Simultaneous quantitation of 3-n-butylphthalide (NBP) and its four major metabolites in human plasma by LC-MS/MS using deuterated internal standards

► Simultaneous determination of NBP and its four major metabolites in human plasma. ► Synthetic deuterated ISs were utilized to compensate for matrix effects. ► (−)ESI and (+)ESI switch was complementary to achieve high sensitivity. ► Mixture of methanol and acetonitrile facilitated separation of isomers.