Understanding Peptide Purity: Why 99%+ Matters and How to Read a COA
A Certificate of Analysis (COA) is the single most important document in research peptide procurement. It’s the only objective evidence that what’s on the label matches what’s in the vial. Yet most buyers never read one — and many vendors count on that.
After the Peptide Sciences shutdown, Paradigm Peptides’ federal charges (products contained testosterone instead of the labeled compounds), and FDA enforcement actions across the industry, the ability to evaluate a COA is no longer optional for serious researchers. This guide explains what purity means, how it’s measured, and exactly how to read a COA to verify what you’re buying.
What “Purity” Actually Means
Peptide purity refers to the percentage of the total sample that consists of the target peptide versus impurities. A peptide sold at 99% purity means that 99% of the material in the vial is the intended peptide, and 1% consists of other substances — synthesis byproducts, degradation products, residual solvents, or truncated sequences.
The remaining impurities matter because they can interfere with experimental results (confounding variables), cause unexpected biological effects (off-target activity), or indicate poor manufacturing quality (suggesting potential issues with identity, stability, or sterility).
Why 99%+ Is the Research Standard
Different purity grades serve different purposes:
| Purity Range | Typical Use | Impurity Level |
|---|---|---|
| 99%+ | Research grade — standard for published research and serious experimental work | Less than 1% |
| 95-98% | General laboratory use — acceptable for some applications but introduces more variables | 2-5% |
| Below 95% | Not suitable for most research — significant impurity burden | 5%+ unknown substances |
For context: a 5mg vial at 90% purity contains only 4.5mg of actual peptide plus 0.5mg of unknown impurities. At 99%+ purity, the same vial contains 4.95mg of peptide with less than 0.05mg of impurities — a 10x reduction in unknowns.
The Two Essential Tests: HPLC and Mass Spectrometry
HPLC (High-Performance Liquid Chromatography)
HPLC answers the question: “How pure is it?”
The technique separates a sample into its individual components by passing it through a column under high pressure. Each component exits the column at a different time (retention time) and is detected by UV absorption. The result is a chromatogram — a graph showing peaks for each component, with the area under each peak proportional to the amount of that substance.
On a good HPLC chromatogram, you’ll see one dominant peak (the target peptide) and minimal smaller peaks (impurities). The purity percentage is calculated as the area of the main peak divided by the total area of all peaks.
What to look for on a COA:
- Purity percentage: Should be 99%+ for research-grade peptides
- Method details: Column type, mobile phase, and detection wavelength should be specified — this allows the test to be reproduced
- Retention time: Should match the expected retention time for the target peptide under the specified conditions
Mass Spectrometry (MS)
Mass Spectrometry answers the question: “Is this the right compound?”
HPLC tells you something is 99% pure — but it doesn’t tell you what that “something” is. Mass Spectrometry measures the molecular weight of the compound and compares it to the known molecular weight of the target peptide. If the observed mass matches the expected mass (within instrument tolerance, typically ±1 Da), the compound’s identity is confirmed.
This is the test that would have caught the Paradigm Peptides fraud — Mass Spectrometry would have immediately shown that the compounds in their vials (testosterone) had a completely different molecular weight than the labeled SARMs.
What to look for on a COA:
- Observed molecular weight: Should match the theoretical molecular weight for the peptide
- Theoretical molecular weight: Should be listed for comparison
- Method: ESI-MS (Electrospray Ionization) or MALDI-TOF are the standard methods for peptide analysis
How to Read a COA: Step by Step
When you receive a COA (or access one on a vendor’s website), check the following in order:
Step 1: Verify It’s Batch-Specific
The COA should include a lot number or batch number that corresponds to the specific product you received — not a generic report. If the COA shows results from six months ago with no batch identifier, it may not represent the actual product in your vial.
Step 2: Check for Both HPLC and Mass Spec
A complete COA includes both tests. HPLC alone (purity without identity confirmation) is incomplete. Mass Spectrometry alone (identity without purity) is also incomplete. You need both.
Step 3: Verify Purity ≥99%
Read the HPLC purity percentage. For research-grade peptides, expect 99%+ purity. Be wary of vague claims like “high purity” without a specific number.
Step 4: Confirm Molecular Weight Match
Compare the observed molecular weight (from Mass Spectrometry) to the expected molecular weight for the target peptide. They should match within ±1-2 Da.
Step 5: Check the Testing Laboratory
The most credible COAs come from independent, third-party laboratories — not the vendor’s own internal testing. In-house testing creates a conflict of interest (the vendor is grading their own product). Independent labs like Janoshik Analytical produce publicly verifiable results that anyone can confirm.
Red Flags in COA Documentation
- No batch/lot number — the COA may not correspond to your specific product
- HPLC only, no Mass Spectrometry — purity is verified but identity is not
- In-house testing only — no independent verification; vendor is self-certifying
- COAs “available upon request” — if a vendor is confident in quality, they publish proactively
- Purity below 98% — not research-grade; significant impurity burden
- Generic or template-looking documents — professional COAs include specific instrument details, analyst signatures, and test dates
- Molecular weight doesn’t match — the compound may not be what’s labeled
PSPeptides Testing Standards
Every PSPeptides product undergoes independent third-party testing via both HPLC and Mass Spectrometry before release. Our COAs are batch-specific, publicly accessible on our Certifications page, and include full method details for reproducibility.
View Our Certificates of Analysis → | Browse Products →
All products are intended for laboratory research use only. Not for human consumption.
PSPeptides — US Made & Shipped | Third-Party Tested | 99%+ Purity | Same-Day Shipping