Question 1

Which physical principle is primarily responsible for the separation of ions in a magnetic sector mass spectrometer?

Accepted Answer

The Lorentz force acting on moving charged particles in a magnetic field

Question 2

In a magnetic sector MS, what is the relationship between the radius of curvature $$r of an $$ion's path and its mass-to-charge ratio $$\frac{m}{q}$$?

Accepted Answer

$$r = \frac{m v}{q B}$$

Question 3

If the magnetic field strength $$B is $$increased in a magnetic sector MS, what happens to the radius $$r of $$the ion's path, assuming all other variables are constant?

Accepted Answer

The radius $$r$$ decreases

Question 4

Given the equation $$\frac{m}{q} = \frac{2V}{B^2$ r^2$}$$, which experimental variable is typically varied to scan a range of $$\frac{m}{q}$$ values in a magnetic sector MS?

Accepted Answer

Accelerator voltage $$V$$

Question 5

Why did Aston's early mass spectra of Ne and Cl show many peaks, even though each element has only two isotopes?

Accepted Answer

Contaminants such as air, water, and CO$$_2$$ were present due to a crude vacuum system

Question 6

A peak at $$m/z = 18 in $$Aston's first MS of Ne is most likely due to which contaminant?

Accepted Answer

H$$_2O$^+$$

Question 7

Which equation correctly expresses the kinetic energy $$E_m of an $$ion in terms of its mass $$m$$ and velocity $$v$$?

Accepted Answer

$$E_m = \frac{1}{2} m v^2$

Question 8

In the context of mass spectrometry, what does the term $$m/z$$ refer to?

Accepted Answer

The mass-to-charge ratio of an ion

Question 9

A voltage scan of a magnetic sector MS for He shows peaks at 300 V, 1500 V, 3150 V, and 3300 V. If the magnetic field and radius are constant, what is the mass of the ion detected at 1500 V, given $$\frac{m}{q} = \frac{2V}{B^2$ r^2$}$$ and $$q=2$$?

Accepted Answer

10 amu

Question 10

Which of the following ions would most likely produce a peak at $$m/z = 32 in a $$crude vacuum MS spectrum?

Accepted Answer

O$$_2^+$$

Question 11

What is the main advantage of modern magnetic sector mass spectrometers compared to Aston's original design?

Accepted Answer

Improved vacuum systems reduce contamination and increase accuracy

Question 12

Which rule is used to determine the direction of the Lorentz force for positive ions in mass spectrometry?

Accepted Answer

Left hand rule

Question 13

If the charge $$q of an $$ion is doubled while keeping mass $$m$$, velocity $$v$$, and magnetic field $$B$$ constant, what happens to the radius $$r of $$its path in a magnetic sector MS?

Accepted Answer

The radius $$r is $$halved

Question 14

A sample contains both $$^{20}Ne$^{2+}$$ and $$^{22}Ne$^+$$ ions. Which will have a larger radius of curvature in a magnetic sector MS, assuming equal velocity and magnetic field?

Accepted Answer

$$^{22}Ne$^+$$

Question 15

In a mass spectrum, what does the height of a peak typically represent?

Accepted Answer

The relative abundance of ions with a specific $$m/z$$

Question 16

Which contaminant is most likely responsible for a peak at $$m/z = 28 in $$Aston's first MS of Ne?

Accepted Answer

N$$_2^+$$

Question 17

If the detector in a magnetic sector MS is set to record only at a fixed radius $$r$$, which variable must be changed to scan different $$m/q$$ values?

Accepted Answer

Accelerator voltage $$V$$

Question 18

Which of the following best describes the function of the ion optics in a magnetic sector MS?

Accepted Answer

They focus and direct ions into the magnetic field for separation

Question 19

A student observes a peak at $$m/z = 17 in a $$mass spectrum of Ne using a crude vacuum. Which ion is most likely responsible?

Accepted Answer

OH$$^+$$

Question 20

Which Nobel Prize-winning chemist is credited with the invention of the first sector mass spectrometer?

Accepted Answer

Francis William Aston

Mass Spectrometry: Principles, Instrumentation, and Applications

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