Supporting Information for
Time-resolved imaging of the MALDI linear-TOF ion cloud: Direct visualisation and
exploitation of ion optical phenomena using a position- and time- sensitive detector.
Shane R. Ellis, Jens Soltwisch and Ron M. A. Heeren *
FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
*Corresponding author: heeren@amolf.nl
Figure S1.
Figure S1. Simulation of ion paths in the ion source showing the dependence of the focal
length (f) for (a) different extraction voltages (m/z = 22 kDa, PIE = 0 ns PIE), (b) different
pulsed-ion extraction (PIE) delay times (m/z = 22 kDa, EV = 1.5 kV) and (c) different masses
(c) (EV = 1.5 kV, PIE = 0 ns). For the simulation of different PIE values, the starting point of
the ions was shifted towards the first electrode based on an average initial velocity of the ions
produced from sinapinic acid of 350 m/s [1].
Figure S2
Figure S2. Corresponding mass spectra for the ion images shown in Figure 2c.
Figure S3
Figure S3. Simulation showing the focal length (f) dependence for different orientations of
the P2-electrode geometry. To simulate the effect of the outer holes the two extreme cases
arising when ions travel through 2 perpendicular planes rotated 45 degrees was modelled. (a)
The red simulation models the case when ions flying through planes 45 degrees to the vertical
and horizontal axes. In this case ions see the electrode geometry shown in the top of (b), i.e., a
steel sheet with a small hole in the centre. The blue simulation corresponds to the case when
ions fly in two planes located along the vertical and horizontal axes. In this case ions see the
electrode geometry shown in the bottom of (b), i.e, just a thin steel ring electrode. (c)
Simulation of resulting ion impact distribution on the detector for both orientations at
different extraction voltages and the expected shape of the overall impact region. Expected
shapes were created by determining the radii in the upright and tilted cross directions from the
simulation (red and blue bars in (c)) and by smoothly connecting the endpoints of the bars.
Simulation parameters were: m/z = 22 kDa, 0 ns PIE-delay (continuous extraction), an initial
ion velocity of 380 m/s [1] and a 10° plume opening angle.
Figure S4
Figure S4 (a) Ion cloud images of [IgG]1+ (m/z 147,000) acquired by varying the extraction
voltage with an Einzel lens voltage of 12 KV and 500 ns PIE-delay. (b) Ion cloud images of
[IgG]1+ (m/z 147,000) acquired by varying the PIE-delay using with an Einzel lens voltage of
6 kV and an extraction voltage of 4.0 kV. The ion counts recorded by each pixel are shown in
the scale bar. The extraction electrode is shown as an inset of (a). (c) Overlayed ion cloud
images of [IgG short chain fragment]1+ (m/z 22000, red), [IgG]2+ (m/z 73500, green) and
[IgG]1+ (m/z 147,000, blue) acquired using extraction voltages of 4.2 KV, 3.0 kV and 2.2 kV
with an Einzel lens voltage of 12 KV and 500 ns PIE-delay. (d) Corresponding integrated
mass spectra generated from analyses shown in (c). All images and spectra are integrated
from 200 laser shots.
Figure S5
Figure S5. Determination of relative initial velocities of Single charged Protein A ions
produced from (a) 2, 5-dihydroxybenzoic acid (DHB), (b) 2, 6-dihydroxyacetophenone
(DHAP), (c) sinapinic acid (SA), (d) ferrulic acid (FA) and (e) α-cyano-4-hydroxycinnamic
acid (CHCA) matrices. The slope of the linear fit function is proportional to the initial ion
velocity. Error bars represent the standard deviation of 3 replicate measurements at each PIE
delay. (f) Comparison of the slopes acquired from the different matrices. The poor linearity
and large errors for DHB arise due to the very broad peaks observed for DHB in this study.
Figure S6
Figure S6. Integrated (1000 laser shots) mass spectrum generated from Protein mixture
covered with a 37 µm pitch transmission electron microscopy grid during acquisition of
images shown in Figure 6a-d.
References
(1)
Glückmann, M., Karas, M., The initial ion velocity and its dependence on matrix,
analyte and preparation method in ultraviolet matrix-assisted laser desorption/ionization. J.
Mass Spectrom. 1999, 34, 467-477.