Page 32 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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2
Flame Atomic Absorption Spectrometry

Flame AAS (often abbreviated FAAS) was until recently the most widely used method for trace metal
analysis. However, it has now largely been superseded by inductively coupled plasma atomic emission
spectrometry (see Chapter 4). It is particularly applicable where the sample is in solution or readily
solubilized. It is very simple to use and, as we shall see, remarkably free from interferences. Its growth
in popularity has been so rapid that on two occasions, the mid-1960s and the early 1970s, the growth in
sales of atomic absorption instruments has exceeded that necessary to ensure that the whole face of the
globe would be covered by atomic absorption instruments before the end of the century.

2.1 Theory

Atomic absorption follows an exponential relationship between the intensity I of transmitted light and
the absorption path length l, which is similar to Lambert's law in molecular spectroscopy:

where I is the intensity of the incident light beam and k,, is the absorption coefficient at the frequency
0
v. In quantitative spectroscopy, absorbance A is defined by

Thus, from Eqn. 2.1, we obtain the linear relationship