HPLC_Greg said:The provenance questions are more useful than the numbers.
I am more sceptical of certificates as a category than this thread is. The document tells you about a sample somebody chose to send, at a moment in time, and nothing about the vial in your hand. Independent purchase-and-test is a different quality of evidence and everything else is inference.
lisa_labSD said:I have a certificate reporting 99.2% purity and 6.1mg content on a vial sold as 5mg, and I cannot work out whether those two numbers are consistent or…
Vendor quality matters when discussing certificates of analysis. I've tested my last 4 batches through Janoshik and purity has ranged from 98.3% to 100.1%. 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.
Dr.SleepRoch said:I am more sceptical of certificates as a category than this thread is.
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: 14.7 minutes (consistent with semaglutide reference standard)
Peak purity: 98.0%
Related substances: 0.7% (single impurity at 8.0 minutes — likely a synthesis intermediate)
Mass spec: m/z 4113.58 (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.
Sigma-Aldrich — Research-Grade Standards
Certified reference materials, analytical reagents, and research-grade standards for peptide verification. Trusted by laboratories worldwide.
Shop Reference StandardsFollowing on from tom_AK — and this may be the naive question:
Whether a purity figure and a content figure can disagree without one of them being wrong?
Closing 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.