Direct analysis - no sample preparation - of bioavailable cortisol in human plasma by weak affinity chromatography (WAC)

Abstract

Pre-analytical treatment of blood plasma is a time consuming and often rate limiting step in the workflow of LC/MS analysis. We present in this pilot study a new approach for quantitative LC/MS based on weak affinity chromatography (WAC) of crude plasma. The steroid hormone cortisol was selected as a clinically relevant biomarker, as it currently requires extensive pre-analytical preparation. A WAC unit with saturating, immobilized albumin as a prototypic weak binder was used in combination with an ion-funnel MS/MS detector to perform zonal affinity chromatography of cortisol directly from a plasma sample, followed by quantitative multiple reaction monitoring (MRM). This procedure also allowed us to determine the amount of bioavailable cortisol in the clinical plasma sample which is of significant therapeutic interest. This WAC-MS approach showed an excellent correlation (R2 = 0.86 (P < 0.0001 (highly significant); n = 60) with a state-of-the-art, clinical competitive immunoassay procedure for plasma cortisol analysis. With integration of WAC into LC/MS workflow, it may be possible to both accelerate and improve assay performance by eliminating the sample extraction step. Preliminary data with other steroid hormones indicate that WAC-MS can be applied to various biomolecules using a plasma transport protein such as albumin.