Quantification of intracellular and extracellular digoxin and ouabain by liquid chromatography/electrospray ionization tandem mass spectrometry

• We developed a LC/MS/MS method for intracellular amount of digoxin and ouabain.
• The validation results showed that an accurate, reproducible and selective assay was achieved.
• The developed method was applied to the transport studies using Transwell chambers.

A liquid chromatography/tandem mass spectrometry method for the determination of intracellular accumulation in addition to transcellular transport of digoxin and ouabain in renal epithelial HK-2 cells was developed. The solid-phase extraction Bond Elut® C18 (100 mg/1 mL) cartridge was used for the extraction of digoxin and ouabain from extracellular (medium) and intracellular (cell lysate) matrices. Chromatographic separation was performed on a CAPCELL PAK C18 MGII column (2.0 mm × 150 mm, 5 μm). This method covered a linear range of 0.5–1000 ng/mL of concentrations in medium and 0.5–1000 ng of concentrations in cell lysate for digoxin and ouabain. The intra-day precision and inter-day precision of analysis were less than 11.9%, and the accuracy was within ±11.6%. The total run time was 16 min. Our method was successfully applied to the transport experiments of digoxin and ouabain by HK-2 cell monolayers.