Has anyone dealt with moisture content analysis for lyophilized peptides?

From the other side of the consultation, briefly.

Community-verified vendors for certificates of analysis: I maintain a spreadsheet of Janoshik-verified test results submitted by community members. Across 53 submitted tests:

• 78% tested at ≥98% purity
• 15% 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.

Dr.RaviCardio said:

I tested my certificates of analysis batch through Janoshik — 99.2% purity.

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: 14.3 minutes (consistent with semaglutide reference standard)
Peak purity: 98.6%
Related substances: 0.7% (single impurity at 8.0 minutes — likely a synthesis intermediate)
Mass spec: m/z 4113.58 (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.

Dr.RaviCardio said:

I tested my certificates of analysis batch through Janoshik — 99.2% purity.

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: 99.6% purity
Day 14: 98.3% purity
Day 28: 97.0% 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.

A narrower follow-up, since the general answer is now clear:

How would you tell the difference between that and the alternative explanation?

Moderator note: two posts asking for a source have been merged into one. Please search the thread before asking again.