- A COA is a lab report that tells you what's actually in the vial. HPLC purity and mass spec are the two critical tests.
- HPLC purity of 98%+ is the standard for research-grade peptides. Below 95% is a red flag.
- Mass spectrometry confirms identity — it tells you the molecule is actually what the label says it is.
- If a supplier doesn't provide COAs at all, that's the biggest red flag of all. Walk away.
- A COA without lot numbers, dates, or actual HPLC chromatograms may be fabricated.
What Is a COA?
A Certificate of Analysis is basically a report card for your peptide. It documents the tests that were performed on a specific batch and their results. It answers two fundamental questions: is this actually the peptide on the label, and how pure is it?
Every reputable supplier provides one — either included with your order, available on the product page, or sent on request. If you've been tossing these aside without reading them, you're skipping the one piece of objective evidence you have about what you're working with.
Here's the thing though — a COA is only as good as the lab that generated it. A supplier running their own in-house testing has an obvious conflict of interest. Third-party COAs from independent analytical labs carry more weight. We'll get into what to look for and what to be skeptical about.
HPLC Purity
This is the headliner. When someone says a peptide is "99% pure," they're almost always referring to the HPLC (High-Performance Liquid Chromatography) result.
HPLC works by dissolving the peptide sample in a solvent and pushing it through a column packed with a stationary phase material. Different molecules travel through the column at different speeds based on their chemical properties. A detector at the end measures what comes out and when, generating a chromatogram — a graph with peaks.
The main peak represents your target peptide. Smaller peaks represent impurities: truncated sequences, deletion sequences, oxidized forms, or other synthesis byproducts. Purity is calculated as the area of the main peak divided by the total area of all peaks.
What purity numbers actually mean
| Purity | Grade | Typical Use |
|---|---|---|
| >99% | Pharmaceutical | Clinical research, in vivo studies requiring highest confidence |
| 98-99% | High research grade | Standard for quality research peptide suppliers |
| 95-98% | Research grade | Acceptable for many applications, lower cost |
| <95% | Crude / low grade | Preliminary screening only, not suitable for quantitative research |
For most research applications, 98%+ is what you want. The difference between 98% and 99.5% is meaningful for pharmaceutical development but less so for general research. The difference between 95% and 98%, however, can significantly affect your results — those extra impurities can introduce confounding variables.
A quality COA includes the actual HPLC chromatogram — the graph showing the peaks. If the COA just states "Purity: 99.2%" with no supporting graph, you're taking their word for it. The chromatogram lets you see the peak shape (sharp and symmetrical is good; broad and tailing suggests problems) and whether there are significant impurity peaks nearby.
Mass Spectrometry
HPLC tells you how pure something is. Mass spectrometry (MS) tells you what it is.
A mass spectrometer measures the molecular weight of the molecules in your sample with extreme precision. Every peptide has a known theoretical molecular weight based on its amino acid sequence. If the mass spec result matches the expected weight (within the instrument's margin of error), you've confirmed that the molecule is structurally what the label claims.
The COA will typically show this as "observed mass" vs. "theoretical mass." For example, BPC-157 has a theoretical molecular weight of 1419.53 Da. If the observed mass on the COA reads 1419.51 Da, that's a match. If it reads 1405.49 Da, something is wrong — you might have a truncated sequence or a different peptide entirely.
ESI-MS vs. MALDI-TOF
Two common techniques you'll see on COAs. ESI-MS (Electrospray Ionization) is the standard for peptides in the 500-5000 Da range — which covers most research peptides. MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization - Time of Flight) is sometimes used for larger peptides and proteins. Both are valid confirmation methods.
The mass spectrum graph on the COA will show a peak at the detected molecular weight. Some COAs show this as an m/z (mass-to-charge) value with different charge states. Don't worry about interpreting the charge states — the important number is the calculated molecular mass, which should match the theoretical value.
Other Tests You Might See
Amino acid analysis (AAA)
Breaks the peptide down into its component amino acids and measures the ratio of each. This confirms the peptide has the right sequence composition. Not all COAs include this — it's more common with pharmaceutical-grade products.
Endotoxin testing (LAL test)
Measures bacterial endotoxin contamination. Endotoxins are lipopolysaccharides from gram-negative bacteria that can cause inflammatory reactions even in tiny amounts. The result is reported in EU/mg (Endotoxin Units per milligram). For injectable-grade peptides, you want to see less than 5 EU/mg, ideally less than 1 EU/mg. Not all research-grade COAs include this test.
Sterility testing
Confirms the product is free of microbial contamination. This is standard for pharmaceutical products but less common on research peptide COAs. When present, it's a good sign about the supplier's quality standards.
Residual solvent analysis
Peptide synthesis and purification involve organic solvents (TFA, acetonitrile, etc.). This test confirms residual solvents are below acceptable limits. You'll see it on higher-end COAs.
Peptide content / net peptide
This is an often-misunderstood number. A vial labeled "5 mg" contains 5 mg of total powder — but not all of that powder is peptide. Some is counter-ions (acetate or TFA salts) and residual moisture. The "net peptide content" tells you the actual percentage that's peptide. Typical values are 60-85%. So a 5 mg vial with 75% net peptide contains about 3.75 mg of actual peptide.
For dosing purposes, most protocols reference the gross weight (5 mg) since that's how the product is sold. But it's useful to know this number exists, especially if you're seeing lower-than-expected results and wondering why.
Red Flags
Not all COAs are created equal. Here's what should make you skeptical:
No lot or batch number
A real COA is tied to a specific manufacturing batch. If there's no lot number, the COA can't be traced to your specific product. It might be a generic template applied to everything.
No date
When was the testing done? If there's no date, you can't know if the COA is from the current batch or one from two years ago. Products degrade; a COA should reflect recent testing.
Round, suspiciously clean numbers
Real analytical results have decimal places and slight variations. "Purity: 99.0%" is less convincing than "Purity: 98.73%." If every number on the COA is round and perfect, it may have been typed rather than generated from instrument data.
No chromatogram or mass spectrum
A COA that lists results without showing the underlying analytical data (HPLC graph, MS spectrum) is essentially asking you to trust the number. Reputable labs include the raw data. It takes up more space on the PDF but gives you actual evidence.
Identical COAs across different peptides
If you order three different peptides and the COA format, results, and even the chromatogram shapes look suspiciously similar, that's a red flag. Different peptides produce different HPLC profiles.
No supplier doesn't provide COAs at all
This is the biggest red flag. Any supplier that doesn't offer COAs on request is telling you something about their quality assurance — or lack thereof. Move on.
What a Good COA Looks Like
A quality COA from a reputable supplier typically includes:
- Product name and catalog number
- Lot/batch number and date of analysis
- HPLC purity with chromatogram
- Mass spectrometry with observed vs. theoretical mass
- Appearance description (white/off-white lyophilized powder)
- Solubility information
- Storage recommendations
- Analyst signature or lab identification
Third-party COAs — where the supplier sends samples to an independent analytical lab — carry additional credibility. The lab has no financial interest in the result. If a supplier offers both in-house and third-party testing, that's a strong signal.
Bottom line: spend 60 seconds reading the COA before you crack open a vial. It's the fastest quality check available to you, and it costs nothing but a moment of attention.