An improved LC‐MS/MS method for the determination of taspoglutide in plasma and urine using orthogonal HILIC–RP column switching,ultra‐performance LC separation and ‘wrong‐way‐round’ electrospray ionization

The synthetic peptide drug taspoglutide, developed for treatment of diabetes, must be quantified at low pg/mL levels in biological samples. This manuscript describes the improvement of a previous method, featuring orthogonal hydrophilic interaction to reversed‐phase chromatography column switching and tandem mass spectrometric detection. Signal‐to‐noise ratio was enhanced and isobaric interferences were reduced by ultra‐performance separation using a basic mobile phase in ‘wrong‐way‐round’ ionization mode and monitoring a selective fragment ion. Tedious solid‐phase extraction cleanup was abandoned in favor of simple protein precipitation. Urine required the addition of surfactants to prevent adsorptive drug loss. Dissociation of complexes with possibly formed anti‐drug antibodies was achieved with formic acid. Lower limits of quantitation (LLOQ) were 4 pg/mL in human plasma and 10 pg/mL in urine using a 250 μL sample, and an LLOQ of 50 pg/mL was obtained in animal plasma using 50 μL. Precision, accuracy and incurred samples reproducibility fulfilled regulatory requirements. Simultaneous determination of unlabeled and stable isotope labeled taspoglutide, interesting for clearance studies in which both compounds are co‐administered, was realized using a structural analog as internal standard. The described method offered excellent sensitivity with low sample consumption, reasonable throughput, moderate costs and high robustness for routine analysis. Copyright © 2011 John Wiley & Sons, Ltd.