Reference
Peptide glossary
23 terms that turn up on a certificate of analysis or a product page, defined plainly and without claims.
- Amino acid
- A small molecule with an amine group, a carboxylic acid group and a distinguishing side chain. Twenty are the standard building blocks of biological proteins.
- Area normalisation
- The arithmetic behind most purity figures: the target peak’s area divided by the total area of all peaks recorded, as a percentage.
- Batch, or lot
- A production run. The batch number is what links a tested sample to a particular vial; when it is blank, that link cannot be made.
- Bacteriostatic water
- Sterile water containing roughly 0.9% benzyl alcohol, which inhibits bacterial growth. Distinct from plain sterile water, which contains no preservative.
- CAS number
- A unique registry identifier assigned to a chemical substance by the Chemical Abstracts Service. Useful because it is unambiguous where names are not.
- Certificate of analysis (COA)
- A laboratory’s report of what it measured in one specific sample on one specific date.
- Counterion
- The salt a synthetic peptide is isolated with, commonly trifluoroacetate or acetate. Real mass in the vial that a purity figure does not account for.
- Endotoxin
- A bacterial cell-wall component. Measured by a separate assay, and not covered by a purity test.
- HPLC
- High performance liquid chromatography. Separates a sample’s components so each can be measured; the standard method for peptide purity.
- Hygroscopic
- Readily absorbing moisture from the air. Lyophilised peptide powder is.
- Lyophilisation
- Freeze-drying. Water is removed from a frozen solution by sublimation under vacuum, leaving a dry solid without heating it.
- Mass spectrometry
- Measures molecular weight, and so addresses identity: whether the substance present is the one named.
- Net peptide content
- How much of the weighed powder is actually peptide, as opposed to salt and residual water. A different number from purity, and often absent.
- N-terminus / C-terminus
- The two ends of a peptide chain — the free amine end and the free acid end. Sequences are written N-terminus first.
- Peptide
- A chain of amino acids joined by peptide bonds, conventionally up to about fifty residues.
- Peptide bond
- The link formed when the acid group of one amino acid joins the amine group of the next, releasing water.
- Purity
- The proportion of the material a method can see that was the target compound. Not the proportion of the vial that is peptide.
- Reconstitution
- The act of dissolving a lyophilised solid back into liquid. Defined here for completeness; we give no guidance on it.
- Residue
- One amino acid within a chain, so called because forming the bonds costs part of the original molecule.
- Sequence
- The order of amino acids in a peptide, which defines it.
- Solid-phase peptide synthesis
- The standard method of making synthetic peptides, building the chain one residue at a time on an insoluble resin bead. Developed by R. B. Merrifield; Nobel Prize in Chemistry, 1984.
- Sublimation
- A solid passing directly to vapour without becoming liquid. The mechanism by which freeze-drying removes water.
- Verification key
- A reference issued with a laboratory report allowing it to be checked against the laboratory’s own records.
Fuller explanations of the analytical terms are on reading a certificate of analysis and what a purity figure measures.
