Certificates of analysis in this industry vary enormously in what they actually establish. Some run one test. Some run two. The difference matters, because the two standard tests answer completely different questions and neither substitutes for the other.
HPLC answers: how clean is this?
High-performance liquid chromatography pushes a dissolved sample through a packed column under pressure. Different compounds interact with the packing material differently and therefore emerge at different times. A detector at the far end records what comes out and when, producing a chromatogram of peaks.
The target peptide is the dominant peak. Everything else — truncated chains, deletion sequences, residual synthesis reagents — shows up as smaller peaks. Purity is expressed as the target peak’s share of total peak area.
What HPLC cannot do is tell you what the dominant peak is. It measures behaviour on a column, not identity.
Mass spectrometry answers: is this the right compound?
A mass spectrometer ionises the sample and measures mass-to-charge ratio, which yields the molecular weight of what is in the vial. That figure is compared against the theoretical molecular weight calculated from the declared amino acid sequence.
If they match within tolerance, the compound is what the label says. If they do not, no purity figure in the world redeems the lot. This is the check that catches substitution — the failure mode with the largest consequences and the fewest external symptoms.
Why one without the other is not enough
A clean synthesis of the wrong peptide passes HPLC with a high purity figure. A correctly identified peptide contaminated with 15% deletion sequences passes mass spec. Only running both closes both gaps, and a certificate that shows only one of them is telling you half a story — usually the half that is easier to make look good.
Our standard
Every lot goes to Janoshik Analytical for HPLC purity, mass-spec identity, and fill weight against label. All three appear on the published report, and the report lives on the lab’s domain rather than ours. Browse them on the certificates page, or search by the lot number printed on your vial.