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How to Read a Certificate of Analysis (COA)

A Certificate of Analysis is the single most important document when sourcing research peptides. Here's exactly what to look for, what the numbers mean, and the red flags that tell you to walk away.

SEQUENCE Editorial2026-04-15

Before you source any research peptide, there's one document you need to know how to read.

A Certificate of Analysis — usually called a COA — is a lab report produced by an independent third-party testing laboratory. It confirms what a compound actually is, how pure it is, and whether it contains contaminants you don't want in your research.

Without a COA, you're trusting a vendor's word. With one, you have evidence.

This guide walks you through every section of a COA, what the numbers mean, and the red flags that should give you pause.

Why COAs exist

The research peptide market has no central regulatory body governing product quality. Unlike pharmaceutical drugs, which must meet strict standards before reaching patients, peptides sold for research are tested only if the supplier chooses to test them — or if you demand it.

Independent testing fills that gap. A legitimate third-party lab has no commercial relationship with the supplier beyond the testing fee. They don't benefit from reporting good results. Their job is to measure what's in the vial and report it accurately.

This independence is what makes a COA meaningful. An in-house "quality certificate" produced by the supplier itself is not a COA — it's marketing.

The anatomy of a COA

A well-formatted COA will typically include six key sections. Here's what each one means.

1. Product identification

At the top of the document you'll see:

Product Name:     BPC-157
Lot Number:       SEQ-2026-0412
CAS Number:       137525-51-0
Molecular Formula: C₆₂H₉₈N₁₆O₂₂
Molecular Weight:  1419.56 g/mol

What to check:

  • CAS Number — the Chemical Abstracts Service number is a globally unique identifier for every chemical compound. Look it up. BPC-157's CAS should be 137525-51-0. If the number doesn't match the compound you ordered, stop.
  • Molecular Formula and Weight — these should match the known values for the compound. Cross-reference against published literature or a chemistry database.
  • Lot Number — links this report to a specific production batch. Ask: does the lot number on your vial match the lot number on the COA?

2. Purity by HPLC

This is the most important section of the document.

Method:           High-Performance Liquid Chromatography (HPLC)
Purity:           99.3%
Specification:    ≥ 98.0%
Result:           PASS

What it means: HPLC separates the components of a sample by how they behave when passed through a liquid at high pressure. It produces a chromatogram — a graph showing peaks for each component. The compound you ordered should be the dominant peak. Purity is the percentage of the total area represented by that peak.

What to look for:

  • ≥ 98.0% is the accepted minimum for research-grade peptides. Some vendors advertise 99%+ — that's excellent, but 98%+ is the baseline.
  • The purity number should be accompanied by the method (HPLC or UHPLC) and ideally a reference to the chromatogram or the ability to request it.
  • A vague "purity: high" or "purity: pharmaceutical grade" without a specific percentage is not a COA entry — it's filler.

3. Identity confirmation by mass spectrometry

Purity tells you how much of the sample is your compound. Identity confirmation tells you whether that compound actually is what the label claims.

Method:           Mass Spectrometry (MS) / LC-MS
Expected m/z:     710.79 [M+2H]²⁺
Observed m/z:     710.79
Result:           PASS

What it means: Mass spectrometry measures the mass-to-charge ratio of ionised molecules. The observed value should match the expected value for the compound. For peptides, you'll often see multiple charge states reported (like [M+2H]²⁺ for a doubly-charged ion).

What to look for:

  • The observed m/z should match the expected m/z within instrument tolerance (typically ±0.1 Da or better).
  • Some labs report this as a full LC-MS trace. That's a higher level of confirmation.
  • If the identity section is missing entirely, be cautious. HPLC alone can tell you how pure something is, but not what it is.

4. Appearance and physical description

Appearance:       White to off-white lyophilised powder
Result:           Conforms

Simple but worth checking. Most peptides are white or slightly off-white powders after lyophilisation (freeze-drying). Significant colour variation — yellowing, browning, or visible clumping — can indicate degradation, contamination, or improper storage.

