a) DART uses a fluid medium to achieve ionization of samples. What medium is used?
Typically, helium is employed. Nitrogen can also be used in some cases.
b) Which mechanism initiates ionization in DART?
A Penning ionization process is initiated by a corona discharge in helium. Metastable He atoms are then emerging from the source and effect ionization of atmopheric nitrogen and water. Ion-molecule reactions in the ambient then lead to the ionization of analyte molecules.
c) Think about operator safety when measuring DART spectra. Is there high voltage applied in proximity to the sample stage, are there other potential hazards?
In DART, there is no high voltage at the sample stage, which makes it even safer than DESI. Nonetheless, a regular daily exposure of skin to the ionizing medium should probably be avoided. The use of tweezers and gloves seems appropriate when exposing samples to a DART source.