The short version of reference standard fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-04-23. Anything still debated is marked as such rather than presented as settled.
High-performance liquid chromatography is an analytical technique that separates components in a liquid sample. A pump moves a liquid mobile phase through a column packed with a solid stationary phase. Compounds interact differently with both phases and travel at different rates, leaving the column at distinct retention times. A detector records these arrivals as peaks on a chromatogram. The resulting pattern supports identification and quantification of substances in mixtures. Modern instruments use high pressure to force solvent through small particles, which improves speed and resolution compared with older low-pressure liquid chromatography methods.
Separation in HPLC depends on the chemistry of the stationary phase, the composition of the mobile phase, and the physical properties of the column. Reverse-phase separations use a nonpolar stationary phase and a polar mobile phase, and they are common for many organic compounds. Ion-exchange, size-exclusion, and normal-phase modes serve other classes of analytes. Gradient elution changes solvent strength over time, while isocratic elution holds it constant. Flow rate, temperature, particle size, and column length all influence peak shape and resolution. Detection may use ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry, depending on the analyte and the required sensitivity.
Routine HPLC testing compares a sample result with a calibration curve prepared from known reference standards. Peak area or peak height is plotted against concentration, and the curve is used to estimate unknown amounts. Retention time supports tentative identification when compared with a standard, though mass spectrometry or another confirmatory method may be needed for definitive identification. Pre-run checks verify repeatability, resolution, and peak symmetry before sample analysis. Limits of detection and quantification describe the smallest amounts that can be reliably observed or measured. Sample preparation, filtration, and degassing help prevent column damage and inconsistent results.
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.
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 |
|---|---|---|
| Common abbreviation | HPLC | High-performance liquid chromatography |
| Separation basis | Differential partitioning | Between liquid mobile phase and solid stationary phase |
| Common mode | Reverse phase | Nonpolar column, polar mobile phase |
| Typical detector | UV-Vis absorbance | Widely used for compounds with chromophores |
| Typical column particle size | 2–5 µm | Smaller particles can improve resolution |
Routine HPLC testing depends on controlled reagents, calibrated instruments, and documented procedures. Columns degrade over time, so retention times and peak shapes are monitored for drift. Mobile phases are filtered and degassed to prevent pump damage and detector noise. Reference standards must be traceable and stored under suitable conditions. Data handling systems record injections, calculations, and audit trails. Quality control samples interspersed with unknowns help detect errors during a run.
Developing an HPLC method begins with defining the purpose, such as quantifying a main component, measuring impurities, or confirming identity. Analysts select separation mode, column, mobile phase, detection, and sample preparation based on analyte properties and matrix. Experiments vary solvent strength, pH, buffer type, and temperature to achieve resolution between critical peaks. The goal is a robust method that produces reliable results across instruments and operators. Method development often involves trial runs and statistical optimization.
Validation demonstrates that a method is suitable for its intended use. Typical performance characteristics include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Regulators and standards organizations provide frameworks, but specific requirements depend on the application and jurisdiction. System suitability tests are run before sample analysis to confirm resolution, peak symmetry, retention time repeatability, and sensitivity. A validated method is not permanently fixed; changes may require partial or full revalidation.
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.
She served as the de facto head of government until she was deposed in the 2021 coup d'état by Commander-in-Chief of Defence Services Min Aung Hlaing, who created the extraconstitutional posts of chairman of the State Administration Council and prime minister for himself to lead the government. The president is elected by members of parliament, not by the general population; specifically the Presidential Electoral College, a three-committee body composed of members of parliament, elects the president. Each of the three committees, made up of Amyotha Hluttaw, Pyithu Hluttaw members of parliament, or military-appointed lawmakers, nominates a candidate for presidency. The presidency is the most powerful position in the civilian leadership structure. Even when an elected civilian government is in place, the president has no command authority over the Tatmadaw, and his executive authority is counterbalanced by the significant governance powers of Commander-in-Chief of Defence Services. The current president is Min Aung Hlaing, who assumed office 10 April 2026, having previously exercised the duties of the role from 2024 to 2026.
