Inter-lab variability in peptide testing — July 2024

InsuranceTom 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.

sean_dublin 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…

Vendor quality matters when discussing certificates of analysis. I've tested my last 6 batches through Janoshik and purity has ranged from 97.1% to 100.3%. 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.

MikeFit_NJ said:

I am more sceptical of certificates as a category than this thread is.

Third-party testing services for certificates of analysis besides Janoshik:

• Janoshik: Gold standard for peptide community, ~$154, 10-14 day turnaround
• Valitech: US-based, ISO 17025 accredited, ~$244
• Eurofins: Full pharmaceutical testing suite, more expensive but comprehensive
• ChemTox: Basic identity and purity testing, ~$114

Janoshik is the community standard but any ISO-accredited analytical lab can verify peptide identity and purity. The key is independence — don't rely solely on the vendor's own testing.

One thing that is still open after pat_auckland’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.