Resource · Updated 27 August 2026

Research Peptide & Laboratory Terminology Glossary

An A–Z reference of the terminology used across peptide research and laboratory documentation, defined in plain English.

A

Amino Acid: The fundamental building block of peptides and proteins. Twenty standard amino acids are encoded by the genetic code, each with a characteristic side chain that shapes chemical properties.
Agonist: A compound that binds to a receptor and activates it. A full agonist produces maximal activation; a partial agonist produces less than maximal.
Antagonist: A compound that binds to a receptor without activating it, blocking the action of an agonist at that same receptor.
Assay: A laboratory procedure that measures a specific property or concentration of a substance — for example, a peptide-content assay.
Aliquot: A precisely measured sub-sample taken from a larger solution, often prepared to avoid repeated freeze–thaw cycles.

Batch: A specific production run, identified by a batch (or lot) number that links physical material to its analytical records.
Batch Number: A unique identifier assigned to a production batch. Matching the batch number on a report to the product is how results are tied to material.
Bacteriostatic Water: Sterile water containing a preservative (0.9% benzyl alcohol), used to reconstitute lyophilised peptides for multi-dose laboratory use.

Certificate of Analysis (COA): A document from a testing laboratory reporting the results of analysis on a specific sample, typically including purity and identity data. How to read a COA
Chromatography: A family of separation techniques in which components of a mixture partition between a stationary phase and a mobile phase, emerging at different times.
Chromatogram: The graphical output of chromatography, where separated components appear as peaks; peak area is proportional to amount.
Concentration: The amount of a solute present in a given volume of solvent, often expressed in units such as mg/mL.
Control Sample: A sample of known composition run alongside unknowns to validate that an assay performed correctly.
Counter-Ion: An associated ion (e.g. acetate or trifluoroacetate) in a peptide salt that contributes weight but is not peptide material.
C-Terminus: The end of a peptide chain bearing a free carboxyl (–COOH) group; by convention sequences are read N-terminus to C-terminus.

Dalton (Da): The unit of molecular mass; one Dalton is one-twelfth the mass of a carbon-12 atom. Peptide masses are reported in Daltons.
Desiccant: A moisture-absorbing material included in packaging to protect a lyophilised product from humidity.

Gradient: In HPLC, a change in mobile-phase composition over time, used to elute components in order of increasing retention.

HPLC: High-Performance Liquid Chromatography — an analytical method that separates, identifies, and quantifies components of a mixture, the standard way peptide purity is reported. HPLC explained
Hydrophobicity: The tendency of a molecule to repel water; a key property exploited by reversed-phase HPLC to separate peptides.

Identity Testing: Testing that confirms a sample is the expected molecule, most commonly by mass spectrometry.
Incremental Purity: A purity figure reported from a single chromatographic run; a statement of what that run showed, not a universal guarantee.

Limit of Detection (LOD): The smallest amount of a substance an analytical method can reliably distinguish from background noise.
Lyophilisation: Freeze-drying — freezing a solution and removing the water by sublimation, producing a stable dry powder suitable for storage.
Lot Number: See Batch Number.

Mass Spectrometry (MS): A technique that measures molecular mass by ionising compounds and determining their mass-to-charge ratio, used to confirm peptide identity. Mass spectrometry explained
Mobile Phase: The solvent that carries a sample through a chromatography column.
Molecular Weight: The mass of a single molecule in Daltons, calculated for a peptide from its amino-acid sequence.
m/z: Mass-to-charge ratio — the quantity reported by mass spectrometry, from which molecular mass is derived.

N-Terminus: The end of a peptide chain bearing a free amino (–NH₂) group; the start of the written sequence.
Net Peptide Content: The actual peptide mass in a sample, excluding counter-ions, salts and residual water — a measure of potency.

Peptide: A short chain of amino acids linked by peptide bonds, typically fewer than about 50 residues.
Peptide Bond: The covalent bond between the carboxyl group of one amino acid and the amino group of the next, formed with the release of water.
Peptide Content: See Net Peptide Content.
Potency: The amount of target material actually present in a sample, as opposed to its proportion (see Purity).
Purity: The proportion of tested material matching the target compound, typically reported as an HPLC peak-area percentage.

Reconstitution: Dissolving a lyophilised peptide in a solvent to prepare a working solution. Reconstitution guide
Reference Standard: A well-characterised, known-purity sample used as a comparison point in analysis.
Retention Time: The time a compound takes to pass through a chromatographic system; a characteristic value under fixed conditions.
Reversed-Phase HPLC: The most common HPLC mode for peptides, using a non-polar stationary phase and a polar mobile phase.

Sample ID: The identifier a laboratory assigns to the specific sample it received, distinct from the manufacturer's batch number.
Sequence: The linear order of amino acids in a peptide, determining its structure and identity.
Stability: The ability of a peptide to retain structure and activity over time under defined storage conditions.
Stationary Phase: The material packed in a chromatography column that interacts differentially with sample components.
Storage Conditions: The temperature, humidity and light parameters under which a peptide is kept to preserve stability.

Theoretical Mass: The molecular mass computed from a peptide's sequence, against which measured mass is compared.
Trifluoroacetate (TFA): A common counter-ion in synthetic peptides, which contributes to total weight but is not peptide.