How to commission independent testing — need advice

CarlaRPh_TPA 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.

jennifer_SEA said:

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

Community-verified vendors for certificates of analysis: I maintain a spreadsheet of Janoshik-verified test results submitted by community members. Across 51 submitted tests:

• 75% tested at ≥98% purity
• 18% tested at 95-98% purity
• 7% tested at <95% purity (concerning)

The vendors with consistently high purity results are listed in the Vendor Directory. We update monthly based on new community submissions.

HPLC_Greg 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, ~$126, 10-14 day turnaround
• Valitech: US-based, ISO 17025 accredited, ~$246
• Eurofins: Full pharmaceutical testing suite, more expensive but comprehensive
• ChemTox: Basic identity and purity testing, ~$126

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.

A narrower follow-up, since the general answer is now clear:

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.