If you have been reading about counterion and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2025-11-13. Where a claim depends on a specific study, the study is described rather than over-claimed.
Storage and handling conditions affect both peptide stability and the accuracy of later purity tests. Lyophilized powders are commonly kept desiccated at -20 °C or below, while reconstituted solutions require a defined buffer, pH, and temperature range. Repeated freeze-thaw cycles can promote aggregation, oxidation, or hydrolysis over time. Each cycle may alter the chromatogram and complicate comparison with earlier results. Stability data, when available, should guide handling intervals and solvent choice.
Independent verification is used when a supplier result needs confirmation or when a material supports regulated work. A second laboratory can repeat reverse-phase HPLC and mass spectrometry on the same sample. Discrepancies may arise from different columns, gradients, detection wavelengths, or sample preparation. Moisture uptake and counterion content can lower net peptide mass without changing area percent. Documentation of methods and raw data helps distinguish analytical variation from a true quality difference.
Quality control for peptides begins with a documented specification that states the required purity, identity, and appearance. Suppliers often release research-grade material at 95% or greater by HPLC area, but this threshold is not universal. A certificate of analysis typically records the lot number, sequence, test methods, and measured values. The document allows a user to compare batches and to trace deviations. Specifications should match the intended use rather than a generic label.
Handling and storage influence measured purity, and peptides can oxidize, deamidate, aggregate, or adsorb to surfaces over time. Lyophilized powders stored at -20 °C or lower are generally more stable than solutions, though some sequences require different conditions. Repeated freeze-thaw cycles can promote aggregation and loss, so testing after storage checks whether purity has changed. Stability-indicating methods compare stressed and unstressed samples to detect degradation pathways. Light exposure and pH can also accelerate modification.
Solid-phase peptide synthesis can produce truncated sequences when coupling reactions fail. Deletion peptides lack one or more internal residues, while truncation peptides end prematurely. Side reactions include aspartimide formation, oxidation of methionine, and aggregation during chain assembly. Crude synthetic peptides therefore contain target peptide plus related impurities, counterions, residual solvents, and water. Purification by preparative chromatography reduces these impurities but does not remove every closely related species, including some that differ by a single amino acid.
Quality control specifications for peptides typically include appearance, identity, purity by RP-HPLC, water content, counterion content, and residual trifluoroacetic acid. Karl Fischer titration measures water, while ion chromatography or elemental analysis can quantify counterions. Purity specifications may be set at 95% or 98% area percent, but the appropriate threshold depends on the application. For research reagents, a lower purity may be acceptable if identity is confirmed. For assays sensitive to impurities, higher purity and orthogonal testing are often required.
| Property | Value | Notes |
|---|---|---|
| Typical storage temperature | -20 °C or below | For lyophilized powder; keep desiccated. |
| Short-term solution storage | 2-8 °C | For reconstituted peptide; follow stability data. |
| Common research-grade specification | 95% or greater by HPLC area | Widely cited threshold; not a universal standard. |
| Documentation | Certificate of analysis | Lists lot, sequence, method, purity, and storage guidance. |
| Independent verification | Second-laboratory HPLC and mass spectrometry | Repeats tests on submitted sample to confirm supplier result. |
Impurity profiles can include deletion peptides, oxidized forms, truncated sequences, and residual solvents. Some impurities arise during synthesis, cleavage, or purification, while others form during storage. Purity testing often focuses on peptide-related impurities, whereas residual solvents and counterions require separate assays. The significance of a given impurity depends on its amount and properties, which may not be established for a research peptide. Reporting an impurity profile is more informative than reporting a single purity number.
Peptide purity specifications describe the minimum acceptable result from a defined test. A certificate of analysis may list HPLC purity, mass spectrometry identity, appearance, and counterion content. Specifications are method-dependent, so a value obtained with one gradient or wavelength may differ from another. For research use, common thresholds include 95% and 98% by RP-HPLC, but the appropriate limit depends on the application. The specification should always name the analytical method and acceptance criterion.
Regulatory frameworks treat peptide purity as part of product quality, though requirements vary by intended use and jurisdiction. Investigational materials may need identity, strength, quality, and purity documentation. Compendial monographs, when available, specify tests and acceptance criteria for certain peptides. For research peptides, oversight is often less prescriptive, and buyers may rely on supplier documentation. Open questions remain about how to standardize impurity reporting across laboratories and how to define purity for complex or modified peptides.
