Peptide specification and characterisation: what to request

Identity

Request molecular mass by mass spectrometry against the theoretical mass, and where the sequence is critical, peptide mapping or direct sequencing. For modified peptides, confirm that the modification is characterised rather than inferred.

Quantity attributes

Ask for chromatographic purity with the method, column, mobile phase and detection wavelength stated; peptide content by amino acid analysis or nitrogen determination; water content by loss on drying or Karl Fischer; and counter-ion content. Together these define how much target molecule you receive per gram.

Impurity profile

Related peptides, deletion and insertion sequences, oxidation and deamidation products, and dimers or aggregates behave differently from small-molecule impurities. Ask for individual and total related-substance limits, the reporting threshold, and whether any impurity above the threshold has been identified.

Physical and microbiological attributes

Appearance, solubility in a named solvent at a named concentration, and where the intended use requires it, bacterial endotoxin and microbial enumeration with the compendial method named.

Stability and storage

A storage statement is only meaningful if stability data support it. Ask what condition was studied, for how long, and which attributes were monitored. Absent data, treat storage guidance as a handling recommendation rather than a shelf-life claim.

Documentation

Each batch should arrive with a Certificate of Analysis referencing the agreed specification version, the batch number, the methods, the results against criteria, the analysis date and an authorising signature, plus a current Safety Data Sheet.

What not to accept

Typical values presented as batch results, purity without a method, peptide content omitted entirely, or a specification that lists tests without acceptance criteria. Each of these leaves the material undefined in exactly the areas that matter.