How to Read a Certificate of Analysis (COA): HPLC vs. Mass Spec
Updated May 2026 · By the Onyx Biolabs Research Team · 7-minute read · For laboratory research use only
TL;DR
A Certificate of Analysis (COA) is the third-party lab report that proves a research peptide is what the supplier claims it is and at what purity. A complete COA includes two tests: HPLC (high-performance liquid chromatography) measures the percentage purity, and Mass Spec (mass spectrometry) confirms the molecular identity matches the expected peptide sequence. Both are required. A COA showing only HPLC tells you the sample is pure but not what it is; a COA showing only Mass Spec tells you the molecule is correct but not how much else is in the vial. Onyx Biolabs publishes both, from independent labs, for every batch.
What is a Certificate of Analysis?
A Certificate of Analysis (COA) is a laboratory-issued document that reports the analytical test results for a specific batch of a chemical compound. For research peptides, a COA documents two things: the purity of the peptide (what percentage of the powder is the target compound vs. impurities) and the identity of the peptide (verification that the molecule matches the expected amino acid sequence).
The COA should always be issued by an independent third-party lab, not by the supplier itself. A self-reported “in-house COA” is not a real COA. The labs whose names you should look for include Kovera Labs, Janoshik Analytical, Anresco, and similar accredited analytical services.
What is HPLC and what does it measure?
HPLC (high-performance liquid chromatography) is the standard analytical method for measuring the purity percentage of a peptide. The result is reported as a number like “99.4% pure” — meaning 99.4% of the powder is the target peptide and 0.6% is everything else (synthesis byproducts, residual solvents, truncated sequences).
How HPLC works in 30 seconds
A small amount of the peptide sample is dissolved and pumped through a column packed with a stationary phase. As the sample travels through the column, different molecules adsorb to the column material at different rates. The result is that the target peptide and any impurities elute (exit the column) at different times. A detector at the end measures everything that comes out, plotting the result as a chromatogram — a graph with peaks.
How to read an HPLC chromatogram
The chromatogram shows a series of peaks plotted against time (the x-axis). The target peptide is the largest peak. The percentage purity is calculated as the area of the target peak divided by the total area of all peaks, multiplied by 100. A 99.4% pure peptide will have one dominant peak with only tiny peaks elsewhere on the chart.
What HPLC does NOT tell you
HPLC measures purity but cannot confirm identity on its own. If you have 99.9% of “something,” HPLC tells you that the sample is exceptionally pure — but it doesn’t confirm the something is the peptide you ordered. That’s why Mass Spec is required alongside HPLC.
What is Mass Spectrometry and what does it measure?
Mass spectrometry (Mass Spec, or MS) measures the molecular mass of the peptide. The measured mass is then compared against the theoretical mass calculated from the expected amino acid sequence. If they match within a tight tolerance (typically +/- 1 Da), the identity is confirmed.
How Mass Spec works in 30 seconds
A small amount of the peptide is ionized (charged) and accelerated through a magnetic field. Different molecular weights deflect through the field at different rates. The detector measures the deflection and reports the mass-to-charge ratio (m/z) of every ion that hits it. The result is a spectrum with a peak at the molecular weight of the target peptide.
What to look for on a Mass Spec report
The report should clearly show one dominant peak at or very near the expected molecular weight of the peptide. For BPC-157, that’s ~1,419 Da; for Retatrutide, ~4,731 Da; for Tirzepatide, ~4,814 Da. If the dominant peak isn’t at the right mass, the sample isn’t what it claims to be, regardless of how pure HPLC says it is.
HPLC vs Mass Spec: why you need both
| HPLC | Mass Spec | |
|---|---|---|
| What it measures | Purity (% of target vs impurities) | Molecular identity (mass match) |
| Typical result | “99.4% pure” | “Observed mass: 1,419.5 Da; theoretical: 1,419.7 Da; match” |
| What it can’t prove | That the sample is the right molecule | What proportion of the sample is the target |
| Required tolerance | 99%+ for research grade | +/- 1 Da from theoretical mass |
| On a complete COA? | Yes, always | Yes, always |
A COA missing either test is incomplete. Be cautious of suppliers who provide only one. Onyx Biolabs publishes both HPLC and Mass Spec results for every batch.
