This is a working overview of quality control, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-02-14. 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.
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.
| 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. |
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.
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.
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.
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.
Data handling and documentation are central to HPLC quality control. Electronic systems should have audit trails that record changes to methods, sequences, and results. Integration parameters, such as peak baseline and threshold, can affect reported areas and must be defined in advance. Out-of-specification results trigger a structured investigation that may include reanalysis, instrument checks, and review of sample preparation. Regulatory inspections often examine raw data, audit trails, and training records to verify that reported results are traceable and reliable.
Method validation establishes that an HPLC procedure is suitable for its intended use. Key parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Accuracy measures agreement with a true or accepted value, while precision describes repeatability and intermediate precision. Specificity confirms that the method measures the analyte without interference from impurities, degradants, or excipients. Validation is documented in a protocol and report, and acceptance criteria are set before experiments begin. Regulatory guidance varies by region, but the general principles are widely harmonized.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Common checks include retention time, peak area, resolution between critical pairs, tailing factor, and theoretical plate count. Results are compared with predefined limits, and a failed check requires investigation before sample results are reported. Quality control samples at low, middle, and high concentrations are injected at intervals to monitor accuracy and precision. Blank injections detect carryover and contamination, while control charts track performance over time.
=== 3 May === French president Emmanuel Macron announced he would consider sending French troops to Ukraine "if the Russians were to break through the front lines" or if Ukraine were to request it. In Donetsk Oblast, three people were killed by Russian attacks in Kurakhove and Chasiv Yar, while one person was killed in a separate attack in Kharkiv. In Russia, the governor of Belgorod Oblast claimed that two people were injured by Ukrainian drone strikes in Voznesenovka and Shebekino. The HUR claimed the destruction of two Russian locomotives by fire over the last few days: one in Orenburg, the other in Vladikavkaz. Ukrainian media also reported that the agency carried out a cyberattack on internet providers and mobile operators in Tatarstan. The SBU arrested a resident of Kharkiv on suspicion of spying for Russia. The FSB claimed to have "liquidated" an agent working for the HUR who was plotting to carry out terrorist attacks against "military and energy objects" in Moscow and Leningrad Oblasts. The US announced plans to purchase new sensors for the JDAM-ER for Ukraine, which are designed to locate and destroy Russian GPS jammers.
An alternative approach to the identification and quantification of patient samples is through the use of mass spectrometry. This approach offers excellent precision and sensitivity in the identification, characterization and quantification of metabolites in multiple patient sample types, such as blood and urine. The mass spectrometry (MS) approach is typically coupled to gas chromatography (GC), in GC-MS or liquid chromatography (LC), in LC-MS, which aid in initially separating out the metabolite components within complex sample mixtures, and can allow for the isolation of particular metabolite subsets for analysis. GC-MS can provide relatively precise quantification of metabolites, as well as chemical structural information that can be compared to pre-existing chemical libraries. GC-MS can be conducted in a relatively high-throughput manner (greater than 100 samples per day) with greater detection sensitivity than NMR analysis. A limitation of GC-MS for this application, however, is that processed metabolite components must be readily volatilized for sample processing. LC-MS initially separates out the components of a sample mixture based on properties such as hydrophobicity, before processing them for identification and quantification by mass spectrometry (MS). Overall, LC-MS is an extremely flexible method for processing most compound types in a somewhat high-throughput manner (20-100 samples a day), also with greater sensitivity than NMR analysis. For both GC-MS and LC-MS there are limitations in the reproducibility of metabolite quantification.
=== Generic names === Ethylestrenol is the generic name of the drug and its INNTooltip International Nonproprietary Name, USANTooltip United States Adopted Name, and BANTooltip British Approved Name, while éthylestrénol is its DCFTooltip Dénomination Commune Française and ethylnandrol is its JANTooltip Japanese Accepted Name. The BANTooltip British Approved Name was formerly ethyloestrenol, but it was eventually changed.
