Scientifically reviewed by Dr Stephan Hansberg
Peptide glossary: 60+ research terms explained
Plain one-sentence definitions of the chemistry, synthesis, testing, storage and documentation terms used in peptide research, from amino acid to UV detection.
Key takeaways
- •A peptide is a chain of amino acids joined by peptide bonds; chains of roughly 2 to 50 residues are usually called peptides.
- •HPLC measures purity, mass spectrometry confirms identity, and a quantity assay measures content: three different terms for three different questions.
- •Net peptide content differs from purity because counter-ions and water add weight to a powder.
- •Batch or lot numbers tie a certificate of analysis to one production run.
- •This glossary covers chemistry, testing and handling vocabulary only; it does not define any terms about use in people or animals.
The short answer
This glossary defines the terms you meet when reading peptide research papers, certificates of analysis and supplier specifications, each in one plain sentence. It covers peptide chemistry, synthesis, analytical testing, contaminants, storage and documentation. For a guided explanation of how the testing terms fit together, see our guide to reading a peptide COA.
Glossary A to Z
| Term | Definition |
|---|---|
| Acetate salt | A peptide form in which positively charged groups are paired with acetate ions, lighter than TFA and often requested for cell-based research. |
| Acetonitrile | The organic solvent most commonly used with water as the mobile phase in reversed-phase HPLC of peptides. |
| Aggregation | The clumping of peptide molecules together in solution, which can reduce solubility and change analytical results. |
| Aliquot | A measured portion taken from a larger sample so the rest is not repeatedly handled. |
| Amide bond | The chemical bond between the carboxyl group of one amino acid and the amino group of the next, also called a peptide bond. |
| Amidation (C-terminal) | A modification in which the C-terminal carboxyl group is replaced by an amide, common in natural and synthetic peptides. |
| Amino acid | A small molecule with an amino group and a carboxyl group that serves as the building block of peptides and proteins. |
| Amino acid analysis (AAA) | A method that hydrolyses a peptide into its amino acids and measures them, used to determine net peptide content. |
| Analyte | The substance a test is designed to detect or measure. |
| Aseptic technique | Laboratory practice designed to prevent microbial contamination of samples and materials. |
| Bacteriostatic water | Sterile water containing a preservative, usually 0.9% benzyl alcohol, that inhibits bacterial growth. |
| Batch (lot) | A quantity of material made in one production run and identified by a single batch or lot number. |
| Blank | A run or sample containing no analyte, used to show which signals come from the method itself. |
| Certificate of analysis (COA) | A laboratory document reporting test results for a specific batch of a material. |
| Chromatogram | The plot produced by chromatography, showing detector signal against time, with peaks for separated components. |
| Cleavage | The step in solid-phase synthesis that releases the finished peptide from the resin, usually with trifluoroacetic acid. |
| Co-elution | When two different components leave a chromatography column at the same time and appear as one peak. |
| Cold chain | Shipping and storage kept within a set temperature range, for peptide solutions typically 2 to 8 C, from dispatch to delivery. |
| Counter-ion | An ion of opposite charge that pairs with charged groups on a peptide, such as trifluoroacetate, acetate or chloride. |
| C-terminus | The end of a peptide chain with a free carboxyl group (or amide), written last in a sequence. |
| Cyclic peptide | A peptide whose chain is joined into a ring, through its ends or side chains. |
| Dalton (Da) | The unit of molecular mass, equal to one twelfth of the mass of a carbon-12 atom; 1 kDa is 1000 Da. |
| Deamidation | A chemical change in which asparagine or glutamine loses an amide group, raising the mass by about 1 Da. |
| Deconvolution | Software processing that converts the multiple charge states in a mass spectrum into one molecular mass. |
| Degradation product | An impurity formed when a peptide breaks down during storage, for example by oxidation or hydrolysis. |
| Deletion sequence | A synthesis impurity in which one amino acid is missing from the intended sequence. |
| Desiccant | A drying agent packed with lyophilised materials to absorb moisture. |
| Disulfide bridge | A covalent bond between the sulfur atoms of two cysteine residues that stabilises a peptide's shape. |
| D-amino acid | The mirror-image form of an amino acid; natural peptides use L-forms, and D-forms are sometimes introduced to resist enzymes. |
| Elution | The process of a component leaving a chromatography column, measured as its retention time. |
| Endotoxin | Lipopolysaccharide from the outer membrane of Gram-negative bacteria, measured in endotoxin units (EU). |
| Endotoxin unit (EU) | The standard unit of endotoxin activity; one USP EU equals one international unit. |
| Electrospray ionisation (ESI) | A gentle method of turning peptides into charged ions in a fine spray so a mass spectrometer can measure them. |
| Fmoc chemistry | The most widely used protecting-group strategy in solid-phase peptide synthesis, using a base-removable Fmoc group. |
| Half-life | The time taken for half of a substance to be broken down or removed in a given system, for example in serum in vitro. |
| HPLC | High-performance liquid chromatography, a technique that separates a sample's components under pressure and is the standard purity test for peptides. |
| Hydrolysis | The breaking of a bond by reaction with water, including the cleavage of peptide bonds. |
| Hygroscopic | Readily absorbing moisture from the air, as many lyophilised peptides do. |
