1. Explain what happens to the analyte sample when it is aspirated into the flam
ID: 569415 • Letter: 1
Question
1. Explain what happens to the analyte sample when it is aspirated into the flame of the AA, including ionization and atomizaiton. (Flame atomic absorption spectroscopy)
2. The flame side of the AA measures concentration in parts per million range and the furnace side of the AA measures in parts per billion. What is the major difference in terms of sample introduction and elctron excitation for these two kinds of the spectroscopy?
3. What are the advantages and disadvantages of using the FAAS (flame atomic asborption spectroscopy) and GFAAS(graphite furnace)?
Explanation / Answer
1. In FAAS, either an air/acetylene or a nitrous oxide/acetylene flame is used to evaporate the solvent and dissociate the sample into its component atoms. In AA spectroscopy the primary need is to convert the analyte into free atoms. In most cases the analyte is in solution form. If the sample is a solid then it must be brought into solution before the analysis.The process of converting an analyte to a free gaseous atom is called atomization.
When the light from a hollow cathode lamp passes through the cloud of atoms , the atoms of interest absorb the light from the lamp. This is measured by a detecctor and used to calculate the concentration of that element in the original sample.
2. In the furnace side of AA, the samples are placed in a carbon tube which is heated electrically. The sample residence time is greater and so we get improved detection limits and sensitivity. Also solid samples can be assayed. In flame atomization, the sample is constantly being consumed and so a large sample size is required and also the sample must be a fluid.
3. Strengths of FAAS include easy to use, very fast, lowest capital cost, relatively few interferences, very compact instrument with good performance. Its limitations are moderate detection limits, element limitations, 1-10 elements per determination and no screening ability. Whereas, the advantages of GFAAS include very good detection limits, small sample size, moderate prize, very compact instryment with few spectral interferences. Its disadvantages are slower analysis time, chemical interferences, element limitations, 1-6 elements per determination, no screening ability andd limited dynamic range.
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