Quality control for peptide products relies on written procedures, batch records, and certificates of analysis. A certificate of analysis typically lists the test methods, specifications, and results for a specific lot. Batch records document synthesis, purification, and testing steps so that results can be traced to process conditions. Method validation establishes accuracy, precision, specificity, linearity, and limits of detection. These records support consistency across lots and allow laboratories to investigate deviations when a specification is not met.
Storage conditions influence purity and therefore testing outcomes. Lyophilized peptides are generally kept cool and dry, while solutions may require refrigeration or freezing depending on sequence and buffer. Repeated freeze-thaw cycles can promote aggregation, oxidation, or hydrolysis. Testing after storage should use the same validated method as release testing to allow comparison. Stability studies examine how purity changes over time under defined temperature and humidity conditions. Results are compared against baseline data collected at release.
Orthogonal separation methods address impurities that RP-HPLC may not resolve. Size-exclusion chromatography detects aggregates and higher-order species, while ion-exchange chromatography separates charge variants. Capillary electrophoresis can assess charge-to-mass ratios and, in some formats, size-based impurities. Amino acid analysis and nitrogen determination estimate peptide content rather than chromatographic purity. Because each technique has a different selectivity, a complete purity profile usually combines results from more than one method. The choice of method depends on the impurity classes of concern.
Reversed-phase high-performance liquid chromatography (RP-HPLC) is widely used to estimate peptide purity. Separation depends on interactions between peptide residues and a hydrophobic stationary phase, with gradients of water and organic solvent. Ultraviolet detection near 214 nm responds to the peptide backbone and to many related impurities. The resulting chromatogram is often expressed as area percent, which reports the proportion of peak area assigned to the main component. Different columns, gradients, and wavelengths can produce different purity values for the same material.
Mass spectrometry provides complementary information about molecular identity and certain impurities. Electrospray ionization and matrix-assisted laser desorption/ionization are common ionization techniques for peptides. A measured mass close to the expected value supports correct sequence length and modifications, while extra mass signals can reveal truncations, adducts, or incomplete deprotection. Mass spectrometry alone is not a quantitative purity assay, because ionization efficiency varies between compounds. Coupling liquid chromatography to mass spectrometry links retention time with mass and helps assign peaks that ultraviolet detection records.
The original design of the NanoSIMS instrument was conceived by Georges Slodzian at the University of Paris Sud in France and at the Office National d'Etudes et de Recherches Aérospatiales. There are currently around 60 NanoSIMS instruments worldwide.
Ritonavir, sold under the brand name Norvir, is an antiretroviral medication used along with other medications to treat HIV/AIDS. This combination treatment is known as highly active antiretroviral therapy (HAART). Ritonavir is a protease inhibitor, though it now mainly serves to boost the potency of other protease inhibitors. It may also be used in combination with other medications to treat hepatitis C and COVID-19. It is taken by mouth. Common side effects of ritonavir include nausea, vomiting, loss of appetite, diarrhea, and numbness of the hands and feet. Serious side effects include liver complications, pancreatitis, allergic reactions, and arrhythmias. Serious interactions may occur with a number of other medications including amiodarone and simvastatin. At low doses, it is considered to be acceptable for use during pregnancy. Ritonavir is of the protease inhibitor class. However, it is also commonly used to inhibit the enzyme that metabolizes other protease inhibitors. This inhibition allows lower doses of these latter medications to be used. Ritonavir was patented in 1989 and came into medical use in 1996. It is on the World Health Organization's List of Essential Medicines. Ritonavir capsules were approved as a generic medication in the United States in 2020.
Combining these alongside psychotherapies like CBT may lead to better outcomes for BED. GLP-1 receptor agonist medications such as semaglutide (Ozempic), dulaglutide (Trulicity), and liraglutide (Saxenda) have been used for treating BED in recent years. Often prescribed for lowering appetite and subsequent weight loss in people with diabetes mellitus and obesity, they can successfully stop or reduce obsessive thoughts about food, binging urges, and other impulsive behaviors. Some users, reported sudden improvement in "food noise" - constant unstoppable thoughts about food, even not being physically hungry, which can be a symptom of BED. To this promising treatment is on the up for success, but additional research is needed as of January 2024.
