From the other side of the consultation, briefly.

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: 99.2% purity, 0.2% total related substances. Clean chromatogram with single sharp peak at expected retention time. Exactly what you want to see.

NicoleRaleigh said:

My vendor review relevant to certificates of analysis: ordered 4 times from my current compounder.

Mass spectrometry confirmation for certificates of analysis: beyond HPLC purity, mass spec tells you the molecule's exact molecular weight. This confirms identity — not just purity.

Why this matters: HPLC can show you a "pure" compound, but if it's pure of the WRONG compound, purity is meaningless. Mass spec at m/z 4113.58 Da confirms it's actually semaglutide. My Janoshik report includes both HPLC and mass spec.

If your testing provider only offers HPLC, consider upgrading to include mass spec for at least your first batch from a new vendor.

NicoleRaleigh said:

My vendor review relevant to certificates of analysis: ordered 4 times from my current compounder.

Thank you — that is the clearest version of this I have read, and I have read a lot of them. Printing the relevant bit and taking it with me.

From the other side of the consultation, briefly.

Vendor quality matters when discussing certificates of analysis. I've tested my last 5 batches through Janoshik and purity has ranged from 97.2% to 99.6%. 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.

Moderator note: the sourcing question belongs in the vendor section and has been split out. Thread quality here is what the rules are for. Keep it up.