How to read a peptide Certificate of Analysis

If you've ever compared research peptide vendors, you know the pattern: everyone claims "≥99% purity." Almost none show a real Certificate of Analysis (COA), and the ones that do often reuse a single generic document across dozens of batches. That is a red flag, not evidence.

This guide walks through what a real COA looks like, what the numbers mean, and the exact checks you can run in under a minute to filter serious suppliers from repackagers.

What a COA is (and isn't)

A Certificate of Analysis is a batch-specific test report issued by a third-party analytical laboratory, not the vendor. It describes exactly what was measured for this vial's lot number — not the vendor's product line in general.

A COA that isn't tied to a lot number is not a COA. It's marketing.

The four sections that must be present

1. Identity — LC-MS or MALDI-TOF

Mass spectrometry confirms that the peptide sequence is what the label claims. A pass looks like:

• Observed mass and theoretical mass listed side by side, in Daltons
• Difference well below 1 Da (typically 0.1–0.5 Da is normal precision)
• Sequence written out in single-letter amino acid code

If your COA lists only "identity: pass" without numbers, that's a summary — ask for the raw MS report.

2. Purity — HPLC (reverse-phase, C18)

High-Performance Liquid Chromatography separates the target peptide from impurities and truncated sequences. What you're looking for:

• A chromatogram image (peak trace) attached to the report
• The main peak integrated to a percentage — this is your purity number
• ≥98% is standard for reference-grade research material; ≥99% is premium
• The retention time (RT) noted in minutes

The most common trick is showing a peak percentage without the chromatogram. Without the trace, you can't tell whether that "99%" is a clean single peak or a ragged mountain range.

3. Endotoxin — LAL assay

Endotoxin measures bacterial contamination. It matters even for research reagents because endotoxin can invalidate cell-culture experiments.

• Reported in EU/mg (Endotoxin Units per milligram)
• Acceptable levels for research: ≤5 EU/mg; lower is better
• USP quality vendors report <0.5 EU/mg

4. Residual solvents & water content

Optional for pure research use, but present on premium COAs:

• Karl Fischer titration for water content (typically <5%)
• Residual acetonitrile / TFA if peptide synthesis used those solvents

The 30-second fake-COA check

Here's the fastest triage in the industry:

1. Look for the third-party lab name and phone. No lab named on the COA? Fake. The three most-cited labs for peptides are Janoshik (Czech Republic), Boston Analytical, and Cambridge Isotope.
2. Check the report number. Serious labs publish an online verifier. Janoshik lets you enter the report number at their website to confirm authenticity.
3. Match the lot number. The lot on the COA must match the lot printed on the vial you receive. If they differ, the COA doesn't apply to your material.
4. Look at the date. COAs older than 12 months on a fresh vial are suspicious — either the peptide is old inventory or the vendor is reusing an old test.

What we do at biotech.bio

Every batch we sell has its own Janoshik report. You can look up any lot number in our COA Library without needing an account. The QR code on the vial links directly to that lot's verification page — the same page a researcher can hand to a colleague as evidence.

If you want the machine-readable summary of what to look for, here it is:

| Section | What to check | Pass criteria | |---|---|---| | Identity | LC-MS observed vs theoretical mass | Δ < 1 Da | | Purity | HPLC chromatogram + peak % | ≥98% (research) / ≥99% (premium) | | Endotoxin | LAL assay result | ≤5 EU/mg | | Lot match | Vial label vs COA header | Identical string | | Third-party lab | Named lab + verifier link | Janoshik / Boston Analytical / equivalent |

If a vendor can't produce this per-lot on request, they haven't tested the material — they've bought the branding.