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Peptide COA Checklist
What to look for — and what to walk away from — before accepting a vial for laboratory use.
A — Identity
Confirms the molecule is the one on the label. Purity does not establish identity.
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Method named
Mass spectrometry (MS/ESI-MS/MALDI-MS) is the standard. Method should be explicit, not implied. -
Theoretical molecular weight shown
Calculated from the target amino-acid sequence; allows you to check the arithmetic independently. -
Observed mass shown and compared
The instrument result next to the theoretical value, within stated tolerance. “Confirmed” with no numbers is insufficient. -
Orthogonal data (if available)
Amino-acid analysis, HPLC retention time vs reference standard, or sequence confirmation strengthens identity significantly.
B — Purity (HPLC)
Quantifies the main-peak fraction. Does not identify what the remaining percentage contains.
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Method is HPLC, peak-area %
Reverse-phase HPLC (RP-HPLC) is standard. “Purity” without naming the technique is unverifiable. -
Result ≥99%
The field benchmark for research-grade synthetic peptides. Below this, the impurity breakdown becomes decisive. -
Chromatogram or representative trace included
The visual record of peaks. A single figure with no trace cannot be cross-checked. Dominant main peak + clean baseline is the target. -
Column and wavelength stated
Conditions define what the method detects. Different wavelengths (UV 210 nm vs 220 nm) can shift apparent purity for some sequences. -
Run date on the chromatogram matches COA date
Chromatograms from an earlier or generic batch can be borrowed. Date consistency is a basic authenticity check.
C — Impurity Profile
The most informative — and most often skipped — section of a peptide COA.
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Individual impurities listed at ≥0.1%
The EMA 2026 synthetic-peptide guideline and ICH Q3A operate around a reporting threshold near 0.1%. Impurities above this level should appear individually, not vanish into “other”.12 -
Nature of major impurities described where possible
Deletion sequences, truncated chains, oxidised or deamidated variants, residual protecting groups — these are the predictable cousins in synthetic peptide chemistry. -
No single impurity dominates unexpectedly
A “99% pure” vial with a single 0.9% impurity differs in risk profile from one with nine 0.1% impurities. -
Residual solvents reported (if relevant)
Particularly for peptides where the synthesis or lyophilisation process uses solvents that could carry over (e.g. acetonitrile, TFA).
D — Batch / Lot Traceability
The most diagnostic section for real-versus-recycled certificates.
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Lot / batch number present on COA
A COA without a lot number describes no specific batch. It is a generic document, not a release certificate. -
COA lot number matches the vial label
Cross-check physically. A mismatch means the certificate was issued for different material. -
Analysis date is plausible
A COA dated years before your order or after your delivery date is a red flag. Dates should precede or closely accompany dispatch. -
Net weight or quantity stated
Relates the certificate to the actual amount in the vial; makes concentration calculations traceable.
E — Water Content & Appearance
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Water content measured and stated
Method: Karl Fischer titration or loss on drying. Lyophilised peptides are hygroscopic; 5–10% water in the vial means 5–10% less peptide per net-weight label. This directly affects reconstitution concentration calculations. -
Appearance described and consistent
Standard: white to off-white lyophilised powder. Discolouration or clumping is a free integrity indicator worth checking against the COA description.
F — Endotoxin (Critical for Cell-Based & In Vitro Work)
Invisible to HPLC. The most common silent confound in immunology and cell-culture models.
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Endotoxin test performed and named
Bacterial endotoxin test (BET/LAL — gel-clot, turbidimetric, or chromogenic) or recombinant Factor C (rFC). The method name must appear; “tested” alone is not sufficient. -
Result expressed in endotoxin units (EU/mg or EU/mL)
A specific measured value, referenced to USP <85> or Ph. Eur. 2.6.14. Acceptable limits depend on the intended research application. -
If not present: supplier can provide on request
For applications where LPS contamination could confound results (cytokine assays, NF-κB reporters, macrophage models), treat an absent endotoxin section as incomplete QC data.
G — Issuing Laboratory
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Laboratory name and location stated
Anonymous “third-party testing” without identifying the lab is unverifiable. Condor Research uses an independent analytical laboratory in the Czech Republic (EU). -
Independent of the manufacturer
Self-certified COAs (manufacturer tests own product without external verification) carry an inherent conflict of interest. -
Accreditation referenced (ISO 17025 or equivalent)
Not universally present on peptide COAs but the strongest quality signal available. Even a named, non-accredited laboratory is better than no laboratory. -
Authorised signatory or stamp
A real laboratory report carries a traceable signature or stamp. A document that could have been edited in a word processor offers weaker assurance.
