VendorMark 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 5 batches through Janoshik and purity has ranged from 97.6% to 99.2%. 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?
PeptideChemSF said:Vendor quality matters when discussing certificates of analysis.
My vendor review relevant to certificates of analysis: ordered 5 times from my current compounder. Consistency has been excellent.
Shipping: Same-day local pickup
Packaging: Professional, discreet, proper labeling with lot/batch numbers
Purity: 97.2% average across orders (Janoshik verified)
Customer service: Responsive within 6 hours
Price: $130/month for semaglutide 2.4mg equivalent
Janoshik Analytical — Independent Testing
Trusted third-party HPLC & mass spectrometry analysis. Verify peptide purity with the lab the community relies on. Independent. Accurate. Transparent.
Verify Your PeptidesGL Biochem (Shanghai) Ltd. — Direct Manufacturer
Est. 1998. The synthesis house behind the vials you send for testing. ISO 9001 and cGMP certified, 1,500+ staff, batch-specific COA with every order.
Browse GL BiochemClosing 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.
TinaHashiRN said:My vendor review relevant to certificates of analysis: ordered 5 times from my current compounder.
That is correct as far as it goes, and here is where it stops going. One addition: an unstated method makes a report close to uninterpretable. "99% pure" without the technique, the standard and the conditions is a claim, not a measurement.
Correct me if the detail matters more than I have assumed.