Atomic absorption spectroscopy AAS Flashcards Preview

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Flashcards in Atomic absorption spectroscopy AAS Deck (8)
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1
Q

AAS- electronic transitions

A
  • The electrons of the atoms (ions) in the flame can be promoted to higher orbitals by absorbing a set of energy (light)
  • This amount of energy is specific to a particular electron transition in each particular element (ion)
  • The absorbance is proportional to the conc. Of the element in the sample being measured
2
Q

AAS- the instrument

A

look at ppt for diagram
- the temperature of the flame is not high enough to promote all atoms (ions) to their excited states

  • this is achieved by the light supplied by the hallow cathode
  • cathode light is then absurd by the atoms and the absorption spectrum is recorded, generally at a single specific wavelength for a particular ion
3
Q

AAS instrument - the light source

A
  • the source of light is a lamp whose cathode is composed of the element being measured
  • each element requires a different lamp
  • the lamp is housed inside the lamp compartment of the instrument
4
Q

AAS instrument - the sample compartment

A
  • One of the most common means of introducing the sample into the flame is by preparing a solution of the sample in a suitable solvent (most frequently water)
    1) Aspirator tube sucks the sample into the flame in the sample compartment
    2) Sample is vaporized in the flame
  • The sample holder is really the flame since it is in the flame that the atoms absorb radiation for the source
5
Q

AAS instrument- flame specifications

A
  • The flame is arranged such that it is laterally long and not deep. The height of the flame must also be controlled by controlling the flow of the fuel mixture.
  • A beam of light is focused through this flame at its longest axis (the lateral axis) onto a detector past the flame.
6
Q

AAS- quantitative analysis

A
  • Quantitative analysis can be achieved by measuring the absorbance of a series of solutions of known concentration.
  • A calibration curve and the equation for the line can be used to determine an unknown concentration based on its absorbance.
7
Q

AAS - applications

A
  • Analysis of the total mercury in human tissues and blood

- The method developed in this study allowed the determination of Hg poisoning levels

8
Q

limitations of flame ionisation sources

A
  • Flame techniques can only detect one element at a time.
  • The optimum excitation condition can vary widely from element to element (temperatures, excitation wavelengths…etc).
  • These techniques are not useful to analyse compounds which are highly resistant to decomposition by heat (i.e. refractive compounds as boron. phosphorus, tungsten, uranium, zirconium).