TOF MASS SPECTROSCOPY - AQA Chemistry A-Level/AS - Flashcards in A Level and IB Chemistry

What is a mass spectrometer used for?

To separate particles according to their masses. They are often used in drugs testing.

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Why do TOF MS need to be in a vacuum?

So that the ions don't collide with air particles.

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What are the 4 stages of TOF MS?

Ionisation, Acceleration, Separation and Detection

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What are the two types of ionisation?

Electron impact and electrospray ionisation

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Electron impact ionisation

high energy electrons are fired at sample through an electron gun. They knock off one electron of each particle of the sample to give them a charge of +1.

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Electron impact ionisation equation

X(g) --> X+(g) + e-

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Electrospray ionisation

sample is dissolved in volatile solvent and then injected through a hyperdermic needle to give a fine mist. The solvent donates a proton to sample to give particles a charge of +1 and and mass of M+1

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Electrospray ionisation equation

X(g) + H+ --> XH+(g) + e-

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Acceleration

the ions accelerate towards a negatively charged plate with a hole in. The plate has a fixed electrical potential so all ions gain the same kinetic energy

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In the drift region, how can you prove that all ions have different velocities?

Velocity is calculated (v=d/t). Ions have different masses and because of KE = 1/2 mv^2, all ions have the same KE and different masses, so therefore they must all have DIFFERENT velocities.

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the lighter the particle, the ______ it travels

faster

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How are ions detected?

The ions strike a detector and become discharged (gain an electron), this movement of electrons produces a small current. signals are amplified and results shown in a mass spectrum

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TOF MASS SPECTROSCOPY - AQA Chemistry A-Level/AS

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