| ICP-MS | Inductively coupled plasma mass spectrometry, the usual method for measuring elemental impurities such as lead and arsenic. |
| Identity test | A test that confirms a sample is the intended compound, usually by mass spectrometry or comparison with a reference standard. |
| In vitro | Research carried out in cells, tissues or reagents outside a living organism. |
| In vivo | Research carried out in a living organism, such as an animal model. |
| Ion exchange | A process that swaps one counter-ion for another, for example converting a TFA salt to an acetate salt. |
| ISO/IEC 17025 | The international standard for the competence of testing and calibration laboratories, used as the basis for lab accreditation. |
| Karl Fischer titration | A chemical method for measuring the water content of a sample. |
| LAL test | The Limulus amebocyte lysate test for endotoxin, based on an extract of horseshoe crab blood cells. |
| LC-MS | Liquid chromatography coupled to mass spectrometry, giving a molecular mass for each separated peak. |
| Limit of quantification (LOQ) | The lowest amount of an analyte a method can measure with acceptable accuracy. |
| Lyophilised | Freeze-dried: water removed under low temperature and vacuum to leave a dry powder or cake. |
| Mass spectrometry (MS) | A technique that measures the mass-to-charge ratio of ions to determine molecular mass. |
| Mobile phase | The liquid that carries the sample through a chromatography column. |
| Molar mass | The mass of one mole of a substance in grams per mole, numerically equal to its molecular mass in daltons. |
| Net peptide content | The percentage of a weighed peptide powder that is peptide, after excluding counter-ions and water. |
| N-terminus | The end of a peptide chain with a free amino group, written first in a sequence. |
| Oxidation | A chemical change, common at methionine and cysteine, that adds oxygen and raises mass by about 16 Da per oxygen. |
| Peptide | A chain of amino acids linked by peptide bonds, usually defined as roughly 2 to 50 residues. |
| Peptide bond | The amide bond joining one amino acid to the next in a peptide chain. |
| pH | A measure of how acidic or alkaline a solution is, which affects peptide solubility and stability. |
| Protecting group | A temporary chemical group that blocks a reactive site during synthesis so only the intended bond forms. |
| Protein | A long chain of amino acids, usually over about 50 residues, that folds into a defined three-dimensional structure. |
| Purity | The share of a sample, as measured by a stated method such as HPLC, that is the target compound. |
| Quantity (assay) | A measurement of how much compound is present, in mg or mg/ml, made against a reference standard. |
| Reconstitution | Dissolving a lyophilised powder in a liquid to make a solution. |
| Recombinant factor C (rFC) | A synthetic endotoxin test reagent that avoids horseshoe crab lysate, described in Ph. Eur. 2.6.32. |
| Reference standard | A highly characterised sample of known identity and content used to calibrate and compare test results. |
| Residue | A single amino acid unit within a peptide chain. |
| Resin | The insoluble solid support on which a peptide chain is built during solid-phase synthesis. |
| Retention time | The time a component takes to pass through a chromatography column, used to compare it with a standard. |
| Reversed-phase HPLC (RP-HPLC) | HPLC using a hydrophobic column, commonly C18, the standard mode for peptide purity. |
| Salt form | The counter-ion with which a peptide is supplied, such as TFA, acetate or hydrochloride. |
| Sequence | The order of amino acids in a peptide, written from N-terminus to C-terminus. |
| Solid-phase peptide synthesis (SPPS) | The method, introduced by Merrifield in 1963, of building a peptide one amino acid at a time on a resin. |
| Solubility | How much of a compound dissolves in a given liquid at a given temperature. |
| Specification | The acceptance limit a test result is judged against, such as purity of at least 98%. |
| Stability | How well a compound keeps its identity and purity over time under stated storage conditions. |
| Sterility test | A test for living microorganisms, such as USP <71>, in which samples are incubated in culture media for at least 14 days. |
| TFA salt | A peptide supplied with trifluoroacetate counter-ions left from synthesis and purification. |
| Truncated sequence | A synthesis impurity in which the peptide chain stopped growing before it was complete. |
| UV detection | Measurement of ultraviolet light absorbance, at about 214 to 220 nm for peptide bonds, used in HPLC. |
Where Celyfe fits
Several of these terms appear on Celyfe's own documentation. Each pen is a pre-mixed solution in a 3ml cartridge, so no reconstitution step is involved, and every batch has a batch number that links it to its certificate. Published certificates from Analiza Białek report 99% purity by HPLC for NAD+ batch A26085 and WOLVERINE batch C26071; GLOW and KLOW certificates are listed in the COA library at /coa when published. Pens ship cold-chain and are kept at 2 to 8 C, not frozen.
Sources
Sources used for this glossary, checked October 2026:
- Merrifield RB. Solid phase peptide synthesis. I. The synthesis of a tetrapeptide. J Am Chem Soc, 1963
- D'Hondt M et al. Related impurities in peptide medicines. J Pharm Biomed Anal, December 2014. PMID 25044089
- United States Pharmacopeia: General Chapters <71>, <85>, <232> and <233>
- EDQM: Recombinant factor C, Ph. Eur. chapter 2.6.32 (edqm.eu)
- GenScript: Examining the components of your peptide sample with AccuPep QC (technical presentation)
- IUPAC: Compendium of Chemical Terminology (Gold Book), entries for dalton and peptide
Research use only
Celyfe supplies research peptides for laboratory and research use only. Nothing on this page is guidance on use in humans or animals.
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