Peptide purity testing notes: chromatograms, QC and the 95 vs 99 gap

A purity figure on a certificate of analysis is a claim. The chromatogram, the identity check and the lot it belongs to are what make it evidence. These notes collect our short posts on how peptide purity is tested and why the details matter in a controlled study.

A chromatogram should be ready on request

An HPLC chromatogram is the raw evidence behind a purity figure. It shows the main peak for the target peptide and any smaller peaks for related impurities, so a reader can see how the percentage was calculated rather than taking it on trust.

Our view is that a supplier with working quality control can produce that trace in minutes. If a chromatogram for a specific lot cannot be found quickly, that delay says something about how the batch was documented.

What batch QC covers

Senna Research describes its batch quality control as four checks applied to every batch without exception: HPLC purity testing, mass spectrometry to confirm identity, endotoxin screening, and third-party verification of the results.

Each check answers a different question. HPLC measures how much of the sample is one compound, mass spectrometry confirms that the compound has the expected mass, and endotoxin screening looks for bacterial contamination that purity testing cannot see. The point is documentation, not marketing copy.

The gap between a purity claim and the proof

Almost every listing in the research peptide market states a purity of 99 percent. Far fewer attach the chromatogram that would show it.

A purity claim without its trace cannot be checked. The useful question for any certificate of analysis is whether the figure is tied to a specific lot and backed by the underlying data.

Why 95 and 99 percent are different experiments

Purity percentage is the most misunderstood number in peptide research. 95 percent and 99 percent sound close, but at 95 percent one part in twenty of the material is something other than the target sequence, compared with one part in a hundred at 99 percent.

In a controlled study, that difference matters. The extra material is usually related sequences or synthesis by-products, and it travels into every sample. Two studies run at different purity levels are not strictly the same experiment.