KevinCompounds said:

Mass spectrometry confirmation for certificates of analysis: beyond HPLC purity, mass spec tells you the molecule's exact molecular weight.

Vendor quality matters when discussing certificates of analysis. I've tested my last 4 batches through Janoshik and purity has ranged from 99.7% to 100.5%. Consistency is key.

For anyone new: always request the COA, and consider independent verification. The $300 for a Janoshik test is worth the peace of mind.

RegAffairsDC said:

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

This answered a question I did not know how to ask.

KevinCompounds said:

Mass spectrometry confirmation for certificates of analysis: beyond HPLC purity, mass spec tells you the molecule's exact molecular weight.

I tested my certificates of analysis batch through Janoshik — 98.7% purity. That's within acceptable range for compounded peptides. Turnaround was 10 business days.

The test costs ~$124 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.

DebRD_ATL said:

I have a certificate reporting 99.2% purity and 6.1mg content on a vial sold as 5mg, and I cannot work out whether those two numbers are consistent or…

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: 98.0% average across orders (Janoshik verified)
Customer service: Responsive within 2 hours
Price: $152/month for tirzepatide 10mg equivalent

Moderator note: leaving this open. It is being argued well and the disagreement is the useful part.