Step-by-step: how to evaluate a COA
Step 1: Confirm the lab is independent
Look at the top of the COA for the issuing laboratory’s name and contact info. It should be a third-party lab (Kovera Labs, Janoshik Analytical, etc.) — not the supplier’s own facility. A real COA has the lab’s logo, address, and contact details on the document.
Step 2: Match the batch number to your vial
Every COA is tied to a specific batch (lot number) of peptide. The batch number on the COA must match the batch number on your vial label. If they don’t match, the COA does not represent the vial you have.
Step 3: Check the test date
COAs should be recent — ideally within the last 12 months. If a supplier shows you a COA from 2022 for a vial you ordered in 2026, that’s a red flag.
Step 4: Read the HPLC purity number
For research-grade peptides, the industry standard is 99%+ purity. Anything below 98% is questionable; above 99.5% is excellent. Look for the integrated peak area percentage on the chromatogram.
Step 5: Verify the Mass Spec match
Find the “Observed Mass” and the “Theoretical Mass” on the Mass Spec section. They should match within +/- 1 Da. The peptide identity is only confirmed if both lines match.
Step 6: Check for any flagged impurities
A good COA will list any impurities detected, with their relative percentages. Common impurities include truncated sequences (missing one or more amino acids from the end), residual solvents (TFA, acetonitrile), and water content. Trace amounts are normal; large amounts indicate poor synthesis.
Red flags to watch for on a COA
- “In-house testing” — not independent, not credible.
- Mass Spec section missing — you only know the sample is pure, not what it is.
- HPLC section missing — you only know the molecule is correct, not how much of it.
- No batch number or mismatched batch number — the COA may not represent your vial.
- Test date older than 12 months — the data may not reflect current production.
- Stock photo or watermark on the COA — possibly fabricated; verify with the issuing lab if suspicious.
How Onyx Biolabs handles COAs
Every batch sold by Onyx Biolabs is tested by Kovera Labs, an independent analytical chemistry lab. Both HPLC and Mass Spec are run on every batch. The full COA is published at /lab-results/ with the batch number printed on each vial label so researchers can match the document to the product. Recent Q1 2026 batches have averaged 99.4% purity across the catalog.
Frequently asked questions
What does HPLC purity 99% mean?
It means that, when the peptide sample was run through an HPLC column, 99% of the integrated peak area corresponded to the target peptide and 1% corresponded to impurities. A 99% pure peptide is research-grade; below 98% is generally unacceptable for serious research.
Can a peptide be HPLC pure but the wrong compound?
Yes. HPLC measures purity, not identity. A sample could be 99.9% pure of the wrong molecule. That’s why Mass Spec is also required: it confirms the molecule is what the label says.
What is the difference between HPLC and Mass Spec for peptide analysis?
HPLC measures how much of the peptide is in the vial (purity). Mass Spec measures what the peptide is (molecular identity). A complete COA includes both because each answers a different question.
What molecular weight should I see on a Mass Spec report for BPC-157?
~1,419 Da (specifically 1,419.53 Da for the standard 15-amino-acid sequence). The observed mass on the Mass Spec report should match this within +/- 1 Da.
What molecular weight should I see for Retatrutide?
~4,731 Da. Retatrutide is a 39-amino-acid triple agonist; its theoretical mass is 4,731.4 Da.
Should a COA be specific to my batch?
Yes. A COA is only valid for the specific batch (lot number) it was issued for. The batch number on the COA must match the batch number on your vial. A generic COA without a batch number is not a real COA.
How recent should a COA be?
Ideally within the last 12 months. Peptide manufacturing batches turn over frequently, and an old COA may not reflect current production quality. Onyx Biolabs re-tests every batch and publishes new COAs as they’re produced.
Where can I see Onyx Biolabs COAs?
All current COAs are at https://onyxbiolabs.com/lab-results/. The page lists every batch with its HPLC chromatogram, Mass Spec spectrum, and purity percentage.
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Disclaimer
For research, laboratory, or analytical use only. The compounds discussed are not approved for human or animal consumption. The statements on this page have not been evaluated by the FDA. Onyx Biolabs is a chemical supplier and is not a compounding pharmacy or chemical compounding facility as defined under 503A or 503B of the Federal Food, Drug, and Cosmetic Act.