SPECTROSCOPY MIX MCQS
Multiple Choice Questions
1. Assuming that no 1H signal can be observed for an aqueous sample, which of the
following is most likely not a cause of the problem?
a. The cable is not connected to the probe after probe tuning
b. There is a loose cable connection around the probe
c. The sample is not shimmed well
d. The probe has a problem
2. Which of the following is most likely not a cause of a VT problem?
a. Heater is not on
b. VT air is disconnected
c. Sample is not in the magnet
d. The set temperature exceeds the maximum set temperature
3. In which of the following situations does it use a 14
wavelength cable?
a. 15N decoupler channel
b. 2H observation
c. Lock channel
d. 13C decoupler channel
4. Which of the following delays should be used in a jump-return experiment on a 500 MHz
instrument to have maximum intensity at 9 ppm? Assume that the water resonance is at
4.8 ppm.
a. 467 μs
b. 119 μs
c. 1.9 ms
d. 238 μs
5. What coil configuration is most likely used for a triple-resonance probe?
a. The inner coil is double-tuned to 1H and 13C
b. The 1H and lock channel use the inner coil, 13C and 15N use the outer coil
c. The probe can be used to observe the correlation of 1H, 13C, 15N, and 31P
simultaneously
d. One of the two probe coils is used for 1H, 13C, and 15N, the other for 2H
6. Which of the following is not a property of an RF amplif ier?
a. It has a linear dependence of output power on attenuation
b. Its output is gated by a transmitter controller
c. It amplifies the signal from the probe
d. The output of the amplifier for a heteronuclear channel is higher than that of the 1H
channel in a high resolution NMR instrument
7. A mixer is used to
a. subtract the frequencies of two input signals
b. add the frequencies of two input signals
c. multiply the frequencies of two input signals
d. produce IF frequency
8. Which of the following frequencies cannot be an intermediate frequency (IF)?
a. 20 MHz
b. 10 MHz
c. 30 MHz
d. 200 MHz
9. Which of the following has the lowest frequency value?
a. Carrier
b. LO
c. IF
d. Lock frequency
10. What is the purpose of using LO?
a. To combine with carrier frequency at transmitter
b. To make a frequency higher than the spectrometer base frequency
c. To use a fixed-frequency receiver for all nuclei
d. To use a fixed-frequency preamplifier for all nuclei
11. Which of the following does not describe IF?
a. It is the fixed frequency of a receiver
b. Its frequency value is much lower than that of carrier or LO
c. Its frequency changes for different carrier frequencies
d. Either the carrier or LO frequency is made from IF
12. Which of the following statements about the effect of salt concentration on a probe is
correct?
a. High salt concentration affects a conventional probe more severely than a cryogenic
probe because it is less sensitive than a cryogenic probe
b. High salt concentration affects a conventional probe less severely than a cryogenic
probe because it is operated at room temperature
c. High salt concentration affects a cryogenic probe more severely than conventional
probe because the salt of sample may precipitate in the cryogenic probe
d. High salt concentration affects a cryogenic probe more severely than a conventional
probe because the high Q value of a cryogenic probe is dramatically decreased due
to the dielectric influence of the salt concentration
13. The sensitivity of a cryogenic probe on a 500 MHz spectrometer is close to that of a
conventional probe on a spectrometer of
a. 600 MHz
b. 750 MHz
c. 900 MHz
d. 1,050 MHz
14. Which of the following pulses should be tried first for water suppression by presaturation
for a 90%H2O/10%2H2O sample? Assume a 50 watt 1H amplifier and a carrier on the
water resonance.
a. 3 s pulse with power attenuation of −55 dB from the maximum power
b. 3 s pulse with power attenuation of −35 dB from the maximum power
c. 3 s pulse with power attenuation of −45 dB from the maximum power
d. 5 s pulse with power attenuation of −60 dB from the maximum power
15. Assuming that data are acquired on a 600 MHz with an acquisition time of 64 ms and
the data are Fourier transformed without zero-filling and linear prediction, what is the
digital resolution of the spectrum?
a. 7.8 Hz/pt
b. 0.013 ppm/pt
c. 3.9 Hz/pt
d. 0.026 ppm/pt
16. If the size of the above data set is doubled by zero-filling, what is the digital resolution
of the spectrum?
