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Biochemical instrumental analysis-2. Dr. Maha Al- Sedik. Atomic absorption spectrophotometer. Atomic absorption spectrophotometer. Atomic absorption spectroscopy is a quantitative method of analysis that is applicable to many metals such as Ca , Fe , Al and copper.

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atomic absorption spectrophotometer
Atomic absorption spectrophotometer
  • Atomic absorption spectroscopy is a quantitative method of analysis that is applicable to many metals such as Ca , Fe , Al and copper.
  • Only a drop of sample is needed.
  • Atomic absorption is so sensitive that it can measure down to parts per billion of a gram in a sample.
slide6

The Atomisation

Process of converting an analyte in solid, liquid or solution form to a free gaseous atom.

slide9

Principle:

  • Atoms of different elements absorb characteristic wavelengths of light.
  • The metal vapor absorbs energy from an external light source, and electrons jump from the ground to the excited states.
  • The greater the number of atoms in the vapor, the more radiation is absorbed.
slide10

How it works?

  • For example with lead, a lamp containing lead emits light from excited lead atoms that produce the right mix of wavelengths to be absorbed by any lead atoms in the sample.
  • Beam of electromagnetic radiation emitted from the lamp is passed through the vaporised sample. Some of the radiation is absorbed by the lead atoms in the sample.
slide12

The greater the number of atoms in the vapor, the more radiation is absorbed.

  • OR
  • The amount of light absorbed is proportional to the number of lead atoms.
slide14

Components :

  • The light source
  • flame
  • Monochromater
  • photomultiplier tube
  • Detector
slide15

The light source:

hollow cathode lamp

hollow cathode lamp for Aluminum (Al) is shown below

slide16

hollow cathode lamp:

  • This contains a tungsten anode and a cylindrical hollow cathode made of the element to be determined. These are sealed in a glass tube filled with an inert gas – egneon or argon.
  • The shape of the cathode concentrates the radiation into a beam which passes through window.
slide17

The cathode lamps are stored in a compartment inside the AA spectrometer. The specific lamp needed for a given metal analysis is rotated into position for a specific experiment.

slide18

The flame:

  • A flame is created, usually using ethyne & oxygen (fuel)
  • The flame gases flowing into the burner create a suction that pulls the liquid into the small tube from the sample container.
  • This liquid is transferred to the flame where the sample is atomized [mixing the sample with air to create fine droplets]. The metal atoms then absorb light from the source (cathode lamp).
slide23

Monochromater:

  • the monochromator is used to select a particular wavelength of light for observation).
  • photomultiplier tube:
  • The intensity of the light is fairly low, so a photomultiplier tube (PMT) is used to strengthen the signal intensity.
  • It can multiply the current produced by incident light by as much as 100 million times.
slide26

Detector:

  • Transform light to electrical impulses.
  • The electricity is directly proportional to the intensity of light.
slide27

http://www.youtube.com/watch?v=_KZjb9G3hB8irst.pptx

http://www.youtube.com/watch?v=HBegTB_WDxQ

slide28

Flameless atomic absorption spectrophotometry

  • It differs from atomic absorption spectrophotometer in how the compounds are atomized.
  • In AAS a flame is used to produce individual atoms.
  • In the other it is carried out by putting the sample in a small graphite tube and passing an electrical current through to heat it.
slide29

Summary of atomic absorption spectrophotometry :

  • Atomic absorption spectrophotometer is used in the measurement of many metal such as Ca , Fe , Al and copper.
  • Only a drop of sample needed.
  • Atomic absorption is so sensitive that it can measure down to parts per billion of a gram in a sample.
slide30

Principle:

  • Atoms of different elements absorb characteristic wavelengths of light to be transformed to the exited state.
  • The greater the number of atoms in the vapor, the more radiation is absorbed.
  • Components :
  • The light source,
  • Flame
  • Monochromater
  • Photomultiplier tube
  • Detector
slide31

Function of each component:

  • Light source: produce the right mix of wavelengths to be absorbed by specific atoms in the sample.
  • Flame: Atomization of the sample.
  • Monochromator: selection a particular wavelength of light for observation).
  • photomultiplier tube: used to strengthen the signal intensity.
  • Detector:transform light to electrical impulses.
slide32

Differences between atomic absorption spectrophotometer and the flameless atomic absorption spectrophotometer:

  • They differ in how the compounds are atomized.
  • In one case a flame is used to produce individual atoms.
  • In the other it is carried out by putting the sample in a small graphite tube and passing an electrical current through to heat it.
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