The Certificate of Analysis (COA) is the document that backs the identity and purity of a peptide batch. Knowing how to read it is a basic skill for any serious researcher.
Typical sections of a COA
- Product identification: name, sequence, theoretical molecular weight, batch number.
- Physical analysis: appearance (white/off-white powder), solubility.
- HPLC: chromatogram with purity percentage.
- Mass spectrometry (MS or LC-MS): observed mass vs. theoretical mass.
- Amino acid analysis (optional; not all suppliers include it).
- Endotoxins (LAL test) — critical for use in cell cultures.
- Net peptide content (vs. gross weight, which includes counterions such as TFA).
HPLC chromatogram: what to look for
Reversed-phase HPLC (RP-HPLC) separates the peptide from impurities by hydrophobicity. A good-quality chromatogram should show:
- A clear, symmetrical main peak representing ≥99% of the total integrated area.
- Línea base estable antes y después del pico (sin “ruido” excesivo).
- Absence of significant secondary peaks near the main peak (this would indicate isomers or truncated sequences).
- Column, gradient and UV detection information (typically 220 nm for the peptide bond, 280 nm for aromatic residues).
Mass spectrometry: identity confirmed
MS confirms that the synthesized peptide has the expected molecular mass. For a peptide of ~5000 Da, a difference of ±1 Da between theoretical and observed mass is acceptable. Larger differences suggest synthesis errors (a missing or duplicated amino acid changes the mass in a recognizable way).
Ejemplo
BPC-157, sequence GEPPPGKPADDAGLV, theoretical monoisotopic mass: 1419.66 Da. A legitimate COA will report an observed mass of 1419–1420 Da.
Endotoxins: the most underestimated figure
Pure synthetic peptides manufactured with good practices usually have a low endotoxin content. However, for experiments in cell cultures or sensitive animal models, the ideal level is:
- <1 EU/mg — suitable for most research applications.
- <0.1 EU/mg — grado “low endotoxin”, requerido en estudios inmunológicos.
Net peptide content vs. gross weight
Un punto técnico que muchos pasan por alto: cuando un péptido se purifica por HPLC en presencia de ácido trifluoroacético (TFA), el péptido final puede contener un 5–30% de TFA y agua adsorbida. Por eso, un vial etiquetado como “10 mg” puede contener en realidad 7–9 mg de péptido neto. Un COA serio reportará este dato como “peptide content” o “net peptide” en porcentaje.
Always check net content before calculating molar doses in your protocol. It is the #1 cause of variability between laboratories using nominally the same peptide.
Trazabilidad NeoPeptidos
Every NeoPeptidos batch includes a downloadable COA with HPLC, MS and endotoxins. The batch number on the COA must match the one printed on the vial — if there is a discrepancy, contact the team before using the material in any protocol.
🔬 Updated on February 18, 2026 · Reviewed by the NeoPeptidos team · Content for research purposes (RUO).