6 April – Jim McKeever, 92, Gaelic footballer (Ballymaguigan, Newbridge, Derry senior team, Ulster). Born in Northern Ireland. 10 April John Joe Walsh, 82, Gaelic footballer (St Laurence's, Kildare senior team) and selector (Kildare). Pat Magner, 82, politician, Senator (1982–1982, 1983–1987 and 1993–1997). 12 April – Senan Louis O'Donnell, 96, Roman Catholic prelate, bishop of Maiduguri (1993–2003). 13 April – Craig Breen, 33, rally driver, car crash. 14 April – Mark Sheehan, 46, singer-songwriter, guitarist and producer. 18 April – Colm Murphy, 70, Irish republican and convicted arms trafficker (Omagh bombing), degenerative lung disease. 22 April Mick Loftus, 93, Gaelic footballer (Mayo senior team), referee and GAA president. Hugh Byrne, 83, politician, TD (1969–1982). 28 April – Johnny Fean, 71, guitarist (Horslips).
Sources: en.wikipedia.org
I am so relieved. I can't even believe it. Exactly two years ago I was forced to have as much security as possible due to threats. Ever since then, i have never walked alone in the streets. It was heavy. Fortunately, I could still do my job. It was a difficult time in my career. When you hear such news, it is an incredible relief. In 2017, writer Raf Sauviller published his book Borgerokko Maffia, which was distributed to many libraries across Flanders (Belgium) and the Netherlands. In his book, he discusses the corruption that takes place in the Port of Antwerp amongst police officers and Customs controls. According to research which was carried out in 2018, the municipality of Borgerhout, Antwerp, had an illegal economy which was larger than the regular economy due to the influx of funds by the Moroccan mafia. During an interview by the newspaper De Morgen on the context of this book, the mayor of Antwerp, Bart De Wever, admitted that there were many difficulties on intercepting the main commanders of the Moroccan mafia in Antwerp. He also stated:
Each of the major stable isotope systems (hydrogen, carbon, oxygen, nitrogen, and sulfur) has a wide variety of references encompassing distinct molecular structures. For example, nitrogen isotope reference materials include N-bearing molecules such ammonia (NH3), atmospheric dinitrogen (N2), and nitrate (NO3−). Isotopic abundances are commonly reported using the δ notation, which is the ratio of two isotopes (R) in a sample relative to the same ratio in a reference material, often reported in per mille (‰) (equation below). Reference material span a wide range of isotopic compositions, including enrichments (positive δ) and depletions (negative δ). While the δ values of references are widely available, estimates of the absolute isotope ratios (R) in these materials are seldom reported. This article aggregates the δ and R values of common and non-traditional stable isotope reference materials.
== Medical uses == When used in low doses, corticosteroids serve as an anti-inflammatory agent. At higher doses, they are considered as immunosuppressants. Corticosteroids inhibit the inflammatory response to a variety of inciting agents and, it is presumed, delay or slow healing. They inhibit edema, fibrin deposition, capillary dilation, leukocyte migration, capillary proliferation, fibroblast proliferation, deposition of collagen, and scar formation associated with inflammation.
== Biomedical applications == The oldest application is also the simplest: the surgical suture. Braided silk is easy to handle and holds a knot securely, and it remains in clinical use, although it can provoke a tissue reaction and lose strength over time, and synthetic threads have replaced it in some procedures. Porous silk scaffolds serve as temporary frameworks for regrowing tissue. Because their strength can be set and their degradation slowed, they suit tissues that either bear load or heal slowly—bone, cartilage, skin, and connective tissues such as ligament and tendon, where the toughness of silk is an advantage. Cells are seeded onto the scaffold, which provides mechanical support while they become established and is gradually replaced by the body's own tissue. Silk films, gels and particles can hold a drug and release it slowly. The mild, water-based processing is the principal advantage: sensitive drugs and proteins survive incorporation, and release can be slowed by increasing the beta-sheet content of the surrounding silk. Silk coatings have also been used to stabilise vaccines and other biologics against heat. Thin silk films are transparent, can be moulded with fine surface patterns and dissolve in the body, a combination well suited to biodegradable electronics and optics. Silicon components have been fabricated on silk films designed to conform to tissue and then dissolve once their function is complete, an approach known as transient or bioresorbable electronics. Silk has also been formed into lenses, diffraction gratings and sensors.
