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few research laboratories possessing very high resolution monochromators. Perhaps the most practical
approach to continuum source atomic absorption has been by O'Haver and his colleagues [A.T. Zander
et al., Anal. Chem. 48, 1166 (1976); J.M. Harnly et al., Anal. Chem. 51, 2007 (1979)]. The basis of their
system is a high-intensity (300 W) xenon arc lamp, an echelle grating monochromator (see Section
4.4.5) with wavelength modulation and an amplifier locked into the modulated signal. Competitive
detection limits have been obtained by these workers, except for lines in the low-ultraviolet region,
where the arc intensity is poor. The technique has the possibility of simple adaptation to multi-element
work with in-built background correction.

A fuller account of atomic absorption is given by Kirkbright and Sargent (see Appendix C).

Q. Why is a plot of the percentage of light absorbed versus concentration a curve? What must be plotted
to give a straight line passing through the origin?

Q. Why are resonance lines always used for analytical AAS?

Q. Why must a line source be used for AAS?

Q. How does the 'lock and key' effect impart great selectivity to AAS?

2.2 Instrumentation

Atomic absorption spectroscopy instrumentation can conveniently be considered under the following
subheadings.

2.2.1 Sources
As we have seen, a narrow line source is required for AAS. Although in the early days vapour
discharge lamps were used for some elements, these are rarely used now because they exhibit self-
absorption. The most popular source is the hollow-cathode lamp, although electrodeless discharge
lamps are popular for some elements.

2.2.1.1 The Hollow-cathode Lamp.

The hollow-cathode lamp is shown diagrammatically in Fig. 2.2. As the name suggests, the central
feature is a hollow cylindrical cathode, lined