Certificate of Analysis (CoA)

A Certificate of Analysis (CoA) is a quality-control document that reports the results of laboratory tests performed on a specific batch of a compound. For research peptides, it is the primary piece of evidence a buyer has to answer two fundamental questions: is this the molecule I ordered? and how pure is it? Without a CoA, you are relying entirely on a supplier's marketing claims.

A meaningful CoA is always tied to a single batch or lot number. Peptides are synthesized in discrete production runs, and purity can vary from batch to batch even at the same facility. A certificate that cannot be matched to the exact vial in your hand — via a lot number printed on both the label and the report — tells you very little. Reputable analyses also state the date of testing, the name of the testing laboratory, and the analytical methods used.

At minimum, a credible peptide CoA includes a high-performance liquid chromatography (HPLC) result for purity and a mass spectrometry (MS) result for identity. Higher-tier certificates add water content (Karl Fischer titration), acetate or trifluoroacetate counter-ion content, and — for injectable research applications — endotoxin and sterility testing.

It is important to understand what a CoA is not. It is not a safety approval, a dosing recommendation, or evidence that a peptide is fit for human use. Most research peptides are sold strictly for research use only and are not approved by the FDA or EMA. This guide explains how to read the data, not how to use the substance. For foundational context, see our overview of what peptides are.

The two headline tests on a peptide CoA measure different things, and confusing them is the single most common mistake buyers make. HPLC measures purity; mass spectrometry confirms identity. You need both, because each is blind to what the other reveals.

HPLC (high-performance liquid chromatography) separates the components of a sample as they pass through a column at different speeds. A detector — usually measuring ultraviolet (UV) absorbance at 214 nm, the wavelength of the peptide bond — records each component as a peak on a chromatogram. The area under the main peak, expressed as a percentage of the total peak area, is reported as the purity. A tall, sharp, well-isolated main peak with minimal smaller peaks indicates a clean synthesis.

Mass spectrometry ionizes the molecules and measures their mass-to-charge ratio, producing a spectrum with a peak at the compound's molecular weight. This is how you confirm the sample is the correct peptide and not a different sequence of similar purity. HPLC alone cannot do this: a 99% pure sample of the wrong peptide would still look excellent on a chromatogram.

Consider a concrete failure mode. A supplier could sell a cheaper, shorter peptide that happens to run cleanly on HPLC and present a beautiful 98% purity chromatogram. Only the mass spectrum would expose that the measured mass does not match the advertised compound. This is why a CoA with HPLC but no MS should be treated with caution — you have half the picture.

A subtle limitation applies to both: standard UV-HPLC only 'sees' components that absorb UV light at the chosen wavelength. Salts, water, and some non-absorbing impurities are invisible to it. That is why complementary tests such as Karl Fischer (water) and counter-ion analysis exist, and why purity should never be read as a statement about the entire physical contents of the vial.

'99% purity' is the most quoted — and most misunderstood — number on a peptide CoA. It almost always refers to HPLC area percent: of all the UV-absorbing material the detector recorded, 99% of the total peak area belonged to the main peak. It is a relative measurement of the peptide fraction, not an absolute measurement of the vial's contents.

Several things are excluded from that figure. A lyophilized peptide typically contains residual water and a counter-ion (commonly acetate or trifluoroacetate, TFA) left over from purification. These can account for a meaningful percentage of the vial's actual mass and are not captured by HPLC purity. A vial labeled '99% pure, 5 mg' may contain somewhat less than 5 mg of the bare peptide once water and salt are subtracted — which is why serious CoAs report net peptide content separately.

The reported percentage also depends on the method conditions: the column, the gradient, the detection wavelength, and the run time. A short gradient can let closely-eluting impurities hide under the main peak, inflating the number. This is why the chromatogram itself matters more than the headline figure — you want to see a clean baseline, a symmetrical main peak, and no suspicious shoulders. A CoA that prints '99%' but shows no chromatogram is asking you to trust a number you cannot verify.

For most research applications, the practical difference between 98% and 99% purity is small; the difference between a genuine 95% and a fabricated 99% is enormous. Rather than chasing the highest decimal, focus on whether the chromatogram supports the claim and whether the identity is independently confirmed by mass spectrometry. Our peptide glossary defines many of these analytical terms in plain language.

The identity check on a CoA rests on a simple comparison: the measured molecular weight from the mass spectrum should match the theoretical molecular weight calculated from the peptide's amino acid sequence. If they agree within the expected tolerance, you have strong evidence that the sample is the advertised compound.

Every peptide has a known theoretical mass. For example, BPC-157 has a molecular weight of approximately 1,419 Da for its 15-amino-acid sequence. If a CoA for BPC-157 reports a measured mass near 1,419, the identity is consistent. A measured mass far from the theoretical value — say, hundreds of Daltons off — signals a wrong sequence, a truncated product, or a mislabeled vial.

Most peptide labs use electrospray ionization (ESI-MS), which often produces multiply-charged ions. You may therefore see peaks at fractions of the true mass (for example, [M+2H]²⁺ at roughly half the molecular weight). A well-presented report either lists the observed charge states or reports the deconvoluted mass — the calculated neutral mass after accounting for charge. Do not be alarmed by a peak that appears to be 'half' the expected weight; that is normal ESI behavior, not an error.

Two caveats keep this honest. First, mass spectrometry confirms mass, not the exact order of amino acids — two different sequences with the same composition can share a mass, though this is rare for well-characterized peptides. Second, MS alone does not tell you purity; a spectrum can look correct even when impurities are present. This circles back to the core principle: HPLC and MS are complementary, and a trustworthy CoA carries both.

