How to Read a Certificate of Analysis (COA) for Peptides

A Certificate of Analysis (COA) is the single most important document for verifying the quality of a research peptide. It provides analytical data confirming the identity, purity, and composition of the compound. Every reputable peptide supplier should provide a COA for each batch, and every researcher should know how to interpret one.

This guide explains each section of a standard peptide COA, what the numbers mean, and what red flags to watch for.

What a COA Contains

A complete peptide COA typically includes four categories of analytical data:

1. Identity confirmation (mass spectrometry)
2. Purity assessment (HPLC)
3. Physical characteristics (appearance, solubility)
4. Contaminant screening (residual solvents, endotoxins, heavy metals)

HPLC: The Purity Standard

High-Performance Liquid Chromatography (HPLC) is the primary method for determining peptide purity. The technique separates a peptide sample into its individual components by passing it through a column under high pressure. Each component elutes at a different time based on its chemical properties.

Reading an HPLC Chromatogram

The chromatogram is a graph with time on the x-axis and detector response (usually UV absorbance at 220nm) on the y-axis. The key features:

• Main peak: This represents the target peptide. Its area relative to all other peaks determines the purity percentage.
• Retention time: The time at which the main peak elutes. This should be consistent with the known retention time for the peptide under the stated conditions.
• Minor peaks: These represent impurities --- deletion sequences, truncated fragments, oxidized forms, or other byproducts of synthesis.
• Baseline: Should be flat and stable. A noisy or drifting baseline may indicate instrument issues or sample contamination.

What Does 99% Purity Mean?

When a COA states 99% purity by HPLC, it means the main peak accounts for 99% of the total peak area in the chromatogram. The remaining 1% comprises all detectable impurities combined.

For most research applications, purity thresholds are:

• Greater than 98%: Research grade, suitable for most in-vitro and preclinical applications
• 95-98%: Acceptable for many applications but may contain enough impurities to affect sensitive assays
• Below 95%: Generally insufficient for rigorous research; impurities may confound results

HPLC Method Details to Verify

A credible COA will specify the HPLC conditions used:

• Column type: Typically C18 reversed-phase
• Mobile phase: Usually acetonitrile/water gradient with TFA (trifluoroacetic acid)
• Detection wavelength: 220nm is standard for peptide bonds; 280nm for aromatic residues
• Flow rate and gradient: These affect separation quality

If a COA provides only a purity number without method details, treat it with caution.

Mass Spectrometry: Identity Confirmation

Mass spectrometry (MS) confirms that the peptide has the correct molecular weight. The two most common MS methods for peptides are:

• ESI-MS (Electrospray Ionization): Produces multiply charged ions; good for peptides up to ~6,000 Da
• MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight): Measures intact molecular mass directly

Reading MS Data

The COA will report an observed molecular weight and a theoretical (expected) molecular weight. These should match within the instrument's tolerance, typically plus or minus 1 Da.

Example for BPC-157:

• Theoretical MW: 1419.53 Da
• Observed MW: 1419.6 Da
• Result: Identity confirmed

If the observed mass deviates significantly from theory, the peptide may be a different sequence, contain modifications, or be degraded.

Additional Quality Tests

Appearance

Lyophilized peptides should appear as a white to off-white powder. Discoloration (yellow, brown) may indicate oxidation or degradation.

Peptide Content

Peptide content (also called net peptide content) reflects the percentage of the vial weight that is actual peptide versus counter-ions (acetate, TFA) and residual moisture. A 10mg vial with 80% peptide content contains 8mg of active peptide and 2mg of salts and water. This is normal and expected.

Residual Solvents

Peptide synthesis uses organic solvents (DMF, DCM, acetonitrile). The COA should confirm these are below ICH Q3C safety limits.

Endotoxin Testing

For in-vivo research applications, bacterial endotoxin levels should be measured by LAL (Limulus Amebocyte Lysate) assay and reported as EU/mg (endotoxin units per milligram).

Red Flags in Peptide COAs

Watch for these warning signs:

• No batch or lot number: Every COA should reference a specific production batch
• Generic or template COAs: The same document reused across different peptides without unique analytical data
• Missing chromatogram: A purity number without the actual HPLC trace
• No MS data: Purity without identity confirmation is incomplete
• Purity claims above 99.9%: While possible, claims of 99.95% or 99.99% for custom peptides should be viewed skeptically
• Undated documents: COAs should carry a testing date
• No method details: Legitimate analytical labs always report their testing conditions

How Viking Labs Handles Quality

Every peptide sold by Viking Labs ships with a batch-specific COA from independent third-party testing. HPLC chromatograms, mass spectrometry data, and testing conditions are all included. Researchers can review COA examples on our Lab Tests page.

Conclusion

Reading a COA is a fundamental skill for any peptide researcher. The document tells you what you actually received versus what was ordered. Focus on the HPLC purity percentage and chromatogram, verify identity through mass spectrometry, and check for the red flags listed above. If a supplier cannot or will not provide a detailed, batch-specific COA, find a different supplier.

*For laboratory research use only. Not for human consumption. These products are not drugs, supplements, or intended to diagnose, treat, cure, or prevent any disease.*