Absorbance flame absorption profiles

Flame Absorption Profiles. Figure 9-4 shows typical absorption profiles for three elements. Magnesium exhibits a maximum in absorbance at about the mid-... 

In Chapter 1, section 7, it was explained that very precise overlap of atomic absorption and emission profiles is required to obtain sensitive absorbance measurements. Absorption spectra of atoms at flame temperatures are much simpler than the emission spectra emitted by hollow cathode lamps. The possible transitions corresponding to electronic excitation of an atom may be shown as vertical lines on an energy level diagram, in which the vertical displacement... 

Cases have been observed where the isotopic line absorption profiles completely overlap, e.g. boron-10 and -11 in a krypton-filled lamp at 249.7 nm [244]. Hannaford and Lowe [245] later showed that this was caused by an unusually large Doppler half-width induced by the fill-gas, and, if neon is used, the 208.9 and 209.0 nm lines can allow the determination of boron-10 and boron-11 isotope ratios. The 208.89/208.96 nm doublet was found to be more useful than the 249.68/249.77 nm doublet. Enriched isotope hollow-cathode lamps were used as sources. A sputtering cell was preferred to a nitrous oxide/acetylene flame as the atom reservoir, as it could be water-cooled to reduce broadening and solid samples could be used, thus avoiding the slow dissolution in nitric acid of samples of boron-10 used as a neutron absorber in reactor technology. 

Absorbance profile for Ag and Cr in flame atomic absorption spectroscopy. 

The absorption line profile in the atomizer (e.g. in the flame) will still peak at the initial emission line peak. Absorbance will be reduced as the emission line becomes broader, and even more dramatically when the emission line shows reversal. Thus atomic absorption signal decreases with increasing lamp current (Figure 2). As might be expected, the drop off in signal is greater for more volatile elements such as cadmium and zinc. 

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