FLAME
PHOTOMETRY
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INTRODUCTION:
Theory and Flame spectrometric techniques
•Flame photometry (more accurately called Flame Atomic
Emission Spectrometry) is a branch of spectroscopy in which
the species examined in the spectrometer are in the form of
atoms
•A photoelectric flame photometer is an instrument used in
inorganic chemical analysis to determine the concentration of
certain metal ions among them sodium, potassium, calcium and
lithium.
•Flame Photometry is based on measurement of intensity of the
light emitted when a metal is introduced into flame.
–The wavelength of colour tells what the element is (qualitative)
–The colour's intensity tells us how much of the element present
(quantitative)
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•The basic principle upon which Atomic Spectroscopy
works is based on the fact that "Matter absorbs light at
the same wavelength at which it emits light".
•Atoms of elements  subjected to hot flame 
specific quantum of thermal energy absorbed by
orbital electrons  become unstable at high energy
level  release energy as photons of particular
wavelength  change back to ground state.
•When a metal salt solution is burned, the metal
provides a colored flame and each metal ion gives a
different colored flame.
•Flame tests, therefore, can be used to test for the
absence or presence of a metal ion
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PRINCIPLE
:
•Liquid sample contaning metal
salt solution is introduced into a
flame,
•Solvent is first vaporized, leaving
particles of solid salt which is then
vaporised into gaseous state
•Gaseous molecule dissociate to
give neutral atoms which can be
excited (made unstable) by
thermal energy of flame
•The unstable excited atoms emit
photons while returning to lower
energy state
•The measurement of emitted
photons forms the basis of flame
photometry.
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• Liquid sample
• introduced into a flame
• Solvent vaporized
• leaving particles of solid salt
• vaporized into gaseous state
• Gaseous molecule dissociate to give
neutral atoms
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excited (made unstable) by thermal energy of flame
The unstable excited atoms emit photons while returning to lower
energy state
Flame photometry
The measurement of emitted photons forms the basis of flame
photometry
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•Under constant and controlled conditions, the light
intensity of the characteristic wavelength produced by
each of the atoms is directly proportional to the number of
atoms that are emitting energy, which in turn is directly
proportional to the concentration of the substance of
interest in the sample.
•Various metals emit a characteristic color of light when
heated.
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Limitation of Flame Emission Photometry
•The number of excited atoms in flame is very
small. It is the alkaline and alkaline earth
metals that can be practically determined.
•It needs perfect control of flame temperature.
•Interference by other elements is not easy to
be eliminated.
•Heavy and transition metals , the number of
absorption
and emission lines is enormous and the
spectra are complex.
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Schematic Representation of the Flame Photometer
Major Components:
1. Sample Delivery
System
2. flame
3. Monochromator
4.Detector
5.Read out device
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Nebulizer
Flame
Burners
Mirrors
Slits
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 This is the component of sample delivery system.
which breaks up the bigger liquid droplet to
smaller liquid droplets.
 The process of conversion of sample to a fine mist of
finely divided droplets using a jet of compressed gas
is known as Nebulization.
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Pneumatic
nebulizers
Electro thermal
vaporizer
Ultrasound
nebulizer
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CONCENTRIC
TUBES
FRITTED
DISK
PNEUMATIC
NEBULIZERS
CROSS
FLOW
BAGINGTON
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The liquid sample is
sucked through a
capillary tube by a high
pressure jet of gas
flowing around the tip of
the capillary.
The high velocity breaks
the sample into a mist
and carries it to the
atomization region.
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The jet stream flows
right angles to the
capillary tip.
It uses a high speed
stream of gas
perpendicular to the
tip of the sample
capillary
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The jet is pumped
through a small orifice
in a sphere on which a
thin film of sample
flows
In this type of nebulizer
the sample solution
flows freely over small
aperture, rather than
passing through a fine
capillary
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The sample is pumped
into a fritted disk
through which the gas
jet is flowing and this
gives fine aerosol than
others
High efficiencies can be
obtained by
introducing the sample
at predetermined
location of the fritted
surface
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It is an electro thermal
vaporizer contains an
evaporator in a closed
chamber through
which an inert gas
carries the vaporized
sample into the
atomizer
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The sample is
pumped onto the
surface of a vibrating
piezoelectric crystal.
The resulting mist is
denser and more
homogeneous than
pneumatic nebulizers
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SAPMLE INTRODUCTION TYPES
AND TECHNIQUES
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Flame and Flame temperature
It should have proper temperature
Temperature should remain constant throughout the
operation
There should not be any fluctuation during burning
To convert the analyte of the liquid sample into vapour
state
To decompose the analyte into atoms and simple molecules
To excite the formed atoms/free atoms/simple molecules
to emit radiant energy
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Structure of Flame:
As seen in the figure, the flame may be
divided into the following regions or zones.
