How to Read a Peptide Certificate of Analysis (COA)

A certificate of analysis is only useful if you know what each line means and what it leaves out. This guide walks through a real laboratory report, field by field.

What a COA is (and isn’t)

A certificate of analysis (COA) is a report issued by a testing laboratory for one specific lot of a material. It lists the tests that were run, the method or standard used for each, the acceptance specification, and the measured result.

A COA tells you what was measured in the sample the lab received. It does not by itself prove anything about other lots, about storage or shipping conditions afterwards, or about tests that were not run. That last point matters: many standard peptide panels do not include endotoxin, sterility or particulate testing, and a well-written report says so.

If a term is unfamiliar, see our peptide research glossary.

Step 1: Check who issued it

• Laboratory name and contact details should be printed on the report (address, phone, email or website).
• Report number and issue date let you ask the lab to confirm the document is genuine.
• Signatures or analyst names indicate the report was reviewed, though they are not proof on their own.

An independent laboratory is one that is separate from the company selling the material. Reports that carry no lab identity at all cannot be checked.

Step 2: Match the header fields to the vial

Field	What to look for
Testing material	The compound name should match what you are holding.
Lot / batch number	Must match the lot printed on the vial or packing slip. A COA for a different lot tells you nothing about yours.
Date tested and report date	Dates should be sensible: testing before the report is issued, and not long before the material was made.
Customer / manufacturer	Shows who submitted the sample. If it names a different company, ask why.
Labeled content	The amount claimed on the label (for example, “10 mg”). This is the number potency is measured against.
Visual description	What the lab received (vial, cap, label, powder colour). Useful for confirming it was the same product.

Step 3: Appearance and mass

Most reports begin with appearance (typically “white powder” for a lyophilized peptide) and a gross mass of the contents. The mass is the weight of everything in the vial, which is usually more than the peptide alone, because lyophilized products often contain a bulking agent or other excipients. Do not read the mass line as “the amount of peptide”.

Step 4: Identity — is it the right compound?

Identity tests confirm the sample is the labeled compound:

• FTIR (Fourier-transform infrared spectroscopy) compares the sample’s spectrum with a reference. It shows the characteristic bands of a peptide and can indicate the presence of fillers, but it is a fingerprint comparison, not a measurement of molecular weight.
• Mass spectrometry (MS or LC-MS) measures the molecular mass, which can be checked against the expected mass for that sequence.

For how to read the mass spectrometry result in detail, see how to read a peptide mass spectrometry report.

A report should say which method was used and what the conclusion was. See our companion guide on how purity and identity are tested.

Step 5: Purity (HPLC)

HPLC purity is the share of the total detected signal that belongs to the main peak in a chromatogram. A result of “99.5%” means that, under that method, 99.5% of the integrated peak area was the main component.

For a closer look at the chart behind this number, see how to read a peptide HPLC chromatogram.

Three cautions help you read the number correctly:

1. Purity is relative, not absolute. It says how clean the peptide is compared with other detected peptide-related species. It does not say how much peptide is in the vial.
2. The method matters. Detection wavelength, column and gradient change what is seen. Peptide bonds absorb strongly at roughly 214–220 nm, while 280 nm mainly detects aromatic residues such as tryptophan and tyrosine, so reports at different wavelengths are not directly comparable.
3. Ask for the chromatogram. A trustworthy report includes it. A single clean peak with a stated retention time and area is easy to inspect; a result with no trace is not.

Step 6: Content (potency) versus purity

These two are often confused.

• Purity asks: of the peptide-related material, how much is the right molecule?
• Content or potency asks: how much of the right molecule is actually in the vial compared with the label?

A sample can be highly pure and still contain less (or more) peptide than labeled, because of excipients, residual moisture or counter-ions such as TFA salts. Labs usually apply a specification such as a percentage range around the labeled amount, and many reports also include a peptide-to-excipient ratio to show how much of the contents is peptide. When you compare reports, compare these two lines separately.

Many reports also print a peptide-to-excipient ratio. Our guide explains how to read and check it, and a separate guide covers purity versus potency.

Step 7: What the report does not cover

Look for the lab’s own statement of scope. Reports for identity, purity and content typically state that they do not provide information on particulate matter, microbial contamination or endotoxins. Tests for sterility, endotoxin, residual solvents or heavy metals are separate analyses, and if they are not listed they were not done.

Common red flags

• No laboratory name, address or report number.
• No lot number, or a lot number that doesn’t match the vial.
• Results with no chromatogram or spectrum.
• The same result repeated across different products or lots.
• A report for a different compound, or one that looks edited or re-typed.
• Dates that don’t make sense, or a report that is much older than the lot.
• A purity figure with no stated method.

How to verify a COA

For the full step-by-step method, see our guide to verifying a peptide COA. In short:

1. Compare the lot number on the report with the one on your vial.
2. Contact the issuing laboratory with the report number and ask them to confirm it.
3. Check that the report’s dates, compound and customer make sense together.
4. If something doesn’t match, ask the seller to explain before you rely on the material.

See real examples

Every HLX Peptide product page shows the batch record for the lot it covers: lot number, date tested, laboratory and HPLC purity, with the full certificate linked as a PDF. You can browse all of them on our certificates of analysis page, and read how we test on the Quality & Testing page.

All products are sold strictly for laboratory research use only. Not for human or veterinary use, and not a drug, food, or cosmetic.