Reading a US Supplier Certificate Line by Line

A certificate of analysis is what stands between a characterized research compound and an unidentified powder in a vial. It is also the document most buyers scroll past. This is what each section is actually telling you, and what you should read into the sections that are missing.

What the document is

A COA is a batch-specific analytical report, written after synthesis, recording what testing was done on one particular lot and what that testing found. Two consequences follow. It describes a batch rather than a product line, so a certificate dated eighteen months ago says nothing about the vial on its way to you. And it reports measurements rather than claims: marketing copy asserts purity, a certificate shows the chromatogram underneath it.

Identity, by mass spectrometry

Identity testing answers one question — is this the molecule named on the label? Mass spectrometry, usually ESI-MS or MALDI-TOF, measures mass-to-charge ratio and compares the observed molecular weight against the value calculated from the sequence.

Both numbers should be on the certificate, theoretical and observed, and they should agree closely. A real discrepancy means a different molecule, an incomplete sequence, or an undisclosed modification. A certificate that reports purity but never confirms identity has established only that the vial contains something pure.

Purity, by HPLC

Purity is normally measured by reversed-phase HPLC. The sample is separated on a column and a detector records absorbance over time; the target compound comes off as a main peak, while impurities, truncations and deletion sequences appear as peaks of their own.

The figure quoted is the main peak’s area as a percentage of total peak area, and research-grade material is commonly reported at 98% or better. Two details carry more weight than the headline number:

• The chromatogram should be attached, not just the percentage. The trace shows whether the remaining 2% is one co-eluting impurity or a scatter of small ones.
• The detection wavelength should be named — usually 214 nm for the peptide bond, sometimes 220 nm. Figures taken at different wavelengths are not comparable to each other.

Peptide content and water

This is the section most often left out, and the one with the most direct effect on your bench work. Lyophilized peptides are hygroscopic and are usually supplied as salts, most often trifluoroacetate, so a vial labeled 10 mg does not necessarily hold 10 mg of peptide — the rest is counter-ion, residual solvent and adsorbed water.

Net peptide content is determined by amino acid analysis or elemental nitrogen analysis and typically lands somewhere in the 70–90% range. Water content comes from Karl Fischer titration or thermogravimetric analysis. Without those figures, any gravimetric calculation you make carries an error nobody has measured, and comparisons between suppliers stop meaning anything.

Tying the paper to the vial

A usable certificate identifies the lot it describes: batch or lot number, manufacture date, analysis date. Each certificate carries photographs of the batch it describes, which is what lets a document be matched to a physical vial rather than taken on faith.

Signs to slow down over

• No chromatogram. A percentage with no trace behind it is an assertion, not a measurement.
• No batch photographs, or caps and crimps that do not match the images shown.
• The same certificate across several products. Chromatograms are effectively unique; a repeated trace means a template, not a test.
• No net peptide content. Common enough, but it means your effective concentration is unknown.
• No testing laboratory named. Third-party analysis should say who performed it.

Using it

Before an experiment, check that observed mass matches theory and that the trace is present and readable. Where net peptide content is given, calculate concentrations from it rather than from nominal vial weight. Keep the certificate with your experimental records — if a result is questioned later, the analytical provenance of the material is part of the answer.

ExoLabz publishes batch certificates on this site. Browse the research peptide catalog, or contact us about a specific lot before ordering.

All products referenced are supplied for laboratory research use only and are not approved for human consumption, clinical, or veterinary use.

Related listings. Ours are published in full on the certificates of analysis page, and what a third-party test actually measures covers which figures decide whether a number means anything.