Preheating zones
Primary reaction zone or inner zone
Internal zone
Secondary reaction zone
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preheating zone- In this, combustion mixture is
heated to the ignition temperature by thermal
conduction from the primary reaction zone.
primary reaction zone- This zone is about 0.1 mm
thick at atmospheric pressure
There is no thermodynamic equilibrium in this
zone and the concentration of ions and free
radicals is very high.
This region is not used for flame photometry.
interconal zone – It can extend up to considerable
height. The maximum temperature is achieved just
above the tip of the inner zone.
This zone is used for flame photometry.
secondary reaction zone - In this zone, the
products of the combustion processes are burnt to
stable molecular species by the surrounding air.
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Fuel
Oxidant
Temperature 0C
Natural gas
Air
1700-1900
Natural gas
Oxygen
2700-2800
Hydrogen
Air
2000-2100
Hydrogen
Oxygen
2550-2700
Acetylene
Air
2100-2400
Acetylene
Oxygen
3050-3150
Acetylene
Nitrous oxide
2600-2800
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BURNERS
Several kinds of burners are used to convert the fine
droplets of sample solution into neutral atom ,which
further due to the high heat or temperature of flame
are excited hence emit radiation of characteristic
wavelength and color.
Types of burner used:
Mekker or Mecker burner
Total consumption burner
Premix burner
Lundergarph’s burner
Shielded burner
Nitrous oxide – Acetylene burner
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Mecker burner
Nitrous
OxideAcetylene
Flames
Total
consumption
burner
Premix of
laminar
flow burner
Shielded
Burner
Lundergraph
burner
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This burner was used
earlier and employed
natural gas and oxygen.
Produces relatively low
temp. and low excitation
energies.
This are best used for
ALKALI metals only.
Now-a-days it is not
used.
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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
the tip of burner.
Entire sample is
consumed.
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In this type of the burner,
aspirated sample, fuel and
oxidant are thoroughly
mixed before reaching the
burner opening and then
entering the flame.
There is high loss of
sample(95%) as large
droplets are drained out.
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In this sample and air is
mixed in a chamber, this
mixed composition is send
to fuel nozzle where it is
atomized.
Here the sample reaches the
flame is only about 5%
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In this flame was
shielded from the
ambient atmosphere by
a stream of inert gas.
Shielding is done to get
better analytical
sensitivity and quieter
flame
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NITROUS OXIDE ACETYLENE FLAME
These flames were
superior to other flames
for effectively producing
free atoms. The drawback
of it is the 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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The radiation from the
flame is emitted in all the
directions in space. Much
of the radiation is lost and
loss of signal results. A
mirror is located behind
the burner to reflect the
radiation back to the
entrance slit of the
monochromator. The
reflecting surface of the
mirror is front-faced.
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The entrance and exit slits
are used before and after
the dispersion elements.
The entrance slit cuts
off most if radiation from
the surroundings and allows
only the radiation from the
flame and the mirror
reflection of
flame to enter the optical
system.
The exit slit is placed
after the monochromator
and allows only the selected
wavelength range to pass
through the detector
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MONOCHROMATORS
The main of the monochromator is to convert
polychromatic light into the monochromatic one
The two types of monochromator generally used are as
under:
1. Prism : Quartz material is used for making prism, as quartz
is transparent over entire region
2. Grating : it employs a grating which is essentially a series
of parallel straight lines cut into a plane surface
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
Device which converts light energy into electrical signals, that
are displayed on readout devices.
The following types of detectors are employed in
instrumentation of Flame Photometer
1.
Barrier layer cell/Photovoltaic cell
2.
Photomultiplier tube
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0
Requirements of an ideal detector:It should give quantitative response.
It should have high sensitivity and low noise level.
It should have a short response time.
It should provide signal or response quantitative to wide
spectrum of radiation received.
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1
BARRIER LAYER CELL or PHOTO VOLTAI CELL
It cosistitutes
 The steel support plate 'A'
 layer of metallic selenium 'B', which is a few
hundredths of a millimetre in thickness.
 'C' is a thin transparent electrically-conductive layer,
applied by cathodic sputtering.
It consists of a metallic base plate like iron or aluminium
which acts as one electrode.
On its surface, a thin layer of a semiconductor metal like
selenium is deposited.
Then the surface of selenium is covered by a very thin layer
of silver or gold which acts as a second collector tube.
When the radiation is incident upon the surface of selenium,
electrons are generated at the selenium- silver surface and the
electrons are collected by the silver.