Purity and identity describe the molecule; endotoxin and sterility testing describe biological safety of the preparation. These tests become relevant for any research that involves administering a peptide to living systems, particularly by injection in animal models, where contamination has direct physiological consequences.

Endotoxins are lipopolysaccharides from the cell walls of Gram-negative bacteria. They are heat-stable, survive ordinary sterilization, and can trigger strong inflammatory and febrile responses even in tiny amounts. Endotoxin content is measured by the Limulus Amebocyte Lysate (LAL) assay and reported in endotoxin units per milligram (EU/mg). A CoA that reports a low, specified endotoxin level provides assurance that a clean synthesis was not undone by bacterial contamination during handling.

Sterility testing asks a different question: is the product free of viable microorganisms? A sterile product can still contain endotoxin (from bacteria killed earlier), and a low-endotoxin product is not automatically sterile — which is why the two tests are separate line items, not interchangeable.

In practice, most research-grade peptides are sold as non-sterile, for-research-use-only material, and many CoAs will not include these tests. That is not automatically a red flag, but the absence of endotoxin and sterility data is a meaningful limitation you should register consciously, especially for any in-vivo application. When these tests are claimed, the CoA should state the method (LAL) and a numerical result, not merely the word 'passed'.

None of this constitutes medical guidance. Research peptides are not approved for human use, and decisions about biological safety should involve appropriate expertise. See our medical disclaimer for the full scope of this limitation.

Because a CoA is just a document, it can be edited, recycled, or fabricated. Learning to read the data critically is the best defense. Several warning signs recur across falsified certificates.

• Missing or mismatched lot number. If the batch number on the CoA does not match the vial label — or if the CoA has no lot number at all — the document cannot be tied to your product. A generic CoA reused across many batches is a classic tell.
• No chromatogram or spectrum image. A summary that states '99% purity, mass confirmed' without the actual HPLC trace and MS spectrum is unverifiable. Genuine reports include the graphical data, with labeled axes, retention times, and peak areas.
• Inconsistent dates or metadata. A testing date that predates the manufacturing date, or a PDF whose creation metadata does not match the stated lab, are quiet giveaways.
• Impossible or copy-pasted numbers. A measured mass that does not match the peptide's theoretical weight, or a chromatogram whose peak area percentages do not add up, indicates fabrication or a mismatched template.
• Editable text over the graph. Purity figures typed as overlaid text on top of a chromatogram — rather than generated by the instrument software — should be treated with suspicion.

A particularly common deception is the recycled chromatogram: a supplier presents one genuine, excellent result and attaches it to every batch, regardless of what was actually shipped. The lot number is your anchor against this; if it never changes, the 'per-batch' testing is fiction.

Finally, be skeptical of certificates that read like marketing. Phrases such as 'guaranteed pure' or laboratory logos with no verifiable report number add nothing analytical. A real CoA is dry, specific, and traceable — its credibility comes from data you can independently check, which is the subject of the next section.

The most robust way to trust a CoA is not to trust the supplier's PDF at all, but to verify the underlying report directly with the independent laboratory that performed the test. This closes the loophole that makes document editing possible in the first place.

Several third-party analytical labs have become widely used in the research-peptide space, the best known being Janoshik Analytical. Reports from such labs typically carry a unique report ID and can be looked up on the lab's own verification portal. When a supplier provides a report ID, you can enter it on the lab's website and see the original, un-editable result — including the purity, the measured mass, and the tested date — exactly as the lab recorded it. If the supplier's PDF disagrees with the source record, the PDF has been altered.

When evaluating source verification, look for these features:

• A report or reference number that resolves on the testing lab's own domain, not a screenshot hosted by the seller.
• Consistency between the batch/lot number on the vial, the supplier's CoA, and the lab's original record.
• A recent testing date that plausibly corresponds to the batch you received, not a certificate from years earlier.
• The presence of the raw chromatogram and mass spectrum in the source record, not just a numeric summary.

Third-party testing is not infallible — a lab only tests the sample it is sent, which may not represent every vial in a batch — but source verification dramatically raises the bar for fraud. A supplier willing to fabricate a PDF is far less able to fabricate an entry inside an independent lab's database. Combined with per-batch lot tracking, source verification is the single most valuable habit a careful researcher can adopt when purchasing from a peptide supplier.

Reading a CoA well is a repeatable process. Work through it in order, and stop at any step that fails — a single unresolved red flag is enough reason to withhold trust.

In prose: first confirm the certificate belongs to your batch. Then confirm identity with the mass spectrum, because a pure sample of the wrong compound is worthless. Next read the chromatogram critically rather than trusting the headline percentage. Note whether content and safety data are present, and treat their absence as a known limitation. Finally — and most importantly — verify at the source using the report ID.

Keep perspective on what a good CoA can and cannot tell you. A flawless certificate confirms that a tested sample of a batch was pure and correctly identified on a given date. It does not make a peptide approved, safe for humans, or legal in your jurisdiction, and legal status varies widely between countries. Research peptides discussed here are sold for research use only and are not approved by the FDA or EMA.

Medical disclaimer: This article is for educational purposes only and does not constitute medical, legal, or safety advice. It distinguishes analytical documentation from clinical evidence, most of which for research peptides remains preclinical. Consult a qualified healthcare professional before making any decision, and review our full medical disclaimer.