Flame Emission Spectroscopy (AQA GCSE Chemistry)

• Flame emission spectroscopy is an example of an instrumental method used to analyse metal ions in solution

How does flame emission spectroscopy work?

• The sample is put into a flame 
• The light given out is passed through a spectroscope 
• The intensity and wavelength of the light emitted is measured
• The output is a line spectrum in which different elements produce lines in different parts of the spectrum
• The spectrum can be analysed to identify the metal ions in the solution and their concentrations
• Flame emission spectroscopy also works for mixtures of ions
• This is a major advantage over flame testing which can only analyse one ion at a time

A line spectrum from flame emission spectroscopy

• Ions in unknown samples can be identified by comparing the sample spectrum to reference spectra
• This is particularly useful if the sample contains a number of different ions
• The following flame spectrum for example was obtained for a solution containing an unknown metal:

Flame spectrum for an unknown metal 

• When compared to the reference spectra below we can see that the solution must contain sodium ions:

Diagram of a reference spectra including an emission spectrum for sodium