Passage
In mass spectrometry, a sample's molecules are ionized in a vacuum and then exposed to a uniform electric field created by a high-voltage plate in the acceleration chamber. The electric field accelerates the ions until they arrive at the next section of the device, designated as the separation chamber. In this section, the drifting ions are sorted by their mass-to-charge ratio (m/q) .The separation chamber in a time-of-flight mass spectrometer (TOF-MS) is linear and has no electric or magnetic fields. The ions travel at a constant velocity through the chamber until they reach the detector. The time it takes for an ion to reach the detector depends on its m/q ratio.
Figure 1 Time-of-flight mass spectrometerA magnetic sector mass spectrometer (MS-MS) has a curved separation chamber where a magnetic field is generated. The magnetic field exerts a centripetal force on drifting ions, bending their trajectories into curved paths. The radius of the curvature depends on the ion's m/q.
Figure 2 Magnetic sector mass spectrometerThe centripetal force (F) acting on a particle can be determined from its mass (m) and velocity (v) and the radius (r) of the curved path:F = mv²/rEquation 1
-When ions X and Y are analyzed in a TOF-MS, ion Y took more time to reach the detector. Which ion will be observed to have the smaller radius of curvature in MS-MS?

Question

Passage
In mass spectrometry, a sample's molecules are ionized in a vacuum and then exposed to a uniform electric field created by a high-voltage plate in the acceleration chamber. The electric field accelerates the ions until they arrive at the next section of the device, designated as the separation chamber. In this section, the drifting ions are sorted by their mass-to-charge ratio (m/q) .The separation chamber in a time-of-flight mass spectrometer (TOF-MS) is linear and has no electric or magnetic fields. The ions travel at a constant velocity through the chamber until they reach the detector. The time it takes for an ion to reach the detector depends on its m/q ratio.

Figure 1 Time-of-flight mass spectrometerA magnetic sector mass spectrometer (MS-MS) has a curved separation chamber where a magnetic field is generated. The magnetic field exerts a centripetal force on drifting ions, bending their trajectories into curved paths. The radius of the curvature depends on the ion's m/q.

Figure 2 Magnetic sector mass spectrometerThe centripetal force (F) acting on a particle can be determined from its mass (m) and velocity (v) and the radius (r) of the curved path:F = mv²/rEquation 1
-When ions X and Y are analyzed in a TOF-MS, ion Y took more time to reach the detector. Which ion will be observed to have the smaller radius of curvature in MS-MS?

Quizplus · Accepted Answer

11ecba2d_12e1_b8ba_a3bf_1f9365c379bb_MD0008_00 The TOF-MS is used to separate ions by the amount of time taken for the ions to travel a fixed distance. The ions are initially accelerated in a uniform electric field prior to entering the separation chamber. Ions of higher mass and lower charge accelerate more slowly and take longer to reach the detector; an ion's travel time is proportional to its m/q ratio. Because ion Y is stated to take more time to reach the detector, ion Y has a higher m/q ratio and ion X has a lower m/q ratio. In MS-MS, the magnetic field exerts a centripetal force on moving charges to separate ions into paths of different curvatures (Choice D). Ions of higher mass and lower charge are less affected by the magnetic field and have a larger radius of curvature (Choice C). Therefore, the radius of curvature is directly proportional to the m/q ratio. As a result, the ion with a lower m/q ratio, ion X, will be observed to have a smaller radius of curvature. (Choice B) Because ion Y has a higher m/q ratio, it is less affected by the magnetic field and has a larger radius of curvature. Educational objective: Ions in TOF-MS are separated by their travel time to the detector, which is proportional to its m/q ratio. Ions in MS-MS are separated by their radius of curvature, which is directly proportional to its m/q ratio. Therefore, an ion that takes less time to reach the detector in TOF-MS has a small m/q ratio and a smaller radius of curvature in MS-MS.

Passage in Mass Spectrometry, a Sample's Molecules Are Ionized in a a Vacuum