Flame photometry (Atomic emmision Spectroscopy)

AES

1. FLAME PHOTOMETRY
1
By Priyanka Yadav

2. CONTENTS:
2
• INTRODUCTION
• HISTORY
• ELECTRON ORBITAL AND ENERGY STATE
• PRINCIPLE
• INTRUMENTATION
• SAMPLE INTRODUCTION
• BURNERS AND FLAME
• MIRRORS
• MONOCHROMATORS
• DETECTORS
• APPLICATIONS
• INTERFERENCES
• LIMITATIONS

3. INTRODUCTION
3
Flame photometry or Flame Atomic Emission spectroscopy.

It is type of emission spectroscopy where atomic emission
is measured using spectrophotometer.

When metallic species is introduced into flame the metal
salt is burnt emitting certain colored wavelength and this
instrument is based on measurement of intensity of color.

Each metal gives characteristic color and the intensity of
color depicts the amount or quantity of metal present.

Hence identifies the presence or absence of metal via color.

4. HISTORY
4
The history of spectroscopy starts with the use of the
lens by Aristophanes about 423 B.C.; and the studies of
mirrors by Euclid (300 B.C.) and Hero (100 B.C.).

In the later 1800, scientists such as Kirchhoff, Bunsen,
Angstrom, Rowland, Michelson and Balmer studied the
composition of the sun based on their emissions at
different wavelengths.

In February of 23
rd
1955 Murray Nelson A. filed a patent
for invention of Flame Photometry which was granted in
year 1958

5. ORBITALS OF ELECTRON
5
oElectrons of atoms reside in concentric spheres known
energy “ shells ” in which they orbit the nucleus of an atom
.

oEach shell is assigned a principal quantum number, n.

oThe value n is integer , 1,2,3, etc.

oThis number determines the relative energy of the orbital
and relates the distance from the shell to the nucleus the
lower the number, the lower the energy of the electron and
the closer it is to the nucleus .

oElectron can be further distinguished according to there
location in atomic orbital, specified region in space that
depend on there energies

6. ENERGY STATE OF ELECTRON
6
All the electrons are in there respective lowest
energy state referred as the ground state or the
state of lowest energy.

As a certain energy is provided to the atom, an
electron from its residence ground state shell to the
higher energy state shell called as excited state ..

As the excited state electrons are in shell with
greater ‘n’ ,hence have more energy and less
stability.

7. Energy level of electron

7
E
2

E ∆E= E
2-E
1
= hn

E
1
∆E = hn
∆E = hc/λ (v=c/λ)
∆E = Energy difference
h = Plank’s constant(6.626068 X 10
-34
m
2
kgs
-1
)
n = frequency of emitted light
c = velocity of light
λ = wavelength

8. Boltzmann law

8
The fraction of free atom that are thermally exited
is governed by a Boltzmann Distribution

 N*/N= ∆e
- ∆E/kT





N* =is the number of exited atom
 N = is the number of atom remaining
 in the ground state
 ∆E = is the difference in energies levels
 k = The Boltzmann constant
 T = the tempeature

9. Principle
9
•Liquid sample containing metal salt solution
introduced into a flame:
•Solvent is vaporized , leaving particles of
solid salt
•Salt is vaporized into gaseous state
•Gaseous molecule dissociate to give
neutral atoms
•The unstable excited atoms emit photons
while returning to lower energy state.
•The measurement of emitted photons
forms the basis of flame photometry using
•photomultiplier tube detectors.

Ground state E
0
Excited state E
1
e
Emission

10. TABLE SHOWING CHARECTERSTIC
WAVELENGTH AND COLOUR
10
ELEMENT OR
METAL
WAVELENGHT OF
EMISSION
COLOR


SODIUM

589

YELLOW

POTTASSIUM

766

VIOLET

CALCIUM

662

ORANGE


LITHIUM

670

RED

BARIUM

554
LIME
GREEN

11. INSTRUMENTATION
11
SAMPLE DELIEVERY SYSTEM

BURNER AND FLAME OR
SOURCE

MONOCHROMATOR

DETECTOR

READ OUT

12. DIAGRAMMATIC REPRESENTATION
12

13. SAPMLE INTRODUCTION TYPES
AND TECHNIQUES
13

14. SAMPLE DELIVERY OR
NEBULIZATION
This is the part of sample delivery system in which liquid
droplets of comparatively larger size are broken or converted
to smaller size.

The process of conversion of sample into a mist of very fine
droplets through the aid of jets of compressed gas is called
nebulization
Types of nebulizers:
 pneumatic nebulizers
Electro-thermal vaporizers
Ultrasound nebulizers


14

15. PEBNEUMATIC NEBULIZERS:
15

16. 16

17. 17

18. ELECTRO-THERMAL VAPORZERS
Electro-thermal Vaporizers
(ETV)-
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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19. ULTRASONIC NEBULIZERS
Ultrasonic Nebulizer-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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20. 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


20

21. MECKER OR MEKKER BURNER
This was the primitive type of burner
used in flame photometry and was
used earlier.

It generally works with aid of natural
gas and oxygen as fuel and oxidant.

The temperature so produced in the
flame was relatively low, resulting in
low excitation energy.

