How to Read a Peptide Certificate of Analysis (COA)

Every COA should begin with identifying information: the compound name or catalog number, the batch or lot number (a unique identifier for the specific manufacturing run), the synthesis date, the analysis date, and the name of the testing laboratory. If the COA lacks a batch number, it may be a generic template document rather than a batch-specific analytical report.

The testing laboratory should be identified by name. Best practice is independent third-party testing at a laboratory separate from the manufacturing facility. In-house testing is common but introduces potential conflicts of interest in reporting. Look for testing laboratories with ISO 17025 accreditation or equivalent quality certification.

The HPLC section reports the compound's chemical purity as a percentage. This is determined by reversed-phase HPLC, typically using a C18 column with a water/acetonitrile gradient and UV detection at 214nm (the peptide bond absorption wavelength).

Key values to examine: Purity percentage should be 98% or higher for research-grade peptides. The chromatogram should show a single dominant peak (the target compound) with minimal secondary peaks. The retention time of the main peak should be consistent with the expected hydrophobicity of the target compound. The method parameters (column type, gradient conditions, flow rate) should be stated so the analysis can be reproduced.

Red flags: Purity below 95%, broad or asymmetric main peak (suggesting co-elution of impurities), multiple peaks of significant size (greater than 2% each), or absence of the chromatogram image. A COA that states only a purity percentage without the supporting chromatographic data provides no independent verification.

The mass spectrometry section confirms the molecular identity of the compound. ESI-MS (Electrospray Ionization Mass Spectrometry) is the standard method for peptide identity confirmation. The COA should report the theoretical (expected) molecular weight, the observed molecular weight, and the mass spectrum showing the characteristic charge state envelope.

For a peptide, the observed mass should match the theoretical mass within 0.05% (0.5 Da per 1000 Da molecular weight). If the compound has a theoretical mass of 1200.5 Da, the observed mass should fall between 1199.9 and 1201.1 Da. Larger discrepancies may indicate incorrect sequence, post-translational modifications, or salt adducts.

The mass spectrum itself should show a clear series of multiply charged ions (e.g., [M+2H]2+, [M+3H]3+, [M+4H]4+) that deconvolute to a single molecular weight. Noisy spectra or spectra with multiple deconvoluted masses suggest impure samples or analytical issues.

Endotoxin testing measures bacterial endotoxin contamination using the Limulus Amebocyte Lysate (LAL) assay. Endotoxins are lipopolysaccharides from gram-negative bacteria that can confound biological assays by triggering inflammatory responses in cell-based or in vivo models.

Results are reported in Endotoxin Units per milligram (EU/mg). Research-grade peptides should test below 1.0 EU/mg. Pharmaceutical-grade compounds require less than 0.25 EU/mg. If your research involves cell culture or animal models, verify that endotoxin levels are within acceptable limits for your specific application.

Comprehensive COAs may include residual solvent analysis (GC method, reporting levels of TFA, acetonitrile, and other process solvents), water content (Karl Fischer titration, typically less than 5% for lyophilized product), appearance (white to off-white powder is standard), solubility (confirmation of dissolution in recommended solvents), and amino acid analysis for sequence-critical applications.

Not all of these sections appear on every COA. At minimum, a credible COA must include HPLC purity data with chromatogram, mass spectrometry identity confirmation with spectrum, batch number and dates, and the testing laboratory identity. The absence of any of these core elements should raise questions about the analytical rigor applied to that batch.