TOF Mass Spectrometry MCQ's PDF

1. In a time-of- ight mass spectrometer, what is done to the sample rst? a) Ionisation b) Vaporisation c) Acceleration d) Detection Answer: b) Vaporisation Explanation: The sample is vaporised to ensure all atoms or molecules are separated before being injected into the spectrometer...

1. In a time-of- ight mass spectrometer, what is done to the sample rst? a) Ionisation b) Vaporisation c) Acceleration d) Detection Answer: b) Vaporisation Explanation: The sample is vaporised to ensure all atoms or molecules are separated before being injected into the spectrometer 2. Which ionisation method involves electrons being red at the sample? a) Electrospray Ionisation b) Chemical Ionisation c) Ion Exchange d) Electron Impact Ionisation Answer: d) Electron Impact Ionisation Explanation: In Electron Impact Ionisation, an electron gun is used to remove electrons from the atoms or molecules of the sample, creating 1+ ions. 3. How are the ions accelerated in a TOF mass spectrometer? a) Using a magnetic eld b) Using a laser c) By a negatively charged plate d) By heating Answer: c) By a negatively charged plate Explanation: The positive ions are accelerated by a negatively charged plate to give them the same kinetic energy. 4. What happens in the ion drift stage of a TOF mass spectrometer? a) Ions are accelerated b) Ions are vaporised c) Ions are separated based on mass d) Ions are detected Answer: c) Ions are separated based on mass Explanation: In the ion drift stage, lighter ions travel faster through the ight tube, allowing them to be separated based on mass. 5. What generates a current in the detector of a TOF mass spectrometer? a) The ions hitting the detector plate b) Electrons hitting the detector plate c) Molecules hitting the detector plate d) Neutrons hitting the detector plate Answer: a) The ions hitting the detector plate Explanation: The 1+ ions hit the negatively charged detector plate, creating a current as they attract electrons. 6. Which unit is commonly used to express the mass-to-charge ratio in mass spectrometry? a) g/mol b) amu c) kg d) m/z Answer: d) m/z Explanation: The mass-to-charge ratio is often expressed as (m/z). i.e. mass divided by charge fl fi fi fi fl 7. What formula is used to calculate the relative atomic mass (Ar) of an element? a) \[ \text{Ar} = \frac{\sum(\text{isotope mass} \times \% \text{abundance})}{50} \] b) \[ \text{Ar} = \frac{\sum(\text{isotope mass} \times \% \text{abundance})}{100} \] c) \[ \text{Ar} = \frac{\sum(\text{isotope mass} \times \% \text{abundance})}{\text{number of isotopes}} \] d) \[ \text{Ar} = \text{sum of isotope masses} \] Answer: b) \[ \text{Ar} = \frac{\sum(\text{isotope mass} \times \% \text{abundance})}{100} \] Explanation: The relative atomic mass is calculated by summing the product of the isotope masses and their percent abundances, then dividing by 100. 8. If an element has two isotopes with masses of 10 and 11, having 60% and 40% abundance, respectively, what is the relative atomic mass? a) 10.0 b) 10.4 c) 10.6 d) 10.5 Answer: c) 10.4 Explanation: Relative Atomic Mass (Ar) = \((10 \times 60) + (11 \times 40)\) / 100 = 10.4. 9. In calculating the relative atomic mass, why must the answer be between the lowest and highest isotope mass used? a) It signi es the isotopic distribution is balanced b) Arbitrary placement of isotopes c) Ensures accurate spectral data d) Isotopic mass must be whole numbers Answer: a) It signi es the isotopic distribution is balanced Explanation: The average must lie between the lowest and highest values as an average outcome is expected from the isotopes masses used. 10. Which sample state is required for time-of- ight mass spectrometry to proceed appropriately? a) Gaseous b) Solid c) Liquid d) Plasma Answer: a) Gaseous Explanation: The sample must be in a gaseous state for proper ionisation and movement through the mass spectrometer. 11. What happens to ions in a mass spectrometer when they hit the detector? a) Lose all their energy b) Attract electrons causing a current c) Break apart into smaller ions d) Show di erent colours Answer: b) Attract electrons causing a current Explanation: When ions hit the negatively charged detector, they attract electrons, generating a current that can be measured. 12. In a TOF mass spectrometer, ions are accelerated to give them what kind of energy? a) Potential energy b) Thermal energy c) Kinetic energy d) Chemical energy Answer: c) Kinetic energy fi ff fi fl  Explanation: In a TOF mass spectrometer, ions are accelerated to provide them with the same kinetic energy. 13. What property of the isotopes does a mass spectrometer measure? a) Atomic number b) Isotopic Mass c) Color d) Molecular formula Answer: b) Isotopic Mass Explanation: A mass spectrometer measures the mass of isotopes, which is presented in the output mass spectrum corrections. 14. If the isotope masses of an element are 35 and 37 with percentages 75 and 25, calculate the Ar value? a) 36.0 b) 35.5 c) 35.3 d) 36.5 Answer: b) 35.5 Explanation: Relative Atomic Mass (Ar) calculation would be \((35 \times 75) + (37 \times 25) / 100\) = 35.5. 15. What results when ions reach the detector in a TOF mass spectrometer? a) They stop moving b) They generate a current c) They change state d) They split into atoms Answer: b) They generate a current Explanation: When ions reach the detector, they attract electrons, causing a current which can be measured to determine abundance and m/z values. 