Simultaneous determination of limonin, dictamnine, obacunone and fraxinellone in rat plasma by a validated UHPLC–MS/MS and its application to a pharmacokinetic study after oral administration of Cortex Dictamni extract

• The report describes the validation of a high precision and accuracy UPLC–MS/MS method for the simultaneous determination of limonin, dictamnine, obacunone and fraxinellone in rat plasma.
• The pharmacokinetic study of Cortex Dictamni in rats is firstly reported.
• Extraction performed with a simple liquid–liquid extraction.
• Sensitivity, specificity and high throughput.

A rapid and selective ultra high performance liquid chromatography–tandem mass spectrometry method was developed for the simultaneous determination of four major ingredients in Cortex Dictamni extract, including limonin, dictamnine, obacunone and fraxinellone in rats plasma. Nimodipine was used as the internal standard. Following extraction by methyl tert-butyl ether, the analytes were separated on a Thermo Syncronis C18 column by a gradient elution within a runtime of 9 min. The mobile phase consisted of A (methanol) and B (2 mmol/L ammonium acetate in water). The detection was accomplished by using positive ion electrospray ionization in multiple reaction monitoring mode. The method was linear for all analytes over investigated range with all correlation coefficients greater than 0.998. The lower limits of quantification were 9.18 ng/mL for limonin, 12.0 ng/mL for dictamnine, 16.05 ng/mL for obacunone and 4.59 ng/mL for fraxinellone. The intra- and inter-day precision (RSD%) was within 10% and the accuracy (RE%) ranged from −12.9% to 9.7%. This rapid and sensitive method was fully validated and successfully applied to the pharmacokinetic study of limonin, dictamnine, obacunone and fraxinellone in the rat plasma after oral administration of Cortex Dictamni extract.