The second concern would be that some of the heavy metals that could be released can have some level of toxicity to not only organisms inhabiting that area but also organisms passing through the mining site area. The concerns surrounding increased sediment release are mainly related to the other two mining waste processes, side cast sediment and seafloor sediment disturbance. The main environmental concern would be the smothering of organisms below as a result of redistributing large amounts of sediment to other areas on the seafloor, which could potentially threaten the population of organisms inhabiting the area. Redistribution of large quantities of sediment can also affect the feeding and gas exchange processes between organisms, posing a serious threat to the population. Finally, these processes can also increase the sedimentation rate on the seafloor, resulting in a predicted minimum of 500 m per every 1–10 km. A large amount of work is currently being engaged in by both of the above-mentioned companies to ensure that the potential environmental impacts of seafloor mining are well understood and control measures are implemented before exploitation commences. However, this process has been arguably hindered by the disproportionate distribution of research effort among vent ecosystems; the best studied and understood hydrothermal vent ecosystems are not representative of those targeted for mining. Attempts have been made in the past to exploit minerals from the seafloor.
African American Cultural Complex Contemporary Art Museum of Raleigh Gregg Museum of Art & Design at North Carolina State University Haywood Hall House & Gardens Marbles Kids Museum North Carolina Museum of Art North Carolina Museum of History North Carolina Museum of Natural Sciences North Carolina Sports Hall of Fame City of Raleigh Museum J. C. Raulston Arboretum Joel Lane House Mordecai Plantation Pope House Museum
Humans use scorpions both practically, for medicine, food, and pets, and symbolically, whether as gods, to ward off harm, or to associate a product or business with the evident power of the small but deadly animal.
Sources: en.wikipedia.org
== Biography == In 1964 Bernd Michael Rode graduated from high school (“Akademisches Gymnasium Innsbruck”) and commenced studies in chemistry at the University of Innsbruck. In 1973 he received his Ph.D. degree in chemistry with sub auspiciis praesidentis from the University of Innsbruck. In 1973 Prof. Rode started his career as an assistant professor at the Institute of Inorganic and Analytical Chemistry of the University of Innsbruck. After research stays in Germany (University of Stuttgart and University of Karlsruhe) he became an associate professor in Innsbruck in the year 1976. After spending a 1-year research stay at the University of Tokyo, Prof. Rode started his professorship at the Institute of Inorganic and Theoretical Chemistry at the University of Innsbruck. From 2006 to 2011 he was head of the Department of Theoretical Chemistry and head of the Institute for General Inorganic and Theoretical Chemistry. One of Prof. Rode’s largest achievements was the foundation of the University Network ASEA-UNINET (Austrian South East Asian University Partnership Network) in 1994. The foundations for this network were laid by informal contacts between the University of Innsbruck and Thai Universities that date back to the 1970s. In the 1980s partnerships between the University of Innsbruck, the University of Vienna, the University of Agricultural Sciences Vienna, the Chulalongkorn University, the Mahidol University, the Kasetsart University and the Chiang Mai University were concluded.
In May 2012, Starbucks opened its first coffeehouse in Finland, with the location being Helsinki-Vantaa Airport in Vantaa. In August 2013, the first Starbucks inside Dansk Supermarked opened in the department stores Salling in Aalborg and Aarhus in Denmark. In November 2014, Starbucks announced its first Channel Island store, in the primary business area of St Peter Port in Guernsey. On April 21, 2015, Kesko, the second largest retailer in Finland, announced its partnership with Starbucks, with stores opened next to K-Citymarket hypermarkets. As of June 2017, three stores had been opened next to K-Citymarkets: In Sello in Espoo and in Myyrmanni and Jumbo in Vantaa. In February 2016, Howard Schultz announced the opening of stores in Italy. The first Italian Starbucks store was inaugurated in Milan on September 6, 2018, at which point Starbucks already had locations in 78 countries. In May 2016, the first Starbucks store in Slovakia opened in Aupark, in Bratislava. In June 2018, Starbucks announced the opening of stores in Serbia. The first store was opened in April 2019 at Rajiceva Mall. On June 1, 2019, Starbucks opened its first coffee store in Valletta, Malta, the 80th country to have a Starbucks outlet. In July 2025, Starbucks opened its first store in Iceland.
== Gene == GRP is located on chromosome 18q21. PreproGRP (the unprocessed form of GRP) is encoded in three exons separated by two introns. Alternative splicing results in multiple transcript variants encoding different isoforms.
=== Paroxetine mesylate === In order to avoid patents on paroxetine hydrochloride, some companies developed alternative salts of paroxetine. In the mid-1990s SmithKline Beecham (now a part of GSK) and Synthon independently developed paroxetine mesylate. They obtained two separate patents. Subsequently, all attempts to produce Synthon's version of paroxetine mesylate ended up with Beecham's version. There were two possibilities: either Synthon's version is a disappearing polymorph, or Synthon's patent application contained erroneous data. Many litigations later, there is still no legal consensus on which possibility is correct.
