Batch-to-batch purity variation — looking for input

Clinical perspective, offered as context rather than as advice.

Community-verified vendors for certificates of analysis: I maintain a spreadsheet of Janoshik-verified test results submitted by community members. Across 48 submitted tests:

• 85% tested at ≥98% purity
• 10% tested at 95-98% purity
• 5% 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.

lisa_labSD said:

My vendor review relevant to certificates of analysis: ordered 5 times from my current compounder.

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 the refrigerator.

Day 1: 99.0% purity
Day 14: 98.3% purity
Day 28: 98.4% purity

Minimal degradation over 28 days when properly refrigerated. This confirms the standard 28-day beyond-use date is appropriate. Beyond 28 days, I'd reconstitute a fresh vial to be safe.

lisa_labSD said:

My vendor review relevant to certificates of analysis: ordered 5 times from my current compounder.

Thank you — that is the clearest version of this I have read, and I have read a lot of them.

Adding the clinical framing, because it changes how the question reads.

Vendor quality matters when discussing certificates of analysis. I've tested my last 4 batches through Janoshik and purity has ranged from 97.1% to 100.5%. 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.

Moderator note: good thread. Keeping it here rather than moving it, because the question is general enough to be useful. Report rather than reply if it drifts again.