How to Read & Verify a Certificate of Analysis (COA)

Last updated: March 5, 2026 — Reviewed by CompoundTalk Analytical Chemistry Advisors

1. What Is a Certificate of Analysis?

A Certificate of Analysis (COA) is a formal document issued by a testing laboratory that reports the results of analytical testing performed on a specific batch or lot of a substance. For compounded peptides such as semaglutide or tirzepatide, a COA typically includes identity confirmation, purity assessment, sterility testing, endotoxin levels, and other quality parameters [1].

COAs serve as the analytical "fingerprint" of a product batch. They are standard practice in pharmaceutical manufacturing under Current Good Manufacturing Practices (cGMP) and are required by USP General Chapters <1058> and <1059> for analytical data documentation [2].

2. Key Parameters on a COA

A comprehensive COA for a compounded peptide should include the following tests. If any of these are missing, treat it as a potential red flag.

3. Understanding Purity by HPLC

HPLC (High-Performance Liquid Chromatography) purity is the single most important metric on a peptide COA. It represents the percentage of the desired peptide in the sample, as distinguished from synthesis impurities (deletion sequences, truncated peptides, oxidized forms, and other byproducts) [3].

• ≥98% purity: Pharmaceutical grade. This is the standard expected for injectable medications intended for human use.
• 95–97% purity: High purity, acceptable for many research applications but below pharmaceutical standards.
• 90–94% purity: Moderate purity. Significant impurities present. Not recommended for injection.
• <90% purity: Low purity. Should not be used for any human application.

When reviewing HPLC data, look for the chromatogram (a graphical trace showing peaks). The main peak should be tall and sharp, with very small or no secondary peaks. The purity is calculated as the area of the main peak divided by the total area of all peaks [3].

4. Understanding Identity by Mass Spectrometry

Mass spectrometry (MS) confirms that the molecule in the vial is actually the peptide it claims to be. The technique measures the mass-to-charge ratio (m/z) of ionized molecules. For semaglutide, the theoretical molecular weight is approximately 4,113.58 Da. The observed mass on the COA should match within a narrow margin (typically ±2 Da) [4].

Common mass spectrometry methods include:

• MALDI-TOF: Matrix-Assisted Laser Desorption/Ionization Time-of-Flight. Fast, suitable for peptides. Most common for COAs.
• ESI-MS: Electrospray Ionization Mass Spectrometry. Higher resolution, can detect post-translational modifications and adducts.
• LC-MS: Liquid Chromatography coupled with Mass Spectrometry. Combines separation with identification for superior analysis.

5. Endotoxin Testing

Endotoxins are lipopolysaccharides (LPS) found in the cell walls of Gram-negative bacteria. They can cause fever, inflammation, sepsis, and organ failure if injected in sufficient quantities. The USP limit for parenteral (injectable) products is <5 EU/kg/hour for non-intrathecal routes. For a peptide COA, the result should typically read <5 EU/mg or specify "below detection limit" [5].

6. Red Flags: Signs of a Fake or Unreliable COA

Not all COAs are created equal. Watch for these warning signs:

• No laboratory name or accreditation number: Legitimate labs include their name, address, and accreditation (e.g., ISO 17025, DEA registration, state license).
• Missing batch/lot number: Every COA should reference a specific batch. If you cannot match it to your product, the COA may be generic.
• Round numbers for purity: A result of exactly "99.00%" is suspicious. Real analytical results have decimal variation (e.g., 98.73%).
• No chromatogram or mass spectrum image: Legitimate third-party COAs typically include the actual analytical traces.
• Missing endotoxin or sterility testing: Essential for any injectable product.
• Vendor-generated (not third-party): A COA produced by the vendor themselves, rather than an independent lab, has an inherent conflict of interest.
• Template inconsistencies: Different fonts, misaligned data, or formatting errors may indicate document manipulation.
• No date of analysis: Testing dates should be present and reasonably recent relative to the batch manufacturing date.
• Impossibly high purity: Claims of 99.9%+ purity for a complex peptide like semaglutide are unrealistic with current synthesis methods.

7. How to Verify a COA Is Legitimate

1. Contact the testing laboratory directly. Call or email the lab listed on the COA and provide the batch/lot number. Ask them to confirm the results match their records.
2. Check the lab's accreditation. Verify ISO 17025 accreditation through the relevant accreditation body's public database (e.g., A2LA, ANAB, PJLA).
3. Cross-reference the batch number with the label on your vial. They must match exactly.
4. Look for a unique report ID or certificate number that the lab can verify.
5. Submit your own sample for independent testing if the product cost justifies it. Services like Janoshik Analytical and Valisure offer consumer peptide testing.

8. Reputable Third-Party Testing Laboratories

The following independent laboratories are commonly used in the peptide industry for third-party verification:

9. USP Reference Standards

The United States Pharmacopeia (USP) establishes reference standards for pharmaceutical substances. When a testing lab performs identity or purity analysis, they compare their results against a USP Reference Standard — a highly characterized, authenticated sample of the substance. For newer peptides like semaglutide, USP reference standards (USP Semaglutide RS) are available and should be used as the comparator in any rigorous analysis [6].

10. Example COA Parameter Summary

Below is an example of what a satisfactory COA for compounded semaglutide might look like: