Everything below concerns HPLC. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Last reviewed on 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
Developing an HPLC test begins with defining the analytes, matrix, and required reporting limits. Chemists select a separation mode, column chemistry, mobile phase composition, flow rate, and detection wavelength or mass transition. Experiments then adjust these variables to achieve adequate retention, resolution, and peak shape. System suitability tests confirm that the instrument and method perform consistently before sample analysis. Without suitable resolution, quantitative results may be unreliable. Preliminary runs often use scouting gradients to locate retention windows.
Validation establishes that a method is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, robustness, and stability of standards and samples. Acceptance criteria are defined in advance, and results are documented in a validation report. Regulatory guidance for pharmaceuticals, foods, and environmental testing differs, so the applicable framework must be identified. Ongoing verification uses control samples and trend charts after validation. Method transfer to another laboratory may require partial revalidation.
Routine quality control includes blanks, duplicates, spiked samples, and certified reference materials. Calibration curves are prepared with standards at several concentrations, and the detector response is checked for linearity. Carryover, column aging, mobile phase evaporation, and temperature drift can shift retention times or peak areas. Maintenance such as replacing seals, filters, and columns helps prevent failures. Records of injections, integration, and deviations support traceability. Audits may request raw data and instrument logs for each batch.
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.
| Property | Value | Notes |
|---|---|---|
| Accuracy | Closeness to true value | Often assessed by recovery of spiked samples |
| Precision | Agreement among repeated measurements | Often reported as relative standard deviation |
| Specificity | Ability to measure analyte without interference | Must separate analyte from impurities and matrix |
| Linearity | Proportional detector response | Evaluated across a defined concentration range |
| Robustness | Resistance to small method changes | Tests flow rate, pH, temperature, and mobile phase composition |
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.
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.
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.
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.
=== Elastosis === Elastosis is the buildup of elastin in tissues, and is a form of degenerative disease. There are a multitude of causes, but the most commons cause is actinic elastosis of the skin, also known as solar elastosis, which is caused by prolonged and excessive sun exposure, a process known as photoaging. Uncommon causes of skin elastosis include elastosis perforans serpiginosa, perforating calcific elastosis and linear focal elastosis.
== History == The lines were first discovered in 1861 by Austrian anatomist Karl Langer (1819–1887), though he cited the surgeon Baron Dupuytren as being the first to recognise the phenomenon. Langer punctured numerous holes at short distances from each other into the skin of a cadaver with a tool that had a circular-shaped tip, similar to an ice pick. He noticed that the resultant punctures in the skin had ellipsoidal shapes. From this testing he observed patterns and was able to determine "line directions" by the longer axes of the ellipsoidal holes and lines.
In the 1961 season, he guest-starred in an episode of NBC's Western Bonanza titled "Broken Ballad". In the 1961–1962 season, he guest-starred on ABC's crime drama Target: The Corruptors! and that network's The Rifleman. In the 1962–1963 season, he guest-starred in NBC's modern Western series Empire starring Richard Egan. In 1964, Culp played Charlie Orwell, an alcoholic veterinarian, in an episode of The Virginian (NBC 1962–1971) titled "The Stallion". That same year, he appeared in yet another Western, Gunsmoke. In the series' episode "Hung High", he portrays an outlaw named Joe Costa, who attempts to frame Matt Dillon for lynching a prisoner who had killed the marshal's friend. In 1965, he was cast as Frank Melo in "The Tender Twigs" of James Franciscus's NBC education drama series, Mr. Novak. Culp then played perhaps his most memorable character, American secret agent Kelly Robinson, who operated undercover as a touring tennis professional, for three years on the hit NBC series I Spy (1965–1968), with co-star Bill Cosby. Culp wrote the scripts for seven episodes, one of which he also directed and an episode earned him an Emmy nomination for writing. For all three years of the series, he was also nominated for an acting Emmy (Outstanding Performance by an Actor in a Leading Role in a Dramatic Series category), but lost each time to Cosby.
