Thermal Desorption Differential Mobility Analyzer (TD-DMA)
Knowledge on the chemical composition of nanoparticles is essential in order to characterize their sources and to study the importance of certain trace gases that are involved in their formation, growth and transformation. However, the measurement of the nanoparticle chemical composition is very challenging due to the miniscule mass these particles provide at ambient concentrations. Moreover, a sensitive instrumental technique requires that the smallest particles can be separated from their carrier gas and other larger particles.
The TD-DMA is an instrument recently designed by Wagner et al., 2018, which uses an online and discontinuous principle for the detection of the chemical composition of nano aerosol particles (5 - 30 nm) on the atmosphere.
The analysis takes place in two main steps.
Collection: the particles are taken from the sample and charged by the X-ray source, a specific size can be selected by differential mobility analysis, subsequently the charged particles with specific size are collected on a filament by electrostatic precipitation.
Evaporation: the particles that are collected on the filament are evaporated in a clean carrier gas and analyzed by a chemical ionization mass spectrometer.
Currently, the TD-DMA is installed on the NO3- LTOF which allows the particle collection while the gas phase measurement is taking place. Hence, the direct comparison with gas phase and particle measurements is possible using the same Chemical Ionization and Time of Flight.