Influence Exerted by the Solvent Effect on the Mobility Peak of 1,8-Naphthalic Anhydride in Ion Mobility Spectrometry.

Abstract

The collision cross-section (CCS) values of ions determined by ion mobility-mass spectrometry (IM-MS) can be used to deduce the shape and size of the ions. For each compound, as well as its isomer or tautomer, a unique arrival time peak was obtained in extracted ion mobility (EIM) spectra, which corresponded to a specific CCS value. However, the generation of solvated ions by electrospray ionization (ESI) increases the number of mobility peaks, which makes the EIM spectra difficult to interpret. In this study, solvent clusters formed by acetonitrile and methanol around 1,8-naphthalic anhydride (1,8-NA) cations ([C12H6O3 + H]+1,8-NA) were investigated using trapped ion mobility spectrometry-time-of-flight mass spectrometry (TIMS-TOF MS). The effects of infusion flow rate, nebulizer gas pressure, drying gas rate, and drying gas temperature on the formation of solvent clusters from acetonitrile and methanolic solution were systematically studied. The formation of solvent clusters was observed with infusion flow rates increased, which was manifested by the larger experimental CCS values of [C12H6O3 + H]+1,8-NA. Acetonitrile tended to form solvent clusters around ions more readily than methanol. These solvent clusters were stable enough to be detected by TIMS, but they cannot survive under ion activation conditions of mass spectrometry (MS). Increasing the nebulizer gas pressure seems to be a better way to eliminate the formation of solvent clusters in TIMS-TOF MS and give a "cleaner" EIM spectra. The current research demonstrates that more attention should be paid to the solvent effect on CCS values and their interpretation.