Simultaneous determination of various cardiac glycosides by liquid chromatography–hybrid mass spectrometry for the purity assessment of the therapeutic monitored drug digoxin

A high performance liquid chromatography–hybrid tandem mass spectrometry (LC–MSn) method utilising electrospray ionisation has been developed and implemented for the simultaneous determination of several cardiac glycosides (CGs) as well as their corresponding aglycones formed by and extracted from herbaceous plants of the genus Digitalis. The method has been validated in-house and its performance characteristics (linearity, repeatability, limits of detection, etc.) were assessed for use in the quantification of CGs and their corresponding aglycones. LODs from 38 to 936 pg g−1 in solution, corresponding to mass fraction impurity levels from 0.0009 (or 0.00008%) to 0.019 mg g−1 (or 0.0019%) detectable in the pure materials have been realized. Moreover, the method was used to characterize and to determine the inherent CG impurities in batches of the therapeutic monitored drug digoxin which served as candidate reference material for an organic purity assessment inter-laboratory study (CCQM-P20.f) organised by the BIPM Chemistry Section and carried out within the framework of the Organic Analysis Working Group (OAWG) of the Consultative Committee for Amount of Substance – Metrology in Chemistry (CCQM). Digoxin was selected from materials required for the establishment of reference measurement systems for clinical chemistry and laboratory medicine.