Understanding peptide purity percentages — what worked for you?

HPLC_Greg said:

I tested my certificates of analysis batch through Janoshik — 99.5% purity.

Thank you for spelling out the reasoning rather than just the conclusion. Printing the relevant bit and taking it with me.

From the other side of the consultation, briefly.

My vendor review relevant to certificates of analysis: ordered 6 times from my current compounder. Consistency has been excellent.

Shipping: 3-day with temperature monitor
Packaging: Professional, discreet, proper labeling with lot/batch numbers
Purity: 98.7% average across orders (Janoshik verified)
Customer service: Responsive within 1 hours
Price: $143/month for tirzepatide 10mg equivalent

MASHdoc_SA said:

My vendor review relevant to certificates of analysis: ordered 6 times from my current compounder.

Same experience, arrived at from the opposite direction.

MASHdoc_SA said:

My vendor review relevant to certificates of analysis: ordered 6 times from my current compounder.

HPLC results interpretation for certificates of analysis: when you get your Janoshik report back, here's what the numbers mean:

• Purity %: Should be >97%. Below 95% is concerning.
• Retention time: Should match reference standard for the peptide
• Related substances: Degradation products should be <2% total
• Single impurity: No individual impurity should exceed 1%

My last batch: 99.4% purity, 0.0% total related substances. Clean chromatogram with single sharp peak at expected retention time. Exactly what you want to see.

MASHdoc_SA said:

My vendor review relevant to certificates of analysis: ordered 6 times from my current compounder.

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

• Janoshik: Gold standard for peptide community, ~$132, 10-14 day turnaround
• Valitech: US-based, ISO 17025 accredited, ~$202
• Eurofins: Full pharmaceutical testing suite, more expensive but comprehensive
• ChemTox: Basic identity and purity testing, ~$102

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.