Peptide content, water, counterion and reading the COA

Reading time: ~2 min · Part of the free certification in peptide science

Beyond identity and purity, there are parameters that describe the actual composition of the powder in the vial:

• Net peptide content. It is a nuance many overlook: purity (by HPLC) measures what fraction of the peptide present is the correct one; content measures how much of the total powder mass is actually peptide, versus water, salts and counterion. A vial can be 99% pure and still contain an appreciable fraction of non-peptide mass.
• Water content. Karl Fischer titration measures the residual moisture of the lyophilizate; excess water compromises long-term stability.
• Counterion. Peptides are usually isolated as salts; acetate (or residual TFA, the trifluoroacetic acid used in purification) is part of the mass and should be known.
• Appearance and solubility. Appearance of the powder (typically white to off-white) and behavior on reconstitution (clear solution); unexpected cloudiness is a warning sign.

Anatomy of a Certificate of Analysis (COA)

The COA is the document a laboratory issues for a specific batch. A complete COA includes: compound name and sequence, batch number and date of analysis, HPLC purity result with its chromatogram, MS mass confirmation with its spectrum, peptide content, water and appearance. The operational key is batch traceability: without a batch number and date, a COA cannot be verified as corresponding to the material in your hand.

Educational content for scientific purposes. It distinguishes preclinical from clinical evidence and is not medical advice, diagnosis or a recommendation for use. NeoPeptidos products are sold labelled for research use only (RUO).