HPLC comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2025-08-12. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Separation mode | Reversed-phase | Common for polar and moderately polar analytes |
| Typical column length | 100-250 mm | Shorter columns can reduce run time |
| Particle size | 3-5 micrometers | Smaller particles improve efficiency but raise pressure |
| Flow rate | 0.5-2.0 mL/min | Depends on column dimensions and pressure limits |
| Detection | UV-Vis absorbance | Widely used for compounds with chromophores |
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.
Regulatory and pharmacopeial texts shape how HPLC testing is performed and documented. The International Council for Harmonisation provides validation guidance, while pharmacopeias publish general chromatography chapters and monographs for specific materials. Accreditation standards such as ISO/IEC 17025 address laboratory competence and traceability. Inspectors may review instrument qualification, analyst training, reference material control, and electronic records. Open questions include how best to validate methods for new complex products and how to handle automated data processing. Laboratories generally resolve these issues through risk assessment, method lifecycle management, and documented scientific justification.
In quality control laboratories, HPLC testing supports batch release, raw material checks, stability studies, and impurity profiling. A validated method defines sample preparation, instrument settings, calibration, and acceptance criteria. Analysts compare results with specifications and investigate out-of-specification outcomes before a batch is approved. Documentation includes chromatograms, integration records, audit trails, and reagent details. Because results influence product decisions, laboratories follow formal quality systems and data integrity rules. The exact tests and limits depend on the material, its intended use, and the applicable regulatory framework.
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.
He also initiated the President's Emergency Plan for AIDS Relief, in 2003, to address the global AIDS epidemic. The September 11 attacks during 2001 decisively reshaped his administration, resulting in the start of the war on terror and the creation of the Department of Homeland Security. Bush ordered the invasion of Afghanistan in an effort to overthrow the Taliban, destroy al-Qaeda, and capture Osama bin Laden. He signed the Patriot Act, expanding surveillance powers for suspected terrorists. He also ordered the 2003 invasion of Iraq to overthrow Saddam Hussein's regime, citing claims that it possessed weapons of mass destruction and had ties with al-Qaeda. Bush later signed the Medicare Modernization Act, which created Medicare Part D. In 2004, Bush was re-elected president in a close race, beating Democratic opponent John Kerry and winning the popular vote. During his second term, Bush negotiated various free trade agreements, appointed John Roberts and Samuel Alito to the Supreme Court, and sought major changes to Social Security and immigration laws, both of which ultimately failed in Congress. He was widely criticized for his administration's handling of Hurricane Katrina and revelations of torture against detainees at Abu Ghraib prison in Iraq. Amid his unpopularity, the Democrats regained control of Congress in the 2006 elections. In January 2007, Bush launched a surge of troops in Iraq.
Avasimibe (INN), codenamed CI 1011, is a drug that inhibits sterol O-acyltransferases (SOAT1 and SOAT2, also known as ACAT1 and ACAT2), enzymes involved in the metabolism and catabolism of cholesterol. It was discovered by Parke-Davis (later Pfizer) and developed as a possible lipid-lowering agent and treatment for atherosclerosis. The first description of avasimibe was published in 1996. Clinical trials began in 1997. However, development was halted in 2003 due to a high potential for interactions with other medicines, and a pivotal study found it had no favorable effect on atherosclerosis and actually increased LDL cholesterol levels significantly. SOAT/ACAT inhibition has since been discredited as a viable strategy for treating high cholesterol and atherosclerosis, but renewed interest in avasimibe has arisen due to its potential antitumor utility through other mechanisms. It has never been marketed or used outside clinical trials.
β-globin chains are encoded by the HBB gene on chromosome 11; in a healthy person with two copies on each chromosome, two loci encode the β chain. In beta thalassemia, a single faulty gene can be either asymptomatic or cause mild disease; if both genes are faulty this causes moderate to severe disease. Mutated alleles are called β+ when partial function is conserved and some beta-globin is generated, or βo when no functioning protein is produced. The situation of both alleles determines the clinical picture:
2-Amino-3-carboxymuconic semialdehyde is an intermediate in the metabolism of tryptophan in the kynurenine pathway. Quinolinic acid is a neurotoxin formed nonenzymatically from 2-amino-3-carboxymuconic semialdehyde in mammalian tissues. 2-Amino-3-carboxymuconic semialdehyde is enzymatically converted to picolinic acid via 2-aminomuconic semialdehyde.
