i) Quantitative Analysis: Gelatinous or very small size particles are difficult to filter and are so difficult to estimate. Such ppt. can be converted into ideal solution (suspension) and then can be estimated by either Nephelometry or Turbidimetry.

ii) The amount of Sulphur present in the coal, Oil, rubber, plastics and several organic materials can be determined. That material which contains sulphur is heated at very high temp so that sulphur present is oxidized to the corresponding SO₄^-2 . This is then treated with BaCl₂ so that suspension of BaSO₄ is obtained. This suspension is then subjected to Nephelometer or Turbidimeter.

iii) Water which is required in power plant (Nuclear Reactor) and steam generating plant (Boiler) must be free from any of the suspended particles that testing can be done by Nephelometer and Turbidimeter. If no response from the instrument it, means water is free from of the suspended impurities.

iv) Air is continuously monitored for dust and other particulate matter using these two methods.

v) Determination of molecular weight of macromolecules i.e. polymer.  Polymers have the property of scattering of light. The turbidity of the solution is related to molecular weight of the polymer. $$ \tau = Hc{ M }_{ w } $$ Where H = constant, depends on polymer and medium.

vi) Turbidimetric Titrations: In this case, the solution of SO₄^-2 is taken in the cuvette and after each addition of the titrant i.e. BaCl₂ the precipitate formation takes place. This ppt, formation goes on increasing till all the SO₄^-2 ions are precipitated and so the turbidance goes on increasing and is maximum at the Equivalence point, after that, it remains constant.

vii) The phenomenon is used in sewage work.

viii) Used in pharmaceutical industries and petroleum refineries.

ix) Used in pulp and paper manufacturing.

x) The phenomenon is applied in the determination of suspended material in liquid found in nature.

i) Quantitative Analysis: Gelatinous or very small size particles are difficult to filter and are so difficult to estimate. Such ppt. can be converted into ideal solution (suspension) and then can be estimated by either Nephelometry or Turbidimetry.

ii) The amount of Sulphur present in the coal, Oil, rubber, plastics and several organic materials can be determined. That material which contains sulphur is heated at very high temp so that sulphur present is oxidized to the corresponding SO₄^-2 . This is then treated with BaCl₂ so that suspension of BaSO₄ is obtained. This suspension is then subjected to Nephelometer or Turbidimeter.

iii) Water which is required in power plant (Nuclear Reactor) and steam generating plant (Boiler) must be free from any of the suspended particles that testing can be done by Nephelometer and Turbidimeter. If no response from the instrument it, means water is free from of the suspended impurities.

iv) Air is continuously monitored for dust and other particulate matter using these two methods.

v) Determination of molecular weight of macromolecules i.e. polymer.  Polymers have the property of scattering of light. The turbidity of the solution is related to molecular weight of the polymer. $$ \tau = Hc{ M }_{ w } $$ Where H = constant, depends on polymer and medium.

vi) Turbidimetric Titrations: In this case, the solution of SO₄^-2 is taken in the cuvette and after each addition of the titrant i.e. BaCl₂ the precipitate formation takes place. This ppt, formation goes on increasing till all the SO₄^-2 ions are precipitated and so the turbidance goes on increasing and is maximum at the Equivalence point, after that, it remains constant.

vii) The phenomenon is used in sewage work.

viii) Used in pharmaceutical industries and petroleum refineries.

ix) Used in pulp and paper manufacturing.

x) The phenomenon is applied in the determination of suspended material in liquid found in nature.

i) Effect of Concentration on Scattering:

The attenuation of a parallel beam of radiation by scattering is given by $$ { I }_{ t }={ I }_{ 0 }{ e }^{ -Jl } $$ $$ \log { \frac { { I }_{ 0 } }{ { I }_{ t } } } =KlC $$ $$where\quad K= \frac { J }{ 2.303C } $$ Where \({ I }_{ 0 }\) and \({ I }_{ t }\) are the intensity of the beam before and after passing through the length \(l\) of a turbid medium. The quantity \(J\) is called turbidity coefficient. Its value is often found to be linearly related to the concentration of the scattering particles. As a consequence, a relationship similar to Beers Law is,

ii) Effect of Particle size on Scattering:

The fraction of radiations scattered at any angle depends upon the size and shape of particles responsible for scattering. Those factors which influence the particle size at the time of precipitation in gravimetric, also affect both turbidimetry and nephelometry. Thus gravimetric factors such as the concentration of reagents, rate, and order of mixing, temperature, pH and Ionic strength are important Experimental variables. For proper scattering see that particles size must be uniform.

