andrew_nyc 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…

Vendor quality matters when discussing certificates of analysis. I've tested my last 3 batches through Janoshik and purity has ranged from 97.4% to 99.0%. 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.

VanRx_Mike said:

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

Thank you — that is the clearest version of this I have read, and I have read a lot of them. I will report back once I have actually tried it.

andrew_nyc 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 vendor review relevant to certificates of analysis: ordered 6 times from my current compounder. Consistency has been excellent.

Shipping: 3-day with temperature monitor
Packaging: Professional, discreet, proper labeling with lot/batch numbers
Purity: 98.7% average across orders (Janoshik verified)
Customer service: Responsive within 1 hours
Price: $127/month for tirzepatide 10mg equivalent

sarah_TO said:

Two reports on the same product from two laboratories, four percentage points apart, and no method stated on either.

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: 99.4% purity, 0.0% total related substances. Clean chromatogram with single sharp peak at expected retention time. Exactly what you want to see.

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