Dr.GastroMayo said:The provenance questions are more useful than the numbers.
Vendor quality matters when discussing certificates of analysis. I've tested my last 4 batches through Janoshik and purity has ranged from 97.9% to 100.5%. Consistency is key.
For anyone new: always request the COA, and consider independent verification. The $300 for a Janoshik test is worth the peace of mind.
A narrower follow-up, since the general answer is now clear:
Why two laboratories report different purity for the same batch, and which number to believe?
dave_SLC said:Vendor quality matters when discussing certificates of analysis.
I tested my certificates of analysis batch through Janoshik — 99.5% purity. That's within acceptable range for compounded peptides. Turnaround was 8 business days.
The test costs ~$143 but gives you actual HPLC chromatography data plus mass spec confirmation. For the peace of mind alone, it's worth every penny. I test every new batch from a new vendor.
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View ResultsClosing the loop on my own question.
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.
TrialTracker_MD said:I tested my certificates of analysis batch through Janoshik — 99.5% purity.
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.
Correct me if the detail matters more than I have assumed.