A Certificate of Analysis is the single most important document in research-peptide purchasing. It’s the lab’s sworn statement of what’s actually in the vial. And yet most COAs get a five-second glance before they’re filed away.
That’s a missed opportunity. A COA is dense, but it’s readable. This guide walks through every section of a real research-peptide COA, top to bottom, so you can hold your own document next to it and know exactly what you’re looking at.
At Elutide, every batch is tested by an independent, US-accredited third-party lab, and a lot-specific COA ships in the box with every order. You can also pull any certificate from our COA library. Grab one and follow along.
The Header: Who, What, and Which Batch
The top of a legitimate COA answers three questions before you read a single number. Who performed the testing. What material was tested. And which specific batch the results belong to.
The Lab’s Identity
The issuing laboratory’s name, address, and contact information should appear prominently. This is the party standing behind the data. If the header shows only the seller’s logo and no lab, you’re reading marketing, not analysis.
Product and Lot Number
The certificate should name the compound (for example, BPC-157 or TB-500), its catalog or sample ID, and a lot number. The lot number is the whole game. It ties this exact document to the exact production batch your vial came from. A COA without a lot number certifies nothing in particular.
Dates
Look for a sample-received date, an analysis date, and a report-issued date. They should form a sensible timeline: the sample arrives, testing happens, the report follows. Compare these against the lot’s production window. Dates that predate the batch, or a report issued months before the sample supposedly arrived, are a problem we’ll return to in the red-flags section.
HPLC Purity: The Headline Number
High-performance liquid chromatography (HPLC) is the workhorse of peptide purity testing. The instrument pushes a dissolved sample through a separation column under pressure. Different molecules travel at different speeds, so the target peptide and its impurities exit the column at different times.
A detector records what comes out, producing a chromatogram: a plot of signal intensity over time. Each compound appears as a peak. The purity figure on your COA is calculated from peak areas. If the main peak accounts for 99.1% of the total peak area, the reported purity is 99.1%.
On the COA, this section typically shows:
- The result, stated as a percentage (e.g., “Purity (HPLC): 99.24%”).
- The method, including column type, mobile phase, gradient, detection wavelength (often 214 nm or 220 nm for peptides), and run time.
- A chromatogram summary, sometimes the full trace, sometimes a peak table listing retention times and area percentages.
The peak table deserves a look. A single dominant peak with a few tiny satellites is what a clean batch looks like. The satellites are usually closely related species: truncated sequences missing a residue, or minor synthesis byproducts. Their combined area is the flip side of the purity number.
One caution: a purity percentage without a stated method is an assertion, not a measurement. “99% pure” means little unless you know what instrument, column, and detection settings produced it. For a deeper dive into what the number does and doesn’t capture, see our companion piece on what HPLC purity testing actually measures.
Mass Spectrometry: Confirming Identity
HPLC tells you how clean the material is. It does not, on its own, tell you the material is the right molecule. That’s the job of mass spectrometry.
A mass spectrometer ionizes the sample and measures the mass-to-charge ratio of the resulting ions. Because every peptide sequence has a precise, calculable molecular weight, the measured mass acts like a molecular fingerprint.
On the COA, this section usually presents two numbers side by side:
| Field | Example | What it means |
|---|---|---|
| Theoretical (expected) mass | 1419.53 Da | Calculated from the peptide’s sequence |
| Observed (found) mass | 1419.6 Da | What the instrument actually measured |
Those two values should agree within the stated tolerance of the method, typically a fraction of a dalton for ESI-MS. Close agreement confirms the vial contains the intended sequence rather than a lookalike, a failed synthesis, or something else entirely.
Some COAs report multiple charge states (the same molecule carrying 2+ or 3+ charges) that all deconvolute to the same parent mass. That’s normal and, if anything, reassuring. We unpack the technique fully in how peptide identity is confirmed by mass spectrometry.