Red Flags — Walk Away
| What you see | What it means | Verdict |
|---|---|---|
| No batch / lot number | Certificate describes no specific production run | Reject |
| Lot number does not match vial label | Certificate was issued for a different (or fictional) batch | Reject |
| Purity stated; no method named | Unverifiable claim — what instrument, what conditions? | Insufficient |
| “Confirmed” identity with no mass data | Identity not actually demonstrated; just asserted | Insufficient |
| No chromatogram or trace | Peak profile cannot be cross-checked; figure could be fabricated | Insufficient |
| Impurity percentage unaccounted for | What is the other 1–5%? If unlisted, it is uncharacterised | Insufficient |
| No laboratory named | No independent verification; self-certification at best | Insufficient |
| COA dated after your delivery | Temporal impossibility — document was backdated or generic | Reject |
| No water content or appearance data | Incomplete specification per ICH Q6A; affects concentration accuracy | Incomplete |
Quick Reference — What Good Looks Like
| COA Section | Method | Minimum Acceptable |
|---|---|---|
| Identity | Mass spectrometry (ESI-MS / MALDI) | Observed mass vs theoretical, both values shown, within stated tolerance |
| Purity | RP-HPLC, peak-area % | ≥99%, chromatogram included, run date consistent |
| Impurities | HPLC profile vs ICH / EMA thresholds | Individual impurities listed at ≥0.1%; not hidden in “other”12 |
| Water content | Karl Fischer / loss on drying | Stated value; relevant for concentration calculations |
| Appearance | Visual / physical description | Matches vial contents; white lyophilised powder is standard |
| Batch / Lot | Traceability | Number present on COA, matches vial; date plausible |
| Endotoxin | BET/LAL or rFC (USP <85> / Ph. Eur. 2.6.14) | Named method, EU/mg value stated; critical for cell-based assays34 |
| Laboratory | Independent, named, EU preferred | Lab identified; ideally ISO 17025; not the manufacturer itself |
Frequently Asked Questions
What purity should a research peptide COA show?
The field benchmark is ≥99% by HPLC peak-area percentage. Below that, the fraction and identity of what accounts for the remainder becomes the deciding question — a 97% purity with a fully characterised 3% impurity profile may be more informative than a 99% figure with no breakdown.
Can a COA be faked?
Yes. Red flags include no batch/lot number, no named analytical method, no observed mass next to theoretical, and a purity figure with no chromatogram or impurity breakdown. Independent re-testing by an accredited laboratory is the only absolute defence. Ask your supplier if they support third-party re-analysis.
Why is the batch number so important?
A COA describes one specific manufacturing lot. Two batches of the same peptide can differ in purity and impurity profile even from the same manufacturer. Without a batch number that matches the one on your vial, the certificate describes a different — or entirely hypothetical — batch.5
Does HPLC purity cover endotoxin contamination?
No. HPLC is essentially blind to lipopolysaccharide (LPS) endotoxins. A separate bacterial endotoxin test (BET/LAL or rFC) is required. High HPLC purity with no endotoxin data leaves a major confound completely uncharacterised for any cell-based or immunological assay.
What does “independent laboratory” mean?
The testing laboratory is separate from the peptide manufacturer — ideally accredited to ISO 17025 — so the result is not self-certified. Condor Research uses an independent EU analytical laboratory based in the Czech Republic. COAs are issued per batch, not per product line.
How do I read the mass spec result if I am not a chemist?
Look for two numbers: theoretical MW (calculated from the sequence) and observed MW (what the instrument measured). If they match within ±1–2 Da (or the stated tolerance), the backbone is the right sequence. If only one number appears, or the result is written as “confirmed” without showing the observed value, the identity check cannot be independently verified.
Further Reading — Condor Research
- How to Read a Certificate of Analysis (COA) for a Research Peptide — full editorial guide
- What “99% Pure” on a Peptide COA Really Means: HPLC, Mass Spec and the Limits of a Purity Number
- Endotoxins and Sterility: The COA Section Almost Nobody Reads
- How to Choose a Research Peptide Supplier in Europe (2026)
- Why Peptide Experiments Fail: Reproducibility and the Reagent Problem
References
- European Medicines Agency. Guideline on the development and manufacture of synthetic peptides. EMA/CHMP/BWP/651353/2022 (effective 2026). ema.europa.eu
- ICH Harmonised Guideline. Impurities in New Drug Substances Q3A(R2). International Council for Harmonisation, 2006. ich.org
- United States Pharmacopeia. USP <85> Bacterial Endotoxins Test. USP-NF. usp.org
- European Pharmacopoeia. 2.6.14 Bacterial Endotoxins. Council of Europe. edqm.eu
- ICH Harmonised Guideline. Specifications: Test Procedures and Acceptance Criteria for New Drug Substances and New Drug Products Q6A. 1999. ich.org