ToF Mass Spectrometry Flashcards
What must be done to atoms before Ionisation AND why?
Vaporisation so that there are free moving gaseous atoms which can be bombarded by electrons during Ionisation
In what state do molecules have to be in order to be detected by magnetic field?
They need to be ions
What is the second stage in ToF MS?
Ionisation
What happens during Ionisation?
Atoms become POSITIVE ions (only 1+)
What is the purpose of having + ions in a ToF MS?
They cause a tiny electrical effect in the detector which a computer will analyse. It compares the strength of the signal for the different arrival times of the different masses of ions
What happens after Ionisation
Acceleration
Explain Acceleration
An electric field transfers an equal amount of kinetic energy to all the ions present
How does Acceleration propel the positive ions?
Using a negative electric plate
Is kinetic energy the same as speed?
No: It’s 1/2mv^2
What happens after Acceleration?
Ion drift
How is Acceleration important to Ion Drift?
During Ion Drift, the ions will whiz across the vacuum in different lengths of time owing to their different speeds. However, as all the ions have the same kinetic energy, the mass can be calculated easily.
What is the effect of Ion Drift?
Separation: lighter ions move across the vacuum and reach the Ion Detector before the heavier ones do
Due to a Acceleration and Ion Drift what do we understand about ToF’s relationship to the mass of ions?
ToF is proportional to the square root of the mass of ions
What is the final stage of ToF MS?
Ion detection
How does an Ion detector work?
As a negatively charged plate, it will grab electrons from the ions it hits. This in turn generates a movement of electrons and hence, an electric current is measured. The size of the current gives a measure of the number of ions hitting the plate, indicating that isotopes abundance in nature.