a. 15.6 Hz/pt
b. 7.8 Hz/pt
c. 3.9 Hz/pt
d. 0.026 ppm/pt
17. Which parameter can saturate the lock signal if it is set too high?
a. Lock gain
b. Lock phase
c. Lock power
d. Lock field (or z0)
18. Which of the following is not true?
a. Magnets (200–900 MHz) are made of superconducting wires
b. The magnet solenoid is in a liquid helium vessel
c. Liquid helium and liquid nitrogen are needed to maintain the magnetic field
d. Room temperature shims are in a liquid nitrogen vessel
19. By using cryogenic shims, field homogeneity can be as good as
a. 1 ppm
b. 10 ppm
c. 1 ppb
d. 0.01 ppm
20. The water-flip-back sequence provides superior water suppression. How is the result
achieved?
a. The selective pulse on water saturates some portion of the water magnetization
b. The selective pulse on water keeps the water magnetization on the xy plane so that
the water magnetization is suppressed by the watergate sequence
c. The selective pulse on water brings the water magnetization to the z axis
d. The selective pulse on water keeps the water magnetization in the xy plane so that
the water magnetization is destroyed by the gradient pulse
21. Which of the following gives a wider decoupling bandwidth for the same amount of RF
power?
a. CW
b. Waltz16
c. GARP
d. BB
22. Which of the following is the better way to set up a water-flip-back experiment after
probe tuning, shimming, and locking?
a. Calibrate VT, 1H 90◦ pulse, transmitter offset and set the offset at the center of the
spectrum
b. Calibrate 1H 90◦ pulse, transmitter offset, 1H 90◦ selective pulse and set the offset
at the center of the spectrum
c. Calibrate 1H 90◦ pulse, transmitter, and decoupler offsets, 1H 90◦ selective pulse
and set the offset on water
d. Calibrate 1H 90◦ pulse, transmitter, offsets, 1H 90◦ selective pulse and set the offset
on water
23. Which of the following data are most likely processed with doubling the size by forward
linear prediction, 90◦-shifted squared sine-bell function, zero-filling once, and Fourier
transformation?
a. One-dimensional watergate data
b. 1H dimension of 3D data
c. 15N dimension of 3D data
d. Two-dimensional COSY
24. What is the correct way to tune a probe for a triple-resonance experiment?
a. Tune 1H channel first, then 13C, and 15N last without filters
b. Tune 1H channel first, then 13C, and 15N last with filters
c. Tune 15N channel first, then 13C, and 1H last without filters
d. Tune 15N channel first, then 13C, and 1H last with filters
25. An NMR transmitter consists of
a. Frequency synthesizer, RF signal generator, transmitter controller and receiver
b. CPU, RF signal generator, transmitter controller, and RF amplifier
c. Frequency synthesizer, RF signal generator, and transmitter controller
d. Frequency synthesizer, RF signal generator, transmitter controller, and RF amplifier
26. Which of the following product operators describes the coherence of a two weakly
coupled two-spin (I and S) system from an initial coherence of −Iy after INEPT where
Ï„ → Ï€(Ix + Sx ) → Ï„ when Ï„ = 1/4JIS?
a. −IzSx
b. IxSx
c. −IxSz
d. Ix
27. Assuming that on a 600 MHz NMR spectrometer the 13C 90◦ pulse length is 15 μs at
60 dB and a higher decibel value means more power for a pulse, what is most likely the
power setting for 13C GARP decoupling over a 50 ppm bandwidth?
a. 45 dB
b. 47 dB
c. 49 dB
d. 51 dB
28. Which of the following is most likely a Gly NH cross-peak?
a.
10 6
105
130
1H (ppm)
15N (ppm)
b.
10 6
105
130
1H (ppm)
15N (ppm)
c.
10 6
105
130
1H (ppm)
15N (ppm)
d.
10 6
105
130
1H (ppm)
15N (ppm)
29. Assuming that on a 500 MHz NMR spectrometer the 15N 90◦ pulse length is 35 μs at
60 dB and a higher decibel value means more power for a pulse, what is most likely the
power setting for 15N WALTZ-16 decoupling over a 30 ppm bandwidth?
a. 40 dB
b. 42 dB
c. 45 dB
d. 49 dB
30. Assuming that on a 500 MHz NMR spectrometer the 15N 90◦ pulse length is 35 μs at
60 dB and a higher dB value means more power for a pulse, what is most likely the power
setting for 15N GARP decoupling over a 30 ppm bandwidth?
a. 35 dB
b. 40 dB
c. 45 dB
d. 49 dB
ANSWER.
1. c. 2. c. 3. b. 4. b. 5. b. 6. c. 7. c. 8. d. 9. c. 10. c.
11. c. 12. d. 13. d. 14. a. 15. d. 16. b. 17. c. 18. d. 19. a. 20. c.
21. c. 22. d. 23. c. 24. c. 25. d. 26. c. 27. b. 28. a. 29. c. 30. b.