This accumulation at the silver surface creates an electric
voltage difference between the silver surface and the basis of
the cell.
The photomultiplier tube
The principle employed in this detector is that, multiplication of photoelectrons by secondary
emission of electrons.
It consists of a photo emissive cathode (a cathode which emits electrons when struck by photons
of radiation), several dynodes (which emit several electrons for each electron striking them) and an
anode.
A photon of radiation entering the tube strikes the cathode, causing the emission of several
electrons.
These electrons are accelerated towards the first dynode (which is 90V more positive than the
cathode). The electrons strike the first dynode, causing the emission of several electrons for each
incident electron.
These electrons are then accelerated towards
the second dynode, to produce more electrons
which are accelerated towards dynode three and
so on.
Eventually, the electrons are collected at the
anode.
By this time, each original photon has
produced 106 - 107 electrons.
The resulting current is amplified and
measured.
Photomultipliers are very sensitive to UV and
visible radiation.
They have fast response times.
Detector
Photomultiplier
Readout device.
In the past nearly all spectrophotometer used ammeters or galvanometers. Newer
digital devices and printers have now replaced these, and many instruments relay their
electrical output directly to computer circuits where calculations are performed,
allowing direct reporting of sample concentration.
Microprocessor and recorders
INTERFERNCES DURING
QUANTITAIVE ESTIMATION
FOLLOWING TYPES OF INTERFERENCES
GENERALLY OCCUR DURING QUANTITAIVE
STIMATION
1.SPECTRAL INTERFERENCE
2. CHEMICALINTERFERENCES
3. IONIZATION INTERFERENCES
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SPECTRAL INTERFERENCES
• The first type of interference arises when two elements exhibit
spectra, which partially overlap, and both emit radiation at some
particular wavelength.
eg. - the Fe line at 324.73 nm overlaps with the Cu line at
324.75 nm.
SOLUTION:It can overcome either by taking measurements at
an alternative wavelength which has no overlap, if available,
or by removing the interfering element by extraction.
• The second type of spectral interference deals with spectral lines of
two or more elements which are close but their spectra do not
overlap
•SOLUTION:It can be reduced by increasing the resolution of the
38 spectral isolation system.
A third type of spectral interference occurs due to the
presence of continuous background which arises due to
high concentration of salts in the sample, especially of
alkali and alkaline earth metals
SOLUTION:This type of interference can be corrected
by using suitable scanning technique.
CHEMICAL INTERFERENCE
The chemical interferences arise out of the
reaction between different interferens and the
analyte . These are of different types:
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CATION- CATION INTERFERENCE
• Due to mutual interferences of cations
• These interferences are neither spectral nor ionic
in nature
• Eg. aluminum interferes with calcium and
magnesium.
Interference due to oxide formation:
It arises due to the formation of stable metal oxide
if oxygen is present in the flame
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CATION- ANION INTERFERENCES
• The presence of certain anions, such as oxalate,
phosphate, sulphate , in a solution may affect the
intensity of radiation emitted by an element,
resulting
in serious analytical error.
•
• For example, calcium in the presence of
phosphate ion forms a stable substance, as
Ca3(PO4) which does not decompose easily,
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resulting in the production of lesser atoms.
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IONIZATION INTERFERENCES
• high temperature flame may cause ionzation of some of the
metal atoms, e.g. sodium
Na
Na+ + e_
The Na+ ion possesses an emission spectrum of its own with
frequencies, which are different from those of atomic
spectrum of the Na atom.
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APPLICATIONS:
•To estimate sodium, potassium, calcium, lithium etc.
level in sample of serum, urine, CSF and other body
fluids.
•Flame photometry is useful for the determination of
alkali and alkaline earth metals.
•Used in determination of lead in petrol.
•Used in the study of equilibrium constants involving in
ion exchange resins.
•Used in determination of calcium and magnesium in
cement.
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Qualitative Analysis
•Group I & II i.e Na, K, Li, Mg, Ca, Ba, Strontium
Quantitative analysis
•Rapid quantitative determination of Group I & II
Element
wavelength
Detection
limit
Element
wavelength
Detection
limit
Al
396
0.5
Pb
406
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Ba
455
3
Li
461
0.067
Ca
423
0.07
Mg
285
1
Cu
325
0.6
Ni
355
1.6
Fe
372
2.5
Hg
254
2.5
Elements, their characteristic emission wavelengths and
detection limits
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Chatwal & Anand; Instrumental Methods of
Chemical Analysis, 5/e 2013, page no- 2.370 to
2.375, Himalaya Publishing House.
B.K Sharma; Instrumental Methods of Chemical
Analysis, 26/e 2007, page no- 430 to 437, GOEL
Publishing House.
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