Endotoxin: The LAL Result
Endotoxins are lipopolysaccharide fragments from the outer membranes of certain bacteria. They can survive processes that remove the bacteria themselves, so labs test for them directly using the Limulus Amebocyte Lysate (LAL) assay, a reagent derived from horseshoe crab blood that reacts in their presence.
On the COA, the result is reported in endotoxin units, usually EU/mg or EU/vial. You’ll typically see either a measured value or a threshold statement like “< 0.5 EU/mg.” The “less than” format means the level fell below the assay’s detection or specification limit.
Check that the units make sense and that a specification limit is stated alongside the result. A number with no limit gives you nothing to judge it against. Our article on what LAL results mean covers the assay formats (gel-clot, turbidimetric, chromogenic) in detail.
Appearance and Description
The humblest line on the certificate still earns its place. A typical entry reads: “Appearance: White lyophilized powder.” This is a simple visual check against specification.
It matters because lyophilized peptides have a characteristic look, a white to off-white cake or powder. Discoloration or an unexpected physical form can flag moisture exposure, degradation, or a handling problem somewhere upstream. If your vial doesn’t match the description on its own COA, stop and contact the seller.
The Accreditation Block
Near the header or footer, a credible COA identifies the lab’s accreditation, most commonly ISO/IEC 17025, the international standard for testing and calibration laboratories. The block should include the accreditation body and a certificate number you can verify with that body directly.
Accreditation means an independent auditor has examined the lab’s methods, equipment calibration, and quality system. It doesn’t make any single result infallible. It does mean the lab operates under documented, externally checked procedures, which is the difference between a measurement and a guess.
Signatures and Approval
The certificate should close with the name, title, and signature (wet or digital) of the analyst and/or a quality reviewer, plus the approval date. Two signatures, one for the person who ran the tests and one for the person who reviewed them, reflect standard lab practice: nobody approves their own work.
An unsigned COA is a draft. Read it as one.
Red Flags: When a COA Doesn’t Add Up
Now the defensive checklist. Hold any COA, ours included, against these tests:
- Not lot-specific. The document lacks a lot number, or the lot on the paper doesn’t match the lot on your vial. A generic “representative” COA recycled across batches tells you about some batch, once. Not yours.
- No lab name. If you can’t tell who performed the analysis, no one is accountable for it. Seller-branded certificates with no identifiable laboratory are the most common failure in this market.
- Purity with no method. A percentage floating free of any HPLC conditions, column, or wavelength. Real labs document methods because results are meaningless without them.
- Dates that don’t line up. An analysis date before the batch existed. A report issued the same day the sample was received for a multi-assay panel. A COA dated years ago attached to a “fresh” lot. Timelines should be boring and plausible.
- Identity missing entirely. Purity alone, with no mass-spec confirmation, leaves open the question of purity of what.
- Suspiciously perfect numbers. A wall of “100.00%” results across every batch and every compound. Real instruments produce real variance.
- No signatures, no accreditation, no contact info. Any one of these alone is a question. All three together is an answer.
A Quick Reference Walkthrough
Here’s the whole document in one pass, in the order you’ll usually encounter it:
| Section | What to verify |
|---|---|
| Header | Lab name and address present; compound named; lot number matches your vial |
| Dates | Received, analyzed, issued — in that order, consistent with the lot |
| HPLC purity | Percentage stated with method details; chromatogram or peak table included |
| Mass spec | Expected vs. observed mass agree within tolerance |
| Endotoxin (LAL) | Result in EU/mg or EU/vial with a stated specification limit |
| Appearance | Description matches what’s physically in your vial |
| Accreditation | ISO/IEC 17025 or equivalent, with a verifiable certificate number |
| Signatures | Analyst and reviewer signed and dated |
Verification Should Be Easy
We built Elutide around a simple idea: “Purity You Can Verify.” Every order ships with its lot-specific COA in the box, and the product insert carries a QR code that resolves to a public verification page for that exact lot. You can also browse every certificate we’ve ever published in the COA library, or read about our testing standards on our quality page.
A COA rewards the ten minutes it takes to read one properly. Now you know where to look.
For Research Use Only. Not Intended for Human Consumption.