1. Introduction to principle and
instrumentation of atomic emission
spectroscopy
BY
Humna Mehmood
BS Chemistry (2017-2021)
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2. Introduction to atomic emission spectroscopy:
• Atomic spectroscopy is thought to be the oldest instrumental
method for the determination of elements.
• Atomic emission spectroscopy uses quantitative
measurement of the optical emission from excited atoms to
determine analyte composition.
• It is used to identify elements and determine their
concentration in analyte.
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3. Principle:
• The working principle involves the examination of the
wavelengths of photons discharged by atoms and molecules as
they transit from a high energy state to a low energy state.
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4. o A characteristic set of wavelengths is emitted by each element or
substance which depends on its electronic structure.
o The atomic spectral line wavelength identifies the element.
o The intensity of light emitted is proportional to the atom count of
the element.
o The sample solution is nebulized and introduced into the
excitation source (flame).
o Atoms are raised to excited states. Upon their return to a lower or
ground electronic state, the excited atoms emit radiations.
o The emitted radiations passes through a wavelength selector that
isolates the specific wavelength .
o A photo detector measures the radiant power of radiation, which
is then amplified and sent to a readout device.
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7. Pretreatment of Sample
• Solid sample must be dissolved in solvent.
• Substances in sample that interfere with the emission
measurement must be removed or masked
• Reagents used to dissolve samples must not contain
substances that lead to interference problems.
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8. Nebulizer
• This is a component of sample delivery system, which breaks up
the bigger liquid droplet to smaller liquid droplets
• The process of conversion of sample to a fined mist of finely
divided droplets using a jet of compressed gas is known as
nebulization.
Types of nebulizer
• Ultrasonic nebulizer
• Electro-thermal vaporizer
• Pneumatic nebulizer
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9. Ultrasonic nebulizer
• The sample is pumped onto the surface of vibrating piezoelectric
crystals.
• The resulting mist is denser and more homogeneous than
pneumatic nebulizer.
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10. Electro-thermal vaporizers
• It is an electro thermal
vaporizer
• It contains an evaporator
in a closed chamber
through which an inert
gas carries the vaporized
sample into atomizer.
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11. Pneumatic nebulizer
It is of four types:
o Cross flow
o Concentric tubes
o Fitted or porous disc
o Babington
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12. Cross flow
• The stream jet flows right angle to capillary tip.
• It uses a high speed stream of gas perpendicular to the tip of the
sample capillary.
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13. Concentric tubes
• The liquid sample is sucked
through a capillary tube by a
high pressure jet of gas
flowing around the tip of the
capillary tube.
• The high velocity breaks the
sample into mist and carries
it to atomization region.
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14. Babington
• The jet is pumped through a
small orifice in a sphere on
which a thin film of sample
flows
• In this type of nebulizer
sample solution flows freely
over small aperture rather than
passing through a fine
capillary tube
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15. Fritted or porous disk
• The sample is pumped into a
fritted disk through which the
gas jet is flowing and this gives
fine aerosol then others
• High efficiency can be obtained
by introducing the sample at
predetermined location of
fritted surface.
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16. Source of flame
A Burner is the source of flame. It is maintained at a constant
temperature. Temperature vary for different fuel-oxidant mixtures as
shown table.
Fuel + Oxidant mixture Temperature ( ℃ )
Natural gas + Air 1700
Propane + Air 1800
Hydrogen + Oxygen 2000
Hydrogen + Oxygen 2650
Acetylene + Air 2300
Acetylene + Oxygen 3200
Acetylene + Nitrous oxide 2700
Cyanogen + Oxygen 4800
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18. Processes occurring in the flame:
• Desolvation: The metal particles are dehydrated and the
solvent is evaporated.
• Vaporization: This also led to the evaporation of the solvent.
• Atomization: Reduction of metal ions in the solvent to metal
atoms by the flame heat.
• Excitation: The atoms jump to the exited energy state.
• Emission process: Atoms jump back to the stable low energy
state with the emission of energy in the form of radiation of
characteristic wavelength.
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19. The emitted radiations generally lie in the visible region of the
spectrum so flame shows color. Each of the alkali and alkaline earth
metals has a specific wavelength.
Element Emitted
wavelength
Flame color
Sodium 589 nm Yellow
Potassium 766 nm Violet
Barium 554 nm Lime green
Calcium 622 nm Orange
Lithium 670 nm Red
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21. Mecker burner
• This burner was used earlier
and employed natural gas
and oxygen.
• Produces relatively low
temperature and low
excitation energies.
• This is best for alkali metals
only. Now a days it is not
used.
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22. Total consumption burner
• In this burner fuel and
oxidant are hydrogen and
oxygen gases.
• Sample solution is aspirated
through a capillary by high
pressure of fuel and oxidant
and burnt at tip of burner.
• Entire sample is consumed.
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23. Premix or laminar burner
• In this type of burner aspirated sample fuel and oxidant is mixed
thoroughly before reaching the burner opening and then entering in
the flame.
• There is high loss of sample (95%) as large droplets are drained
out.
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24. Shielded burner
• This flame is shielded from ambient atmosphere by a stream
of inert gas.
• Shielding is done to get better analytical sensitivity and
quieter flame.
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25. Nitrous oxide -acetylene flame
• This flame is superior to other flames
for effectively producing free atoms.
• The drawback of it is its high
temperature reduces its usefulness for
the determination of alkali metals as
they are easily ionized and intense
background emission, which makes
the measurement of metal emission
very difficult.
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26. Lundergraph burner
• In this burner sample and air
is mixed in a chamber, this
mixed composition is send to
fuel nozzle where it is
atomized.
• Here sample reaches flame
only about 5%.
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27. Mirror, Lens and Wavelength selector
Mirror
o The radiation from flame are emitted in all the directions in the
space.
o Mirror is located behind the burner to reflect radiations back to
slit of monochromator. The reflecting surface of mirror is front
faced.
Lens:
o It helps to focus the light on a point or slit.
Wavelength selector:
o The radiations from the mirror pass through the slit and reach
the filters.
o Filters will isolate the light of different wavelengths.
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28. Photodetector, Amplifier and Readout device
Photo-detector:
o The intensity of radiation emitted by the flame is measured by
photo detector.
o Here the emitted radiation is converted to an electrical signal
with the help of photo detector.
o These electrical signals are directly proportional to the intensity
of light.
Amplifier:
o It amplify electrical signals.
Readout device:
o LCD display is used as readout device.
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