How to read a certificate of analysis for a research peptide
A certificate of analysis is the batch's test record. It is worth reading properly, because it is the only document that says what is actually in the vial.
What it must carry
The batch number, the product and strength, the date of analysis, the method for each test, the limit for each test, and the result. A certificate that lists results without limits, or limits without methods, cannot be checked against anything.
The lines that matter
Purity by RP-HPLC. The share of the peak area belonging to the target peptide, measured by reverse-phase liquid chromatography, usually at 220 nm. Our release limit is not less than 98.0 percent. A figure of 99 percent means the remaining one percent is related substances: truncated or deletion sequences, oxidised forms and the like.
Identity by mass spectrometry. The measured molecular weight against the calculated one. This is what separates the right peptide from a wrong one that happens to be pure.
Water content. Lyophilised peptides hold water. Our limit is not more than 8 percent by Karl Fischer titration. It matters for weighing: 10 mg of powder at 6 percent water is 9.4 mg of solids.
Net content. The labelled amount per vial, within plus or minus 5 percent by weight.
Acetate and residual solvents. Peptides are supplied as the acetate salt and are purified in acetonitrile and trifluoroacetic acid. The certificate states how much of each remains.
Reading a percentage honestly
Purity is an area percentage of a chromatogram, not a weight. A vial labelled 10 mg at 99 percent purity does not contain 9.9 mg of peptide: it contains 10 mg of material, of which the peptide fraction of the peak area is 99 percent, less water, less counter-ion. If you need peptide content by weight, ask for it as a separate figure.
Checking a certificate you were sent
Every batch number we ship can be looked up on the certificate page, which takes you to the testing laboratory's own verification. A certificate forwarded three times is worth checking against the source before it is relied on.