Dr.GutHealth said:

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

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: 99.6% purity, 0.2% total related substances. Clean chromatogram with single sharp peak at expected retention time. Exactly what you want to see.

One thing that is still open after Dr.GutHealth’s answer:

What would you measure differently if you were starting again?

quinn_sf said:

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

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

• Janoshik: Gold standard for peptide community, ~$122, 10-14 day turnaround
• Valitech: US-based, ISO 17025 accredited, ~$232
• Eurofins: Full pharmaceutical testing suite, more expensive but comprehensive
• ChemTox: Basic identity and purity testing, ~$112

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.

quinn_sf said:

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

Agreed, with the usual condition: that holds for the average and this board is a collection of individuals. A population claim and a personal prediction are different things and get quoted interchangeably.

quinn_sf said:

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

That reframing is the part I needed.