SaraMom3 said:Inter-laboratory variation comes from real methodological differences, not sloppiness: which reference standard was used and how it was itself…
My HPLC chromatogram analysis for certificates of analysis — I sent my batch to Janoshik and here's what the results showed:
Main peak retention time: 16.4 minutes (consistent with semaglutide reference standard)
Peak purity: 98.2%
Related substances: 0.4% (single impurity at 10.2 minutes — likely a synthesis intermediate)
Mass spec: m/z 4113.5 (matches expected molecular weight)
This is a clean result. The mass spec confirmation is particularly important — it proves the molecule is actually semaglutide and not a substitution.
One thing that is still open after TrialNerd_Beth’s answer:
Why two laboratories report different purity for the same batch, and which number to believe?
dave_SLC said:My HPLC chromatogram analysis for certificates of analysis — I sent my batch to Janoshik and here's what the results showed: Main peak retention time:…
HPLC results interpretation for certificates of analysis: when you get your Janoshik report back, here's what the numbers mean:
- Purity %: Should be >97%. Below 95% is concerning.
- Retention time: Should match reference standard for the peptide
- Related substances: Degradation products should be <2% total
- Single impurity: No individual impurity should exceed 1%
My last batch: 99.5% purity, 0.3% total related substances. Clean chromatogram with single sharp peak at expected retention time. Exactly what you want to see.
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Purity and content being different measurements was the piece I was missing. The vial was overfilled and pure, which is a very different problem from the one I thought I had.
Dr.PulmRoch said:HPLC results interpretation for certificates of analysis: when you get your Janoshik report back, here's what the numbers mean: Purity %: Should be…
Agreed, and mass spec answers a question purity does not: identity. High purity tells you one thing dominates the chromatogram, not that it is the molecule you ordered. A mass within about a dalton of expected is the identity check.