How to Read a Certificate of Analysis (COA): A Complete Guide for Peptide Buyers

A Certificate of Analysis (COA) is your primary tool for verifying peptide quality. Whether you're a researcher, clinician, or informed consumer, understanding how to read and interpret a COA is essential for ensuring you receive what you paid for.

This guide breaks down every section of a peptide COA, explains what the numbers mean, and shows you how to spot red flags that indicate poor quality or potential fraud.

What Is a Certificate of Analysis?

A Certificate of Analysis is a document issued by a manufacturer or testing laboratory that certifies the identity, purity, and quality of a specific batch of product. For peptides, a proper COA should include:

• Product identification (peptide name, sequence, molecular weight)
• Batch/lot number (links the COA to your specific vial)
• Purity analysis (usually via HPLC)
• Identity confirmation (usually via mass spectrometry)
• Additional testing (endotoxins, sterility, residual solvents)
• Test date and laboratory information

Think of a COA as a "report card" for your peptide batch. A legitimate COA tells you exactly what's in the vial and whether it meets quality specifications.

The Five Critical Sections of a Peptide COA

1. Product Identification

The top of a COA should clearly identify:

**Why it matters:** The batch number connects the COA to your actual product. If a vendor can't provide a COA matching your batch number, that's an immediate red flag.

2. HPLC Purity Analysis

High-Performance Liquid Chromatography (HPLC) is the gold standard for measuring peptide purity. This test separates compounds in a sample and measures their relative concentrations.

What the numbers mean:

• Purity percentage: Typically shown as ">98%" or "99.2%"
• Retention time: When the main compound elutes from the column
• Peak area: Relative abundance of the main compound vs. impurities

Interpreting HPLC results:

**Red flags in HPLC data:**

• Purity claims without an actual chromatogram image
• Chromatograms showing multiple large peaks (indicates impurities)
• Missing retention time or peak area data
• Round numbers like exactly "99.00%" (suggests fabrication)

3. Mass Spectrometry (MS) Confirmation

Mass spectrometry confirms the molecular identity of the peptide by measuring its mass-to-charge ratio. This is how you verify you received the correct compound.

Key MS data points:

• Observed mass: The actual measured molecular weight
• Theoretical mass: The expected molecular weight based on the sequence
• Mass accuracy: How close the observed mass is to theoretical

Acceptable mass accuracy:

For peptides, the observed mass should be within ±0.1% of the theoretical mass. For BPC-157 (MW 1419.53):

• Acceptable range: 1418.11 - 1420.95
• If observed mass is 1425.8, that's a different compound

Types of MS you'll see:

• MALDI-TOF: Common, good for peptide identification
• ESI-MS: Very accurate, shows multiple charge states
• LC-MS: Combines HPLC separation with MS identification

4. Endotoxin Testing (For Injectable Peptides)

Endotoxins are bacterial toxins that can cause severe reactions if injected. This test is critical for any peptide intended for injection.

Understanding endotoxin results:

• Unit: Endotoxin Units per milligram (EU/mg)
• Specification: Typically less than 5 EU/mg for research peptides
• Pharmaceutical standard: Less than 0.25 EU/mg

Test method:

• LAL (Limulus Amebocyte Lysate): Standard endotoxin detection method
• rFC (Recombinant Factor C): Newer, animal-free alternative

Red flags:

• No endotoxin testing on injectable peptides
• Results showing "Pass" without actual numbers
• Missing test method information

5. Additional Quality Tests

Depending on the peptide and intended use, a comprehensive COA may include:

Sterility Testing:

• Confirms absence of microbial contamination
• Essential for injectable products
• Should reference USP 71 or equivalent standard

Residual Solvent Analysis:

• Measures leftover solvents from synthesis (ACN, TFA, etc.)
• Important for safety
• Should be below ICH Q3C guidelines

Water Content (Karl Fischer):

• Measures moisture content
• Affects peptide stability and accurate dosing
• Typically less than 10% for lyophilized peptides

Peptide Content:

• Net peptide content as percentage of total weight
• Accounts for counterions, moisture, etc.
• Typically 80-90% for acetate salts

How to Verify a COA Is Legitimate

Step 1: Check Batch Number Matching

Your product vial should have a batch/lot number that exactly matches the COA. If they don't match, the COA doesn't apply to your product.

