Chiral liquid chromatography-tandem mass spectrometry assay to determine that dexpramipexole is not converted to pramipexole in vivo after administered in humans.

•A chiral LC–MS/MS assay was developed and qualified to measure dexpramipexole in human plasma.•The sensitivity of the method is 0.150ng/mL.•The quantitative chiral selectivity of the method is 0.150:1000 (0.015%).•The assay was used to monitor the potential chiral conversion of dexpramipexole in humans.