This set of Analytical Instrumentation Multiple Choice Questions & Answers (MCQs) focuses on “Quadrupole Mass Spectrometer”.
1. Which of the following is not a feature of quadrupole mass spectrometer?
a) Low cost
b) Light weight
c) Low speed electronic scanning
d) Simple in construction
View Answer
Explanation: In quadrupole mass spectrometer, electronic scanning takes place. The scanning takes place at high speed.
2. Which of the following is not a component of quadrupole mass filter?
a) Electrodes
b) Choke
c) DC potential
d) Detector
View Answer
Explanation: Detector is not a part of the filter. The filter uses DC potential.
3. The mass selection scheme uses a dc potential and not a radio frequency potential.
a) True
b) False
View Answer
Explanation: The mass selection scheme uses a dc potential. It also uses radio frequency potential.
4. If to one pair of electrodes one potential with one sign is applied, which of the following is applied to the other pair of electrodes?
a) Same potential with same sign
b) Different potential with same sign
c) Different potential with different sign
d) Same potential with different sign
View Answer
Explanation: If to one pair of electrodes one potential with one sign is applied, same potential with a different sign is applied to the opposite electrodes.
5. Which of the following is the heart of quadrupole instrument?
a) Electrodes
b) Choke
c) DC potential
d) Detector
View Answer
Explanation: Electrodes are the heart of quadrupole instrument. Opposite electrodes are electrically connected.
6. Which of the following has to be done to increase the resolution of the quadrupole mass spectrometer?
a) Increasing distance between detector and reflectron
b) Increasing difference between the individual rf accelerating stages
c) Increasing the length of the drift tube
d) Increasing the rod length of the electrode
View Answer
Explanation: The resolution depends upon the electrode. The length of the electrode has to be increased for increasing the resolution.
7. Which of the following does not affect the resolution of the instrument?
a) Changing length of electrode
b) Changing slope of scan line
c) Quality of machining of the rods
d) Changing length of drift tube
View Answer
Explanation: Changing length of drift tube does not affect the resolution of the instrument. Increase in resolution results in an increase in the number of ions reaching the detector.
8. In cases where differentiation is required between very similar substances, which of the following techniques making use of quadrupole principle is preferred?
a) Evaporation mass spectrometry
b) Pyrolysis mass spectrometry
c) Plasma mass spectrometry
d) Trapped ion mass spectrometry
View Answer
Explanation: In cases where differentiation is required between very similar substances, pyrolysis mass spectrometry is used. The sample is usually solid or involatile liquid in this case.
9. In pyrolysis spectrometry, heating is done until which of the following is reached?
a) Curie point
b) Boiling point
c) Until production of superheated vapour
d) Until 100oC
View Answer
Explanation: In pyrolysis spectrometry, heating is done until curie point is reached. At this point, magnetic permeability drops abruptly.
10. Which of the following is used to cool the ion source?
a) Liquid sodium shield
b) Liquid nitrogen shield
c) Water
d) Freon
View Answer
Explanation: Liquid nitrogen cooled shield is used to cool the ion source. It reduces source contamination.
11. In quadrupole mass spectrometer, the ratio u/v is mass dependent, where ‘u’ is the DC voltage and ‘v’ is the peak amplitude.
a) True
b) False
View Answer
Explanation: In quadrupole mass spectrometer, the ratio u/v is mass independent, where ‘u’ is the DC voltage and ‘v’ is the peak amplitude. This ratio is kept constant.
12. When a value of q is kept constant, the value of m/e is proportional to which of the following when ‘m’ is the mass number, ‘e’ is the electric charge, ‘u’ is the DC potential, ‘v’ is the peak amplitude and ‘f’ is the frequency?
a) u/v ratio
b) u
c) v
d) f
View Answer
Explanation: When a value of q is kept constant, the value of m/e is proportional to ‘v’. By variation of rf amplitude the m/e ratio varies.
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