a) What is the meaning of EHC in FD-MS?
Emitters can be heated by passing through an electric current, i.e., the emitter heating current (EHC), supplied via the emitter holders.
In practice, moderate heating of the emitter at constant EHC serves to reduce adsorption to its surface during FI measurements. Heating at a constant rate is frequently employed to enforce desorption of analytes from the emitter in FD-MS. Baking of the emitter (2-5 s to 800-1000 °C) is used to clean it for subsequent measurements.
b) What is the meaning of BAT in FD-MS?
Among other parameters, the onset of desorption of an analyte depends on EHC. Usually, desorption starts before the competing thermal decomposition of the analytes becomes significant. Nevertheless, increasing temperature of the emitter causes increasing thermal stress that can effect fragmentation. The optimum temperature of the emitter where a sufficiently intense signal at the lowest level of fragmentation is obtained has been termed best anode temperature (BAT).
c) What distinguishes LIFDI from conventional FD?
Liquid injection field desorption ionization (LIFDI) avoids decomposition prior to starting the measurement. The solution of the analyte can be handled under inert conditions making LIFDI ideal for FD-MS of reactive analytes.