Mass Spectometry

Diagram of mass spectrometer

Parts of mass spectrometer (4)

• High voltage/electron gun

• Magnetic field

• Vacuum pump

• Detector

Stages of mass spectrometry (4)

• Ionisation

• Acceleration

• Deflection

• Detection

What happens in ionisation

• Element is vapourised

• High energy electrons fired at sample to knock electrons from shell to ionise it

What happens in acceleration

• Negatively charged electromagnetic field

• Accelerates positively charged ions

What happens in deflection

• Electromagnetic field

• Particles with higher m/z ratio deflect the most

• Heavier particles are deflected less

What happens in detection

• Only particles deflected a certain amount reach the detector

• Causes a small current - electrons transfer from detector to positive ions to make them atoms again

• Size of current is proportional to abundance of species

Graph for mass spectrum for chlorine

• Cl-35 (75%)

• Cl-37 (25%)

• Cl35-Cl35 = 70

• Cl35-Cl37 = 72 (x2)

• Cl37-Cl37= 74

Graph for mass spectrum of bromine

• Br79 = 50%

• Br81 = 50%

• Br79-Br79 = 158

• Br79-Br81 = 160 (x2)

• Br81-Br81 = 162