mobile phase raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-02-09. Anything still debated is marked as such rather than presented as settled.
Quality control samples are inserted at intervals to monitor accuracy and precision throughout a batch. Blank samples detect contamination, while spiked samples assess recovery from the sample matrix. Calibration standards establish the relationship between detector response and concentration, and control samples are prepared independently from them whenever possible. Laboratories also participate in proficiency testing and maintain audit trails, instrument logs, and reagent records. Ongoing review of control charts can reveal trends before they cause out-of-specification results.
Method validation demonstrates that an HPLC procedure is suitable for its intended purpose. Common validation parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, and robustness. Accuracy reflects agreement with a reference value, while precision describes repeatability under defined conditions. Specificity shows whether the method can measure the analyte in the presence of impurities or matrix components. Validation documents are reviewed before a method is used for routine testing or regulatory submissions.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Typical checks include retention time, peak area precision, resolution between critical pairs, tailing factor, and theoretical plate count. Acceptance criteria are set in the method or pharmacopeial monograph. If a suitability check fails, the run may be rejected and the instrument or sample preparation may need investigation. This practice helps prevent release of data from a system that has drifted out of control.
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.
| Property | Value | Notes |
|---|---|---|
| Validation parameter | Accuracy | Closeness to a reference value. |
| Validation parameter | Precision | Repeatability or intermediate precision. |
| Validation parameter | Linearity | Proportional response across a range. |
| System suitability check | Resolution | Separation between adjacent peaks. |
| Quality control tool | Control chart | Tracks results over time for trends. |
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.
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.
In 1910, Hahn was appointed professor by the Prussian Minister of Culture and Education, August von Trott zu Solz. Two years later, Hahn became head of the Radioactivity Department of the newly founded Kaiser Wilhelm Institute for Chemistry (KWIC) in Berlin-Dahlem (in what is today the Hahn-Meitner-Building of the Free University of Berlin). This came with an annual salary of 5,000 marks (equivalent to €29,000 in 2021). In addition, he received 66,000 marks in 1914 (equivalent to €369,000 in 2021) from Knöfler for the mesothorium process, of which he gave 10 per cent to Meitner. The new institute was inaugurated on 23 October 1912 in a ceremony presided over by Kaiser Wilhelm II. The Kaiser was shown glowing radioactive substances in a dark room. The move to new accommodation was fortuitous, as the wood shop had become heavily contaminated by radioactive liquids that had been spilt, and radioactive gases that had vented and then decayed and settled as radioactive dust, making sensitive measurements impossible. To ensure that their clean new laboratories stayed that way, Hahn and Meitner instituted strict procedures. Chemical and physical measurements were conducted in different rooms, people handling radioactive substances had to follow protocols that included not shaking hands, and rolls of toilet paper were hung next to every telephone and door handle. Strongly radioactive substances were stored in the old wood shop, and later in a purpose-built radium house on the institute grounds.
However, in a preprint study, Carnegie Mellon University researchers tested the behavior of agents in a simulated software company and found that none of the agents could complete a majority of the tasks assigned to them. Other researchers had similar findings with Devin AI and other agents in both formal business settings and freelance work. In June 2025, CNN argued that CEOs's statements on AI replacing their employees were a strategy to "[keep] workers working by making them afraid of losing their jobs." Tech companies have pressured employees to use generative AI models in their work, including AI coding agents. Brian Armstrong, the CEO of Coinbase, fired several employees who did not. Some business leaders have replaced some of their employees with agents, but have said that the agents would need more supervision than those employees. In October 2025, Futurism questioned whether Amazon's previously announced efforts to replace parts of its workforce with generative AI and AI agents could have led to the October 2025 outage of Amazon Web Services. Large technology companies such as Salesforce, Klarna and IBM announced layoffs in 2025, replacing hundreds of their employees in human resources or customer service with AI agents. However, Klarna later rehired several human employees. Yoshua Bengio warned at the 2025 World Economic Forum that "all of the catastrophic scenarios with AGI or superintelligence happen if we have agents". Financial authorities have warned that more complex and autonomous "agentic" AI could become a channel for systemic risk in finance.
Thus, in the presence of the inhibitor, the enzyme's effective Km and Vmax become (α/α')Km and (1/α')Vmax, respectively. However, the modified Michaelis-Menten equation assumes that binding of the inhibitor to the enzyme has reached equilibrium, which may be a very slow process for inhibitors with sub-nanomolar dissociation constants. In these cases the inhibition becomes effectively irreversible, hence it is more practical to treat such tight-binding inhibitors as irreversible (see below). The effects of different types of reversible enzyme inhibitors on enzymatic activity can be visualised using graphical representations of the Michaelis–Menten equation, such as Lineweaver–Burk, Eadie-Hofstee or Hanes-Woolf plots. An illustration is provided by the three Lineweaver–Burk plots depicted in the Lineweaver–Burk diagrams figure. In the top diagram the competitive inhibition lines intersect on the y-axis, illustrating that such inhibitors do not affect Vmax. In the bottom diagram the non-competitive inhibition lines intersect on the x-axis, showing these inhibitors do not affect Km. However, since it can be difficult to estimate Ki and Ki' accurately from such plots, it is advisable to estimate these constants using more reliable nonlinear regression methods.
