Deck 4: Chromatography and Mass Spectrometry

Question 1

In GC, the more the analyte interacts with the solid phase, the

A) the faster the mobile phase flows
B) the faster it elutes from the column
C) the greater the back pressure in the injector
D) longer it takes to elute from the column
E) none of the above

Answer 1

D

Question 2

With a hyphenated instrument such as GC-MS, the GC serves to

A) detect the compounds electronically
B) pre-separate analytes so that they enter the detector one at a time
C) ensure that the carrier gas is pure when entering the MS
D) ionize the analytes for characterization by MS
E) none of the above

Answer 2

B

Question 3

If two compounds enter the MS in a GC-MS at the same time, this results in

A) coeluting peaks
B) coordinated ionization
C) a pressure spike in the ionization source
D) saturation of the electron multiplier
E) none of the above

Answer 3

A

Question 4

Theoretical plates are

A) a measure of chromatographic column efficiency
B) thin wall structures manufactured into chromatographic columns
C) Lenses in the ionization region of an EI-MS
D) A type of virtual thin-layer chromatography device
E) none of the above

Question 5

In GC and LC, a compound that is unretained

A) forms a precipitate in the injection port
B) interacts extensively with the stationary phase
C) is the last compound that elutes during an analysis
D) does not interact at all with the stationary phase
E) none of the above

Question 6

Given the following data obtained from a GC-MS analysis using a 15m column:
Peak 1: Retention time 4.32 minutes; FWHM 16. seconds
Peak 2: Retention time 5.87 minutes; FWHM 19 seconds
Calculate the number of theoretical plates based on the second peak

A) 0.25
B) 85
C) 97
D) 1.1
E) none of the above

Question 7

Given the following data obtained from a GC-MS analysis using a 15m column::
Peak 1: Retention time 4.32 minutes; FWHM 16. seconds
Peak 2: Retention time 5.87 minutes; FWHM 19 seconds
Calculate the HETP in mm based on the first peak

A) 58
B) 17
C) 167
D) 239
E) none of the above

Question 8

Given the following data obtained from a GC-MS analysis using a 15m column::
Peak 1: Retention time 4.32 minutes; FWHM 16. seconds
Peak 2: Retention time 5.87 minutes; FWHM 19 seconds
Calculate the resolution

A) 2.8
B) 1.9
C) 0.94
D) 1.1
E) none of the above

Question 9

Given the following data obtained from a GC-MS analysis using a 15m column::
Peak 1: Retention time 4.32 minutes; FWHM 16. seconds
Peak 2: Retention time 5.87 minutes; FWHM 19 seconds
What does the calculated resolution value, based on these two peaks, mean in terms of chromatographic appearance?

A) These peaks will be baseline resolved
B) These peaks will coelute
C) These peaks will overlap slightly
D) These peaks will be widely separated and will not interfere with each other.
E) none of the above

Question 10

Why are peaks that elute towards the end of a GC run typically broader than the first peaks to elute?

A) Mass transfer is slower for these compounds
B) Eddy diffusion increases with retention time
C) Mass transfer is faster for these
D) Normal diffusion is most pronounced for compounds that elute later
E) none of the above

Question 11

The primary purpose of the retention index is to

A) standardize mass spectrometry performance across systems
B) allow comparisons of retention data obtained from different instruments
C) eliminate the need to calculate resolution
D) increase the number of theoretical plates for a column
E) none of the above

Question 12

An analyst runs an alkane standard on a GC-MS prior to running a sample from a case. The following data is obtained:
Retention time of the compound in the sample: 7.21 minutes
Retention time of the C7 test alkane: 6.42 minutes
Retention time of the C8 test alkane: 7.58 minutes
Calculate the retention index of the compound in the sample

A) 821
B) 768
C) 792
D) 702
E) none of the above

Question 13

Why do HPLC and UPLC columns operate at high pressures?

A) The analysis is much faster when pressurized
B) To keep air out of the column
C) To increase the column lifetime
D) The mobile phase is tightly packed into the column so it takes pressure to force it through
E) none of the above

Question 14

Which chromatographic instrument is better suited for analysis involving drug molecules with ionizable centers?

A) Capillary electrophoresis
B) GC
C) HPLC/UPLC
D) All work fine with ionizable molecules
E) none of the above

Question 15

Why is EI considered a hard ionization source?

A) It causes extensive fragmentation of molecules
B) It operates under hard vacuum
C) It is really hard to use
D) It requires water with calcium (hard water) as the mobile phase
E) none of the above

Question 16

Why do mass filter devices operate under vacuum?

A) To minimize contamination
B) To ensure that charged molecules or fragments don't collide with extraneous compounds
C) Because the electric fields applied will not work at ambient pressure
D) Because it is less expensive to operate
E) none of the above

Question 17

What procedure is used to ensure that EI-MS are comparable between instruments?

A) All retention times are reported as the retention index
B) Instruments are operated at the same vacuum level
C) Instruments are adjusted to set criteria using PFTBA tuning
D) Modern instruments are engineered to perform the same
E) none of the above

Question 18

The EI mass spectrum and structure shown below is for phentermine, a compound related to methamphetamine.
Which m/z peak is the molecular ion M+?