16. For TOF mass spectrometry, what happens to lighter ions compared to heavier ones? a) Lighter ions travel slower b) Heavier ions reach the detector rst c) Lighter ions travel faster d) Both travel at the same speed Answer: c) Lighter ions travel faster Explanation: Lighter ions reach the detector rst because they travel faster with the same kinetic energy applied to all ions. 17. Which of the following equations is useful for nding ion velocity in TOF mass spectrometry? a) \(E_k = \frac{1}{2}mv^2\) b) \(v = \frac{d}{t}\) c) Both a and b d) None of the above Answer: c) Both a and b Explanation: Both equations are essential for calculating ion velocity and kinetic energy in TOF mass spectrometers: \(E_k = \frac{1}{2}mv^2\) for kinetic energy and \(v = \frac{d}{t}\) for velocity. 18. What could be the kinetic energy (J) of an ion with mass \(5.32 \times 10^{-26}\) kg and velocity \(2 \times 10^5 \) m/s? a) \(5.32 \times 10^{-20} J\) b) \(1.06 \times 10^{-16} J\) c) \(0.53 \times 10^{-16} J\) d) None of the above fi fi fi  Answer: b) \(1.06 \times 10^{-16} J\) Explanation: \( E_k = \frac{1}{2}mv^2 = \frac{1}{2} \times 5.32 \times 10^{-26} \times (2 \times 10^5)^2 = 1.06 \times 10^{-16} J \). 19. Given \( E_k = 3.24 \times 10^{-18} J \) and \( m = 4.55 \times 10^{-26} kg \), what is the velocity? a) \(1.3 \times 10^4 m/s\) b) \(4.3 \times 10^5 m/s\) c) \(7.5 \times 10^3 m/s\) d) \(2.67 \times 10^5 m/s\) Answer: a) \(1.3 \times 10^4 m/s\) Explanation: \( v = \sqrt{\frac{2E_k}{m}} = \sqrt{\frac{2 \times 3.24 \times 10^{-18}}{4.55 \times 10^{-26}} }= 1.3 \times 10^4 m/s\). 20. If an ion travels 0.5 meters with time of ight of \(2 \times 10^{-5} sec\), what is its velocity? a) 20000 m/s b) 25000 m/s c) 15000 m/s d) 10000 m/s Answer: b) 25000 m/s Explanation: \( v = \frac{d}{t} = \frac{0.5}{2 \times 10^{-5} } = 25000 m/s \). 21. Why does the peak at m/z typically represent the isotropic mass of an isotope? a) Because most isotopes have one charge b) Because masses are always the same c) It determines molecular weight d) None of the above Answer: a) Because most isotopes have one charge Explanation: With most isotopes assuming a 1+ charge, the m/z value e ectively equals the isotope's mass. 22. In relative atomic mass calculations, what action follows multiplying isotope mass by its abundance? a) Divide by 100 b) Add another isotope c) Subtract center isotope d) Estimate the mean Answer: b) Add another isotope Explanation: Adding results of each isotope’s product accumulates to a sum, and then nally divide by 100 for the average. 23. Which values are essential to calculate velocity in TOF mass spectrometry? a) Time taken to reach the detector b) Length of the ight tube c) Kinetic energy of ions d) All of the above Answer: d) All of the above Explanation: To calculate velocity in TOF, factors like time, distance travelled, and kinetic energy are critically considered. 24. How do ions generate a current in TOF mass spectrometry? a) By breaking down into electrons b) By capturing electrons from the detector c) Generating kinetic energy fl fl ff fi  d) By releasing neutrons Answer: b) By capturing electrons from the detector Explanation: When ions hit the detector, they attract electrons, leading to current generation depicted in the detector’s reading. 25. In a TOF mass spectrometer, if lighter ions travel faster, how does this a ect detection? a) Lighter ions get detected last b) Heavier ions get detected rst c) Detection order is mass-dependent d) All ions gets detected simultaneously Answer: c) Detection order is mass-dependent Explanation: The ight tube design ensures that ions reach the detector based on their mass, with lighter ions arriving faster, giving accurate mass identi cation. 26. If an element has three isotopes with mass 30g, 32g, 33g, and abundances 60%, 25%, 15%, what’s Ar? a) 31.25 b) 31.2 c) 31.15 d) 31.5 Answer: a) 31.25 Explanation: \[ \text{Relative Atomic Mass (Ar)} = \frac{(30 \times 60) + (32 \times 25) + (33 \times 15)}{100} = 31.25 \]. 27. What adjustment is made if the abundances are given as relative values, not percentages? a) Use 100 as denominator b) Use abundance sum as denominator c) Use the mid-value d) Use the highest value Answer: b) Use abundance sum as denominator Explanation: When relative values are used instead of percentages, sum of the abundances substitutes 100 in the denominator. 28. In TOF, what parameter remains consistent for all ions during acceleration? a) Mass b) Kinetic energy c) Velocity d) Charge Answer: b) Kinetic energy Explanation: All ions are accelerated to the same kinetic energy in TOF mass spectrometry ensuring accurate velocity determination. 29. If Time of ight = \(3 \times 10^{-4} s\), Flight tube length = 1.2 meters, what’s the velocity? a) 4000 m/s b) 5000 m/s c) 1000 m/s d) 2500 m/s Answer: a) 4000 m/s Explanation: \( v = \frac{d}{t} = \frac{1.2}{3 \times 10^{-4}} = 4000 m/s \). 30. Why does the mass spectrometer run in a vacuum? a) To increase pressure b) To prevent interference from other substances c) To enhance ion acceleration fl fl fi fi ff  d) To manipulate isotope distribution Answer: b) To prevent interference from other substances Explanation: Running the mass spectrometer in a vacuum ensures no other particles interfere with the sample during its analysis. I hope these questions help you understand the functionalities of TOF mass spectrometry, Ar calculations, and velocity computations for the mass spectrometer. Let me know if you need more information or additional questions!