How to Read a Certificate of Analysis (COA)

What a COA Is

A Certificate of Analysis (COA) is a document issued by a laboratory confirming that a compound has been tested and meets certain quality specifications. For research peptides, a COA should verify identity, purity, and in some cases sequence confirmation.

A legitimate COA is issued by a third-party analytical laboratory independent of the manufacturer or vendor. It is not a marketing document and it is not produced by the vendor themselves.

Key Sections to Verify

1. Issuing Laboratory

The most important check: who produced this document?

• The lab name should be searchable and independently verifiable
• The lab should be separate from the vendor. A vendor producing their own "in-house" COA is not third-party testing
• Look for accreditation indicators (ISO 17025, CLIA, etc.) where available
• The lab contact information (address, phone, web) should be real and consistent

Red flag: no lab name, generic lab name with no web presence, or the lab is registered at the same address as the vendor.

2. Sample Identification

The COA should clearly state what was tested:

• Peptide name (common name and/or sequence)
• Lot or batch number
• Sample quantity received
• Date of analysis

Verify that the lot number on the COA matches the lot number printed on or accompanying the vial you received. If there is no lot number, that is a significant gap in traceability.

3. Purity

Purity is typically measured by HPLC (High-Performance Liquid Chromatography) and reported as a percentage.

• Research-grade peptides are typically expected at 95% or higher purity
• 98%+ is common for higher-tier suppliers
• The COA should state the analytical method used (e.g., "RP-HPLC at 220 nm")
• A raw chromatogram or peak area data is a positive sign; a bare percentage with no methodology is weaker documentation

Red flag: purity stated without method, purity below 95% presented without context, or suspiciously round numbers (exactly 99.00% with no decimal precision).

4. Identity Confirmation

Purity alone does not confirm you have the correct compound. Identity testing verifies what the molecule actually is.

Common identity methods:

• Mass spectrometry (MS): Measures the molecular weight of the compound. The observed mass should match the theoretical mass for the peptide sequence within acceptable tolerance (typically within 0.02% or 1 Da for peptides under 2000 Da)
• Amino acid analysis (AAA): Verifies the composition of amino acid residues
• Sequence confirmation: Less commonly included but most definitive

What to check: The COA should state observed molecular weight, theoretical molecular weight, and the method used. A COA that only reports purity and not identity is incomplete for research purposes.

Red flag: no mass spec data, or a stated mass that does not match the known molecular weight of the peptide (cross-reference with PubChem or the primary literature).

5. Water and TFA Content (where present)

Lyophilized peptides typically contain residual water and trifluoroacetic acid (TFA, a counterion from synthesis). Higher-quality COAs report these.

• Excess TFA can affect cell culture experiments and may cause cytotoxicity artifacts at high concentrations
• Water content affects net peptide content per vial (a vial stated as 5 mg may be 4.2 mg peptide + water if content is not declared)

This section is not always present, but its inclusion indicates a more complete analytical process.

6. Date of Analysis and Expiry

• The COA should include the analysis date
• Some COAs include a stability estimate or recommended retest date
• An undated COA cannot be used to verify current quality

Red flag: no date, or the analysis date predates the vial lot by a year or more without explanation.

Common Red Flags: Summary

| Red Flag | What It Suggests | |---|---| | No third-party lab identified | Vendor self-certification, not independent testing | | Lot number missing or unverifiable | Cannot confirm this document applies to this vial | | Purity only, no identity data | Compound identity unconfirmed | | Observed mass inconsistent with known MW | Possible wrong compound or synthesis failure | | No analysis date | Document cannot be placed in time | | Identical COA reused across multiple lots | Template document, not lot-specific testing | | Lab address matches vendor address | Not independent |

Worked Example: Reading Mass Spec Data

Peptide: BPC-157 (Ala-Gly-Glu-Ala-Gly-Val-Pro-Gly-Gly-Ala-Gly-His-Gly-Val-Pro-Ala-Phe-Leu-Glu-Leu)

• Molecular formula: C62H98N16O22
• Theoretical monoisotopic mass: 1418.68 Da

A COA for BPC-157 showing mass spec should list an observed mass in the range of 1418.5 to 1419.0 Da (depending on instrument and method). If the COA shows 1480 Da, 1400 Da, or no mass at all, the identity is not confirmed.

For multiply-charged ions (ESI-MS), the instrument may report the m/z ratio rather than the intact mass. At charge state +2, BPC-157 would appear at approximately 710.3 m/z. The COA should clarify which format the reported value uses.

Using the Reconstitution Calculator

Once you have verified your COA and confirmed the purity, use PeptaBase's Reconstitution Calculator to calculate the exact concentration and syringe draw volume for your research doses. The calculator accounts for purity-adjusted net mass.

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This guide is for research reference only. It does not constitute purchasing guidance, regulatory advice, or endorsement of any vendor or product.