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AAS - Atomic Absorption Spectroscopy Introduction Atomic...

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A tomic A bsorption Spectroscopy Introduction Atomic absorption absorption spectroscopy (AA or AAS) is one of the commonest instrumental methods for analyzing for metals and some metalloids. Metalloids like antimony, arsenic, selenium, and tellurium are now routinely analyzed by hydride generation AAS (HGAAS; see www.shsu.edu/~chm_tgc/sounds/sound.html and www.shsu.edu/ ~chemistry/primers for animations and primers on that method). Inductively coupled plasma (ICP) is also a powerful analytical, instrumental method for these elements but at this point its much higher cost limits it widespread use as compared to AAS. As the animation on AAS here shows, the main parts of the AAS system are a hollow cathode lamp, nebulizer, air/acetylene flame, and optical system. Alternate sample introduction systems such as graphite furnaces are also available but will not be discussed here. The job of each are detailed below: Job of the hollow cathode lamp Provide the analytical light line for the element of interest Provide a constant yet intense beam of that analytical line Job of the nebulizer Suck up liquid sample at a controlled rate Create a fine aerosol for introduction into the flame Mix the aerosol and fuel and oxidant thoroughly for introduction into the flame Job of the flame Destroy any analyte ions and breakdown complexes Create atoms (the elemental form) of the element of interest Fe0, Cu0, Zn0, etc. Job of the monochromator Isolate analytical lines' photons passing through the flame Remove scattered light of other wavelengths from the flame In doing this, only a narrow spectral line impinges on the PMT. Job of the photomultiplier tube ( PMT ) As the detector the PMT determines the intensity of photons of the analytical line exiting the monochromator. The Hollow Cathode Lamp The hollow cathode lamp (HCL) uses a cathode made of the element of interest with a low internal pressure of an inert gas. A low electrical current (~ 10 mA) is imposed in such a way that the metal is excited and emits a few spectral lines characteristic of that element (for instance, Cu 324.7 nm and a
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