Now a days it is not used but it was
best suited for alkali metal. 21

22. TOTAL CONSUMPTION BURNER
Due to the high pressure of fuel
and oxidant the sample solution is
aspirated through capillary and
burnt at the tip of burner

Hydrogen and oxygen are generally
employed as fuel and oxidant.

The advantage over other is the
entire consumption of sample,

It’s disadvantage is the production of
non uniform flame and turbulent.
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23. PREMIX BURNER
In this burner the sample , fuel
oxidant are thoroughly mixed
before aspiration and reaching
to flame.

The main advantage of it is the
uniformity of flame produced.

The main disadvantage is the
heavy loss of mix up to 95%.
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24. LUNDENGARPH’S BURNER
A small sample liquid droplets vaporized and move to base of
flame in the form of cloud

Large droplets condensed at side and then drained off.

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SHIELDED BURNER
•In this flame was shielded from the
ambient atmosphere by a stream of
inert gas.
•Shielding is done to get better
analytical sensitivity.
•Following results are obtained with
shielded burner

25. NITROUS OXIDE-ACETYLENE FLAME
•These flames were superior to other flames
for effectively producing free atoms
•E.g.-metals with very reflective oxides such as
aluminum and titanium.
The drawback of it is:
• the high temperature reduces its usefulness
for the determination of alkali metals as they
are easily ionized
•Intense background emission, which makes
the measurement of metal emission very
difficult

25

26. STRUCTURE OF FLAME
•As seen in the figure, the flame
may be divided into the
following regions or zones.
i) Preheating zones
ii) Primary reaction zone or
inner zone
iii) Internal zone
iv) Secondary reaction zone

26

27. LIST OF FUEL AND OXIDANT USED
27
FUEL OXIDANT TEMPERATUREº
C
TOWN GAS AIR 1700
PROPANE AIR 1900
BUTANE AIR 1925
ACETYLENE AIR 2200
TOWN GAS OXYGEN 2700
PROPANE OXYGEN 2800
BUTANE OXYGEN 2900
ACETYLENE NITROUS OXIDE 2955

28. MIRRORS
The radiation emitted by the flame
is generally towards all the direction

Hence a mirror is place behind the
flame to focus the radiation towards
the entrance slit of the
monochromator.

A concave mirror is used as it is
front faced reflecting type.

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29. 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

29

30. 30

31. DETECTORS
Photomultiplier tube


Photo emissive cell


Photo voltaic cell

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32. PHOTOMULTPLIER TUBE
The intensity of the light is fairly low, so a photomultiplier
tube (PMT) is used to boost the signal intensity
A detector (a special type of transducer) is used to generate
voltage from the impingement of electrons generated by the
photomultiplier tube

32

33. PHOTOVOLTAIC CELL
It has a thin metallic layer coated with silver or gold
act as electrode , also has metal base plate which act as
another electrode.

Two layers are separated by semiconductor layer of
selenium, when light radiation falls on selenium layer.

 This creates potential diff. between the two electrode
and cause flow of current.


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34. APPLICATIONS
QUALITATIVE ANALYSIS:
Generally alkali and alkaline earth metal can be estimated by flame
photometry
As characteristic wavelength is emitted by the element hence
detector recognizes that wavelength and atom is detected.
Manual method of detection is via flame characteristic color e.g.
Na produces yellow color.
•QUANTITATIVE ANALYSIS :
many alkali and alkaline metals amount can be detected by the
flame photometry by:
1.Method of standard addition.
2.Method of internal standard.

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35. ELEMENTS AND THEIR
CHARACHETRISTIC WAVELENGTHOF
EMISSION AND DETECTION LIMIT
Element wavelength Detection
limit
Element wavelength Detection
limit
Al 396 0.5 Pb 406 14
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
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36. OTHER APPLICATIONS:
TO ESTIMATE Na , K, Ca, Li IN SERUM, BODY FLUID,
CSF AND URINE.
Na IN EXTRACELLULAR FLUID AND K
INTERACELLULAR FLUID.
LITHIUM ESTIMATION IN PSYCHIATRIC THERAPY.
IN SOIL ANALYSIS.
IN INDUSTRIAL WASTE , GLASS,CEMENT AND
PETROLUEM PRODUCTS.

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37. INTERFERNCES DURING
QUANTITAIVE ESTIMATION
FOLLOWING TYPES OF INTERFERENCES GENERALLY
OCCUR DURING QUANTITAIVE STIMATION
1.SPECTRAL INTERFERENCE

2.CHEMICAL INTERFERENCES

3. IONIZATION INTERFERENCES

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38. 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
spectral isolation system.

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39. CHEMICAL INTERFERENCE
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.

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The chemical interferences arise out of the
reaction between different interferens and the
analyte . These are of different types:

40. 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

40

41. 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 Ca
3(PO
4)
2 which
does not decompose easily, resulting in the
production of lesser atoms.

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42. 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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43. LIMITATIONS
•The temperature is not high enough to excite
transition metals, therefore the method is selective
towards detection of alkali and alkaline earth
metals.
•The relatively low energy available from the flame
leads to relatively low intensity of the radiation
from the metal atoms.
•The low temperature renders to interference and
the stability of the flame and aspiration conditions.
•Interference by other elements is not easy to be
eliminated.

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