Unit-IV Chapter 4.3
FLAME PHOTOMETERY
Blow up of syllabus General Principle, Instrumentation, Types of Flames, Interfernces
Analytical applications offlamne photometry in estimations of Na,K and Ca 3hrs
Flame photometry is an extremelysensitive method for quantitative analysis of alkali and
alkaline earth metals. In this flame is used as the excitation source and an electronic
photodetector is used as the measuring device. In this method, measurement is based on the
intensity of the light emitted when a metal is introduced into a flame. The wavelength of the
colour is used to identify the element and intensity of the colour describes the concentration of
the element.
Flame photometry is also named as Flame emission Spectroscopy because of the use of
a flame to provide the energy excitation to atoms introduced into the flame.
Principle :
The metallic salt solution is introduced into the flame. The following reaction takes place
during the process.
1 The solvent vapourises leaving the particles of the solid salt.
2. The salt vapourises or converts into gaseous state.
3. Some of these gaseous atoms may excited to a higher energy level. On returning to a
lower-eF ground state, the excited atoms emit radiations characteristic of the element.
The emitted radiation ispassed through a monochromator and spectrum is registered by
a photodetector. The intensity of the emitted radiation is proportional to the concentration
of the element responsible for the emission of radiation. This forms the basis of
quantitative analysis.
The diagrammatic representation of the process is
Mx (solution) M'x evaporation MX (solid)
(mist) vapourisation
Thermal Dissociation
M+ X + M(gas)x ,(gas) - MX (gas)
excitation
thermal excitation
hy
M+m M
gas emission
292
, Chapter 4.3: Flame PhotometrY
Instrumentation
The essential components of a flame photometer are
() Pressure regulators and flow meter to the fuel and oxidant gases These are
essential to have a uniform spray and constant thermal environment. The fuel can be
directed from a cylinder while the oxidant (air) is sent from a compressor.
(i) A
Nebulizer - Burner Assembly : This system is used to convert the test solution to
gaseous atoms. The function of the nebuliser is to prtduce amist or aerosol of the test
solution. This is achieved by drawing up the test solution through a capillary tube using
a jet of air at high pressure. The mixture of fuel gas, oxidant and aerosol of the test
solution move towards the burner head.
3. Optical system and Detector :
These are used to select a given emission line and to isolate it from the rest. The
radiation coming from the optical system is allowed to fall on the detector which
measures the intensity of the radiation on it.
In moden flame photometers, the photo multiplier detectors are employed which
produce an electrical signal from the radiation falling on them.
4 Amplifier and readout system :
The filtered radiation passes into the photocell, the output of which is measured using an
amplifier and read out digital system.
Flame
Photomultiplier
DA Amplifer
Fuel
Oxidant
Sample
Recorder
293
FLAME PHOTOMETERY
Blow up of syllabus General Principle, Instrumentation, Types of Flames, Interfernces
Analytical applications offlamne photometry in estimations of Na,K and Ca 3hrs
Flame photometry is an extremelysensitive method for quantitative analysis of alkali and
alkaline earth metals. In this flame is used as the excitation source and an electronic
photodetector is used as the measuring device. In this method, measurement is based on the
intensity of the light emitted when a metal is introduced into a flame. The wavelength of the
colour is used to identify the element and intensity of the colour describes the concentration of
the element.
Flame photometry is also named as Flame emission Spectroscopy because of the use of
a flame to provide the energy excitation to atoms introduced into the flame.
Principle :
The metallic salt solution is introduced into the flame. The following reaction takes place
during the process.
1 The solvent vapourises leaving the particles of the solid salt.
2. The salt vapourises or converts into gaseous state.
3. Some of these gaseous atoms may excited to a higher energy level. On returning to a
lower-eF ground state, the excited atoms emit radiations characteristic of the element.
The emitted radiation ispassed through a monochromator and spectrum is registered by
a photodetector. The intensity of the emitted radiation is proportional to the concentration
of the element responsible for the emission of radiation. This forms the basis of
quantitative analysis.
The diagrammatic representation of the process is
Mx (solution) M'x evaporation MX (solid)
(mist) vapourisation
Thermal Dissociation
M+ X + M(gas)x ,(gas) - MX (gas)
excitation
thermal excitation
hy
M+m M
gas emission
292
, Chapter 4.3: Flame PhotometrY
Instrumentation
The essential components of a flame photometer are
() Pressure regulators and flow meter to the fuel and oxidant gases These are
essential to have a uniform spray and constant thermal environment. The fuel can be
directed from a cylinder while the oxidant (air) is sent from a compressor.
(i) A
Nebulizer - Burner Assembly : This system is used to convert the test solution to
gaseous atoms. The function of the nebuliser is to prtduce amist or aerosol of the test
solution. This is achieved by drawing up the test solution through a capillary tube using
a jet of air at high pressure. The mixture of fuel gas, oxidant and aerosol of the test
solution move towards the burner head.
3. Optical system and Detector :
These are used to select a given emission line and to isolate it from the rest. The
radiation coming from the optical system is allowed to fall on the detector which
measures the intensity of the radiation on it.
In moden flame photometers, the photo multiplier detectors are employed which
produce an electrical signal from the radiation falling on them.
4 Amplifier and readout system :
The filtered radiation passes into the photocell, the output of which is measured using an
amplifier and read out digital system.
Flame
Photomultiplier
DA Amplifer
Fuel
Oxidant
Sample
Recorder
293
