plane polarized with the field. During that part of the
cycle when the source radiation is polarized similarly,
absorption of radiation by the analyte takes place. During
the other half cycle, no analyte absorption can occur.
Broad-band molecular absorption and scattering by
the matrix products occur during both half cycles,
which leads to the cyclical absorbance pattern shown in
F The data acquisition system is programmed to subtract
the absorbance during the perpendicular half cycle
from that for the parallel half cycle, thus giving a background
corrected value.
A second type of Zeeman effect instrument has
been designed in which a magnet surrounds the hollow
cathode source. Here, it is the emission spectrum of the
source that is split rather than the absorption spectrum
of the sample. This instrument configuration provides
an analogous correction. To date, most instruments are
of the type illustrated in Figure 9-15.
Zeeman effect instruments provide a more accurate
correction for background than the methods. ~escribed
earlier. These instruments are particularly useful for
electrothermal atomizers and permit the direct determination
of elements in samples such as urine and blood.
The decomposition of organic material in these samples
leads to large backgrQund corrections (background
A 2: 1) and consequent shsceptibility to significant error