Research notes
Evaluating a Certificate of Analysis for research-grade peptides
A certificate of analysis is the supplier's record of what their instrument measured on their sample of a lot. Read well, it tells a receiving laboratory what was tested, by what method, and what was not tested at all. This page is a line-by-line reading guide. It is not a release procedure, and a certificate is never a statement that material is safe for any purpose.
Identity
Identity is normally established by mass spectrometry. The certificate should state the method, the observed mass and the expected mass for the intended molecule, and the two should agree within the instrument's stated tolerance. An observed mass with no expected mass beside it, or a certificate that says only that identity was confirmed, has not shown its work. For a compound identified by development code, the expected mass is the one published for that code.
Purity
Purity is normally reported by reversed-phase HPLC as the main peak's percentage of total peak area. That figure depends on the column, the gradient, the detection wavelength and the integration parameters, and a certificate that reports a percentage without the method has reported a number that cannot be compared with any other. Peak area purity also counts only what absorbs at the detection wavelength: salts, water and non-absorbing contaminants are invisible to it.
What a standard certificate omits
Most peptide certificates do not report endotoxin, heavy metals, residual solvents from synthesis and purification, water content, counter-ion content or net peptide content. Each of those is a separate assay and each is a legitimate line in an incoming specification. A laboratory that needs any of them should either require them from the supplier in writing or run them on receipt. The longer treatment of what a certificate leaves out is on its own page.
Where supplier certificates fall short
The paperwork itself
Check that the lot number on the certificate matches the lot number on the shipment paperwork, that the testing laboratory is named, that the certificate is dated, and that the sample tested is stated to come from the lot supplied. A certificate that satisfies all of that is a good starting point for the receiving laboratory's own inspection. It is a starting point; the release decision belongs to the laboratory that will use the material.