Dr.EM_Chicago said:

The provenance questions are more useful than the numbers.

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

Clinical perspective, offered as context rather than as advice.

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: 99.5% purity, 0.3% total related substances. Clean chromatogram with single sharp peak at expected retention time. Exactly what you want to see.

Dr.LipidDallas said:

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:…

I tested my certificates of analysis batch through Janoshik — 98.1% purity. That's within acceptable range for compounded peptides. Turnaround was 14 business days.

The test costs ~$130 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.

nick_SD_fit 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 3 times from my current compounder. Consistency has been excellent.

Shipping: Next-day with cold pack
Packaging: Professional, discreet, proper labeling with lot/batch numbers
Purity: 97.4% average across orders (Janoshik verified)
Customer service: Responsive within 2 hours
Price: $148/month for semaglutide 2.4mg equivalent

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