The peptide COA, decoded

Q: What is a peptide Certificate of Analysis?

A Certificate of Analysis (COA) is a batch-specific laboratory report that documents the identity, purity, and quality metrics of a synthesized peptide. Reputable research suppliers generate one per batch, typically using High-Performance Liquid Chromatography (HPLC) for purity and mass spectrometry for identity. A COA is the primary (often only) document verifying that what is in the vial matches the label.

Q: What purity percentage is acceptable?

Research-grade peptides are typically expected to be ≥ 98% pure by HPLC; 99%+ is common for high-quality suppliers. Pharmaceutical-grade compounds (e.g. semaglutide sourced through a licensed pharmacy) are held to pharmacopoeial standards, often 99.5%+. Below 95% purity raises questions about manufacturing controls and should be approached with caution regardless of price.

Q: How do I verify a COA is real?

Four practical checks: (1) it lists a specific batch number that matches your vial label; (2) it includes test dates and analyst names; (3) the analytical traces (HPLC chromatogram, mass spectrum) are actually attached, not just summary numbers; (4) the lab named on the COA exists and, ideally, is a third party rather than the vendor's in-house lab. Vendor-only COAs are not inherently fake, but third-party verification is stronger.

Q: What does an HPLC chromatogram show?

HPLC separates the mixture in a vial by how strongly different compounds interact with a column. Each compound produces a peak on the output graph; the area under each peak represents how much of that compound is present. A high-purity peptide shows one dominant peak (the target peptide) with minor peaks for impurities. Purity % is calculated as (target peak area ÷ total peak area) × 100. A single-peak chromatogram is the ideal — multiple significant peaks suggest contamination or synthesis byproducts.

Q: What does mass spectrometry confirm?

Mass spectrometry confirms the identity of a peptide by measuring its molecular weight. A correct result for, say, semaglutide should report a monoisotopic mass of ~4113.6 Da (with a characteristic isotope pattern). A peptide labeled as one compound but showing a mass inconsistent with that compound is a hard fail, regardless of purity. MS establishes WHAT is in the vial; HPLC establishes HOW MUCH of it is pure.

Q: Do I need endotoxin and heavy metal testing?

For injectable peptides, endotoxin testing (LAL assay, typically reporting results in EU/mL or EU/mg) is a meaningful safety metric — high endotoxin levels cause fever and systemic inflammation. Heavy metals testing covers residues from synthesis reagents (lead, arsenic, cadmium, mercury). Pharmaceutical-grade peptides should have both; research-grade COAs often omit them. For injected compounds, their presence is a quality signal worth paying for.

10 min readUpdated April 2026Pillar guideBy the Peptide Protocol editorial team · reviewed

A Certificate of Analysis is the single document that distinguishes "I think this is semaglutide" from "I have evidence of what is in this vial." Anyone injecting compounds should be able to read one. This guide walks through every section, explains the analytics, and flags the red signals for fake or recycled documents.

What a COA is and why it matters

A Certificate of Analysis is a batch-specific lab report that documents the identity, purity, and safety metrics of a synthesized compound. It is generated at the end of manufacturing, ideally by an independent analytical laboratory, and should accompany every vial of research or pharmaceutical-grade peptide.

Without a COA, you have:

No verification that the vial contains what the label claims.
No measurement of purity — the target peptide could be anywhere from 50% to 99% of the contents.
No information on toxic contaminants (endotoxin, heavy metals, synthesis byproducts) that could cause injection reactions.

This is not theoretical. Independent testing of research peptides has repeatedly found mislabeled contents, wildly varying potency, and products that contain the wrong peptide entirely. A COA — even a vendor-issued one — shifts the situation from "trust the label" to "trust the documented lab result."

The nine sections of a COA

A complete, well-formatted COA contains roughly nine sections. Not every COA has all nine, but the absence of multiple sections is itself a signal.

Section	What it tells you
1. Product identity	Peptide name, molecular formula, theoretical molecular weight, sequence (single-letter amino acid code)
2. Batch / lot number	Unique identifier tying the COA to a specific manufacturing run — should match vial label
3. Manufacturing date	When synthesis was completed; some COAs include retest or expiry date
4. Physical appearance	Typically "white to off-white lyophilized powder"
5. HPLC purity	Primary purity metric, with chromatogram attached — see section below
6. Mass spectrometry	Identity confirmation via measured molecular weight — see section below
7. Water content	Karl Fischer titration, typically < 5–8%. Higher values mean less peptide per mg.
8. Endotoxin / LAL	Bacterial pyrogen level. Required for injectables; often missing on research-grade COAs
9. Analyst signature + lab details	Who tested it, at what lab, on what date — key for third-party verification

Understanding HPLC purity

High-Performance Liquid Chromatography (HPLC) is the standard technique for peptide purity. The principle is simple: a liquid sample is pushed through a column packed with a stationary material. Different compounds interact with the column with different affinity, so they emerge (or "elute") at different times. A detector on the output records each as a peak on a chromatogram.

Reading the chromatogram

X-axis: retention time (how long it took each compound to pass through the column).
Y-axis: detector signal (usually UV absorbance at 214 or 220 nm, characteristic of peptide bonds).
Main peak: the target peptide, typically the largest. Should be sharp, symmetrical, and clearly separated from other features.
Minor peaks: impurities — synthesis byproducts, truncated sequences, oxidation products.

Purity is calculated as: (main peak area ÷ total peak area) × 100. A peptide labeled "> 98% pure by HPLC" means 98% of the UV-detectable material in that sample is the target peptide. The remaining 2% is other stuff — which is why endotoxin and heavy metals testing also matters for injectables.

