A Certificate of Analysis (COA) is the primary quality documentation for research-grade peptides. Understanding how to interpret COA data is essential for researchers evaluating compound suitability and vendor credibility.
What a COA Contains
A properly structured peptide COA includes identification of the testing laboratory, the sample tested, the methods employed, and the results of each analytical test. Key fields to evaluate include purity, potency, identity confirmation, and physical appearance.
HPLC Purity
High-performance liquid chromatography (HPLC) is the standard method for assessing peptide purity. The instrument separates the components of a sample by pushing them through a column under high pressure; components elute at different times based on their chemical properties.
The purity result is expressed as a percentage of the target compound relative to total detected components. A result of ≥98% is the accepted threshold for research-grade peptides. Results below this threshold indicate the presence of impurities — potentially synthesis byproducts, degradation products, or unrelated compounds — that could confound experimental data.
HPLC purity is typically reported alongside a chromatogram showing the peak profile. A clean research-grade peptide will show a single dominant peak with minimal baseline noise.
HPLC Potency
Potency (also called assay or content) measures the actual mass of the target compound present, expressed as a percentage of the labeled amount. Acceptable ranges are typically 95-105% of label claim.
A potency result of 102.5% on a 30mg vial means the vial contains approximately 30.75mg of active compound — slightly above label, which is preferable to underdosing. Results significantly outside the 95-105% window suggest formulation inconsistency.
FTIR Identification
Fourier-transform infrared spectroscopy (FTIR) confirms compound identity by generating a spectral fingerprint. Each compound produces a characteristic absorption pattern when exposed to infrared radiation. The COA should state that the sample spectrum matches the reference spectrum for the labeled compound.
FTIR is a qualitative test — it confirms identity but does not quantify purity or potency. It is used in conjunction with HPLC, not as a replacement.
Mass
The recorded mass of the sample is noted as a reference point for the analysis. This is not the labeled content — it is the total mass of sample submitted for testing, which includes the active compound plus any excipients (such as mannitol, a common lyoprotectant).
Excipients
Many lyophilized peptides contain excipients — inert substances added to stabilize the compound during freeze-drying. Mannitol is the most common. Its presence on a COA is expected and does not indicate adulteration.
Red Flags
- Purity below 95%
- Potency outside the 95-105% range
- No FTIR or identity confirmation
- Lab not independently verifiable (check the lab's website and certificate verification portal)
- COA date significantly older than the product (>12 months)
- Generic or templated COA with no unique sample identifiers
A legitimate third-party lab will provide a verifiable certificate with a unique report number and digital signature. Researchers should verify COAs directly with the issuing laboratory when possible.