Q1. Why is helium used in a 3-D ion trap? a. to collisionally cool ions to the c
ID: 1025626 • Letter: Q
Question
Q1. Why is helium used in a 3-D ion trap?
a. to collisionally cool ions to the center of the trap
b. to diffuse ions out of the trap
c. to slow ions down entering the trap
d. it is less expensive than nitrogen
Q2. Ion traps store ions when
a. the RF and DC potentials place ions just outside the apex of their stability diagram
b. the RF and DC potentials place ions in the confines of their stability diagram
c. the RF and DC potentials place ions outside of their stability diagram
d. the RF and DC potentials allow ions to move in circular motions
Q3. Ion isolation in 3-D traps
a. is done by ejecting all undesired m/z ions out of the trap
b. is the first step in MSn experiments
c. is done by only storing one desired m/z ratio in the trap
d. all of the above
Explanation / Answer
1.a.
A helium gas of about 1 mtorr within the trapping volume greatly improves the mass resolution of the instrument by reducing the kinetic energy of the ions and contracting the ion trajectories to the center of the trap.
2.c.
The 3D ion trap basically works on the same principle as a quadrupole mass analyzer, using static DC current and RF oscillating electric fields, but the hardware is configured differently, where the parallel rods are replaced with two hyperbolic metal electrodes (end caps) facing each other, and a ring electrode placed halfway between the end cap electrodes; ions are trapped in a circular flight path based on the applied electric field.
3.c.
Isolation of ion means singling out the required ion.Thus,it is done only by storing the desired m/z ratio.The first step in MSn experiments is generating the molecular ion.Thus,eliminating option b.
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