Clinical perspective, offered as context rather than as advice.

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.

Clinical perspective, offered as context rather than as advice.

Vendor quality matters when discussing certificates of analysis. I've tested my last 5 batches through Janoshik and purity has ranged from 98.8% 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.

PedsEndoPhilly said:

Vendor quality matters when discussing certificates of analysis.

This is my experience too, for whatever a second data point is worth. The detail I would add is minor and it is already implied above.

PedsEndoPhilly said:

Vendor quality matters when discussing certificates of analysis.

I tested my certificates of analysis batch through Janoshik — 98.4% purity. That's within acceptable range for compounded peptides. Turnaround was 8 business days.

The test costs ~$133 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.

Moderator note: good thread. Keeping it here rather than moving it, because the question is general enough to be useful. No action needed from anybody.