Defense Secretary Robert McNamara and General Maxwell Taylor advised the president to use nuclear weapons should the Americans intervene in such a situation. Kennedy insisted that Washington defend India as it would any ally, saying, "We should defend India, and therefore we will defend India." Kennedy's ambassador to India was the noted liberal economist John Kenneth Galbraith, who was considered close to India. While in India, Galbraith helped establish one of the first Indian computer science departments, at the Indian Institute of Technology in Kanpur, Uttar Pradesh.
Sources: en.wikipedia.org
=== Extrinsic factors === The malformations of arthrogryposis can be secondary to environmental factors such as: decreased intrauterine movement, oligohydramnios (low volume or abnormal distribution of intrauterine fluid), and defects in the fetal blood supply. Other causes could be: hyperthermia, limb immobilization and viral infections. A specific virus that may cause arthrogryposis is contraction of the Zika virus during pregnancy. Congenital Zika syndrome (CZS), may occur when there is vertical transmission of the Zika virus to the fetus. Myasthenia gravis of the mother leads also in rare cases to arthrogryposis. The major cause in humans is fetal akinesia; however, this is disputed lately.
Subsequent industry developments have included the involvement of major tobacco companies in the e-cigarette market through subsidiaries and acquisitions; for example, British American Tobacco's U.S. unit Reynolds American markets Vuse products, and in 2023 Altria acquired NJOY's e-vapor product portfolio. In parallel with regulatory scrutiny and industry consolidation, e-cigarette manufacturers have faced significant product liability and consumer protection litigation. In April 2023, Juul Labs agreed to pay $462 million to settle claims brought by six U.S. states and the District of Columbia alleging unlawful marketing of its products to minors. Public safety concerns related to lithium ion batteries have also extended beyond consumer use to storage, disposal, and waste handling. Public safety authorities have warned about fire risks associated with lithium ion batteries in disposable e-cigarettes during storage, disposal and waste handling. Ahead of the United Kingdom's disposable vape ban taking effect in June 2025, the Local Government Association cautioned that lithium batteries inside disposable vapes could pose a fire and risk-to-life hazard if not stored correctly. In the UK, these concerns have been reflected in government and media reporting on waste-related fires. In 2025, reporting linked discarded single use vapes to fires in waste collection vehicles and recycling facilities, citing warning from the Department for Environment, Food & Rural Affairs and estimates of more than 1,200 battery-related fires at waste sites in 2023.
Advanced delivery systems such as gene therapies, nanoparticles, or implants have been costly, and therefore, only patients within wealthy countries can afford them. This indicates that healthcare no longer considers equality and fairness. Another ethical concern is the issue of privacy. Digital tools have been used to determine and track patient medical adherence. Although these tools may help improve patient welfare, they may also be used to expose patient data, and there are increasing insecurities regarding patients' personal information.
The board included members with relevant biomedical expertise such as past president of the American Association for Clinical Chemistry Susan A. Evans; William Foege, former director of the U.S. Centers for Disease Control and Prevention (CDC); David Helfet, director of the Orthopedic Trauma Service at the Hospital for Special Surgery; and professors Ann M. Gronowski, Larry J. Kricka, Jack Ladenson, Andy O. Miller and Steven Spitalnik. Balwani left his position as president and COO in May 2016. At that time, the company announced its new board members, Fabrizio Bonanni (former executive vice president of Amgen), Richard Kovacevich and William Foege, who would help to publicly introduce its technologies. In May 2016, members of the Theranos board of directors were:
Sources: en.wikipedia.org
In women with polycystic ovary syndrome (PCOS), a condition of androgen excess, testosterone levels are typically around 50 to 80 ng/dL, with a range of about 30 to 140 ng/dL. Total testosterone levels are about 20-fold and free testosterone levels about 40-fold higher in men than in women on average. Similarly, testosterone production is approximately 30 times higher in men than in women.
