How to Read a Peptide Certificate of Analysis (COA)

A Certificate of Analysis is the single most useful document for judging a research peptide — and one of the most misread. A COA is where a vague brand claim like "99% pure" either gets backed by data or falls apart. This guide explains, in plain terms, what each part of a peptide COA means, what "good" looks like, and the red flags that separate a real analytical report from a decorative PDF. It is educational and makes no health, therapeutic, or performance claims.

What a COA actually is

A Certificate of Analysis is a lab report describing what a specific batch of material was tested for and what the results were. For a peptide, it answers two questions:

1. Identity — is this actually the molecule the label says?
2. Purity — how much of the sample is that molecule, versus everything else?

A COA is only meaningful if it corresponds to the exact lot in your hand. This is the first and most important idea in this entire guide, so it gets its own section.

The single most important check: lot matching

Every batch of peptide gets a lot number (sometimes "batch number"). It's printed on the vial or its label. A legitimate COA lists that same lot number.

If the lot number on the COA doesn't match the lot number on the vial, the COA tells you nothing about what you have — it's a report on some other batch. This is the most common way a genuine-looking document is used misleadingly: a real COA from one good batch gets shown for every subsequent batch.

Do this first: find the lot number on the vial, find the lot number on the COA, confirm they're identical. If a seller can't produce a lot-specific COA, treat everything else on the document as unverified.

HPLC purity: the headline number

The purity figure almost always comes from HPLC — High-Performance Liquid Chromatography. Here's the concept without the jargon:

HPLC pushes the dissolved sample through a column that separates its components by how they interact with the material inside. Each distinct component comes out at a different time and registers as a peak on a graph (the chromatogram). The target peptide is one big peak; impurities and byproducts are smaller peaks.

Purity is reported as the target peak's area as a percentage of all peak area. So "99.2% by HPLC" means the main peptide accounts for 99.2% of what the detector saw.

What "good" looks like:

• One clearly dominant peak with only small peaks around it.
• Purity generally ≥ 98% for a quality research peptide; many report ≥ 99%.
• The reported number should be backed by an actual chromatogram (the graph), not just stated in text.

What's concerning:

• A cluster of sizable secondary peaks — that's synthesis byproducts or degradation.
• A purity number with no chromatogram to support it.

Reading the chromatogram itself

If the COA includes the HPLC graph (it should), you don't need to be a chemist to sanity-check it:

• The x-axis is time (retention time), the y-axis is detector signal.
• Look for one tall, sharp peak that dominates the picture. That's your peptide.
• Small bumps near the baseline are normal — no synthesis is perfect.
• Several large peaks competing with the main one is a red flag, even if the stated purity number looks high.

A clean chromatogram and a high purity number should agree with each other. If the graph looks messy but the number says 99.5%, be skeptical.

Mass spectrometry: confirming identity

Purity tells you how much of one thing you have; it doesn't by itself prove that thing is the right peptide. That's what Mass Spectrometry (MS) is for.

MS measures the molecular weight of the peptide. Every peptide has a known, calculable mass based on its amino-acid sequence. A good COA shows:

• The theoretical (expected) molecular weight, and
• The observed molecular weight from the MS run.

If the observed mass matches the expected mass, the identity is confirmed. A COA with a strong HPLC purity number and a matching MS result is far more trustworthy than one with purity alone — purity without identity can't rule out "very pure… of the wrong molecule."

Other lines you may see

Depending on the lab and peptide, a COA may also report:

• Appearance — e.g., "white lyophilized powder." A basic sanity check.
• Net peptide content — the actual peptide fraction of the powder (the rest can be water and counter-ions like acetate). Distinct from HPLC purity.
• Water / moisture content — often by Karl Fischer titration.
• Acetate content — a common residual from synthesis.
• Sequence — the amino-acid sequence the batch was made to.

None of these replace the core trio — lot match, HPLC purity + chromatogram, MS identity — but they add confidence.

Red flags checklist

Treat a COA with suspicion if:

• ❌ No lot number, or a lot number that doesn't match the vial.
• ❌ No third-party lab named — an in-house-only number is a claim, not verification.
• ❌ A purity figure with no chromatogram to back it.
• ❌ No MS / identity data at all.
• ❌ An image-only PDF with numbers typed on it and no actual instrument output.
• ❌ The same COA reused across obviously different batches or dates.
• ❌ Results that are suspiciously perfect (e.g., "100.0%") with nothing supporting them.

What a strong COA looks like, in one line

A lot number that matches your vial, an HPLC purity of ~98–99%+ shown with its chromatogram, and a mass-spec result whose observed weight matches the expected weight — ideally from a named third-party lab. Hit those, and the headline "purity" number actually means something.

Frequently asked questions

What purity should I look for?
For research peptides, ~98% and up is typical for quality material, with many reporting 99%+. But the number only matters if a chromatogram and a matching lot number back it.

Is a high purity number enough on its own?
No. Purity (HPLC) tells you how much of one component you have; identity (MS) confirms it's the right molecule. You want both.

What's the difference between "purity" and "net peptide content"?
HPLC purity is the target peak vs. all peaks. Net peptide content is how much of the total powder is actually peptide (the rest being water, salts, counter-ions). They measure different things.

Why does third-party testing matter?
An in-house number is a self-reported claim. A COA from an independent, named analytical lab is verification someone else can check.

A note on where COAs come from

At The Peptide Review's supported source, NovaForge Labs, every lot is third-party HPLC-tested with a lot-specific Certificate of Analysis — which is exactly the standard this guide describes. Whatever source you evaluate, apply the same three checks: lot match, purity with a chromatogram, and identity by MS.

Want to practice? The best way to get comfortable reading a COA is on real ones. You can browse actual, lot-specific Certificates of Analysis here and try the three checks yourself — find the lot number, read the HPLC purity off the chromatogram, and confirm the mass-spec identity. After a few, the pattern becomes second nature.

For the related question of keeping a verified peptide stable once you have it, see how to store peptides.

The Peptide Review publishes educational summaries and reference guides. Nothing here is medical advice, and nothing here describes a use for any product. Compounds discussed are reference materials for qualified in-vitro laboratory research only and are not drugs, supplements, or products for human or animal consumption.