stop harming people who need help and support". The parliamentary debate was held on 8 April, one day after the 2010 general election had been announced, meaning it was during the so-called "wash-up period" when legislation is passed with little scrutiny. Only one hour was spent debating the ban, and all three parties agreed, meaning no vote was required.
In 1917–18, two groups of scientists, Lise Meitner in collaboration with Otto Hahn of Germany and Frederick Soddy and John Cranston of Great Britain, independently discovered another isotope, 231Pa, having a much longer half-life of 32,760 years. Meitner changed the name "brevium" to protactinium as the new element was part of the decay chain of uranium-235 as the parent of actinium (from the Greek: πρῶτος prôtos, meaning "first, before"). The IUPAC confirmed this naming in 1949. The discovery of protactinium completed one of the last gaps in early versions of the periodic table, and brought fame to the involved scientists. Aristid von Grosse produced 2 milligrams of Pa2O5 in 1927, and in 1934 first isolated elemental protactinium from 0.1 milligrams of Pa2O5. He used two different procedures: in the first, protactinium oxide was irradiated by 35 keV electrons in vacuum. In the other, called the van Arkel–de Boer process, the oxide was chemically converted to a halide (chloride, bromide or iodide) and then reduced in a vacuum with an electrically heated metallic filament:
Pseudoephedrine is a sympathomimetic drug of the phenethylamine and amphetamine chemical classes. Pseudoephedrine may be used as a nasal/sinus decongestant, as a stimulant, or as a wakefulness-promoting agent. The salts pseudoephedrine hydrochloride and pseudoephedrine sulfate are found in many over-the-counter preparations, either as a single ingredient or (more commonly) in combination with antihistamines, guaifenesin, dextromethorphan, or paracetamol (acetaminophen) or another NSAID (e.g., aspirin or ibuprofen). Pseudoephedrine is also used as a precursor chemical in the illegal production of methamphetamine.
== Mechanism == As previously mentioned, BCKDC's primary function in mammals is to catalyze an irreversible step in the catabolism of branched-chain amino acids. However BCKDC has a relatively broad specificity, also oxidizing 4-methylthio-2-oxobutyrate and 2-oxobutyrate at comparable rates and with similar Km values as for its branched-chain amino acid substrates. The BCKDC will also oxidize pyruvate, but at such a slow rate this side reaction has very little physiological significance. The reaction mechanism is as follows. Please note that any of several branched-chain α-ketoacids could have been used as a starting material; for this example, α-ketoisovalerate was arbitrarily chosen as the BCKDC substrate.
Sources: en.wikipedia.org
== Chemistry == Levothyroxine is a synthetic form of thyroxine (T4), which is secreted by the thyroid gland. Levothyroxine and thyroxine are chemically identical: natural thyroxine is also in the "levo" chiral form, the difference is only in terminological preference. T4 is biosynthesized from tyrosine. Approximately 5% of the US population suffers from over- or underproduction of T4 and T3. See Thyroid hormones § Thyroid metabolism for more information on its biosynthesis. Industrially, levothyroxine is made by chemical synthesis. Tyrosine is a common starting material. The produced hormone is incorporated into drugs as its sodium salt, levothyroxine sodium. Solid drugs such as tablets contain the pentahydrate form of the salt. Dextrothyroxine is the mirror form of levothyroxine with the opposite, non-natural chirality.
The Federal Bureau of Narcotics (FBN) was established as an agency of the US Department of the Treasury by an act of June 14, 1930, with Harry J. Anslinger replacing Levi G. Nutt (who left under scandal) to be appointed as commissioner, a position he held for 32 years, until 1962. Anslinger supported Prohibition and the criminalization of all drugs, and spearheaded anti-drug policy campaigns. He did not support a public health and treatment approach, instead urging courts to "jail offenders, then throw away the key." He has been characterized as the first architect of the punitive war on drugs. According to a report prepared for the Senate of Canada, Anslinger was "utterly devoted to prohibition and the control of drug supplies at the source" and is "widely recognized as having had one of the more powerful impacts on the development of US drug policy, and, by extension, international drug control into the early 1970s." During his three decades heading the FBN, Anslinger zealously and effectively pursued harsh drug penalties, with a particular focus on cannabis. He used his stature as the head of a federal agency to draft legislation, discredit critics, discount medical opinion and scientific findings, and convince lawmakers. Publicly, he used the media and speaking engagements to introduce hyperbolic messages about the evils of drug use. In the 1930s, he referred to a collection of news reports of horrific crimes, making unsubstantiated claims attributing them to drugs, particularly cannabis.
==== Raman spectroscopy ==== Raman spectroscopy is one of the easiest methods to integrate into a heterogeneous operando experiment, as these reactions typically occur in the gas phase, so there is very low litter interference and good data can be obtained for the species on the catalytic surface. In order to use Raman, all that is required is to insert a small probe containing two optical fibers for excitation and detection. Pressure and heat complications are essentially negligible, due to the nature of the probe. Operando confocal Raman micro-spectroscopy has been applied to the study of fuel cell catalytic layers with flowing reactant streams and controlled temperature.
