1: Mass Spectrometry Flashcards
Describe electrospray ionisation.
The sample is dissolved in a volatile solvent and passed through a hypodermic needle.
The end of the needle is attached to the end of a positive terminal.
This adds a H+ ion to the molecule.
Describe electron impact ionisation.
The sample is vapourised and a high energy electron gun fires electrons at the molecule and knocks them off.
How are positive ions accelerated in the flight tube?
A negative electric field propels the ions at a high speed, providing all ions with the same kinetic energy.
Despite all ions having the same kinetic energy, why are some accelerated faster than others?
Some ions are lighter than others, and others are heavier. The lighter ions travel at a faster speed.
What is the ion drift region?
The part of the spectrometer where there is no electric field, and ions drift freely.
How does the ion detector record the mass of the ions?
The ions hit the plate and records the current generated and the time taken to drift through the spectrometer. This is then used to calculate mass/charge values.
Give 2 reasons why it is necessary to ionise the isotopes of chromium before they can be analysed in a TOF mass spectrometer.
Ions must be able to gain an electron so an electrical current can be generated.
They must be able to be accelerated by the negative electric field.
