18 Questions
What is the purpose of including mass spectrometers in planetary space probes?
To identify elements on other planets with different compositions of isotopes.
Why does the 160 peak in the mass spectra of Cl2 and Br2 have double the abundance of the other two peaks?
Because there is double the probability of forming Br79-Br81 compared to the other combinations.
What is the significance of the peak with the largest m/z in a mass spectrum?
It represents the complete molecule and its mass is equal to the relative molecular mass (Mr) of the molecule.
In mass spectrometry, what happens in the Electron Impact Ionisation stage?
The molecule often breaks up and gives a series of peaks due to fragmentation.
When a molecule is analyzed using Electrospray Ionisation, what is different compared to Electron Impact Ionisation?
Fragmentation does not occur.
What does the abbreviation 'm/z' stand for in the context of mass spectrometry?
Mass-to-charge ratio.
Describe the process of electron impact ionisation.
A vaporised sample is injected at low pressure and high energy electrons are fired at the sample, knocking out an outer electron to form positive ions.
What is the key difference between electron impact ionisation and electrospray ionisation?
Electron impact ionisation causes larger organic molecules to fragment, while electrospray ionisation does not result in fragmentation.
Explain the process of electrospray ionisation.
The sample is dissolved in a volatile, polar solvent and injected through a fine needle to create a mist. The sample gains a proton from the solvent to form MH+ ions.
What is the purpose of acceleration in ionisation techniques?
Acceleration is used to give positive ions a constant kinetic energy, where the velocity of each particle depends on its mass.
How do the kinetic energy and velocity of particles relate in acceleration?
All particles have the same kinetic energy, so the velocity of each particle varies based on its mass.
Why is electrospray ionisation preferred for larger organic molecules?
Electrospray ionisation is preferred for larger organic molecules because it operates under 'softer' conditions that prevent fragmentation.
Explain how ions with different m/z values can be distinguished in a mass spectrometer.
Ions with different m/z values can be distinguished by their different flight times in the flight tube of the mass spectrometer.
What is the relationship between the flight time (t), length of the flight tube (d), and velocity of the particle (v) in a mass spectrometer?
The flight time (t) in a mass spectrometer is directly proportional to the length of the flight tube (d) and inversely proportional to the velocity of the particle (v).
How is current generated in a mass spectrometer detection process?
Current is generated in a mass spectrometer by electrons transferring from the detector to the positive ions.
What does a 2+ charge on an ion indicate in mass spectrometry?
A 2+ charge on an ion indicates that two electrons have been removed from the particle, forming a 2+ ion.
Explain how the kinetic energy of ions is used in mass spectrometry analysis.
The ions are accelerated to have a specific kinetic energy, and this energy is used to propel the ions through the flight tube for analysis.
If a sample of 59Ni+ ions had 1.000 x 10^-16 J of kinetic energy and traveled through a flight tube that was 0.8000 m long, how long would one ion of 59Ni+ take to travel along the flight tube?
One ion of 59Ni+ would take 1.33 x 10^-8 seconds to travel along the 0.8000 m long flight tube.
Test your ability to rearrange equations related to flight tubes and calculate time of flight. Understand how ions with different m/z values move through the drift area based on their kinetic energy.
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