LDTD-APCI Process

The Laser Diode Thermal Desorption (LDTD) technology combined the ultra-fast thermal desorption with an efficient gas-phase Atmospheric Pressure Chemical Ionization (APCI) process.

Introducing a volume between 0.5 and 10 µL into a well and evaporating the solvent leads to the formation of a nano cristal scale layer of material on the stainless steel alloy sheet forming the bottom of the well. 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 as neutrals 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 contained in 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 involved in LDTD is very efficient.

See the following posters presented at the ASMS meeting :

• 57^th ASMS Mechanisms Involved in Positive Atmospheric Pressure Chemical Ionization (APCI) of a LDTD Source.
• 56^th ASMS Laser Diode thermal Desorption Ionization Source (LDTD) : Fundamental Aspects.

See the following posters presented at the ASMS meeting on the comparison between LC-APPI, LC-ESI, LC-APCI and LDTD-APCI.

• 57^th ASMS Highly Efficient Ionization of Liquid Crystals by Laser Diode Thermal Desorption-Atmospheric Pressure Chemical Ionization (LDTD-APCI).
• 55^th ASMS High Throughput Accurate Mass Measurement Using the LDTD Ion Source on the LTQ Orbitrap.