Gramicidin S differs from other gramicidin types in that it is a cationic cyclic decapeptide and has a structure of an anti-parallel beta-sheet. Gramicidin S molecule is amphiphilic, with hydrophobic amino acids (D-Phe, Val, Leu side chains) and charged aminoacid (L-Orn). It exhibits strong antibiotic activity towards Gram-negative and Gram-positive and even several pathogenic fungi. The mode of action is not entirely agreed upon, but it is generally accepted that it is disruption of the lipid membrane and enhancement of the permeability of the bacterial cytoplasmic membrane. Unfortunately, being hemolytic at even low concentrations, gramicidin S is only used as topical applications at present. Additionally, Gramicidin S has been employed as a spermicide and therapeutic for genital ulcers caused by sexually transmitted disease.
Sources: en.wikipedia.org
== Interactions == Interactions with other drugs acting on the serotonin system or impairing the metabolism of serotonin may increase the risk of serotonin syndrome or neuroleptic malignant syndrome (NMS)-like reaction. Such reactions have been observed with SNRIs and SSRIs alone, but particularly with concurrent use of triptans, MAO inhibitors, antipsychotics, or other dopamine antagonists. The prescribing information states that paroxetine should "not be used in combination with an MAOI (including linezolid, an antibiotic which is a reversible non-selective MAOI), or within 14 days of discontinuing treatment with an MAOI", and should not be used in combination with pimozide, thioridazine, tryptophan, or warfarin. Paroxetine interacts with the following cytochrome P450 enzymes:
== Mechanism of action == Pegulicianine is non-fluorescent in its intact parent form. However, in breast cancer tissue, where cathepsins and matrix metalloproteinases are overexpressed, it is enzymatically cleaved into two fragments, one of which is fluorescent. Pegulicianine consists of the following four components that are covalently linked to each other:
==== Employee opposition to AI militarisation ==== In May 2026, workers at Google DeepMind's London headquarters voted to unionise, requesting joint representation by the Communication Workers Union (CWU) and Unite the Union. The unionisation drive was heavily motivated by ethical concerns regarding Google's military-industrial AI contracts, specifically the provision of AI technology to the US Department of Defense and the Israeli military.
== Further reading == Aird, William C. "Blood Endothelial Cells" in Endothelial Cells In Health and Disease. Boca Raton: Taylor & Francis, 2005. Milosevic, V., Edelmann, R.J., Fosse, J.H., Östman, A., Akslen, L.A. (2022). Molecular Phenotypes of Endothelial Cells in Malignant Tumors. In: Akslen, L.A., Watnick, R.S. (eds) Biomarkers of the Tumor Microenvironment. Springer, Cham. https://doi.org/10.1007/978-3-030-98950-7_3 Stem Cells, Therapeutic Applications by Mariusz Z. Ratajczak Advances in Experimental Medicine and Biology
=== Sanger sequencing === Sanger sequencing recently was used to evaluate the enrichment of mutant DNA from a mixture of 1:20 mutant:wildtype DNA. The variant DNA containing a mutation was obtained from a breast cancer cell line known to contain p53 mutations. Comparison of Sanger sequencing chromatograms indicated that the mutant allele was enriched 13 fold when COLD-PCR was used compared to traditional PCR alone. This was determined by the size of the peaks on the chromatogram at the variant allele location. As well, COLD-PCR was used to detect p53 mutations from lung-adenocarcinoma samples. The study was able to detect 8 low level (under 20% abundance) mutations that would likely have been missed using conventional methods that don't enrich for variant sequence DNA.
Sources: en.wikipedia.org
HPLC testing measures the presence and amount of one or more compounds in a liquid sample. It separates mixture components and records detector responses as peaks, which are compared with reference standards. Results are usually reported as concentrations or relative percentages.
Retention time is the interval between sample injection and the detector response for a given compound. It depends on the compound's interactions with the stationary and mobile phases under set conditions. Matching a retention time to a standard supports tentative identification but is not always unique.
HPLC alone can separate unknown compounds and provide retention times, but it often cannot identify them with certainty. Coupling HPLC to mass spectrometry gives mass information that improves identification. Confirmation usually requires comparison with reference standards or complementary techniques.
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.