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 97.8% 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.

Dr.GutHealth said:

Reconstituted peptide stability data for certificates of analysis: I had Janoshik test my reconstituted vial at day 1, day 14, and day 28 stored in…

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.

Dr.GutHealth said:

Reconstituted peptide stability data for certificates of analysis: I had Janoshik test my reconstituted vial at day 1, day 14, and day 28 stored in…

I tested my certificates of analysis batch through Janoshik — 99.2% purity. That's within acceptable range for compounded peptides. Turnaround was 12 business days.

The test costs ~$125 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.

Following on from Dr.GutHealth — and this may be the naive question:

What would you measure differently if you were starting again?

Moderator note: good thread. Keeping it here rather than moving it, because the question is general enough to be useful.