Sensitive and robust LC–MS/MS analysis of digoxin in human plasma through optimization of in-source adduct formation

Aim: To develop and validate an LC–MS/MS assay for the quantification of digoxin in human plasma. An LLOQ of 10 pg/ml using a 100 μl sample was required to support drug–drug interactions studies. Results: Digoxin formed multiple precursor ions in positive and negative ESI and methods based on several of these have been reported previously. After screening viable precursor ions, we found the ammonium adduct gave the best combination of sensitivity and selectivity on our LC–MS/MS platform. Samples were extracted using a simple liquid-liquid procedure. Conclusion: The assay was successfully validation to current EMA guidelines. To the best of our knowledge the developed assay is the most sensitive published to date.