Delayed extraction grid

Reflectrons (ion mirrors) are used to increase the resolution, as well as the ability to obtain accurate mass measurements, by counteracting the effect of the energy spread not compensated for by collisional cooling at the delayed extraction grid (in MALDI sources). A reflectron is a cylinder composed of concentric rings and grids... 

Ions leaving the sample plate are lined up at the delayed extraction grid that reduces both their spatial and energy spreads, the latter through collisional cooling, before their release into the flight tube. 

Figure 2.31. Scheme of a linear TOF system employed for a MALDI experiment with the grid to be used for delayed extraction of the ions from the source. 

Mineo, P., Vitalini, D., Scamporrino, E., Bazzano, S., and Alicata, R. (2005) Effect of delay time and grid voltage changes on the average molecular mass of polydisperse polymers and polymeric blends determined by delayed extraction matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry. Rapid Commun. Mass Spectrom., 19, 2773-2779. 

Figure 6 Schematic drawing of a MALDI-TOF instrument that is equipped with a reflectron mass analyzer. The extraction grids allow one to diminish the initial width of the ion cloud by delayed extraction (DE) and thus to achieve higher mass resolution (see also Fig. 10 for fragment ion analysis in a reflectron). (From Ref. 19.)...

Acquisition parameters were set to acceleration voltage, 20 kV first grid voltage, 94% guide-wire voltage, 0.05% extraction delay time, 200 ns. Each spectrum was an average of 500 laser shots at 100 Hz. 

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