How to Read a Peptide Lab Report (COA Guide for Beginners)

One of the most important skills in the peptide research space is knowing how to read a Certificate of Analysis (COA). It’s also one of the most overlooked.

A vendor can claim anything on their website. A COA is the actual evidence. Here’s how to read one.

What is a Certificate of Analysis?

A COA is a document from an independent testing laboratory that verifies the identity, purity, and composition of a chemical compound. For peptides, a legitimate COA should confirm:

1. Identity — the compound is what it claims to be
2. Purity — the percentage of the compound that is the target peptide (vs. impurities)
3. Absence of contaminants — no harmful byproducts or solvents

The key word is independent. A COA from the vendor’s own in-house lab is worth far less than one from a third-party laboratory with no financial relationship to the vendor.

The Two Core Tests: HPLC and Mass Spectrometry

HPLC (High-Performance Liquid Chromatography)

HPLC measures purity. The test separates the components in a sample and measures what percentage of the total is your target compound.

What to look for:

• Purity of ≥98% is considered research-grade for most peptides
• Purity of 95–97% is borderline acceptable
• Anything below 95% is a red flag

The COA should show a chromatogram (a graph with peaks) with the main peak labeled and a purity percentage stated clearly.

Mass Spectrometry (MS)

Mass spectrometry confirms identity. It measures the molecular weight of the compound to verify it matches the expected molecular weight of the peptide.

What to look for:

• The observed mass should match the theoretical molecular weight of the peptide (usually within ±1 Da)
• Look for the molecular formula and calculated vs. found mass values
• A peptide with correct HPLC purity but wrong mass means something else is in the vial

Both tests together — HPLC + MS — give you high confidence that the compound is both what it claims to be and is pure enough for research purposes.

What a COA Should Include

A trustworthy COA contains:

• Compound name and CAS number (or sequence identifier for peptides)
• Batch or lot number — matches the product you received
• Test date — should be recent (within 12–18 months)
• Third-party lab name and contact information
• HPLC purity result with chromatogram
• Mass spec result with observed vs. calculated mass
• Appearance (typically white powder or lyophilized cake)

Red Flags to Watch For

• No COA at all — walk away
• COA from the vendor’s own lab — conflicts of interest are real
• COA doesn’t match the batch you ordered — vendor is recycling old test results
• Missing mass spec — purity alone isn’t enough to confirm identity
• Purity listed without a chromatogram — unverifiable numbers
• Test date is years old — degradation is a real concern
• Lab name isn’t searchable online — may be fabricated

Beginner’s COA Checklist

Before ordering from a new vendor, run through this:

• COA is available (not “upon request only”)
• COA is from a named third-party laboratory
• Batch number on COA matches the listing
• HPLC purity ≥98%
• Chromatogram included
• Mass spectrometry confirms molecular weight
• Test date is within 12–18 months
• Lab name returns results in a web search

If a vendor fails more than one of these, keep looking.

Why This Matters

Peptides that fail purity or identity tests aren’t just ineffective — they can contain unknown compounds. In research contexts, bad data from impure compounds is worse than no data. And for anyone considering personal use (which remains outside approved medical practice), the risks of unknown impurities are significant.

The COA isn’t a formality. It’s the foundation of any serious peptide sourcing decision.

The content on PeptideHQ is for informational and educational purposes only and does not constitute medical advice.