A further approach to correction for broad band interference utilizes the Zeeman effect. Under the effect
of a strong magnetic field atomic orbitals can be split into sets with energies higher or lower than the
original. The orbitals responsible for the broad band absorption remain largely unaffected.
Measurement of absorption at the wavelength of a characteristic atomic absorption line in the absence
of a magnetic field will include both background and atomic absorption contributions. Under the
influence of the magnetic field only the background absorption will be recorded, allowing correction for
it to be made. High levels of background correction are possible by the Zeeman effect approach. The
Zeeman effect is illustrated schematically in Figure 8.27.
Figure 8.27
Zeeman effect splitting of atomic absorption lines. (Redrawn from
Concepts Instrumentation and Techniques in Atomic Absorption
Spectrophotometry (R. D. Beaty and J. D. Kerber). Perkin-Elmer,
Norwalk, Connecticut, USA)More sophisticated instruments employ the double beam principle (p. 277), which may be operated in
two different ways. One method is to split the incident beam into two, directing one half through the
sample and the other through a reference burner, the signals from two separate but matched detectors
then being compared. This method is cumbersome and expensive as it requires duplication of part of the
optical system and the detector. An alternative and preferable method is to direct the sample and
reference signals in rapid sequence on to a single detector by means of a rotating mirror, thus
eliminating the need for the second matched detector. These different instrument configurations are
sometimes known as 'double-beam-in-space' and 'double-beam-in-time' respectively. The double beam
principle is applied to atomic absorption measurements in a limited way and reference burners are not
normally employed. Hence corrections for