VendorMark said:The provenance questions are more useful than the numbers.
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.
MariaRD said:Two reports on the same product from two laboratories, four percentage points apart, and no method stated on either.
Reconstituted peptide stability data for certificates of analysis: I had Janoshik test my reconstituted vial at day 1, day 14, and day 28 stored in the refrigerator.
Day 1: 100.1% purity
Day 14: 99.1% purity
Day 28: 99.5% purity
Minimal degradation over 28 days when properly refrigerated. This confirms the standard 28-day beyond-use date is appropriate. Beyond 28 days, I'd reconstitute a fresh vial to be safe.
SarahChen_PharmD said:I am more sceptical of certificates as a category than this thread is.
I tested my certificates of analysis batch through Janoshik — 97.3% purity. That's within acceptable range for compounded peptides. Turnaround was 10 business days.
The test costs ~$126 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.
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 SurmountFan_IN’s answer:
Whether a purity figure and a content figure can disagree without one of them being wrong?
OP back with an update, since a thread like this is useless without one.
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.