How to actually read a peptide COA (and the three ways they get faked)
Most people buying research peptides have learned to ask for a COA. Far fewer know how to read one, and the gap is where money gets wasted on underdosed or mislabelled vials.
A COA (certificate of analysis) is a lab report on a specific batch. Here is what actually matters on it, and what to ignore.
The three numbers that matter
Identity. Mass spec (usually MS or LC-MS) confirms that the molecule matches the label by molecular weight. If there is no identity test, then having a purity number for an unknown compound is useless.
Purity. HPLC gives a percentage. 98%+ is the working floor for most peptides. The number alone is not enough, though: check it's HPLC purity of the named peptide, not "total solids", which is a different and much easier number to inflate.
Net peptide content. This is the one almost nobody checks. A vial can be 99% pure and still contain far less actual peptide than the label mg, because lyophilised powder includes salts and water. Net peptide content (sometimes "peptide content by nitrogen") tells you how much is actually the active compound. Two vials both labelled 10mg can differ by 30% in what you are really getting.
The three ways COAs get faked
- Reused document. The same COA stapled to every batch for a year. A real COA has a batch or lot number that should match the vial. If they will not show a lot number, assume it is decorative.
- In-house testing dressed up as third party. "Tested" is meaningless if the vendor ran the test. You want a named independent lab on the document. If the lab is unnamed or is the vendor's own, treat the numbers as marketing.
- The purity bait and switch. A clean HPLC purity number with no identity test, no lot number, and no net peptide content. One real number surrounded by absences.
The 20 second check before you buy
Lot number present and matches. Independent lab named. Identity test present. HPLC purity of the named peptide at 98%+. Net peptide content stated. Miss two of those and it is not a vetted product, it is a vial with a nice PDF.
Happy to go deeper on any of these in the comments.