Stationary phase 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 2025-12-20. Where a claim depends on a specific study, the study is described rather than over-claimed.
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 in a liquid sample by passing them 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 how analytes partition between the mobile phase and the stationary phase cause them to exit the column at different times. Detection then records a signal proportional to the amount of each separated substance. The resulting chromatogram provides retention times and peak areas for identification and quantification.
Instrumentation includes a solvent delivery system, an autosampler, a column oven, and one or more detectors. Reversed-phase columns with chemically modified silica are widely used, but normal-phase, ion-exchange, size-exclusion, and affinity modes exist for specific separations. Detectors may rely on ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry. Column temperature, mobile phase composition, and flow rate are adjusted to improve resolution. System pressure is monitored because rising pressure can indicate column blockage or deteriorating packing.
| Property | Value | Notes |
|---|---|---|
| Accuracy | Recovery near 100% | Depends on acceptance criteria and matrix |
| Precision | Relative standard deviation | Often at or below 2% for replicate injections |
| Limit of detection | Signal-to-noise ratio 3:1 | Approximate and method-specific |
| Limit of quantitation | Signal-to-noise ratio 10:1 | Confirmed by precision and accuracy |
| Resolution | 1.5 or greater | Typical system suitability target |
Method validation examines whether an HPLC procedure is suitable for its intended purpose. Common parameters include accuracy, precision, specificity, linearity, range, detection limit, quantification limit, and robustness. Accuracy describes closeness to a true or accepted value, while precision describes agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from related substances. Robustness tests small deliberate changes in flow, temperature, or solvent composition. Validation is not a one-time event; methods may need partial revalidation after changes to instruments, columns, sample handling, or specification limits. Regulatory guidance provides frameworks, but some details remain method-specific.
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.
== Political composition == It was possible for the ILEA to have a majority of Labour members when the GLC had a majority of Conservative members, and this happened from 1970 to 1973 and 1977 to 1981. In addition, most of the important decisions taken by the ILEA were taken by its Education Committee, on which every member sat. The Education Committee could also co-opt members with experience of education, some of them representing the teaching unions. The initial composition of the ILEA in 1964 was 43 Labour members to 9 Conservatives, with one Independent. After the 1967 election the Conservatives won a majority, and Christopher Chataway became Leader. However, Labour won control in 1970 and Ashley Bramall began his long leadership. His term saw the ILEA go over to comprehensive education, and the abolition of school corporal punishment. He retained power despite the Conservative election victory in the 1977 GLC elections. When the Left, under Ken Livingstone, won control of the GLC after the 1981 elections, Bramall lost his position in an internal Labour Party vote, being replaced by Bryn Davies. Livingstone later expressed regret for this decision and expressed his admiration for Bramall's leadership abilities. The remaining years of the ILEA saw a succession of left-wing leaderships, none of which lasted long or established a strong reputation. Frances Morrell, formerly an assistant to Tony Benn, led a feminist ILEA from 1983 to 1987 which threatened to defy its rate-capping in November 1984, before Neil Fletcher took over.
The tea leaves are packaged loosely in a canister, paper bag, or other container such as a tea chest. Some whole teas, such as rolled gunpowder tea leaves, which resist crumbling, are vacuum-packed for freshness in aluminised packaging for storage and retail. The loose tea is individually measured for use, allowing for flexibility and flavour control at the expense of convenience. Strainers, tea balls, tea presses, filtered teapots, and infusion bags prevent loose leaves from floating in the tea and over-brewing. A traditional method uses a three-piece lidded teacup called a gaiwan, the lid of which is tilted to decant the tea into a different cup for consumption.
Because vitamin K aids mechanisms for blood clotting, its deficiency may lead to reduced blood clotting, and in severe cases, can result in increased bleeding and increased prothrombin time. Normal diets are usually not deficient in vitamin K, indicating that deficiency is uncommon in healthy children and adults. An exception may be infants who are at an increased risk of deficiency regardless of the vitamin status of the mother during pregnancy and breast feeding due to poor transfer of the vitamin to the placenta and low amounts of the vitamin in breast milk. Secondary deficiencies can occur in people who consume adequate amounts, but have malabsorption conditions, such as cystic fibrosis or chronic pancreatitis, and in people who have liver damage or disease. Secondary vitamin K deficiency can also occur in people who have a prescription for a vitamin K antagonist drug, such as warfarin. A drug associated with increased risk of vitamin K deficiency is cefamandole, although the mechanism is unknown.
