Answer 13.2

a) Draw the common setup for DESI-MS. Take care to clearly mark from where the ionizing fluid medium comes, where the sample is, and how electrically charged species are entering the analyzer.

Desorption electrospray

b) What kind of instrumentation is suitable to be modified for DESI? Think of different mass analyzers and ion source configurations.

Effective DESI operation requires a mass analyzer capable of fast and sensitive spectrum acquisition. Therefore, TOF, LIT ,and QIT analyzers are preferred.
Any atmospheric pressure ionization interface, typically an ESI/APCI interface, can be converted to DESI simply by exchanging the standard sprayer for the DESI unit in front of the sampling orifice.

c) Do you remember the typical settings of liquid and gas flow, solvents, temperatures, and angles for DESI operation? Give useful ranges.

Solvent flow: 3-5 µl/min
Nebulizer gas pressure: 8-12 bar
Spray voltage: 2-6 kV
Sprayer-to-surface distance: 1-5 mm
Sprayer-to-surface angle: 30-70°
Surface-to-desolvation capillary distance: 1-5 mm
Surface-to-desolvation capillary angle: 10-30°
Temperature of desolvation capillary: 200-300°C