REFERENCE

Peptide glossary

The terms that appear on our certificates and product pages, explained without hand-waving.

Acetate contentANALYTICAL: The proportion of the supplied mass that is acetate counter-ion rather than peptide. Peptides purified by RP-HPLC with TFA are usually converted to the acetate salt; typical content is 4–12%. It matters because it is part of why the vial weighs more than the peptide in it.
Amino acid analysisANALYTICAL: Complete hydrolysis of the peptide followed by quantification of the released amino acids. It is the reference method for peptide content. It is the only one that tells you how much actual peptide, rather than salt and water, is in the vial.
Area normalisationANALYTICAL: Expressing the main peak's area as a percentage of the total integrated area in a chromatogram. It is the standard way purity is reported, and it assumes every impurity absorbs like the main compound, which is why the trace matters as much as the number.
Bacteriostatic waterHANDLING: Sterile water containing roughly 0.9% benzyl alcohol as a preservative, used in the laboratory to prepare stock solutions where repeated withdrawal from a sealed vial is expected.
Certificate of analysisANALYTICAL: The document recording the analytical results a specific lot was released against: purity, identity, water, counter-ion, endotoxin, the methods used, the dates, and who signed it off. A certificate that omits the chromatogram is showing you conclusions without evidence.
CLPREGULATORY: The GB Classification, Labelling and Packaging Regulation, which governs how chemical hazards are classified and communicated on labels and safety data sheets.
COSHHREGULATORY: Control of Substances Hazardous to Health Regulations 2002. Places the duty on the employer, meaning the receiving laboratory, to assess and control exposure to hazardous substances. It is why handling decisions rest with you, not with your supplier.
Counter-ionCHEMISTRY: The ion paired with the charged groups on a peptide, most commonly acetate or trifluoroacetate. It affects mass, solubility and, in some cell-based assays, the result. TFA in particular can be cytotoxic at concentrations that are easy to reach accidentally.
Deletion sequenceCHEMISTRY: A synthesis by-product missing one or more residues, caused by an incomplete coupling step. It is often the largest single impurity in a crude peptide and typically elutes close to the main peak, which is why gradient resolution matters.
EndotoxinANALYTICAL: Lipopolysaccharide from Gram-negative bacterial cell walls. Measured by LAL assay in endotoxin units per milligram. Relevant to any cell-based or in-vivo work because it triggers immune responses at very low concentrations.
ESI-MSANALYTICAL: Electrospray ionisation mass spectrometry. Confirms molecular identity by comparing observed mass against theoretical. Peptides typically show several charge states, so the spectrum has a family of peaks rather than one.
Freeze–thaw cyclingHANDLING: Repeated freezing and thawing of a solution, which drives aggregation and physical loss. The single most common avoidable cause of a peptide stock quietly losing activity. Aliquot on first reconstitution.
HygroscopicHANDLING: Readily absorbing moisture from the air. Most lyophilised peptides are, which is why a vial should reach room temperature before its seal is broken, otherwise atmospheric water condenses onto the powder.
Karl Fischer titrationANALYTICAL: The reference method for water content in a solid. Reported as a percentage; typically 1–8% in a lyophilised peptide. Water drives hydrolysis in the solid state, so it is a stability indicator as much as a composition one.
LAL assayANALYTICAL: Limulus amoebocyte lysate assay, the standard method for detecting bacterial endotoxin. The kinetic chromogenic variant is quantitative and is what we use.
Lot numberREGULATORY: The identifier for a single production and release batch. It is what ties a physical vial to a specific set of analytical results. A certificate without a lot number tells you nothing about the vial in your hand.
LyophilisationCHEMISTRY: Freeze-drying: freezing the material then removing water by sublimation under vacuum. Produces a dry solid that is far more stable than a solution and can be reconstituted to a known volume.
Molecular weightCHEMISTRY: The mass of one mole of the compound in g/mol. For peptides the monoisotopic mass is normally used for MS comparison and the average mass for weighing.
Retention timeANALYTICAL: How long a compound takes to elute from the column under a given method. Reproducible within a method, so it supports identity, but it is not proof of it, which is why mass confirmation is run alongside.
Retest dateREGULATORY: The date by which a lot should be re-analysed to confirm it still meets specification, as distinct from an expiry date. It reflects the stability data for that material under the stated storage conditions.
RP-HPLCANALYTICAL: Reverse-phase high performance liquid chromatography. Separates by hydrophobicity on a C18 column using a water/acetonitrile gradient. The workhorse method for both purifying and assaying peptides.
RUOREGULATORY: Research Use Only. A designation meaning the material is supplied as a laboratory reagent for in-vitro research and for nothing else. Not for human or veterinary use, and not for any therapeutic or diagnostic purpose. It is a position that has to be maintained by how a product is described, not just by a label.
SPPSCHEMISTRY: Solid-phase peptide synthesis. Builds the chain one residue at a time on an insoluble resin, allowing excess reagent to be washed away at each step. Merrifield's method, and still the basis of essentially all synthetic peptide manufacture.
TFACHEMISTRY: Trifluoroacetic acid. Used as an ion-pairing agent in RP-HPLC and in resin cleavage. Residual TFA can be cytotoxic in cell culture, which is why material intended for cell work is usually supplied as the acetate salt.