== Principle == In normal-phase chromatography, the stationary phase is polar and the mobile phase is nonpolar. In reversed-phase, the stationary phase is nonpolar and the mobile phase is polar. Typical stationary phases for normal-phase chromatography are silica or organic moieties with cyano and amino functional groups. For reversed phase, alkyl hydrocarbons are the preferred stationary phase; octadecyl (C18) is the most common stationary phase, but octyl (C8) and butyl (C4) are also used in some applications. The designations for the reversed phase materials refer to the length of the hydrocarbon chain. In normal-phase chromatography, the least polar compounds elute first and the most polar compounds elute last. The mobile phase consists of a nonpolar solvent such as hexane or heptane mixed with a slightly more polar solvent such as isopropanol, ethyl acetate or chloroform. Retention decreases as the amount of polar solvent in the mobile phase increases. In reversed phase chromatography, the most polar compounds elute first with the more nonpolar compounds eluting later. The mobile phase is generally a mixture of water and miscible polarity-modifying organic solvent, such as methanol, acetonitrile or THF. Retention increases as the fraction of the polar solvent (water) in the mobile phase is higher. Normal phase chromatography retains molecules via an adsorptive mechanism, and is used for the analysis of solutes readily soluble in organic solvents.
== Use in diagnostic tests == Fecal elastase is an enzyme originally thought to be pancreatic elastase 1 (CELA1), but this was discovered to be an error, and it is actually likely be CELA3B. Fecal elastase is not degraded in intestinal transit, so that its concentration in feces reflects exocrine pancreatic function. In inflammation of the pancreas, fecal elastase is released into the bloodstream. Thus the quantification of fecal elastase in serum allows diagnosis or exclusion of acute pancreatitis. Main indications:
Sources: en.wikipedia.org
Flame ionization detector which uses ionizing flame to detect most hydrocarbon molecules Flame photometric detector which uses atomizing flame to get light emitted from specific elements to detect and quantify them Nitrogen Phosphorus Detector a thermionic detector with photometeric detection, sensitive specifically to nitrogen and phosphorus hydrocarbons Atomic-emission detector is a hyphenation between gas chromatography and atomic emission spectrophotometer for detection of elements. In all types of chromatography:
During the early 20th century, the Russian movement of Cosmism, as represented by Nikolai Fyodorovich Fyodorov, envisioned scientific resurrection of dead people. The idea was so popular that, after Vladimir Lenin's death, Leonid Krasin and Alexander Bogdanov suggested to cryonically preserve his body and brain in order to revive him in the future. Necessary equipment was purchased abroad, but for a variety of reasons the plan was not realized. Instead his body was embalmed and placed on permanent exhibition in the Lenin Mausoleum in Moscow, where it is displayed to this day. The mausoleum itself was modeled by Alexey Shchusev on the Pyramid of Djoser and the Tomb of Cyrus.
== Further reading == Açbay O, Celik AF, Kadioğlu P, Göksel S, Gündoğdu S (1999). "Helicobacter pylori-induced gastritis may contribute to occurrence of postprandial symptomatic hypoglycemia". Dig. Dis. Sci. 44 (9): 1837–42. doi:10.1023/A:1018842606388. PMID 10505722. S2CID 22096584.
== External links == Progesterone MS Spectrum Progesterone at the U.S. National Library of Medicine Medical Subject Headings (MeSH) Kimball JW (27 May 2007). "Progesterone". Kimball's Biology Pages. Archived from the original on 18 June 2008. Retrieved 18 June 2008.
=== Bath salts === Magnesium sulfate is used in bath salts, especially for foot baths to soothe sore feet. The reason for the inclusion of the salt is partially cosmetic: the increase in ionic strength prevents some of the temporary skin wrinkling (partial maceration) which would occur with plain water baths. Epsom salt baths have been claimed to also soothe and hasten recovery of muscle pain, soreness, or injury. However, these claims have not been scientifically confirmed. The solubility of magnesium sulfate water is inhibited by lipids in lotions resulting in variable absorption rates when applied to the skin. Temperature and concentration are also factors.
