Dr.SurgeonPGH said:

HPLC results interpretation for certificates of analysis: when you get your Janoshik report back, here's what the numbers mean: Purity %: Should be…

Community-verified vendors for certificates of analysis: I maintain a spreadsheet of Janoshik-verified test results submitted by community members. Across 50 submitted tests:

• 82% tested at ≥98% purity
• 12% tested at 95-98% purity
• 6% tested at <95% purity (concerning)

The vendors with consistently high purity results are listed in the Vendor Directory. We update monthly based on new community submissions.

RetaRick_CA said:

One addition: an unstated method makes a report close to uninterpretable.

That reframing is the part I needed. Printing the relevant bit and taking it with me.

Dr.SurgeonPGH said:

HPLC results interpretation for certificates of analysis: when you get your Janoshik report back, here's what the numbers mean: Purity %: Should be…

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 the refrigerator.

Day 1: 100.7% purity
Day 14: 99.4% purity
Day 28: 98.1% purity

Minimal degradation over 28 days when properly refrigerated. This confirms the standard 28-day beyond-use date is appropriate. Beyond 28 days, I'd reconstitute a fresh vial to be safe.

Dr.RaviCardio said:

Two reports on the same product from two laboratories, four percentage points apart, and no method stated on either.

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.

Moderator note: the sourcing question belongs in the vendor section and has been split out. Report rather than reply if it drifts again.