Laser Diode Thermal Desorption technology combined the ultra-fast thermal desorption of a dry sample with the ionization of the produced neutral molecules in the gas phase without solvent, mobile phase or external matrix. Both process, a low sample size thermal desorption and the APCI in "dry" environment, provide to the LDTD its tremendous analytical speed and analytical performances.
Introducing a low volume size into a well and evaporating the solvent lead to the formation of a nano-cristal scale layer of material on the stainless steel alloy sheet. Applying a laser irradiation on the back of the stainless steel sheet in a short period of time (typically within 4-6 seconds) allows the analyte nano-crystals to thermally desorbed into the gas phase at a temperature lower than the reported melting point. Moreover, the newly desorbed molecules enter into a gas flow at 3 L/min which act as a heat buffer. The molecules internal energy is dissipated via elastic collisions with the carrier gas molecules travelling into a transfer tube held at room temperature. This thermalization process lowers the occurrence of thermal fragmentation.
The neutrals enter the corona discharge region to undergo APCI. The main source of protons (+APCI) is provided by the water contains into the air (compressed air from cylinder or generated from a compressor). Research has demonstrated the presence of H3O+ and (H2O)H3O+ as the species initiating the ionization via a direct proton-transfer reaction. Unlike traditional APCI where the proton transfer occurs via protonated solvent molecules or water clusters (i.e. (H2O)nH3O+ where n ≥ 3) the proton transfer involve in LDTD is very efficient.
See the following posters presented at the ASMS meeting :
See the following posters presented at the AMSM meeting on the comparison between LC-APPI, LC-ESI, LC-APCI and LDTD-APCI.
