Nanoelectrospray versus electrospray in chiral analysis by the kinetic method

Electrospray ionization generates trimeric diastereoisomeric clusters as the first important step in chiral analysis by mass spectrometry using the Cooks′ kinetic method. Cu2+ and L-tryptophan were used as a central metal and as a chiral reference ligand, respectively. The comparison of electrospray and nanoelectrospray showed that although the electrospray system was generally more robust, the application of nanoelectrospray was essential for performing successful analysis in some cases, especially for real samples. Basically, no significant differences between the ion sources were observed for model samples of analytes (isoleucine, ephedrine, phenylalanine) without interfering matrix. On the other hand, model samples containing sodium chloride and a buffer containing a real sample (drug formulation Mucoseptonex E in which D-ephedrine is the active substance) could not be analyzed using ESI, whereas nano-ESI gave satisfactory results. An explanation is based on the differences of ionization processes occurring in the compared sources.