julia.endo said:Inter-laboratory variation comes from real methodological differences, not sloppiness: which reference standard was used and how it was itself…
I am more sceptical of certificates as a category than this thread is. The document tells you about a sample somebody chose to send, at a moment in time, and nothing about the vial in your hand. Independent purchase-and-test is a different quality of evidence and everything else is inference.
I would rather be corrected than agreed with, if it comes to it.
steph_laguna said:Two reports on the same product from two laboratories, four percentage points apart, and no method stated on either.
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: 98.4% average across orders (Janoshik verified)
Customer service: Responsive within 2 hours
Price: $156/month for tirzepatide 10mg equivalent
DanielChem_CHI said:I am more sceptical of certificates as a category than this thread is.
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 chromatography graph, it's not a real COA
- Exact 100% purity: Suspicious — real testing always shows slight variation
- No batch number: Can't trace back to specific production
- No endotoxin testing: For injectables, this is essential
- Template looks like it was made in Word: Professional labs have standardized formats
I have seen fake COAs that are literally photoshopped. Always verify independently if possible.
Sigma-Aldrich — Research-Grade Standards
Certified reference materials, analytical reagents, and research-grade standards for peptide verification. Trusted by laboratories worldwide.
Shop Reference StandardsOne thing that is still open after KetoKyle’s answer:
Why two laboratories report different purity for the same batch, and which number to believe?
Reporting back.
Purity and content being different measurements was the piece I was missing. The vial was overfilled and pure, which is a very different problem from the one I thought I had.