Sources: en.wikipedia.org
In June 2023, The U.S. Food and Drug Administration (FDA) authorized for marketing Eroxon, an over-the-counter non-medicated hydro-alcoholic gel indicated for treatment of erectile dysfunction. In the clinical trial, erection was achieved by most men within ten minutes after applying the gel. The gel is manufactured by Futura Medical, a British medical company. The gel is regulated as a medical device and not as a drug, because its mode of action is a physical one and it doesn't have an active pharmaceutical ingredient. Eroxon is the first topical ED treatment sold over the counter in the United States. The gel had been on sale in Europe under a CE mark since 2023, and it reached American shops in October 2024. As of 2026, the gel is sold in the United States, United Kingdom, Europe, and several countries in Latin America and the Middle East.
=== „Das Alphabet bis S“ (2023) === „Das Alphabet bis S“ [The Alphabet up to the letter S], Kermani's most expansive novel since „Dein Name“, can be read as a complementary text to it: while „Dein Name“ leads up to a separation between the male first-person narrator and his partner (without the breakup actually occurring in the novel), Das „Alphabet bis S“ looks back on a failed marriage. It is noteworthy that „Das Alphabet“ is told from the perspective of an unnamed female narrator, whose undated (but numbered) diary entries structure the text. The novel’s composition is more stringent than in „Dein Name“, partly because the 365 chapters—beginning with New Year's Day—cover exactly one year. And partly because—as the title suggests—the self-proclaimed “reader- writer” works her way alphabetically through the unread books on her bookshelf over the course of the year, reaching the surnames beginning with S. Kermani’s play with autofiction familiar from previous texts takes on a new direction here in that the protagonist's life, her reading, and thinking show numerous parallels to the author Navid Kermani (from her Muslim background to her work as a writer to her affinity for soccer to her committed commemoration of the dead). In addition, the combination of narrative and essayistic passages resembles the technique used in „Dein Name“. On the one hand, then, the separation between author and narrator seems obvious here. On the other hand, the text ironically suggests that it might be read as a femalely inverted mirror version of Kermani's own life and writing.
== Optical excitation and ionization schemes == Optical ionization schemes are developed to produce element-selective ion source for various elements. Most of the elements of the periodic table have been resonantly ionized by using one of five major optical routes based on the principle of RIMS. The routes were formed by the absorption of two or three photons to achieve excitation and ionization and are provided on the basis of optically possible transitions between atomic levels in a process called the bound-bound transition. For an atom of the element to be promoted to a bound-continuum, the energies emitted from the photons must be within the energy range of the selected tunable lasers. Also, the ionization energy of the last emitted photon must exceed that of the atom. The optical ionization schemes are denoted by the amount of photons necessary to make the ion pair. For the first two Schemes 1 and 2, two photons (and processes) are involved. One photon excites the atom from the ground state to an intermediate state while the second photon ionizes the atom. In Schemes 3 and 4, three photons (and processes) are involved. The first two distinct photons create consecutive bound-bound transitions within the selected atom while the third photon is absorbed for ionization. Scheme 5 is a three-photon two-intermediate-level photoionization process. After the first two photons have been absorbed by the optical energy, the third photon achieves ionization. The RIS process can be used to ionize all elements on the periodic table, except helium and neon, using available lasers.
== Definition == According to the United Nations Statistics Division, wholesale is the resale of new and used goods to retailers, to industrial, commercial, institutional or professional users, or to other wholesalers, or involves acting as an agent or broker in buying merchandise for, or selling merchandise to, such persons or companies. Wholesalers frequently physically assemble, sort, and grade goods in large lots, break-bulk, repack, and redistribute in smaller lots. While wholesalers of most products usually operate from independent premises, wholesale marketing for foodstuffs can take place at specific wholesale markets where all traders are congregated. In the International Standard Industrial Classification (ISIC Rev.4), wholesale trade is primarily Division 46 ("Wholesale trade, except of motor vehicles and motorcycles"). In the NAICS, wholesale trade is Sector 42, commonly separated into merchant wholesalers and agents/brokers (including electronic markets). A common way to distinguish wholesale from retail is by the main customer:
Sources: en.wikipedia.org
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.
Quantification usually compares detector response to a standard curve made from reference standards. The curve may be external, internal, or based on standard addition depending on matrix effects. Results are reported with units and, when required, uncertainty.
Carryover occurs when analyte from a previous injection remains in the system and appears in a later chromatogram. It can come from the injector, column, or tubing. Blank injections and needle washes help detect and reduce it.
HPLC separates and detects individual compounds in a liquid sample, producing peaks at characteristic retention times. Peak area or height can be used to estimate concentration when calibrated with known standards. It does not identify unknown compounds with certainty unless additional detectors or reference materials are used.