Protein Engineering Multiple Choice Questions on “Structural Study – MALDI-TOF”.
1. Which mass analyzer is most frequently used with MALDI?
A. Magnetic sector
B. Quadrupole
C. Ion trap
D. TOF
Answer: D
Clarification: TOF is most commonly used with MALDI. It is best suited for MALDI as it can sort virtually all range of masses. The magnetic sector, Quadrupole, and ion trap are not used frequently with MALDI.
2. Which of the following ionization technique uses a short laser pulse to achieve ionization?
A. ESI
B. Chemical Ionization
C. FAB
D. MALDI
Answer: D
Clarification: MALDI is the ionization technique that uses a short laser pulse to achieve ionization. ESI, Chemical Ionization, and FAB do not use a short laser pulse to achieve ionization. The target plate containing the sample is placed in a vacuum chamber with high voltage and short laser pulses are applied.
3. Sublimation occurs in which of the following ionization methods?
A. ESI
B. FAB
C. Chemical Ionization
D. MALDI
Answer: D
Clarification: Sublimation occurs in MALDI. The laser energy applied on the target plate gets adsorbed by the matrix and is transferred to the analyte molecules which undergo rapid sublimation resulting in gas-phase ions. Whereas, sublimation does not occur in ESI, FAB, and chemical ionization.
4. Which of the following ionization method uses aromatic compounds and organic solvents to achieve ionization?
A. ESI
B. Chemical ionization
C. FAB
D. MALDI
Answer: D
Clarification: The ionization method which uses aromatic compounds and organic solvents to achieve ionization is MALDI. ESI, chemical ionization, and FAB do not use aromatic compounds and organic solvents to achieve ionization.
5. In the TOF analyzer, all the ions are accelerated at the same velocity.
A. True
B. False
Answer: B
Clarification: The above statement is false. In TOF, ions of lower mass are accelerated to higher velocities. Thus, in the TOF analyzer, all the ions are not accelerated at the same velocity.
6. What is the relation of time of flight with the molecular mass of the ion in the TOF mass analyzer?
A. Time of flight is inversely proportional to the square root of the molecular mass of the ion
B. Time of flight is inversely proportional to the molecular mass of the ion
C. Time of flight is directly proportional to the molecular mass of the ion
D. Time of flight is directly proportional to the square root of the molecular mass of the ion
Answer: D
Clarification: In TOF mass analyzer, the time of flight is directly proportional to the square root of the molecular mass of the ion. Hence, a charge having a small mass will have a smaller time of flight and an ion having a large mass would have a large time of flight.
7. Which of the following type of mass analyzer uses a magnetic field and cyclotron motion to trap ions?
A. Quadrupole
B. Orbitrap
C. TOF
D. Fourier transform ion cyclotron resonance
Answer: D
Clarification: Fourier transform ion cyclotron resonance is a type of mass analyzer that uses a magnetic field and cyclotron motion to trap ions. Quadrupole, orbitrap, and TOF do not use magnetic field and cyclotron motion to trap ions.
8. In TOF, ions of lower mass are accelerated to lower velocities and reach the detector last.
A. True
B. False
Answer: B
Clarification: The above statement is false. In TOF, ions of lower mass are accelerated to higher velocities and reach the detector first. Thus, ions are accelerated at different velocities depending on their mass-to-charge ratio.
9. If a charge has a mass of 3 kg and it is traveling at a speed of 10 m/s in-flight tube, then what will be it’s kinetic energy?
A. 300 J
B. 90 J
C. 100 J
D. 150 J
Answer: D
Clarification: The kinetic energy of that charge would be 150 J.
Formula: K.E=(frac{1}{2})mv2
: K.E=(frac{1}{2}) x 3 x 102
K.E=150 J.
10. Which of the following cannot be used as a MALDI matrix compound?
A. α-Cyano-4-hydroxycinnamic acid
B. Sinapinic acid
C. 3-Hydroxypicolinic acid
D. 2,3-Dihydroxybenzoic acid
Answer: D
Clarification: 2,3-Dihydroxybenzoic acid cannot be used as a MALDI matrix compound. α-Cyano-4-hydroxycinnamic acid, sinapinic acid, and 3-Hydroxypicolinic acid can be used as a MALDI matrix compound.
11. Which of the following is the correct equation of the time of flight?
A. t=((frac{m}{2q}))0.5 x l
B. t=((frac{m}{2q}))2.0 x l
C. t=((frac{m}{2v^{circ}}))2.0 x l
D. t=((frac{m}{2v^{circ}q}))0.5 x l
Answer: D
Clarification: The correct equation for the time of flight is t=((frac{m}{2v^{circ}q}))0.5 x l.
Where, t is the time of flight,
m is the mass of ion,
q is the charge on ion,
v° is the accelerating potential.
12. Which of the following charge has the lowest m/z ratio?
Given data: q1 has a charge +1 and mass of 800 Da,
q2 has a charge +3 and mass of 3900 Da,
q3 has a charge +2 and mass of 2970 Da,
q4 has a charge +4 and a mass of 3480 Da.
A. q4
B. q3
C. q2
D. q1