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Atomic spectroscopy

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by

Hesham Hady2

on 2 May 2017

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Transcript of Atomic spectroscopy

Atomic spectroscopy
atomic spectroscopy process:
when a solution having a mixture of metallic species is introduced into the flame , the solvent evaporates and metallic vapour is obtained . Some of metal atoms can be raised to an energy level sufficiently high to emit characteristics radiation of metal phenomena used in flame photometry.
The radiant source
For atomic absorption spectroscopy the radiant source is a hollow cathode lamp .
Theory
Atomic absorption
Absorption of a photon results in excitation of an electron from a lower energy level to a higher energy level of atomic orbital .
Atomic Emission
Thermal or electric energy from an arc, flame, spark or plasma is used to excite an electron from a lower energy level to a higher energy level when excited electrons returns to it's original .
Atomic fluorescence

Like atomic absorption, ground state atoms created in a flame are excited by focusing a beam of light into the atomic vapor.the intensity of this fluorescence increases with increasing atom concentration, used for quantitative determination .
This technique incorporate of

both atomic absorption and emission .
principle
Applications
Agriculture
Analysing soil, plants and minerals necessary for growth
petrochemicals
analysing products for metal and other substance that can have adverse affects such as oil and gas.
Environmental
study
Determination of heavy metals in water, soil and air.
pharmaceutical
In quality control for detecting impurities in drug .
Determination of the dissolution rate of digoxin tablets.
Determination of aluminium in water for injection as a fluorescent complex.
Determination of stability of peptide drugs in solution .
Food industry
quality assurance and testing for contamination
Nuclear energy
monitoring potentially hazardous elements in water and wastes output.
Instrumentation
The apparatus consists of :
1) Radiant source .
2) Atomizer .
3) Monochromator .
4) Detector .
consists of :

I) cathode :
is made of the element to be determined or coated with it .

2) anode :
is made of Tungsten , Zirconium or Nickle .

3) Pyrex glass :
depending on wavelength of emitted radiation.

4) the lamp
: filled with neon or argon gas

Hollow cathode lamp
Atomizer
burners are used to break the liquids sample into droplets and then allowed to enter into the flame.

the droplets are then evaporated and sample element is then left in residue . the residue is then decomposed by the flame. In this process the sample is reduced into atoms .

how can you determine quantitatively ?
As we know that each element has its own characteristic emission spectrum , hence the intensity of the lines is compared with standard and the concentration can be easily evaluated from the graph .
 Advantages of Atomic Absorption Spectroscopy
(1) It does not suffer from spectral interference, which occurs in flame emission spectroscopy.

(2) It is independent of flame temperature.

(3) By atomic absorption technique, traces of one element can easily be determined in presence of high concentration of other elements.

(4) It has proved very successful in the analysis of bronze and copper alloys and in the determination of metals like platinum, gold etc.

(5) More sensitive than AES . A highly specific method of analysis useful in some aspects of quality control .



Disadvantages of Atomic Absorption Spectroscopy
(1) This technique has not proved very successful for the
estimation of elements like V, Si , Mo, Ti and A1
because these elements give oxides in the flame.

(2) In aqueous solution, the anion affects the signal to a
noticeable degree .

(3) Only applicable to metallic elements .

(4) Each element requires a different hallow cathode
lamp for its determination .
Definition :

is The study of absorption , emission & fluorescence of electromagnetic radiation ( EMR ) by mono atomic particles in gaseous state ( being present in flame ) .

Flame Spectroscopic methods:

The methods of analysis where the concentration of an element in a solution is determined by measuring the absorption , emission & fluorescence of ( EMR ) by mono atomic particles in gaseous state in the flame .

Atomic spectroscopy
Factors affecting atomic spectroscopy
1- Temperature :

Atomic spectroscopy is temperature dependent since temperature can promote the loss of excitation by collision and bond vibration . A molecule that is not fluorescent at room temperature may become fluorescent at lower temperature .

2- Complex formation :

Formation of a chemical complex with other molecules in sol. can change fluorescence behaviour e.g. the presence of caffeine in solution reduces fluorescence of riboflavin.
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