Research Peptide Glossary: Key Terms Explained
New to research peptides, or just want a quick reference? This glossary defines the terms you will see most often on product pages, Certificates of Analysis, and lab documentation. Every definition here is written for laboratory research context.
Peptide. A short chain of amino acids linked by peptide bonds. Peptides are smaller than proteins and are widely used in laboratory research.
Amino acids and sequence. Amino acids are the building blocks of peptides. The sequence is the specific order in which they are arranged, and it defines the peptide. The three-letter and one-letter symbol systems you see in a sequence are not informal shorthand; they are set by an international nomenclature standard.[1]
Research Use Only (RUO). A designation meaning a product is intended solely for laboratory research and is not approved for human or animal use. It is a regulatory status rather than a disclaimer, and FDA assesses it against how a seller actually behaves, not only against the wording on the label.[4] More detail in What Does Research Use Only Mean?
Certificate of Analysis (COA). A laboratory report documenting a compound’s identity and purity for a specific lot. See how to read a COA.
Lot or batch number. A code identifying a single production run. Testing is tied to the lot, so the COA you review should match the lot printed on your vial. You can verify a lot here.
Lyophilized. Freeze-dried. Peptides are typically supplied as a lyophilized powder because it is more stable for storage and shipping. See how to store research peptides.
Reconstitution. The process of dissolving a lyophilized compound into a liquid so it can be worked with in laboratory research.
Bacteriostatic water. A common solvent used to reconstitute lyophilized compounds in a lab setting. It contains a small amount of preservative that inhibits bacterial growth.
Purity. The proportion of a sample that is the intended peptide, as opposed to impurities. It is usually measured by HPLC and shown as a percentage on the COA. More in What Is Peptide Purity?
HPLC (high-performance liquid chromatography). The analytical method most commonly used to measure a peptide’s purity. The compendial chapter governing it also defines the system suitability a run must satisfy before its result is meaningful.[2]
Mass spectrometry (MS). A method that confirms a peptide’s identity by measuring its molecular weight and matching it to the expected value.
Endotoxin. A bacterial contaminant that quality-focused labs test for, often using the LAL test. A low endotoxin result is a quality indicator. Since May 2025 the animal-free recombinant method has had its own compendial chapter alongside the traditional one.[3]
Net peptide content. The percentage of a vial’s total mass that is actually peptide, as opposed to residual water, salts, or counterions. It is different from purity.
Third-party testing. Testing performed by an independent laboratory rather than the manufacturer, which adds objectivity to the results.
Milligram (mg) and microgram (mcg). Units of mass. One milligram equals 1,000 micrograms. Vials are typically labeled by the mass of peptide they contain.
References
Definitions here follow the compendial and regulatory sources that set them. Each was checked on 11 August 2026.
- IUPAC and IUBMB Joint Commission on Biochemical Nomenclature, Nomenclature and Symbolism for Amino Acids and Peptides (Recommendations 1983), published 1984. Full recommendations.
- United States Pharmacopeia, General Chapter <621> Chromatography, PDG Stage 4, official 1 December 2022. PDG harmonisation record.
- United States Pharmacopeia, General Chapters <85> Bacterial Endotoxins Test and <86> Bacterial Endotoxins Test Using Recombinant Reagents, the latter official May 2025 as an alternative to <85>. USP-NF announcement.
- U.S. Food and Drug Administration, Distribution of In Vitro Diagnostic Products Labeled for Research Use Only or Investigational Use Only, final, November 2013. Cited for the principle; the guidance addresses in vitro diagnostics. FDA guidance page.
Related reading
- What Is MOTS-C? Sequence, CAS and What Its COA Should Say
- What Made in the USA Means for Research Peptides
- What Is Peptide Purity, and How Is It Measured?
- All research guides
- Frequently Asked Questions
Related reading: what >98% purity actually means, and how to read a Tesamorelin COA.
Related reading: what is Melanotan 2, identity and research context.
Product identity guides
Plain-language, identity-first guides to the compounds we carry, each with its registry identifiers and a link to look up its COA: Tesamorelin, CJC-1295 and Ipamorelin, Melanotan 2, Sermorelin, Hexarelin, Selank, Semax, GHK-Cu, PT-141, Thymosin Alpha 1, DSIP, Epitalon, VIP, Oxytocin, NAD+, L-Glutathione, KLOW, GLOW Blend, SS-31, MOTS-C, KPV.
All products are sold strictly for research use only (RUO) and are not for human or animal consumption.