The mass spectrometer is a tool that helps chemists find the mass of molecules by breaking down molecules into fragments.
Parts of the mass spectrometer:
Ionisation Area: The place where a portion of the molecules is converted into ions.
Acceleration area: The ions are accelerated so that they all have the same kinetic energy.
Flight Path: The place where the ions are deflected according to their masses using a magnetic field.
Ion-Detector: Detection of the ions, giving a spectrum of the mass peaks.
Molecular ion peak: The peak that corresponds to the mass of the parent molecule. This is the peak with highest mass number in the mass spectrum.
Isotopes
Mass spectrometry can be used to identify the ratio of isotopes in an element, such as chlorine.
Chlorine can be found as two isotopes; 35-Cl and 37-Cl at a ratio of 3:1. This can be easily observed in the mass spectrum.
To find the RMM from a mass spec simply averages the two masses out. For Chlorine this would be:
Molecules
Unlike elements, a molecule can fragment into different pieces.
One of the most common peaks is 15 which represents CH3-.
When the difference between two peaks is 14 this represents an additional C group, adding -CH2– to the chain.
When a molecule fragments this creates two peaks.
Example of a fragmented molecule could be seen in the mass spectrum of ethanol:
