Chiral differentiation of the noscapine and hydrastine stereoisomers by electrospray ionization tandem mass spectrometry

Energy‐dependent collision‐induced dissociation (CID) of the dimers [2 M + Cat] + of the noscapine and hydrastine stereoisomers was studied where Cat stands for Li + , Na + , K + and Cs + ions. These dimers were generated ‘ in situ ’ from the electrosprayed solution. The survival yield (SY) method was used for distinguishing the noscapine and hydrastine dimers. Significant differences were found between the characteristic collision energies (CE 50 , i.e. the collision energy necessary to obtain 50% fragmentation) of the homo‐ (R,R; S,S) and heterochiral (R,S; S,R) stereoisomers. To distinguish the enantiomer pairs L‐, D‐tyrosine ([M + Tyr + Cat] + ) and L‐, D‐lysine ([M + Lys + Cat] + ) were used as chiral selectors. Furthermore, these heterodimers [M + amino acid + Cat] + were also applied to determine the stereoisomeric composition. It was found that the characteristic collision energy (CE 50 ) of the noscapine and hydrastine homodimers ([2 M + Cat] + ) was inversely proportional to the ionic radius of the cations. Furthermore, the structures of the dimers [2 M + Cat] + were studied by high level quantum chemical calculations. Copyright © 2015 John Wiley & Sons, Ltd.