Visualizing Mass Transport in Desorption Electrospray Ionization using Time-of-Flight Secondary Ion Mass Spectrometry, an In-Depth Study
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to visualize the transport of analyte desorbed by a desorption electrospray ionization (DESI) technique. We investigated the effect of probe incidence angle, height, and distance on the relative amount and the spatial distribution of desorbed analyte molecules, aimed at the optimization of settings that would maximize signal, minimize material loss, and produce consistent results. Incidence angle was found to be critical for desorption, as an order of magnitude decrease in intensity was observed when the incidence angle was changed from 20° to 75°, due to decreased forward momentum and increased lateral dispersion that led to a significant loss of analyte in the lateral direction. Longer probe distances were seen to increase both lateral and vertical dispersions due to the diverging flow of the spray, and increase the extent of scattering that led to loss of material. Therefore, shorter probe distances were preferred for maximum entry of analyte into the inlet of the mass spectrometer (MS). Changing the tip height from (1 to 2 to 3) mm changed the the diameter of the spray impact area from (1.3, 1.8, to 2.1) mm, respectively, corresponding to a factor of 2 increase in area for a change in tip height from 1 mm to 2 mm, and to a factor of 2.5 increase in area for a change in tip height from 1 mm to 3 mm. This corresponded almost exactly to the intensity of the analyte, where a factor of 1.8 increase was seen for a change in tip height from 1 mm to 2 mm, and a factor of 2.6 increase was seen for a change in tip height from 1 mm to 3 mm. The study showed how ToF-SIMS can be used as a unique tool for characterizing the transport of desorbed analyte for reproducible data acquisition, potentially offering new interface designs for improved transmission of analyte into the mass spectrometer.
Visualizing Mass Transport in Desorption Electrospray Ionization using Time-of-Flight Secondary Ion Mass Spectrometry, an In-Depth Study, Analyst, [online], https://doi.org/10.1039/C4AN01481B
(Accessed June 5, 2023)