Step 2: Look for Third-Party Verification

The most trustworthy COAs come from independent third-party laboratories, not the manufacturer. Look for:

• Independent lab name and address
• Lab accreditation (ISO 17025, GLP)
• Contact information for verification
• Unique report number

Step 3: Verify the Lab Exists

For third-party COAs, verify the laboratory:

• Search for the lab online
• Check their accreditation status
• Contact them to verify the report number (reputable labs will confirm)

Step 4: Analyze the Data Consistency

Cross-check the data:

• Does the observed mass match the theoretical mass for that peptide?
• Is the sequence correct for the named peptide?
• Are the test dates reasonable (recent, not years old)?
• Do the methods match standard industry practices?

Step 5: Request Raw Data

For high-stakes purchases, ask for:

• Raw HPLC chromatogram files
• Raw MS spectra files
• Multiple pages showing all test details

Legitimate vendors will provide this. Scammers typically can't.

Common Red Flags in Peptide COAs

Generic or Template COAs

• Same document format used for all products
• No specific batch numbers
• Suspiciously identical results across different products

Missing Key Information

• No molecular weight verification (MS)
• No batch/lot number
• No testing date
• No laboratory identification

Too-Perfect Numbers

• Exactly 99.00% purity (real results have decimals)
• All tests showing exactly at specification
• Round numbers throughout

Inconsistent Data

• Observed mass doesn't match sequence
• Test dates in the future
• Newer test dates than manufacture date

Unverifiable Sources

• No lab contact information
• Lab doesn't exist when searched
• Lab denies issuing the report
• "In-house" testing with no third-party verification

Understanding Third-Party Testing

Why Third-Party Testing Matters

Manufacturer COAs have an inherent conflict of interest—they're testing their own products. Third-party testing by independent laboratories provides unbiased verification.

What Third-Party Labs Test For

Reputable third-party peptide testing labs like Janoshik, Valisure, or accredited analytical laboratories test for:

1. Identity confirmation (is this the right peptide?)
2. Purity (how pure is it?)
3. Sterility (is it free from microbial contamination?)
4. Endotoxins (is it safe for injection?)
5. Heavy metals (are there toxic contaminants?)

How to Get Your Own Third-Party Testing

If you want independent verification:

1. Select an accredited analytical laboratory
2. Submit a sample following their instructions
3. Request specific tests (HPLC, MS, endotoxin)
4. Compare results to the manufacturer's COA

Cost is typically $100-300 per sample for basic testing.

Practical COA Checklist

Use this checklist when evaluating any peptide COA:

Essential Elements:

• Batch/lot number present and matches product
• Peptide name and sequence clearly stated
• Molecular weight matches known value for peptide
• HPLC purity >95% with chromatogram
• Mass spectrometry confirming identity
• Test date within reasonable timeframe

For Injectable Peptides:

• Endotoxin testing with actual values
• Sterility testing results
• Residual solvent analysis

Quality Indicators:

• Third-party lab identified
• Lab contact information verifiable
• Accreditation mentioned (ISO, GLP)
• Specific methods referenced (USP, EP)

Red Flag Check:

• No suspiciously round numbers
• Data internally consistent
• Not a generic template
• Not suspiciously identical to other batch COAs

Conclusion

Reading a COA effectively is one of the most important skills for anyone purchasing peptides. A legitimate, comprehensive COA provides confidence that you're receiving a pure, properly identified product. Conversely, missing information, inconsistent data, or unverifiable claims should prompt serious questions about the vendor's reliability.

When in doubt:

1. Ask for additional documentation
2. Request third-party testing
3. Verify the laboratory independently
4. Compare COAs across multiple batches

The extra diligence is worth it—both for safety and for ensuring you get what you pay for.

---

Last updated: January 2026

Related Articles:

• How to Evaluate Peptide Providers: The 5-Tier Framework
• Understanding Third-Party Testing for Peptides