Peptide Purity: what 99% actually means in a COA
HPLC purity, mass-spec confirmation and endotoxin testing — a plain-English guide to reading a certificate of analysis.
A Certificate of Analysis (COA) is the single most important document accompanying any research peptide. It states, in measurable terms, what is actually in the vial you just received.
HPLC purity
High-Performance Liquid Chromatography separates the target peptide from residual by-products of synthesis. A "99%" figure on a Peptogenic COA is the integrated peak area of the target compound compared to everything else UV-detectable at 214 nm.
Mass spectrometry
HPLC tells you *how much*. Mass spectrometry confirms *what*. A molecular mass matching theory to within 0.1 Da confirms the intended sequence was synthesised.
Endotoxin & sterility
For injectable-format research, endotoxin (<0.1 EU/mg) and bioburden are non-negotiable. Peptogenic lots are LAL-tested at accredited third-party laboratories.
What to do with a COA
Record the lot number, purity value and expiry alongside your experimental data. When results look anomalous, the COA is the first place to look.