LC-MS/MS vs HPLC for peptide analysis — November 2025

ingrid_STO said:

Third-party testing services for certificates of analysis besides Janoshik: Janoshik: Gold standard for peptide community, ~$124, 10-14 day turnaround…

My HPLC chromatogram analysis for certificates of analysis — I sent my batch to Janoshik and here's what the results showed:

Main peak retention time: 16.5 minutes (consistent with semaglutide reference standard)
Peak purity: 99.5%
Related substances: 0.6% (single impurity at 10.1 minutes — likely a synthesis intermediate)
Mass spec: m/z 4113.5 (matches expected molecular weight)

This is a clean result. The mass spec confirmation is particularly important — it proves the molecule is actually semaglutide and not a substitution.

jim_asheville said:

Agreed, and mass spec answers a question purity does not: identity.

That reframing is the part I needed. Adding it to my notes with a link back to this thread.

ingrid_STO said:

Third-party testing services for certificates of analysis besides Janoshik: Janoshik: Gold standard for peptide community, ~$124, 10-14 day turnaround…

Community-verified vendors for certificates of analysis: I maintain a spreadsheet of Janoshik-verified test results submitted by community members. Across 63 submitted tests:

• 75% tested at ≥98% purity
• 18% tested at 95-98% purity
• 7% 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.

pat_auckland 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: two posts asking for a source have been merged into one. Please search the thread before asking again. Carry on.