Sources: en.wikipedia.org
=== 1972 === February 21: Nixon visits China, the first visit by a U.S. president since the establishment of the People's Republic of China. March 30: Viet Cong goes to the offensive in South Vietnam, only to be repulsed by the South Vietnamese regime with major American air support. April: The Ikiza mass killings occurred in Burundi committed by the Tutsi-dominated army against the Hutus. April 10: Biological Weapons Convention is signed banning the production, development and stockpiling of biological weapons. May 22: Richard Nixon attends Moscow Summit (1972), becoming the first US president to visit Moscow. May 26: Strategic Arms Limitation Talks (SALT I) agreement signals the beginning of détente between the U.S. and USSR. September 1: Bobby Fischer defeats Russian Boris Spassky in a chess match in Reykjavík, Iceland, becoming the first official American chess champion (see Match of the Century). September 2–28: The Summit Series, an ice hockey tournament between Canada and Soviet Union. September 21: Philippine president Ferdinand Marcos declares martial law, officially in response to the growing communist threat in the Philippines. September 26: The short border war occurred between the Yemen Arab Republic and South Yemen. December 18: Richard Nixon announces the beginning of a massive bombing campaign in North Vietnam.
This was confirmed to be as effective as the antibiotic vancomycin at inhibiting Clostridioides difficile infection without having a significant effect on the overall microbial composition of the gut. Glycerol solutions have been used for the preservation and storage of tissue grafts at ambient conditions as an alternative to frozen storage. Glycerol has also been incorporated as a component of bio-ink formulations in the field of bioprinting. The glycerol content acts to add viscosity to the bio-ink without adding large protein, saccharide, or glycoprotein molecules. It is on the World Health Organization's List of Essential Medicines for its use in treating atopic eczema.
=== Claims of innocence === Norris appealed against his conviction in 2009. Originally, Norris planned to appeal on the grounds that the trial judge had shown a "lack of balance", but then scrapped these plans and sacked his legal team. He subsequently appealed on the grounds that the judge had "misdirected" the jury in his final summary but he lost this appeal, with judge Lord Justice Aikens ruling the convictions were "safe" and saying that the case against Norris was "very strong indeed". The appeal court rejected both grounds of the appeal, saying that the judge's directions "cannot validly be criticised" and that there was no misdirection to the jury. The appeal court instead said that the judge's summary in the original case was an exemplary "tour de force". The judges also refused to believe that the deaths were "coincidental". Norris's defence team had argued that the deaths could have been the result of 'naturally' raised insulin levels caused by severe spontaneous hypoglycaemia, but the judges rejected this possibility. On 4 October 2011, the BBC reported that retired Professor Vincent Marks – a leading expert on insulin poisoning – was concerned about Norris's conviction. He had been asked by the Norris family to find evidence in the case. He claimed the jury at Norris's trial was wrongly led to believe by experts that a cluster of hypoglycaemic episodes, among people who were not diabetic, was sinister. After carrying out his own studies, he said: "Looking at all the evidence, all I can say is I think Colin Norris's conviction is unsafe".
== Medical uses == Recombinant human epidermal growth factor, sold under the brand name Heberprot-P, is used to treat diabetic foot ulcers. It can be given by injection into the wound site, or may be used topically. Tentative evidence shows improved wound healing. Safety has been poorly studied. EGF is used to modify synthetic scaffolds for manufacturing of bioengineered grafts by emulsion electrospinning or surface modification methods.
== General and cited references == Sherman, Philip (1963). Rheology of Emulsions: Proceedings of a symposium held by the British Society of Rheology ... Harrogate, October 1962. British Society of Rheology / Macmillan. ISBN 9780080102900. Nalwa, H. S., ed. (2000). Handbook of Nanostructured Materials and Nanotechnology. Vol. 5. New York: Academic Press. pp. 501–575.
Sources: en.wikipedia.org
Lyophilized powders are typically kept desiccated at -20 °C or below. Reconstituted solutions require a defined buffer, pH, and storage condition based on available stability data.
A certificate commonly lists sequence, lot number, appearance, purity method, purity value, mass confirmation, and storage guidance. It may also note counterion, water content, and test date.
Not always, but independent testing reduces reliance on a supplier's internal result. It is common when a material is used in regulated or repeatable work.
No. Purity testing measures chemical composition and does not assess biological activity, sterility, or endotoxin levels. Functional performance must be tested in the intended assay.