counterion raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2026-07-17 and is reviewed periodically as new material appears.
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.
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.
Purity results are only meaningful when linked to a defined sample and method. A certificate of analysis typically lists the analytical technique, column type, gradient, detection wavelength, and integration parameters. It may also report mass confirmation, water content, and counterion composition. For research peptides, laboratories often request the raw chromatogram rather than only a summary percentage. This allows independent review of baseline, peak shape, and any unresolved shoulders that might be missed by a single number.
Stability testing examines how purity changes under controlled conditions. Samples are stored at defined temperatures, such as -20 °C or -80 °C, and analyzed at intervals. Lyophilized powders are generally more stable than solutions because water promotes hydrolysis and aggregation. Repeated freeze-thaw cycles can also degrade peptides, especially those with oxidation-prone residues. Accelerated studies at elevated temperature provide useful comparisons, but they do not always predict long-term behavior at lower temperatures.
Handling practices influence measured purity. Peptides may adsorb to plastic or glass surfaces, particularly when hydrophobic or positively charged. Weighing hygroscopic powders can introduce water and alter concentration. Dissolving in appropriate solvents and using low-binding tubes can reduce losses. Each laboratory should validate its own procedures because recovery and stability vary with peptide sequence, formulation, and container material. Open questions remain about how best to standardize stability reporting across different peptide classes.
| Property | Value | Notes |
|---|---|---|
| Typical purity specification | ≥95% by RP-HPLC | Common for research-grade material; some assays require 98% or higher. |
| Water content | 5–10% w/w | Lyophilized peptides retain moisture; Karl Fischer titration measures it. |
| Counterion | Trifluoroacetate or acetate | Counterion identity affects mass balance and assay compatibility. |
| Storage temperature | -20 °C or lower | Store desiccated and protected from light; avoid repeated freeze-thaw. |
| Common impurity | Deletion or truncation peptide | Similar sequence complicates chromatographic separation. |
Jacky Klein (born 28 January 1977) art historian, broadcaster, author; co-presented Britain's Lost Masterpieces for BBC4; co-authored book with sister, Suzy Klein, What is Contemporary Art? A Children's Guide, commissioned by the Museum of Modern Art, New York, published by Thames & Hudson; has also authored works on Wyndham Lewis and Grayson Perry; in 2015, was Executive Editor at Tate Publishing Melanie Klein (30 March 1882 – 22 September 1960), Austrian Jewish British author and psychoanalyst known for work in child analysis; was primary figure in development of object relations theory, suggesting that pre-verbal existential anxiety in infancy catalysed formation of unconscious, resulting in unconscious splitting of the world into good and bad idealizations; how child resolves that split depends on constitution of child and the character of nurturing the child experiences, and quality of resolution can inform presence, absence, and/or type of distresses a person experiences later in life. Suzy Klein (born 1 April 1975) author and radio and television presenter; Head of Arts and Classical Music TV for the BBC; winner of William Hardcastle Award for Journalism; was assistant producer at BBC Radio 4 on programmes including Start the Week; then moved to BBC Television, working as director and producer on arts and music films.
In contrast to ALP, levels of ALT, AST, GGT, and lactate dehydrogenase are only slightly changed or largely unchanged during pregnancy. Bilirubin levels are significantly decreased in pregnancy. In pregnancy conditions such as hyperemesis gravdirum, ALP levels can reach 215 IU/L, meanwhile, in pre-eclampsia, ALP can reach 14 IU/L, and in HELLP syndrome ALP levels can reach 15 IU/L.
== Further reading == Kenmoku H, Shimai T, Toyomasu T, Kato N, Sassa T (March 2002). "Erinacine Q, a new erinacine from Hericium erinaceum, and its biosynthetic route to erinacine C in the basidiomycete". Bioscience, Biotechnology, and Biochemistry. 66 (3): 571–5. Bibcode:2002BsBtB..66..571K. doi:10.1271/bbb.66.571. PMID 12005051. S2CID 46327735.
Sources: en.wikipedia.org
=== Legality of South West Africa, 1946–1960 === After World War II, Jan Smuts headed the South African delegation to the United Nations Conference on International Organization. As a result of this conference, the League of Nations was formally superseded by the United Nations (UN) and former League mandates by a trusteeship system. Article 77 of the United Nations Charter stated that UN trusteeship "shall apply...to territories now held under mandate"; furthermore, it would "be a matter of subsequent agreement as to which territories in the foregoing territories will be brought under the trusteeship system and under what terms". Smuts was suspicious of the proposed trusteeship, largely because of the vague terminology in Article 77. Heaton Nicholls, the South African high commissioner in the United Kingdom and a member of the Smuts delegation to the UN, addressed the newly formed UN General Assembly on 17 January 1946. Nicholls stated that the legal uncertainty of South West Africa's situation was retarding development and discouraging foreign investment; however, self-determination for the time being was impossible since the territory was too undeveloped and underpopulated to function as a strong independent state. In the second part of the first session of the General Assembly, the floor was handed to Smuts, who declared that the mandate was essentially a part of the South African territory and people.
mistranslation The insertion of an incorrect amino acid in a growing peptide chain during translation, i.e. the inclusion of any amino acid that is not the one specified by a particular codon in an mRNA transcript. Mistranslation may originate from a mischarged transfer RNA or from a malfunctioning ribosome.
New methods including the use of biosensors can help monitor the content of polyphenols in food. Quantitation results produced by the mean of diode array detector–coupled HPLC are generally given as relative rather than absolute values as there is a lack of commercially available standards for all polyphenolic molecules.
Sources: en.wikipedia.org
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.
Water adds mass and can affect concentration calculations. A peptide labeled 95% pure may contain water and counterions that reduce the actual peptide content.
Identity can be checked by mass spectrometry, and purity by RP-HPLC. Store according to supplier instructions and retest if experimental performance changes.
It typically includes the peptide sequence, molecular mass, purity method and result, storage recommendations, and date of analysis. Raw chromatograms and mass spectra may be provided on request. The absence of method details makes a purity value difficult to interpret.