AAS is a time proven analysis used extensively in Pharmacopoeial and environmental analysis for the quantitative determination of metals, mostly as minor or trace constituents. It is now becoming superseded by the more modern ICP techniques, although still used largely used in pharmacopoeia methods for single element analysis.
The sample is injected into a flame or graphite cell and the instrument measures light absorption at characteristic wavelengths as it passes through the atomic vapour generated in the flame or cell. The light comes from a hollow cathode lamp specific to the element being determined.
The technique has the following modes of operation:
- Flame absorption. The sample is introduced as a mist into a flame for atomic absorption measurements
- Flame emission. Most used for the alkali elements that emit light such that their light emission can be used to determine the concentration of that element in solution.
- Electrothermal or graphite cell. The sample is injected into a graphite cell which undergoes a heating program that progressively dries, ashes and then atomises the sample within the confines of the cell. The atomic cloud is more concentrated significantly improving the sensitivity of the technique.
- Cold vapour: Used specifically for mercury only as it is the only element that will generate an atomic vapour at room temperature. Stannous chloride added to the sample solution generates the mercury vapour that is blown into a quartz tube placed in the light path in place of the burner.