Computing absorbance
The simulated data in Fig. 1 shows a band of elevated
intensities running through the frame parallel to the wavelength
axis. This band is a single order of the echelle viewed over a
´
short wavelength interval, typically less than 1 nm. In Fig.1,
intensities above and below the band (between orders) are
also seen. Stray radiation and osets in the electronic circuitry
determine the magnitude of the intensities between orders. The
height of the order above the between order intensity is
determined by the source intensity and the order being viewed
and fluctuates with time. The width of the band (on the order
axis) will depend on the entrance slit height. The dip in the
middle of the band is the analyte absorption and the depth
will vary with analyte concentration. Additional dips in the
band may be seen if non-analyte absorption, or spectral line ´
Fig. 2 Echelle order containing absorption profile for 250 pg of Cu
interferences, occur. The simulated data in Fig. 1 are con- (324.7 nm) obtained with an entrance slit 25 mm wide and 100 mm
structed with only 22 columns and 54 rows of pixels. In high. Large vertical oset is electronic and not stray light.
J. Anal. At. Spectrom., 1999, 14, 137–146 139