kevin_tulsa said:The provenance questions are more useful than the numbers.
Vendor quality matters when discussing certificates of analysis. I've tested my last 3 batches through Janoshik and purity has ranged from 99.6% to 99.0%. 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.
Following on from Dr.SportsMedIN — and this may be the naive question:
Why two laboratories report different purity for the same batch, and which number to believe?
Dr.GutHealth said:Vendor quality matters when discussing certificates of analysis.
I tested my certificates of analysis batch through Janoshik — 97.6% purity. That's within acceptable range for compounded peptides. Turnaround was 10 business days.
The test costs ~$144 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.
Sigma-Aldrich — Research-Grade Standards
Certified reference materials, analytical reagents, and research-grade standards for peptide verification. Trusted by laboratories worldwide.
Shop Reference StandardsClosing 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.
pat_auckland said:I tested my certificates of analysis batch through Janoshik — 97.6% purity.
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.