Argon DART is more selective than helium. Because the internal energy of Ar* is 11.55 eV, water is not ionized. Only compounds with a low ionization energy are detected. Charge transfer or proton transfer reactions can be induced by adding a dopant such as acetone, methanol, toluene, fluorobenzene or chlorobenzene[3, 4]. Dopant-assisted argon DART can complement helium DART by producing molecular ions for compounds such as polynuclear aromatic hydrocarbons (PAHs), and may reduce fragmentation and enhance protonation for labile compounds.
Argon DART mass spectrum showing molecular ions for lycopene and other compounds in a hexane extract of ketchup.