How to Read a Peptide Certificate of Analysis (COA)

A Certificate of Analysis (COA) is the primary quality document for research peptides. It provides objective, laboratory-measured data on the identity, purity, and quality of a specific peptide batch. Reading a COA correctly is essential for evaluating supplier quality and ensuring research reproducibility.

HPLC Purity — The Headline Number

High-Performance Liquid Chromatography (HPLC) purity is the most important metric on any COA. It measures what percentage of the total material is the intended peptide versus impurities — truncated sequences, deletion sequences, oxidized variants, and other synthesis byproducts.

What to look for:

• Research-grade peptides should show ≥95% HPLC purity.
• Premium quality is ≥98%.
• Below 95% should be questioned — a higher fraction of the sample is unknown impurities.

The COA should include the actual chromatogram — the graphical trace showing peaks. The main peak (your peptide) should dominate, with minimal secondary peaks. A number without the chromatogram provides less verification. Reverse-phase HPLC (RP-HPLC) with C18 columns and UV detection at 214 nm or 220 nm is the most common method.

Mass Spectrometry (MS) — Identity Confirmation

Mass spectrometry confirms the peptide is the correct molecule. It measures molecular weight and compares it to the theoretical weight of the target sequence.

What to look for:

• Observed mass should match theoretical mass within ±1 Da.
• Common notations: ESI-MS (Electrospray) or MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight). Both are valid.

HPLC alone cannot confirm identity — a sample could be 99% pure but be the wrong peptide. MS provides that check. HPLC + MS together = purity and identity.

Appearance and Physical Description

Most research peptides should appear as a white to off-white lyophilized powder. Significant discoloration (yellow, brown) may indicate oxidation or degradation. Some peptides (e.g., tryptophan-containing sequences) are naturally slightly off-white.

Solubility

The COA indicates recommended solvents and expected solubility. Most peptides are soluble in sterile or bacteriostatic water. Hydrophobic peptides may require a small amount of DMSO or acetic acid to dissolve initially. Follow COA guidance for optimal dissolution.

Batch Number and Date

Every legitimate COA should have a unique batch/lot number tying the document to a specific production run. This enables traceability — if a quality issue is discovered, the batch number identifies affected vials. A synthesis or testing date should also be present.

Be cautious of COAs without batch numbers: they may be generic templates rather than batch-specific analyses.

Red Flags to Watch For

• Generic COAs without batch numbers — may not reflect your actual product.
• Missing MS data — HPLC alone does not confirm identity.
• Purity below 95% without explanation.
• No chromatogram included — a bare number is less trustworthy.
• COA from a different company than the seller — indicates reselling without independent verification.
• Identical COAs across different batches — suggests the document is not batch-specific.

Bottom Line

A COA is a falsifiable quality claim. If it is specific (chromatogram + MS + batch number + date), you can evaluate it. If it is vague (just a purity percentage with no supporting trace), it is marketing copy, not documentation.

Educational content only. Not medical advice.