Sources: en.wikipedia.org
=== Conceptual development === Ilyushin began work on the aerobus in late 1969, initially by assessing the development potential of existing aircraft. An enlarged Il-62 (the Il-62-250) would have had a 30-tonne payload, 259 seats and a 6.8 metre/22 ft longer fuselage: a virtual analogue of the Douglas DC-8 "Super Sixty" series. Other proposed Il-62 modifications involved double-deck and "two fuselages side-by-side" developments. There was also a project to "civilianise" the Il-76. From March 1970 the bureau developed all-new designs under the Il-86 designation. Instead of the "appropriate technology" approach of the Il-62, these designs were to have powered controls, complex high-lift devices and advanced automation which would reduce the number of flightdeck crew. An early avanproyekt was shown to the Soviet leadership at an exhibition of civil aviation innovations at Vnukovo-2 Airport near Moscow on May 17, 1971. A scale model with the designation of "Il-86" showed the "self-loading" concept with integral boarding stairs, below-deck luggage stores, and below-deck midships galley. It had a twin-aisle interior with nine-abreast seating in a "3–3–3" layout. Ilyushin considered it politic to make the interior wider than any planned airliner except the Boeing 747. The 6.07 m (19.9 ft) fuselage diameter was partly dictated by the need to provide standing room in the underfloor luggage compartments. The Il-86 had the second-widest fuselage of any airliner until the Boeing 777. On this basis, on 9 March 1972, the bureau was asked to proceed with detailed design.
Occupants in buildings can be exposed to fungal spores, cell fragments, or mycotoxins which can arise from a host of means, but there are two common classes: (a) excess moisture induced growth of mold colonies and (b) natural substances released into the air such as animal dander and plant pollen. While mold growth is associated with high moisture levels, it is likely to grow when a combination of favorable conditions arises. As well as high moisture levels, these conditions include suitable temperatures, pH and nutrient sources. Mold grows primarily on surfaces, and it reproduces by releasing spores, which can travel and settle in different locations. When these spores experience appropriate conditions, they can germinate and lead to mycelium growth. Different mold species favor different environmental conditions to germinate and grow, some being more hydrophilic (growing at higher levels of relative humidity) and other more xerophilic (growing at levels of relative humidity as low as 75–80%). Mold growth can be inhibited by keeping surfaces at conditions that are further from condensation, with relative humidity levels below 75%. This usually translates to a relative humidity of indoor air below 60%, in agreement with the guidelines for thermal comfort that recommend a relative humidity between 40 and 60%.
This incident made me feel sad, though many Chinese have been understanding. It disclosed many problems for government and company supervision of the milk sources, quality and marketing administration ... The government will put more efforts into food security, taking the incident as a warning. What we are trying to do is to ensure no such event happens in future by punishing those leaders as well as enterprises responsible. None of those companies without professional ethics or social morals will be let off. On 1 October, CPC general secretary Hu Jintao noted the importance of food safety to the public, and said that "Chinese companies should learn from the lessons of the Sanlu tainted milk powder incident." On 6 October 2008, putting the blame on "illegal production and greed", the country's "chaotic dairy production and distribution order", and the "gravely absent supervision" for the crisis, the State Council announced new dairy industry regulations. In response to the crisis, the State Council of China issued the "Regulations on the Supervision and Administration of Dairy Product Quality and Safety" on October 10, 2008, to regulate the production, processing, packaging and sales of dairy products, thereby ensuring content and quality compliance. On November 19, 2008, the State Council promulgated the "China Dairy Industry Reorganization and Revitalization Plan" to rectify the chaos in China's dairy industry.
DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, thymine, cytosine, and guanine. The advent of rapid DNA sequencing methods has greatly accelerated biological and medical research and discovery.
Sources: en.wikipedia.org
System suitability is a set of checks performed before and during a run to confirm that the instrument, column, and method work as expected. Common checks include resolution, tailing factor, theoretical plates, and relative standard deviation of replicate injections. Failure triggers troubleshooting or method adjustment.
Validation demonstrates that a method produces reliable results for a defined purpose. It documents performance limits and acceptance criteria. Regulated industries require validation before routine testing of products or samples.
Retention time shifts can arise from changes in mobile phase composition, pH, temperature, column age, or flow rate. Contamination or worn seals may also alter pressure and delivery. Systematic checks of these factors help identify the cause.
System suitability is a set of checks that confirm the instrument and method perform within limits before sample analysis. It typically includes resolution, tailing factor, retention time, and peak area reproducibility. If a check fails, the run is invalidated until the cause is resolved.