Peptide enrichment by ion-pair solid-phase extraction.

The technique of Solid-Phase Extraction (SPE) is widely used in various fields to concentrate samples and the search for tools to improve recoveries remains of outmost importance. The use of polymer based cartridges has become prevailing in a broad range of fields to enrich peptides from biological matrices. However, the existing SPE protocols are characterized by disparity. Ion-pairing (IP) reagents are commonly used in chromatographic applications, but their combination with SPE is less known. The aim of this study was to evaluate various SPE loading conditions, including the use of IP reagents, to improve the recoveries of nine selected peptide molecules. Control of pH and the use of IP reagents were found to be crucial to improve the enrichment of the peptides, especially cationic peptides, for which an up to ten-fold increase was observed. The practical potential of the presented theoretical findings were verified by employing IP-SPE for the development of an efficient extraction method for the doping relevant peptide Synacthen. The general proof of principle was obtained by analysis of excretion study urine samples and validation was performed with focus on the limit of detection (20 pg/ml) and recovery (37%).