== Tolerance and overdoses == Fatal opioid overdose typically occurs due to bradypnea, hypoxemia, and decreased cardiac output (hypotension occurs due to vasodilation, and bradycardia further contributes to decreased cardiac output). A potentiation effect occurs when opioids are combined with ethanol, benzodiazepines, barbiturates, or other central depressants which can result in rapid loss of consciousness and an increased risk of fatal overdose. Substantial tolerance to respiratory depression develops quickly, and tolerant individuals can withstand larger doses. However, tolerance to respiratory depression is quickly lost during withdrawal and may be completely reversed within a week. Many overdoses occur in people who return to their previous dose after having lost their tolerance following cessation of opioids. This puts addicts who receive medical treatment for opioid addiction at great risk of overdose when they are released, as they may be particularly vulnerable to relapse. Less commonly, massive overdoses have been known to cause circulatory collapse from vasodilation and bradycardia. Opioid overdoses can be rapidly reversed through the use of opioid antagonists, naloxone being the most widely used example. Opioid antagonists work by binding competitively to μ-opioid receptors and displacing opioid agonists. Additional doses of naloxone may be necessary and supportive care should be given to prevent hypoxic brain injury by monitoring vital signs.
=== 1 April === A court in Kyiv ordered the house arrest of Metropolitan Pavlo (born Petro Lebid) of the Ukrainian Orthodox Church (Moscow Patriarchate) for allegedly supporting the Russian invasion of Ukraine. He was later taken under police custody on 14 July. Russia assumed the presidency of the UN Security Council for the month, a role in which Russia was able to maneuver meetings on Ukraine to portray the US and other Western countries as making false accusations against Russia.
Sources: en.wikipedia.org
Wandering blue tangs are often chased by other fish, and also visit cleaning stations more often than those in the other modes. Wandering is found most often in the reef back zone (enclosed region with irregular patches of algae, rock and sand) and during the morning. With an increase in conspecific population density, blue tang individuals become more territorial. Small, juvenile blue tangs are territorial, but the incidence of territoriality in the larger classes decreases. However, in these fish, schooling and wandering increases.
== Other uses == Adult Nurse Practitioner Aircraft Nuclear Propulsion Lee Airport, Annapolis, Maryland, US (IATA airport code and FAA location identifier "ANP") Angika language (ISO language code "anp") Absolut Null Punkt, a Japanese band featuring KK Null Anpao or Anp, the two-faced Lakota god of the dawn in Native American mythology Aviação Naval Portuguesa or Portuguese Naval Aviation
6 April – The new England women's national football team home kit is worn for its inaugural match as England participates in the 2023 Women's Finalissima against Brazil. At Wembley Stadium, England beat Brazil 4–2 in a penalty shootout to win their first Finalissima. 8 April – The NASUWT is to ballot its members on strike action after 87% of those who voted rejected the government's pay offer for teachers in England, which the union says fails to address concerns over pay and conditions. 11 April – Junior doctors in England begin a four-day strike. 14 April – Two police officers are dismissed from the Metropolitan Police over offensive WhatsApp messages, some of them including offensive comments about model Katie Price's son, Harvey. The Royal College of Nursing rejects a pay offer for nurses in England and announces a 48-hour strike from 8pm on 30 April to 8pm on 2 May. UNISON confirms its members working for the NHS have voted unanimously to accept a 5% pay offer from the UK government. Following a trial at Derby Crown Court, Stephen Boden and partner Shannon Marsden are convicted of the murder of their ten-month-old son Finley Boden on Christmas Day 2020, 39 days after he had been returned to them by social services. 15 April – Merseyside Police say that 118 people have been arrested at Aintree Racecourse after protestors delay the start of the 2023 Grand National. The race, which is delayed by 14 minutes, is won by Corach Rambler, ridden by Derek Fox.
This stage contributes a significant fraction of the entire downstream processing expenditure. Examples of operations include affinity, size exclusion, reversed phase chromatography, ion-exchange chromatography, crystallization and fractional precipitation. Product polishing describes the final processing steps which end with packaging of the product in a form that is stable, easily transportable and convenient. Crystallization, desiccation, lyophilization and spray drying are typical unit operations. Depending on the product and its intended use, polishing may also include operations to sterilize the product and remove or deactivate trace contaminants which might compromise product safety. Such operations might include the removal of viruses or depyrogenation. A few product recovery methods may be considered to combine two or more stages. For example, expanded bed adsorption (Vennapusa et al. 2008) accomplishes removal of insolubles and product isolation in a single step. Affinity chromatography often isolates and purifies in a single step.
Sources: en.wikipedia.org
Method validation is the documented process of showing that an HPLC procedure produces reliable results for a defined purpose. It examines parameters such as accuracy, precision, specificity, linearity, and robustness. Regulators and quality systems often require validation before routine use.
System suitability is a set of checks run on the chromatographic system before sample analysis. It confirms that resolution, peak shape, retention time, and response meet predefined limits. Failure can invalidate the run and trigger corrective action.
Blank injections reveal peaks or baseline disturbances that come from solvents, reagents, or the instrument rather than the sample. They help distinguish contamination from actual analyte signals. Comparing blanks with sample runs supports accurate interpretation.
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.