How do I reconcile 98.4% from VendorInvestigate with 98.8% from the supplier?

The case in front of me: 98.4% · VendorInvestigate · 98.8%.

I have two candidate explanations and no way to distinguish them.

The same procedure has worked without incident several times previously, which argues against technique.

Is this recoverable, and how would I tell?

Specifically, gradient slope is the most powerful parameter and almost nobody mentions it, which is why two reports on the same material disagree by a point.

Mass on column affects detector linearity and peak overlap — overloading broadens peaks and hides neighbours, while underloading improves resolution but loses sensitivity.

Retention time is sequence-specific and method-specific, so comparing your result to a supplier value using a different method is meaningless without method documentation.

The Arrhenius relationship for peptide degradation is the basis of accelerated stability testing and also governs how quickly methods drift with temperature.

The limitation is that single-digit micro-impurities become invisible at typical reporting thresholds, so "no impurities detected" means "none above one in two thousand."

If you are ranking vendors, specify a method and have all samples tested at the same place.

edited 27 Apr 2025 by Dr_Rosalind_Achebe — added the placebo-arm figures