Nondigest liberation of biomarkers from plasma: a novel two-stage ultrafiltration approach.

A simple procedure for sample preparation of human plasma by two stages of ultrafiltration using one device is described. Our approach is useful for nondigest liberation of biomarkers bound to albumin and other plasma proteins. The analyte contained in the ultrafiltrate can be directly analyzed without additional sample preparation, and quantified by 2-D RP-RP LC/MS.