The sodium carboxymethyl cellulose can be cross-linked to give the croscarmellose sodium (E468) for use as a disintegrant in pharmaceutical formulations. Furthermore, by the covalent attachment of thiol groups to cellulose ethers such as sodium carboxymethyl cellulose, ethyl cellulose, or hydroxyethyl cellulose mucoadhesive and permeation enhancing properties can be introduced. Thiolated cellulose derivatives (see thiomers) exhibit also high binding properties for metal ions.
Sources: en.wikipedia.org
=== Competing reactions === The most common side reactivity associated with the Stille reaction is homocoupling of the stannane reagents to form an R2-R2 dimer. It is believed to proceed through two possible mechanisms. First, reaction of two equivalents of organostannane with the Pd(II) precatalyst will yield the homocoupled product after reductive elimination. Second, the Pd(0) catalyst can undergo a radical process to yield the dimer. The organostannane reagent used is traditionally tetravalent at tin, normally consisting of the sp2-hybridized group to be transferred and three "non-transferable" alkyl groups. As seen above, alkyl groups are normally the slowest at migrating onto the palladium catalyst.
The Bateman equation predicts the relative quantities of all the isotopes that compose a given decay chain once that decay chain has proceeded long enough for some of its daughter products to have reached the stable (i.e., nonradioactive) end of the chain. A decay chain that has reached this state, which may require billions of years, is said to be in equilibrium. A sample of radioactive material in equilibrium produces a steady and steadily decreasing quantity of radioactivity as the isotopes that compose it traverse the decay chain. On the other hand, if a sample of radioactive material has been isotopically enriched, meaning that a radioisotope is present in larger quantities than would exist if a decay chain were the only cause of its presence, that sample is said to be out of equilibrium. An unintuitive consequence of this disequilibrium is that a sample of enriched material may occasionally increase in radioactivity as daughter products that are more highly radioactive than their parents accumulate. Both enriched and depleted uranium provide examples of this phenomenon.
In chemical reactors, the goal is to make components react with a high yield. In a homogeneous, first-order reaction, the probability that an atom or molecule will react depends only on its residence time:
Daniel Levy (political analyst); analyst, commentator, author, journalist, former advisor to Israeli government; formerly Israeli negotiator Taba summit and Oslo 2 peace process; current president of U.S./Middle East Project (USMEP); among founders of J Street; son of Lord Michael Levy; was World Chairman of World Union of Jewish Students in Jerusalem; served in Israel Defense Forces (IDF) as non-commissioned officer; worked as head of Jerusalem Affairs unit under Minister Haim Ramon; served as advisor to Justice Minister Yossi Beilin; served as an Israeli negotiator in peace talks with Palestinian leaders during his IDF years under Israeli Prime Ministers Yitzhak Rabin and Ehud Barak; was lead drafter of 2003 Geneva Initiative along with Ghaith al-Omari; current president of the U.S./Middle East Project He previously headed the Middle East and North Africa program at the European Council on Foreign Relations from 2012 to 2016. He has also worked at the director level on the New America Foundation's Middle East Task Force and as a fellow with the Century Foundation.
Inspections and audits like also be conducted on a regular basis to assess hazards due to chemical handling and storage, electrical equipment, biohazards, hazardous waste management, chemical waste, housekeeping and emergency preparedness, radiation safety, ventilation as well as respiratory testing and indoor air quality. An important element of such audits is the review of regulatory compliance and the training of individuals who have access to or work in the laboratory. Training is critical to the ongoing safe operation of the laboratory facility. Educators, staff and management must be engaged in working to reduce the likelihood of accidents, injuries and potential litigation. Efforts are often made to ensure laboratory safety videos are both relevant and engaging.
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.
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.