Comprehensive comparison of ambient mass spectrometry with desorption electrospray ionization and direct analysis in real time for direct sample analysis

Abstract

Ambient ionization mass spectrometry is a powerful analytical method for direct analysis of raw samples. Desorption electrospray ionization (DESI) and direct analysis in real time (DART) are two pioneer ambient ionization techniques and have been widely used in various fields. Despite it is a fact that the application and development of DESI and DART are gaining significant attention in analytical science, few comprehensive comparisons of DESI and DART have been made for in-depth understanding their characteristics for direct sample analysis. In this work, substituent effect on DESI and DART were systematically investigated using a serial of model molecules (i.e., tripeptides and fatty acids) that containing same molecular skeleton and different substituents, revealing that DESI response was determined by substituent hydrophilic effect and DART response of analyte was determined by substituent steric effect. Furthermore, matrix effects on DESI and DART were compared by detecting same analyte in different matrices, revealing respective characteristics of DESI and DART for direct sample analysis. Moreover, DESI and DART also were further compared for detecting same samples, including thermostable, thermally unstable, small and larger molecules, demonstrating complementation of DESI and DART to obtain comprehensive information of raw samples for different purposes in real-world applications. Overall, our results provided new insights into the mechanisms and applications of ambient MS with DESI and DART.