1 Mass Spectrometry

Question 1

Ionisation Methods (2)

Answer 1

1) Electron impact
2) Electrospray

Question 2

Explain Electron impact as an ionisation technique

Answer 2

A high energy electron is fired at the sample, this knocks an electron off the atom to form a 1+ ion.

Question 3

Electron impact ionic equation

Answer 3

x(g) + H(+) → xH(+) (g)

Question 4

Explain electrospray as an ionisation technique

Answer 4

Dissolve the sample into a volatile solvent and pass this through a hypodermic needle which is attached to a positively charged terminal of a high voltage power supply, this causes the atoms to gain a proton and become a positive ion.

Question 5

Step 1 of mass spectrometry

Answer 5

Ionisation

Question 6

Step 2 of mass spectrometry

Answer 6

Acceleration

Question 7

Explain acceleration in mass spectrometry

Answer 7

+ve ions are attracted to a -ve charged plate, they accelerate towards it. The lighter and more highly charged an ion is, the higher velocity it travels at.

Question 8

Step 3 of mass spectrometry

Answer 8

Ion drift

Question 9

Explain Ion drift in mass spectrometry

Answer 9

the ions pass through a hole in the -ve charged plate and form a beam travelling through the tube to the detector

Equation - t=d/v

Question 10

Step 4 of mass spectrometry

Answer 10

Detection

Question 11

Explain detection is mass spectrometry

Answer 11

Lighter ions arrive at the detector first due to their higher velocities, the flight times are recorded, +ve ions pick up an electron, this causes a current to flow, this current is proportional to the abundance of the isotope.