How to Read a Peptide Certificate of Analysis (COA)

High-Performance Liquid Chromatography (HPLC) purity is the most important metric on any COA. It measures what percentage of the total material in the vial is the intended peptide, versus impurities (truncated sequences, deletion sequences, oxidized variants, or other byproducts of synthesis). What to look for: Research-grade peptides should have ≥95% HPLC purity. Premium quality is ≥98%. Anything below 95% should be questioned — lower purity means a higher percentage of unknown impurities in your research material. The COA should include the actual HPLC chromatogram — the graphical trace showing peaks. The main peak (your peptide) should be dominant, with minimal secondary peaks. If the COA shows only a number without the chromatogram, it provides less verification.

Mass spectrometry confirms that the peptide in the vial is actually the correct molecule. It measures the molecular weight of the compound and compares it to the expected (theoretical) molecular weight of the target peptide. What to look for: The observed mass should match the theoretical mass within ±1 Da (Dalton). This confirms that the peptide has the correct amino acid sequence. HPLC alone cannot confirm identity — a peptide could be 99% pure but be the wrong peptide entirely. MS provides the identity check. Common notation: You may see ESI-MS (Electrospray Ionization) or MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight). Both are valid methods. The key data point is the observed vs. expected molecular weight.

The COA typically describes the physical appearance of the peptide. Most research peptides should appear as a white to off-white lyophilized powder. Significant discoloration (yellow, brown) may indicate oxidation or degradation. Some peptides naturally have a slight color due to their amino acid composition — for example, peptides containing tryptophan may have a slight off-white appearance.

This section indicates the recommended solvents and expected solubility. Most peptides are soluble in sterile or bacteriostatic water. Some hydrophobic peptides may require a small amount of DMSO or acetic acid to dissolve initially. If the COA specifies a particular solvent, follow that recommendation for optimal dissolution.

Every COA should have a unique batch/lot number that ties the document to a specific production run. This enables traceability — if any quality issue is discovered, the batch number identifies exactly which vials are affected. The COA should also include a synthesis or testing date. Be cautious of COAs without batch numbers, as they may be generic templates rather than batch-specific analyses.

Generic COAs without batch numbers — may not reflect your actual product. Missing MS data — HPLC alone doesn't confirm identity. Purity below 95% without explanation. No chromatogram included — just a number is less trustworthy. COA from a different company than the seller — indicates reselling without independent verification. Identical COAs across different batches — suggests the document is not batch-specific.