Ion Sources for Time‐resolved Mass Spectrometry

The ion source is the component of a mass spectrometer where ionization takes place. Some ion sources, such as electron ionization (EI) and chemical ionization (CI) impose the requirement that the samples are in the gaseous form even before they are introduced to the ion source chamber. This chapter describes the most common ionization techniques, including EI, CI, atmospheric pressure chemical ionization (APCI), electrospray ionization (ESI), desorption/ionization (DI), as well as the recently developed ion sources operating at atmospheric pressure. The time spent on ionization contributes to temporal resolution of time-resolved mass spectrometry (TRMS). This intrinsic dead time of the analytical procedure is discussed for different ionization technique. Atmospheric pressure photoionization (APPI) complements APCI and ESI in its functionality and application scope. It can be used to ionize analytes with relatively low polarity, which is difficult to be ionized using other atmospheric pressure ionization techniques.