A 2015 review recommended topical antifungal agents, topical corticosteroids, and topical calcineurin inhibitors like tacrolimus as the main treatments for seborrheic dermatitis based on good-quality evidence, rather than selenium disulfide for which evidence is much more limited. However, the review did suggest use of over-the-counter selenium disulfide shampoos as an inexpensive option for managing mild symptoms of seborrheic dermatitis.
== Further reading == Lampe, Markus, and Paul Sharp. A Land of Milk and Butter: How Elites Created the Modern Danish Dairy Industry (U of Chicago Press, 2018) online review Boberg-Fazlic, Nina; Jensen, Peter Sandholt; Lampe, Markus; Sharp, Paul; Skovsgaard, Christian Volmar (2023). "'Getting to Denmark': the role of agricultural elites for development". Journal of Economic Growth. 28 (4): 525–569. Kærgård, Niels (2023). "The Danish Economy, 1973–2009: From National Welfare State to International Market Economy". Scandinavian Journal of History
Sources: en.wikipedia.org
=== Dental === Silanization is often used to treat ceramics used for dental restorations and repairs. Applying silane coupling agents after grit blasting the ceramic material has been shown to produce durable resin bonding. Additionally, for titanium and other metal implant features in wires and crowns, application of silane coupling agents followed by resin composite cement has produced durable bonding in a clinical application. While silane coupling agents are widely used in dental practices, they are subject to bond degradation due to the environment of the oral cavity, weakening the adhesion between the surfaces that they are used to connect.
Bacteria can use flagella in different ways to generate different kinds of movement. Many bacteria (such as E. coli) have two distinct modes of movement: forward movement (swimming) and tumbling. The tumbling allows them to reorient and makes their movement a three-dimensional random walk. Bacterial species differ in the number and arrangement of flagella on their surface; some have a single flagellum (monotrichous), a flagellum at each end (amphitrichous), clusters of flagella at the poles of the cell (lophotrichous), while others have flagella distributed over the entire surface of the cell (peritrichous). The flagella of a group of bacteria, the spirochaetes, are found between two membranes in the periplasmic space. They have a distinctive helical body that twists about as it moves. Two other types of bacterial motion are called twitching motility that relies on a structure called the type IV pilus, and gliding motility, that uses other mechanisms. In twitching motility, the rod-like pilus extends out from the cell, binds some substrate, and then retracts, pulling the cell forward. Motile bacteria are attracted or repelled by certain stimuli in behaviours called taxes: these include chemotaxis, phototaxis, energy taxis, and magnetotaxis. In one peculiar group, the myxobacteria, individual bacteria move together to form waves of cells that then differentiate to form fruiting bodies containing spores. The myxobacteria move only when on solid surfaces, unlike E. coli, which is motile in liquid or solid media.
== Typical technique == A sample is introduced, either manually or with an autosampler, into a sample loop of known volume. A buffered aqueous solution known as the mobile phase carries the sample from the loop onto a column that contains some form of stationary phase material. This is typically a resin or gel matrix consisting of agarose or cellulose beads with covalently bonded charged functional groups. Equilibration of the stationary phase is needed in order to obtain the desired charge of the column. If the column is not properly equilibrated the desired molecule may not bind strongly to the column. The target analytes (anions or cations) are retained on the stationary phase but can be eluted by increasing the concentration of a similarly charged species that displaces the analyte ions from the stationary phase. For example, in cation exchange chromatography, the positively charged analyte can be displaced by adding positively charged sodium ions. The analytes of interest must then be detected by some means, typically by conductivity or UV/visible light absorbance. Control an IC system usually requires a chromatography data system (CDS). In addition to IC systems, some of these CDSs can also control gas chromatography (GC) and HPLC.
=== Made by Nacho === In April 2021, Flay, with Elly Truesdell and Katja Lang, launched Made by Nacho, a premium cat food company named for his Maine Coon, Nacho Flay. The brand sells wet cat food, dry kibble, and freeze-dried protein treats. Made by Nacho sells cat food from their website and in PetSmart in addition to offering a subscription service. Flay has also founded the Made By Nacho Charitable Fund as part of The New York Community Trust.
Sources: en.wikipedia.org
System suitability is typically performed before each batch or according to the validated method and laboratory procedure. Some long runs include periodic checks during analysis. The required frequency depends on regulatory expectations and method performance.
Retention time drift can result from changes in mobile phase composition, column temperature, pump flow, or column age. A gradual shift often points to column degradation. A sudden shift may indicate a leak, mixing error, or incorrect mobile phase.
Retention time alone cannot confirm identity because different compounds may elute at similar times. Coupling HPLC with mass spectrometry or comparing against authenticated standards increases confidence. Confirmation usually requires orthogonal data.
Validation establishes suitability for a new method, while verification confirms that a method works in a specific laboratory. Verification is often used when a validated method is adopted with existing equipment and staff. Both rely on documented acceptance criteria.