How to Read a Peptide Certificate of Analysis
Key takeaways
- Identity match first. Mass spec (LC-MS) must confirm the compound is what the label claims.
- Quantitation second. Compare measured amount to claimed amount; under-dosing more than 10 percent is a red flag.
- Purity third. HPLC peak area at the target wavelength. Below 95 percent on a finished peptide warrants investigation.
- Contamination fourth. Heavy metals, endotoxin (LAL), microbial counts (USP 61) for any injectable.
- Methodology last. The COA must name the method and uncertainty range, or it is marketing copy.
Most readers focus on a single number (purity percentage) and miss the rest. Here is the order to actually read a peptide certificate of analysis, in plain English, from a Manila independent lab that issues them every day.
1. Identity match first
Before anything else, the mass spec result must match the expected compound. If the compound is not what the label claims, every other number is irrelevant. Look for an LC-MS or co-injection result that confirms the molecular mass within a few parts per million of the theoretical mass.
2. Quantitation second
Compare measured amount against claimed amount. A 5 mg semaglutide vial that measures 4.95 mg passes. A 10 mg tirzepatide vial that measures 8.4 mg is underdosed by 16 percent. Significant under-dosing (more than 10 percent below claimed) is a red flag. Modest over-dosing can also indicate poor quality control at the source.
3. Purity third
HPLC peak area at the target wavelength, expressed as a percentage. For finished pharmaceutical-grade peptides, anything above 95 percent is normal. Below 95 percent warrants investigation. Below 90 percent is a reject. Note that purity above 99 percent on a peptide is rarely achievable by any commercial vendor.
4. Contamination fourth
Heavy metals above ICH Q3D limits, endotoxin above 0.5 EU/mg for injectables, or microbial counts above USP 61 limits make the product unsafe to inject regardless of identity and purity. A defensible peptide COA includes at minimum heavy metals (As, Cd, Pb, Hg) and endotoxin (LAL).
5. Methodology last
Confirm the method is appropriate for the analyte. HPLC alone cannot confirm peptide identity; LC-MS or co-injection with a reference standard is required. A COA that reports purity without naming the column, wavelength, and gradient is missing critical information.
A COA without the method, the uncertainty range, and a verification key is a flyer. Reject it.
For more, read our full guide to certificates of analysis, or verify a Lumen Labs COA.