How to read a peptide certificate of analysis

What a certificate is, and what it is not

A certificate of analysis is a record of measurements performed on a specific lot of material at a specific date by a specific laboratory. It is not a guarantee of performance in your assay, it is not a specification for the compound in general, and it is not transferable to a different lot of the same sequence.

That last point is where most sourcing errors originate. A supplier who provides 'the COA for BPC-157' rather than the COA for the lot printed on your vial has given you a document about material you do not have. The lot code on the label and the lot code on the certificate must match, and the report date should precede your order rather than follow it.

The purity figure and its integration window

Purity on a peptide certificate is almost always an area-percent figure from a reverse-phase HPLC chromatogram: the area under the primary peak divided by the total integrated peak area, measured at a stated detection wavelength — typically 214 nm, where the amide bond absorbs, or 280 nm where aromatic residues are present.

Two certificates reporting the same number can mean different things. Integration that excludes the solvent front, a different wavelength, or a shorter gradient will all shift the result. This is why a purity figure without a named method and a visible chromatogram is an assertion rather than a measurement, and why the trace matters more than the headline percentage.

Read the chromatogram for shape as well as area. A single sharp peak with a flat baseline is a different quality signal than a primary peak with a shoulder, even when both integrate to the same figure — a shoulder usually indicates a closely related impurity such as a deletion sequence or an oxidised variant.

Mass spectrometry: the identity half of the answer

HPLC tells you how much of one thing is present. It cannot tell you whether that thing is the sequence you ordered. Mass spectrometry supplies the missing half: an observed molecular mass consistent with the theoretical mass calculated from the sequence is the evidence that the correct peptide was synthesised.

Small offsets are normal and explainable. Peptides commonly ship as acetate or trifluoroacetate salts, and charge-state or adduct assignment shifts the observed value. An offset near the mass of a single residue is a different matter entirely and points to a deletion or insertion sequence — the impurity class HPLC is least likely to resolve.

Peptide content is not purity

Peptide content is the fraction of the vial mass that is actually peptide, as opposed to counter-ion, bound water, or residual salt from purification. A vial can legitimately be 99% pure by HPLC and still contain noticeably less peptide by mass than the label weight, because purity and content answer different questions.

For qualitative work the distinction rarely matters. For quantitative concentration calculations it does, and where a content figure is published it should be carried into the molarity arithmetic rather than assuming the full label mass is peptide.

The omissions that should stop an order

Missing lot number, missing laboratory identity, missing method, missing chromatogram, or a report date after your order date are each sufficient reason to pause. So is an endotoxin or sterility line that is absent — absence of a result means not tested, not passed, and research-grade material should never be assumed sterile.

One more signal is worth naming: certificates presented as images with the laboratory letterhead cropped or the report reference obscured. A genuine independent report carries a reference the issuing laboratory can verify, and any supplier confident in its analytics will point you to that verification route rather than away from it.