Answer these questions: 6. For detecting trace (small amounts) of an element, wh

Question

Answer these questions:

6. For detecting trace (small amounts) of an element, which method would be better, AAS or AES? Explain why.

7. For one the following types of atomic spectroscopy instruments do some research on-line and an example of an instrument that is commercially available. Report on its cost, components, if it is considered a high end or low end model, what accessories or variations are available, if there are any special operating considerations or housing requirements and anything else notable.

a. Flame Atomic Absorption Spectrometer

b. Graphite Furnace Atomic Absorption Spectrometer

c. Atomic Emission Spectrometer

d. ICP (inductively coupled plasma) Atomic Emission Spectrometer

e. Energy dispersive x-ray spectrometer (EDS or EDXRF)

Explanation / Answer

6. For detecting trace (small amounts) of an element, AES is found to be better then AAS. AES measured the wavelength of the light emitted from the excited atoms in the atomic emission spectroscopy as ICP-OES. It directly relates the concentration of the excited atoms to the intensity of the emitted light of a particular wavelenght. This technique does not require the use of Beer-Lambert's law for concentration determination. On the other hand in AAS, the light is absorbed, calibration graph is plotted with known concentration of analyte and the amount of light absorbed being proportional to the concentration is used for measuring the concentration of analyte in the sample. Here applying the Beer-Lambert law directly in AAS is difficult due to the variations in atomization efficiency from the sample matrix, the non-uniformity of concentration observed and the path length of analyte atoms (as in graphite furnace AA). It is thus more beneficial to employ AES for small amounts of trace element detection.

7. Of the techniques given below, Energy dispersive x-ray spectrometer (EDS or EDXRF) can be considered a high end model. The basic accessories of the instrument being, the excitation source (electron beam or x-ray beam), the X-ray detector, the pulse processor and the analyzer. The approximate cost of the instruments can be anywhere aound US$40,000 and above. Anumber of detector types are available now in the recent modified model of the instrument. the placement of the instrument must be a separate room or chamber with no or minimum vibrations If any as it can affect the beam.

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