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
-Which of the following best describes the high voltage plate if it accelerates positive ions away from it?

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
-Which of the following best describes the high voltage plate if it accelerates positive ions away from it?

Quizplus · Accepted Answer

11ecba2d_12e1_6a99_a3bf_93f23f252e79_MD0008_00 For the positive ion to be accelerated away from the plate, the charge on the plate needs to repel the ion. Charges with the same sign repel each other, and charges with opposite signs attract. Therefore, the accelerating plate needs to be positively charged to repel and accelerate positive ions away. Electric field lines are used to denote the direction that a positive charge would be accelerated in an electric field. Because positive charges repel positive charges, electric field lines point outward from positive charges and point toward negative charges (Choice B). Because the accelerating plate is positively charged, its electric field lines nearby must be pointing away, as shown in the figure. (Choices C and D) If the plate were negatively charged, it would attract positive ions, preventing them from moving past the acceleration chamber. In addition, electric field lines would point toward the negatively charged plate. Educational objective: Electric charges with the same sign repel, and charges with opposite signs attract. Electric field lines point out from positive charges and into negative charges. Therefore, a positively charged plate repels positively charged ions, and the electric field lines point away from a positively charged plate.

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