Continuum radiation sources

In order to make the lamp change rapid, various arrangements are offered by the manufacturers. For instance, by a ferris-wheel like turret a sequence of elements can be measured during each turret rotation. Another approach is a combination of a continuum radiation source and a high-resolution spectrometer. However, this combination has not achieved great acceptance. A common problem with continuum sources is their relatively low intensity in the UV region. 

The background correction with a continuum radiation source is an... 

Molecular absorption methods described in the literature are based on the use of continuum light sources (deuterium lamp with a thermal cathode or hollow cathode) or line-like radiation sources (hollow cathode lamps). Measurements using a continuum light source are carried out with a dual-channel instrument. The other channel is needed for the background correction. With a line-like radiation source, a conventional AA spectrometer can be used. In this technique the non-specific absorption is measured with a continuum radiation source. 

When using a continuum radiation source, the observed absorption signal is dependent on the slit width (Figure 100). Some cations, such as Ni, Fe, and Co, improve the sensitivity and decrease the background absorbance in... 

Figure 100 Effect of spectral bandwidths on the absorption intensities of AlCl (%) and AlBr ( ) by using a continuum radiation source. (Adapted from K. Tsunoda, K. Fujiwara and K. Fuwa, Anal. Chem., 1978, 50, 861)...

Figure 142 Intensity of the fluorescence as a function of analyte concentration when using (A) a line-like radiation source, and (B) a continuum radiation source...

Dispersive Instruments. In dispersive instruments monochromators are employed for selection of the wavelength. When a line-like radiation source is employed, a monochromator of low resolution is adequate, but for a continuum radiation source a high resolution monochromator is required. In dispersive equipment the exit slit width is narrower than that in non-dispersive equipment. In this way, thermal background emission and stray light originating from the atomizer can be considerably decreased, but at the same time the optical transmission also decreases. The schematic construction of a dispersive AFS instrument is shown in Figure 144. 

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