A) 144
B) There is no molecular ion in this spectrum
C) 147
D) 58
E) none of the above

Question 19

The EI mass spectrum and structure shown below is for phentermine, a compound related to methamphetamine.
Which peak is the base peak?

A) 58
B) 91
C) 134
D) 147
E) none of the above

Question 20

The EI mass spectrum and structure shown below is for phentermine, a compound related to methamphetamine.
Which fragmentation location generated the base peak??

A) A
B) B
C) C
D) D
E) none of the above

Question 21

The EI mass spectrum and structure shown below is for phentermine, a compound related to methamphetamine.
Which fragmentation location generated the peak at m/z 91?

A) A
B) B
C) C
D) D
E) none of the above

Question 22

The EI mass spectrum and structure shown below is for phentermine, a compound related to methamphetamine.
If the molecule is fragmented at location B, which m/z peak does this likely correspond to?

A) 58
B) 85
C) 91
D) 134
E) none of the above

Question 23

Suppose an analyst must determine the elemental profile of a bullet. Which MS instrument is best suited to this task?

A) GC-MS
B) UPLC-MS
C) ICP-MS
D) DART-MS
E) none of the above

Question 24

Which of the following ionization sources operates at atmospheric pressure?

A) EI
B) APCI
C) ESI
D) More than one
E) none of the above

Question 25

What type of ions are most commonly formed using soft ionization, such as ESI?

A) Fragment ions
B) Positively charged ions
C) Molecular ions
D) Negatively charged ions
E) none of the above

Question 26

In ESI, the matrix effect refers to

A) the effect of the matrix chromatographic efficiency
B) the effect of matrix components on ionization efficiency
C) changes in the vacuum pressure because of excess matrix ions
D) clogging of the skimmer cone by matrix salts
E) none of the above

Question 27

Where are ions fragmented in a triple quadrupole instrument?

A) Q1
B) Q2 collision cell
C) Q3
D) Filament chamber
E) none of the above

Question 28

The most common type of mass filter used in HRMS is

A) single large quadrupole
B) extended lens stack
C) QQQ
D) time-of-flight
E) none of the above

Question 29

The typical mass resolution of a QQQ and EI mass detector is about

A) 1 Da
B) 0.5 Da
C) 0.01Da
D) 0.0001 Da
E) none of the above

Question 30

The typical mass resolution of a HRMS is about

A) 1 Da
B) 0.5 Da
C) 0.01Da
D) 0.0001 Da
E) none of the above

Question 31

A laboratory purchases a new UPLC-QQQ system that can differentiate between peaks that are 0.6 Da wide. The instrument is used to quantitate cocaine and one of the key transitions monitored yields a peak of m/z 182. What is the mass resolution of the instrument based on the peak with a nominal mass of 182 Da?

A) 109
B) 18
C) 139
D) 97
E) none of the above

Question 32

An analyst performs a LC-HRMS scan of an extract of post-mortem blood. The sample contains fentanyl, which is used to calculate the mass accuracy of the instrument. The exact mass is 336.2202 Da. The analysis produces a measured mass of 336.2189 Da. What is the mass accuracy in ppm?

A) 3.9
B) -3.9
C) -2.6
D) 2.6
E) none of the above

Question 33

Which isotopes of elements (C, H, O, and N here) are targeted in IRMS?

A) Natural isotopes
B) Radioactive isotopes
C) Natural and artificially generated isotopes
D) Natural and radioactive isotopes
E) none of the above

Question 34

Heavy water (D₂O) has a higher boiling point and a lower vapor pressure than H₂O. This is an example of

A) plain old bad luck
B) biotic fractionation
C) kinetic isotope effect
D) mass isotope reversal
E) none of the above

Question 35

A sample containing a 50/50 mixture of water and D₂O (1:1 D₂O:H₂O) is placed in a vial and sealed. The liquid/vapor system is allowed to come to equilibrium at room temperature. What will be the relative concentration ratio of the vapor?

A) there will be more D₂O than H₂O
B) there will be less D₂O than H₂O
C) Still 1:1
D) Indeterminate
E) none of the above

Question 36

A sample containing a 50/50 mixture of water and D₂O (1:1 D₂O:H₂O) is placed in a vial and sealed. The liquid/vapor system is allowed to come to equilibrium at room temperature. What will be the relative concentration ratio of the remaining liquid?

A) there will be more D₂O than H₂O
B) there will be less D₂O than H₂O
C) Still 1:1
D) Indeterminate
E) none of the above

Question 37

Compounds separate in electrophoresis based on differences in

A) size/charge
B) mass/charge
C) charge/volume
D) surface tension
E) none of the above

Question 38

Electroosmotic flow arises because

A) buffers are used and they contained charged species
B) the neutral species are constantly pumped through the capillary
C) positive ions in the mobile phase collect near the capillary surface and are drawn toward the cathode
D) the apparent mobility is always in the forward direction
E) none of the above