5. Water content (Karl Fischer titration)

Method:           Karl Fischer Titration
Water Content:    4.8%
Specification:    ≤ 8.0%
Result:           PASS

What it means: Lyophilised peptides absorb moisture from the air. Water content affects the actual peptide content by weight — if you have 10mg in a vial but 5% of it is water, you have approximately 9.5mg of active compound.

What to look for:

  • ≤ 8% is a reasonable specification.
  • Some vendors don't report this at all, which means the "10mg" on the label may be less peptide than it seems. High-quality suppliers adjust dosing calculations accordingly.

6. Residual solvents

Method:           Gas Chromatography (GC)
Solvents Tested:  Acetonitrile, TFA, DMF, DCM
Results:          All within ICH Q3C limits
Result:           PASS

What it means: Peptide synthesis involves organic solvents, and trace amounts can remain in the final product. Trifluoroacetic acid (TFA) is particularly relevant — it's used in HPLC purification and has been shown to be cytotoxic at elevated levels.

What to look for:

  • Residual solvent testing should be present.
  • TFA should be explicitly tested and reported.
  • Results should conform to ICH Q3C Class 2 or Class 3 solvent limits.
  • Some premium suppliers perform TFA removal steps and can demonstrate near-zero TFA levels.

7. Heavy metals (bonus — not always present)

Method:           ICP-MS
Lead (Pb):        < 0.1 ppm
Mercury (Hg):     < 0.05 ppm
Arsenic (As):     < 0.1 ppm
Cadmium (Cd):     < 0.05 ppm
Result:           PASS

Not all COAs include heavy metals testing, but it's a positive sign when they do. ICP-MS (Inductively Coupled Plasma Mass Spectrometry) can detect trace metals at parts-per-billion levels.

Red flags: when to walk away

A COA can be legitimate or it can be theatre. Here are the warning signs:

The lab name is unfamiliar or unverifiable. Reputable third-party labs have a web presence, publish accreditation information, and can be contacted independently. If the lab name produces zero search results, or the website appears to have been created last week, that's a problem.

The COA is undated or perpetually current. Test results should have a date. If a supplier is using the same COA document for every batch — or if the date is missing — the document is not batch-specific and therefore meaningless.

Purity is reported without a method. "Purity: 99.8%" means nothing without knowing how it was measured. HPLC is the standard. A "proprietary analysis method" is not reassuring.

The lot number doesn't match your order. A COA for Lot A doesn't apply to Lot B. Ask your supplier to confirm which lot your order comes from, and verify the lot number matches the COA.

There's no identity confirmation. HPLC purity alone tells you how pure the dominant compound is — but not whether that compound is what it claims to be. Without identity confirmation (MS, NMR, or LC-MS), a high purity number could theoretically reflect a very pure sample of the wrong compound.

The document is a PDF image, not a native PDF. Scanned images of documents are easy to fabricate. Native PDFs generated directly from lab software are harder to alter. This isn't definitive, but it's a yellow flag.

How to verify a COA independently

If you have the time and the resources, you can go further than reviewing the document:

  1. Contact the lab directly. Most reputable labs will confirm whether a given lot was tested by them if you provide the lot number and compound name. This takes five minutes and immediately distinguishes real from fabricated.

  2. Request the raw chromatogram. For HPLC results, ask to see the actual trace. It should show a dominant peak with integration data. A clean chromatogram is harder to fabricate convincingly than a number on a PDF.

  3. Use independent testing services. In some markets, you can submit a sample to a third-party lab directly for verification. Services like Janoshik (used widely in the research community) test samples for a modest fee.

What SEQUENCE does differently

Every product in our catalogue comes with a batch-specific COA from an accredited third-party laboratory. We make these available directly — not just on request — because we think verification should be the default, not an exception you have to ask for.

We also display the lot number on every order so you can match your product to its specific test report, not a general certificate that might refer to an entirely different batch.

Quality verification shouldn't require detective work. We try to make it simple.

Where to go next

Now that you can read a COA, you're equipped to evaluate suppliers critically — not just take their word for it.

A few related guides that build on this:

Or, if you're ready to source, browse our catalogue — every product includes the COA you just learned to read.

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