sarah_TO said:

The provenance questions are more useful than the numbers.

Thank you — that is the clearest version of this I have read, and I have read a lot of them. Printing the relevant bit and taking it with me.

Adding the clinical framing, because it changes how the question reads.

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

• Purity %: Should be >97%. Below 95% is concerning.
• Retention time: Should match reference standard for the peptide
• Related substances: Degradation products should be <2% total
• Single impurity: No individual impurity should exceed 1%

My last batch: 99.6% purity, 0.0% total related substances. Clean chromatogram with single sharp peak at expected retention time. Exactly what you want to see.

NurseAsh_DET said:

COA red flags for certificates of analysis — here's what to look for when reviewing a Certificate of Analysis: No HPLC data: If there's no…

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: 16.7 minutes (consistent with semaglutide reference standard)
Peak purity: 99.2%
Related substances: 0.4% (single impurity at 10.7 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.

LabKate said:

Inter-laboratory variation comes from real methodological differences, not sloppiness: which reference standard was used and how it was itself…

My vendor review relevant to certificates of analysis: ordered 4 times from my current compounder. Consistency has been excellent.

Shipping: 2-day priority with gel ice
Packaging: Professional, discreet, proper labeling with lot/batch numbers
Purity: 99.1% average across orders (Janoshik verified)
Customer service: Responsive within 4 hours
Price: $129/month for semaglutide 1.7mg equivalent

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