Abstract: AIM: To develop a sensitive and selective liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS)method for clinical identification and quantification of digoxin in human plasma.METHODS: The method was based on simple liquid-liquid extraction (LLE).A Kromasil C₁₈ column (150 mm ×2.00 mm, 3.5 μm)was used as the analytical column, while a mixture of acetonitrile and 500 μmol/L ammonium chloride was used as the mobile phase.MS detection was performed using a single quadrupole mass spectrometer in a negative selected ion monitoring (SIM)mode.The deprotonated molecules [M +Cl] (-)at m z 815.40 and 819.00 were used to quantify digoxin and RgC₂(internal standard, I. S.), respectively.RESULTS: The method was linear in the concentration range of 0.05-10.0 ng/mL.The determination of digoxin was not interfered by internal material.The method recovery of digoxin was higher than 75 %.The intra-day and inter-day precisions (RSD %)were within 15.0 %for the analyte, and the freeze-thaw stability of digoxin was excellent.CONCLUSION: While requiring less human plasma, the method was proved to be simple, accurate, sensitive, and had very good reproducibility.Thus, the proposed method enables unambiguous identification and quantification for the therapeutic drug monitoring and pharmacokinetic studies of digoxin.

Key words: digoxin, liquid chromatographic electrospray ionization mass spectrometric method, therapeutic drug monitoring