From the other side of the consultation, briefly.

Vendor quality matters when discussing certificates of analysis. I've tested my last 3 batches through Janoshik and purity has ranged from 98.8% to 99.0%. 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.

Dr.Martinez said:

Vendor quality matters when discussing certificates of analysis.

This is my experience too, for whatever a second data point is worth.

Dr.Martinez said:

Vendor quality matters when discussing certificates of analysis.

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

• Janoshik: Gold standard for peptide community, ~$133, 10-14 day turnaround
• Valitech: US-based, ISO 17025 accredited, ~$243
• Eurofins: Full pharmaceutical testing suite, more expensive but comprehensive
• ChemTox: Basic identity and purity testing, ~$103

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.

Dr.Martinez said:

Vendor quality matters when discussing certificates of analysis.

I tested my certificates of analysis batch through Janoshik — 98.4% purity. That's within acceptable range for compounded peptides. Turnaround was 8 business days.

The test costs ~$133 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.

Following on from Dr.Martinez — and this may be the naive question:

Whether a purity figure and a content figure can disagree without one of them being wrong?