=== February === 2 February Scientists report a possible way of solving the three-body problem; a notable problem of particular importance to physics and classical mechanics. Apple releases the Vision Pro as a virtual reality tool with visionOS. 5 February The proposed name Zoozve for Venus' quasi-moon 2002 VE is approved and announced by the International Astronomical Union's Working Group Small Bodies Nomenclature (WGSBN). A study based on 300-years-long temperature records preserved in Caribbean sclerosponge carbonate skeletons shows industrial-era warming already began in the mid-1860s and that by 2020, global warming was already 1.7±0.1 °C above pre-industrial levels. However, their reference period is not used by the IPCC and the 1.5 °C climate goal and the study's authors suggest their results show a better baseline. A study reports high life satisfaction in people with low incomes among small-scale societies outside mainstream societies, in contrast with conclusions of a 2023 adversarial collaboration. 6 February Scientists report a new species of mussel named Vadumodiolus teredinicola. Biologists report a new species of jellyfish named Santjordia pagesi. 7 February Reported science studies suggest that cosmic dust particles may have spread, in a process termed panspermia, life to Earth and elsewhere in the Universe. A battery based on calcium, able to charge and discharge fully 700 times at room temperature, is presented. It is described as a potential alternative to lithium, being 2,500 times more abundant on Earth.
Ba(Cl2C=C(Cl)COO)2 → BaCl2 + ClC≡CCl + 2CO2 Dichloroacetylene was discovered as an intermediate in the synthesis of diphenylacetylene with calcium carbide, chlorine and benzene in 1918. It was first synthesized from trichloroethylene by Erwin Ott, W. Ottemeyer and K. Packendorff in 1930.
==== Oral activity and hepatotoxicity ==== Non-17α-alkylated testosterone derivatives such as testosterone itself, DHT, and nandrolone all have poor oral bioavailability due to extensive first-pass hepatic metabolism and hence are not orally active. A notable exception to this are AAS that are androgen precursors or prohormones, including dehydroepiandrosterone (DHEA), androstenediol, androstenedione, boldione (androstadienedione), bolandiol (norandrostenediol), bolandione (norandrostenedione), dienedione, mentabolan (MENT dione, trestione), and methoxydienone (methoxygonadiene) (although these are relatively weak AAS). AAS that are not orally active are used almost exclusively in the form of esters administered by intramuscular injection, which act as depots and are long-acting prodrugs. Examples include testosterone, as testosterone cypionate, testosterone enanthate, and testosterone propionate, and nandrolone, as nandrolone phenylpropionate and nandrolone decanoate, among many others (see here for a full list of testosterone and nandrolone esters). An exception is the long-chain ester testosterone undecanoate, which is orally active, albeit with only low oral bioavailability (approximately 3%). In contrast to most other AAS, 17α-alkylated testosterone derivatives show resistance to metabolism due to steric hindrance and are orally active, though they may be esterified and administered via intramuscular injection as well.
Metallopeptides (also called metal-peptides or metal peptide complexes) are peptides that contain one or more metal ions in their structure. This specific type of peptide are, just like metalloproteins, metallofoldamers. And very similar to metalloproteins, metallopeptide's functionality is attributed through the contained metal ion cofactor. These short structured peptides are often employed to develop mimics of metalloproteins and systems similar to artificial metalloenzymes. A multitude of naturally occurring peptides display biological and chemical activities when bound to various metal ions. Where different metal ion cofactor can lead to different reactivity and even different folding and physical characteristics (e.g. solubility or stability) of the structure. Synthetic equivalents of such peptides are engineered to bind metal ions and display a variety of physical, chemical, and biological reactivity and characteristics.
Sources: en.wikipedia.org
It measures the amounts and identities of compounds in liquid samples by separation and detection. Depending on the detector and reference standards, results can be qualitative or quantitative. The technique is used in fields such as pharmaceutical analysis, food safety, and environmental monitoring.
Performance checks confirm that the chromatographic system works within preset limits before results are accepted. They examine factors such as peak resolution, tailing, and repeatability. If criteria fail, the run may need correction or repetition.
Retention time alone is not definitive proof because other compounds can elute at similar times. Confirmation usually uses a second method, a different column, or a detector such as mass spectrometry. Authentic standards strengthen identification.
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.