Flame emission spectroscopy

1. Presented by: Mahewash A
Pathan

2.  Definition:- “Flame emission spectroscopy /
Atomic emission spectroscopy is a method of
chemical analysis that uses the intensity of light
emitted from a flame at a particular wavelength to
determine the quantity of an element in a sample.
The wavelength of the atomic spectral lines gives
the identity of an element while the intensity of
the emitted light is proportional to the no. of
atoms of the element”.
 In flame emission spectroscopy, the sample
solution is nebulized and introduced into the
flame where it is desolvated, vaporized, &
atomized, all in rapid succession.
 Subsequently, atoms & molecules are raised to
excited states via thermal collisions with the
constituents of the partially burned flame gases.

3.  Upon their return to a lower or ground
electronic state, the excited atoms &
molecules emit radiation characteristic of the
sample component.
 The emitted radiation passes through a
monochromater that isolates the specific
wavelength for the desired analysis.
 A photodetector measures the radiant
power of the selected radiation, which is
then amplified & sent to a readout device,
meter, recorder or microcomputer system.
 The intensity of radiation emitted by these
excited atoms returning to the ground
state provides the basis for analytical
determinations in flame emission
spectroscopy.

4.  Flame photometers are probably the
simplest type of atomic spectrometers.
 They are normally designed to make
measurements on up to 10 different
elements, usually thus from group I & II of
periodic table. This is achieved using
interchangeable colored filters or diffraction
gratings, which isolates an area of the
spectrum containing the chosen emission
line.

6.  Consist of 2 components:
1. Nebulizer
2. Burner along with air or oxygen and a
fuel gas.

7.  It is a device used for sample
introduction into the flame. The process
called nebulisation.
 Various nebulization methods are used,
some are;
a) Pneumatic nebulisation
b) Ultrasonic nebulisation
c) Electro thermal vaporization
d) Hydride generation

15.  The following processes occur in the
flame:
1) Desolvation: dehydration by the heat of
flame and solvent is evaporated.
2) Vaporization: heat of flame vaporizes
the sample constituents. No chemical
change takes place at this stage.
3) Atomization: ions are reduced to atoms.
e.g.
Mg++ (aq) + 2e- Mg (g)
4) Excitation: atoms at this stage are able
to absorb energy from the heat of the
flame.
5) Emission of radiations

16. 3.Detector
Function- measure the intensity of
radiations falling on it.
1. Photoemmisive cell
2. Photomultiplier tube
4. Amplifier & Readout device
-Meter or digital display
-microprocessors controlled devices
2.Monochromator
Generally a grating or prism
monochromator are used.

18. Qualitative Applications:-

19.  The intensity of the spectral line is directly
proportional to solution concentration of the
analyte.
 Quantitative measurement are made by
reference to a previously prepared calibration
line or by the method of standard addition.

20.  In quality control where a simple and quick
determination of alkali or alkali earth
elements is required.
 Determination of Na, K,Ca & Mg in body
fluids & other biological samples.
 Determination of calcium & iron in beer.
 In agriculture, the fertilizer requirement of
the soil is analyzed by flame test analysis of
soil.
 Analysis of soft drinks, fruit juices, and
alcoholic beverages can also be analyzed.

21. 1. Spectral interferences
i. When 2 elements exhibit spectra, which
partially overlap, & both emit radiation at
some particular wavelength. Such interference
are common at flame temperatures. e.g. Fe
line at 324.73nm overlaps with the Cu line at
324.75nm.
ii. When spectral lines of 2 or more elements
which are close but their spectra do not
overlap. Such interference can be reduced by
increasing the resolution of the spectral
isolation system.
iii. Due to the presence of continuous
background which arises due to high
concentration of salts in the samples.

22. 2. Ionization interferences:-
 In some cases, high temperature flame
may cause ionization of some of the
metal atoms.
 E.g. Sodium
Na Na+ + e-

23. 3. Chemical interferences:-
i. Cation- Anion interference: presence of
certain anions such as oxalate,
phosphate, sulphate & aluminate in
solution may affect intensity of
radiation. E.g. Ca in presence of
phosphate ions form a stable
substance, which does not decompose
easily, resulting in production of less
atoms, thus Ca signals are depressed
ii. Cation-cation interference: mechanism
of this interference is not well
understood. e.g. Na & K , Al with Ca &
Mg.

24.  Simple quantitative analytical test.
 Inexpensive.
 Quite, convenient, selective and sensitive to
even ppm to ppb range.

25.  The conc. Of the metal ion in the solution cannot
be measured accurately.
 A std solution with known molarities is required for
determining the concentration of the ions which
will corresponds to the emission spectra.
 It is difficult to obtain the accurate results of the
ions with higher conc.
 The information about the molecular structure of
the compound present in the sample solution can
not be determined.
 The elements such as Carbon, hydrogen & halides
can not be detected due to its non-radiating
nature.

26.  The method is selective towards detection
of alkali & alkaline earth metals.
 The relatively low energy available from
the flame leads to relatively low intensity
of radiation from the metal atoms.
 Information about the molecular form of
the metal is not obtained.
 Only liquid samples are used.