Unit 1.3

• A mass spectrometer is used to identify the relative atomic mass of an element. It measures the mass of each different isotope as well as the relative abundance.
• The main stages of a spectrometer are injection, vaporisation, ionisation, acceleration, deflection and detection.
• Injection is the first stage of the spectrometer. It is when you inject the sample into the machnie.
• The second stage of the spectrometer is vaporisation. In order for a sample to be analysed, it needs to be in a gaseous state.
• The third stage in mass spectrometry is ionisation. The sample is bombarded with high energy electrons, which when collided with the sample atoms will knock electrons off and create positive ions.
• The fourth stage in mass spectrometry is acceleration. The ionised sample atoms will be accelerated to a high speed by an electric field.
• The fifth stage of mass spectrometry is deflection. As the accelerated sample ions pass through a magnetic field, they deflect according to the mass of the atom and its charge. Lighter ions are deflected more than heavier ones, and higher charged ions will also be defected more in comparison to ions with a charge of +1.
• The final stage of mass spectrometry is detection. A detector measures the number of ions that reach the end of the machine. This can then be used to determine the relative abundance of different elements within the sample.
• A vacuum is needed for the mass spectrometer to work. Otherwise, the sample molecules will collide with the air molecules in the ionisation chamber.
• The isotopes of chlorine are Cl-35 and Cl-37. The ratio between them in the atomic ion region, Cl+, is 3:1
• The ideal gass equation is pV = nRT. P is pressure measured in pascals, V is volume (m3), n is number of moles, R is the gas constant (8.31 JK-1mol-1) and T is temperature (in kelvin).