Research Peptide Terminology: A Plain-English Glossary
Last updated June 7, 2026
Research peptide documentation is dense with shorthand. A single COA can mention sequences, analogs, lyophilization, HPLC, and net content in one breath. This glossary defines the terms in plain English so the rest of the knowledge base — and any primary literature you read — makes sense.
Structure terms
| Term | Meaning |
|---|---|
| Amino acid | The building block of peptides and proteins. |
| Peptide bond | The chemical link joining one amino acid to the next. |
| Sequence | The ordered list of amino acids that defines a peptide. |
| Residue | A single amino acid unit within a chain. |
| Analog | A deliberately modified version of a parent molecule. |
| Fragment | A portion of a larger peptide or protein. |
| Truncation | A chain missing one or more residues — a common impurity. |
Forms and handling terms
| Term | Meaning |
|---|---|
| Lyophilized | Freeze-dried into a stable powder. See why peptides ship as powder. |
| Reconstitution | Dissolving a lyophilized powder back into liquid for laboratory work. |
| Counter-ion | An ion such as TFA or acetate paired with the peptide; adds mass. |
| Excipient | An inactive component included for stability or handling. |
| Stability | How well a compound retains integrity over time and conditions. |
Quality and testing terms
| Term | Meaning |
|---|---|
| COA | Certificate of Analysis — lab results for a batch. See how to read one. |
| HPLC | The chromatography method used to measure purity. |
| Mass spectrometry | Measures molecular weight to confirm identity. |
| Purity % | The share of detected material that is the target compound. |
| Net peptide content | The actual mass of peptide in the powder, after water and salts. |
| Endotoxin | A bacterial residue screened by the LAL test. |
| Batch / lot | One production run, identified by a code. |
Using the glossary
With the vocabulary in hand, the rest of the knowledge base reads more easily. For how these structures differ at a high level, see peptides vs proteins vs small molecules, and to apply the quality terms in practice, start with how to read a COA.
Frequently asked questions
What is a peptide?
A peptide is a short chain of amino acids linked by peptide bonds. Peptides are smaller than proteins, which are long amino-acid chains, though the boundary between the two is a matter of length and convention.
What does lyophilized mean?
Lyophilized means freeze-dried. Removing water under vacuum leaves a stable powder, which is the typical shipping form for research peptides.
What is an analog?
An analog is a molecule with a structure deliberately modified from a parent compound — for example by changing or adding amino acids — to alter properties such as stability while retaining a similar core.
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