Biochemical instrumental analysis 2
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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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Biochemical instrumental analysis-2

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Biochemical instrumental analysis 2

Biochemical instrumental analysis-2

Dr. Maha Al-Sedik


Biochemical instrumental analysis 2

Atomic absorption spectrophotometer


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.


Biochemical instrumental analysis 2

In AAS, the sample is atomised – ieconverted into free atoms in the vapourstate.


Biochemical instrumental analysis 2

The Atomisation

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


Biochemical instrumental analysis 2

  • 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.


Biochemical instrumental analysis 2

  • 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.


Biochemical instrumental analysis 2

  • 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.


Biochemical instrumental analysis 2

Components


Biochemical instrumental analysis 2

Components :

  • The light source

  • flame

  • Monochromater

  • photomultiplier tube

  • Detector


Biochemical instrumental analysis 2

The light source:

hollow cathode lamp

hollow cathode lamp for Aluminum (Al) is shown below


Biochemical instrumental analysis 2

  • 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.


Biochemical instrumental analysis 2

  • 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.


Biochemical instrumental analysis 2

  • 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).


Biochemical instrumental analysis 2

The Manganese Flame


Biochemical instrumental analysis 2

The Potassium Flame


Biochemical instrumental analysis 2

The Copper Flame


Biochemical instrumental analysis 2

The Calcium Flame


Biochemical instrumental analysis 2

  • 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.


Biochemical instrumental analysis 2

photomultiplier tube


Biochemical instrumental analysis 2

  • Detector:

  • Transform light to electrical impulses.

  • The electricity is directly proportional to the intensity of light.


Biochemical instrumental analysis 2

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

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


Biochemical instrumental analysis 2

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.


Biochemical instrumental analysis 2

  • 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.


Biochemical instrumental analysis 2

  • 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


Biochemical instrumental analysis 2

  • 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.


Biochemical instrumental analysis 2

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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