Why peptide lab reports can disagree
Updated October 29, 2026. Based on a peer reviewed study of research peptides, cited below. It does not name or test Growth Guys.
in one study, only 44% of 98 supplier peptides met the 95% purity that came with their certificates.
- Independent testing matters, which is why a named independent lab and batch-level reports you can look up, as in the Growth Guys COA library, are worth checking.
What the researchers did
They ordered 98 synthetic peptides for lab work, each requested at 95% purity or better, and every one arrived with a certificate of analysis. Then they ran their own quality control.
What they found
| Finding | Result |
|---|---|
| Met required purity | 44.0% |
| One example | Certificate said 95% or more, authors measured 80.6% |
| Cyclic peptides (9) | None above 90% purity, 8 below 80% |
| Wrong main compound | One sample had a different structure than intended |
| Most common impurity | About 74% involved missing amino acids |
What to take from it
- A certificate is a claim. Ask for a batch specific report.
- Purity and identity are different tests, see how to read a COA.
- The authors recommend in house testing, including mass spectrometry, rather than relying on supplier certificates.
More: why impurities happen and vendor red flags.
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Common questions
Do COAs always match real purity?
Not always. In this study, many certificates did not match independent results.
Does this study test Growth Guys?
No. It tested research peptides from other suppliers. Growth Guys publishes batch reports from Janoshik Analytical that you can match to your vial.
What test confirms identity?
Mass spectrometry is the method the authors recommend alongside purity testing.
Sources
- Quality evaluation of synthetic quorum sensing peptides used in R&D (PMC5762210)
- Xiao et al., Advance in peptide-based drug development, Signal Transduction and Targeted Therapy (2025)
Summarised in my own words. Read the originals for the full detail.