Important limitation. HPLC purity only measures what the detector can see (typically UV-active compounds). It says little about water content, inorganic salts, or compounds that do not absorb UV. A peptide can be "98% pure" by HPLC and still be only 70% of the vial mass due to water and salt content — which is why water content testing matters.

Understanding mass spectrometry

Mass spectrometry (MS) confirms identity where HPLC measures purity. The sample is ionized and accelerated through a field; the instrument measures each molecule's mass-to-charge ratio. The output is a spectrum with a dominant peak at the molecular weight of the target compound.

For semaglutide, the theoretical monoisotopic mass is ~4113.6 Da. A COA showing a measured mass matching this value (within instrument tolerance, typically ±0.5 Da or better for modern MS) confirms the vial contains semaglutide. A measured mass far from the theoretical value is a hard fail — regardless of what the HPLC says.

Common MS techniques used on COAs:

ESI-MS (electrospray ionization) — most common for peptides; produces multiply-charged ion series.
MALDI-TOF — time-of-flight, typically produces singly-charged ions; used for larger peptides.
LC-MS — chromatography coupled to mass spec; provides both purity and identity in one analysis.

Endotoxin, water content, heavy metals

Endotoxin (LAL assay)

Bacterial endotoxin is a structural component of Gram-negative bacteria cell walls. Even tiny amounts in an injectable cause fever, chills, and systemic inflammation. The Limulus Amebocyte Lysate (LAL) assay detects endotoxin at sub-nanogram levels.

Results are reported in Endotoxin Units (EU) per mg of peptide. For injectable use, < 10 EU/mg is a typical ceiling; pharmaceutical-grade compounds are often < 1 EU/mg. Missing endotoxin data on a COA for an injectable compound is a meaningful gap.

Water content (Karl Fischer titration)

Lyophilized peptides always retain a small amount of water. Karl Fischer titration measures it precisely. Typical values:

< 5% — excellent, clean lyophilization
5–8% — acceptable, standard
> 10% — poor lyophilization; reduces shelf life and means less peptide per labeled mg

Heavy metals

Residual lead, arsenic, cadmium, and mercury from synthesis reagents should be below pharmacopoeial limits (typically < 10 ppm for each, often much lower). Heavy metals data is more common on pharmaceutical-grade COAs than research-grade ones.

Acceptable thresholds by grade

Metric	Research grade	Pharma grade
HPLC purity	> 98%	> 99.5%
Mass spec identity	Within ±1 Da	Within ±0.5 Da
Water content	< 8%	< 5%
Endotoxin	Often untested or < 10 EU/mg	< 1 EU/mg
Heavy metals	Often untested	Tested, < pharmacopoeial limits
Third-party lab	Variable	Standard

Red flags on a COA

Signs a COA is fake, recycled, or not worth the PDF it is printed on:

No batch number — a COA without a unique identifier tied to a manufacturing run is not a batch-specific report. It is a generic document.
Batch number on COA does not match vial label — the single most common "recycled COA" failure mode. A clean COA from a real batch, reused across many later batches.
No HPLC chromatogram image — only a "purity: 99%" text field with no supporting trace. There is no way to verify the claim.
No mass spec spectrum image — same issue: just a text field claiming the MW matches.
Test dates significantly older than manufacturing date — the analytical data predates the batch it supposedly describes.
Typos in the peptide name or molecular formula — unserious lab work. Real labs catch these.
Non-existent or unreachable testing laboratory — the lab named on the report should be a real organization you can find.
Identical COAs across multiple vendors — strong sign of a shared fake template.
Watermark removed or obscured — someone altered the original document.

Vendor-only COAs are not automatically fake — most reputable research vendors issue their own. But third-party COAs from independent labs (Janoshik Analytical, EAG Labs, Intertek, SGS, etc.) are a stronger quality signal and easier to verify.

How to verify a COA is real

Cross-check batch numbers. The COA batch must match the vial label. If they do not match, the COA does not describe your vial.
Look up the testing lab. Search for the lab name; if it exists and has a real website, confidence is higher.
Request a third-party COA if the vendor only provides in-house. Many vendors will oblige for a small fee; refusal is a signal.
Inspect the analytical traces. Real chromatograms and spectra have characteristic noise, baseline drift, and labeled peaks. Fake ones are often too clean or copied from textbook examples.
Compare across batches. If you buy from the same vendor multiple times, request the COA each time. Variations between batches look realistic; identical traces across months of production look synthetic.
Cross-check with community reports. Users often share COAs publicly. If your COA is identical to someone else's with a different batch number, you have a recycled document.

Frequently asked questions

What is a peptide Certificate of Analysis?

A batch-specific lab report documenting identity, purity, and quality of a synthesized peptide. The primary document verifying what is in the vial.

What purity percentage is acceptable?

Research-grade: > 98% by HPLC. Pharma-grade: > 99.5%. Below 95% should be approached with caution.

How do I verify a COA is real?

Match batch number to vial label, verify the testing lab exists, check that analytical traces are attached (not just summary numbers), and prefer third-party over in-house testing.

What does an HPLC chromatogram show?

Separates components of the vial by retention time; each appears as a peak. Main peak = target peptide; purity is its area as a percentage of total peak area.

What does mass spectrometry confirm?

Identity. The measured molecular weight should match the theoretical value for the claimed peptide. HPLC measures purity; MS confirms identity.

Do I need endotoxin and heavy metal testing?

For injectable peptides, yes — both are meaningful safety metrics. Pharmaceutical-grade COAs include them; research-grade often omit them.

Log vial batches with your doses

Peptide Protocol stores batch numbers and COA references per vial, so when anything unusual happens you can trace it back to the source rather than scrolling chat history.

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Related COA guides

Educational use only. This guide is for research and informational purposes. It is not medical, legal, or regulatory advice. Always follow applicable laws regarding peptide acquisition and use in your jurisdiction.