Determination of digoxin and digitoxin in whole blood

A liquid chromatography-tandem mass spectrometry (LC-MS-MS) method has been developed and validated for the determination of digoxin and digitoxin in whole blood samples in autopsy cases. Samples were prepared by liquid-liquid extraction (LLE) with ethyl acetate/heptane/dichloromethane (3:1:1). LC separation was achieved using an Atlantis dC(18)-column (2.1 x 50 mm, 3 microm). The time between injections was 11 min. Mass detection was performed by positive ion mode electrospray LC-MS-MS on the ammonium adducts with two transitions for each analyte and one for the internal standard (digoxin-d(3)). Within-day precision was between 8.3 and 10.8%, between-day precision was between 8.7 and 14.2% and accuracy (bias) was between -17.3 and 11.5%. LOQ was 0.1 nmol/L (0.08 ng/mL), with an accuracy and precision of 19% and -17% (digoxin) and 18% and 3% (digitoxin). Matrix effects ranged from 104 to 117%. Good qualitative correlation with previous findings was achieved for 38 autopsy cases. The median (range, number of cases) B-digitoxin and B-digoxin found with the LC-MS-MS method in this very limited material were 9.3 (3.4-23.8, n = 24) and 5.6 (3.4-26.5, n = 4) nmol/L, respectively.