Page 55 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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Figure 2.15
Automatic simultaneous background corrector.

are seen. The non-shifted p component is not seen. The magnet operates at about 50-60 Hz, and each
measurement cycle is comprised of two phases. The magnet is off for one of them and on for the other.
When the magnet is off, the atomic absorption is superimposed on molecular and non-specific
absorption. This therefore contains both atomic and background absorption signals. When the magnet is
on, the lines are split and the two s components have no atomic absorption but do have background
absorption. The atomic signal may therefore be obtained by subtraction of this signal from the total
signal (i.e. signal with magnet off—signal with magnet on). The strength of the magnetic field of
Zeeman spectrometers is typically 0.9-1.0 T, which shifts the lines approximately 0.01 nm either side of
the original wavelength.

Another type of background correction system that has found some use is that developed by Smith and
Hieftje. The Smith-Hieftje background correction technique is of especial use when there is strong
molecular interference, such as that observed by phosphate on selenium or arsenic determinations. If the
hollow-cathode lamp is run at its normal operating