Is 98% purity actually good or should I be worried — need advice

LibrarianMeg said:

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…

I tested my certificates of analysis batch through Janoshik — 99.5% purity. That's within acceptable range for compounded peptides. Turnaround was 8 business days.

The test costs ~$149 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.

RunnerRach said:

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

Saving this. It is the first explanation that did not require me to already understand it. Printing the relevant bit and taking it with me.

LibrarianMeg said:

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…

Community-verified vendors for certificates of analysis: I maintain a spreadsheet of Janoshik-verified test results submitted by community members. Across 53 submitted tests:

• 78% tested at ≥98% purity
• 15% 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.

Dr.PulmRoch said:

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

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

• Janoshik: Gold standard for peptide community, ~$151, 10-14 day turnaround
• Valitech: US-based, ISO 17025 accredited, ~$211
• Eurofins: Full pharmaceutical testing suite, more expensive but comprehensive
• ChemTox: Basic identity and purity testing, ~$111

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.

Moderator note: a couple of off-topic posts removed. Thread quality here is what the rules are for. Keep it up.