Introduction of Mass Spectrometry and Ambient Ionization Techniques

With the evolution of contemporary analytical chemistry, and in order to get spatial or time-resolved information on the composition and nature of matter, the concept of open-air analysis under ambient conditions in Mass Spectrometry (MS) was proposed and successfully proved its applicability in the first decade of the twenty-first century. This chapter discusses the characteristics and applications of some ambient ionization technologies. Among various ambient ionization techniques, two general categorizations based on the primary ionization mechanism: atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) are described. Direct analysis in real time (DART) can be regarded as a member of APCI-related ionization techniques, and has a common feature with all the other techniques in this group in that it uses a stream of heated gas derived from atmospheric components for analyte ion generation. The ionization process can be generated by electrical discharge or ion evaporation, while desorption mechanisms mostly combine thermal desorption with momentum desorption.