iii) Effect of Wavelength on scattering:

It has been shown experimentally that the turbidity Coefficient varies with wavelength as given by the equation \(J=S{ \lambda }^{ -t }\) Where S is Constant for a given system. The quantity t depends on the particle size and has a value of 4 when scattering particles are smaller than the wavelength of the radiations incident on it. For particles with a dimension similar to wavelength, \( \lambda \) is found to be 2. For purpose of analysis ordinary white light is used, but if the solution is colored then we have to select that wavelength so that absorption by the medium is minimum.

i) Effect of Concentration on Scattering:

The attenuation of a parallel beam of radiation by scattering is given by $$ { I }_{ t }={ I }_{ 0 }{ e }^{ -Jl } $$ $$ \log { \frac { { I }_{ 0 } }{ { I }_{ t } } } =KlC $$ $$where\quad K= \frac { J }{ 2.303C } $$ Where \({ I }_{ 0 }\) and \({ I }_{ t }\) are the intensity of the beam before and after passing through the length \(l\) of a turbid medium. The quantity \(J\) is called turbidity coefficient. Its value is often found to be linearly related to the concentration of the scattering particles. As a consequence, a relationship similar to Beers Law is,

ii) Effect of Particle size on Scattering:

The fraction of radiations scattered at any angle depends upon the size and shape of particles responsible for scattering. Those factors which influence the particle size at the time of precipitation in gravimetric, also affect both turbidimetry and nephelometry. Thus gravimetric factors such as the concentration of reagents, rate, and order of mixing, temperature, pH and Ionic strength are important Experimental variables. For proper scattering see that particles size must be uniform.

iii) Effect of Wavelength on scattering:

It has been shown experimentally that the turbidity Coefficient varies with wavelength as given by the equation \(J=S{ \lambda }^{ -t }\) Where S is Constant for a given system. The quantity t depends on the particle size and has a value of 4 when scattering particles are smaller than the wavelength of the radiations incident on it. For particles with a dimension similar to wavelength, \( \lambda \) is found to be 2. For purpose of analysis ordinary white light is used, but if the solution is colored then we have to select that wavelength so that absorption by the medium is minimum.

When the light is incident on a solution containing suspended particles. The fraction of the light it scattered and the remaining is transmitted. If we know the intensity of transmitted radiations then we can have quantitative analysis. This phenomenon is known as Turbidimetry. And if we measure the intensity of scattered radiation then also we can have quantitative analysis, This phenomenon is known as Nephelometry.

When the light is incident on a solution containing suspended particles. The fraction of the light it scattered and the remaining is transmitted. If we know the intensity of transmitted radiations then we can have quantitative analysis. This phenomenon is known as Turbidimetry. And if we measure the intensity of scattered radiation then also we can have quantitative analysis, This phenomenon is known as Nephelometry.

When the light is incident on a solution containing suspended particles. The fraction of the light it scattered and the remaining is transmitted. If we know the intensity of transmitted radiations then we can have quantitative analysis of sample. That phenomenon is known as Turbidimetry.

But if we know intensity of scattered radiations then we can also have quantitative analysis. This phenomenon is Known as Nephelometry.

The scattered radiation is always observed at the angle of either 45°, 90° or at 135° to the incident light.

Turbidimetry and Nephelometry involve the use of Very dilute Solutions Therefore suspended particles must have negligible solubility. Such particles scatter the light considerably and therefore great care must he taken that samples are free of dust particles. The particles of the disperse phase must be very fine so that they do not settle down rapidly.

When the light is incident on a solution containing suspended particles. The fraction of the light it scattered and the remaining is transmitted. If we know the intensity of transmitted radiations then we can have quantitative analysis of sample. That phenomenon is known as Turbidimetry.

But if we know intensity of scattered radiations then we can also have quantitative analysis. This phenomenon is Known as Nephelometry.

The scattered radiation is always observed at the angle of either 45°, 90° or at 135° to the incident light.

Turbidimetry and Nephelometry involve the use of Very dilute Solutions Therefore suspended particles must have negligible solubility. Such particles scatter the light considerably and therefore great care must he taken that samples are free of dust particles. The particles of the disperse phase must be very fine so that they do not settle down rapidly.

1. The studies of phosphorescence phenomenon are, more complicated, than Fluorescence.

2. Phosphorimetry has limited applications while Fluorescence has very large applications.

3. Phosphorimetry studies are done at low temperatures which are -196°C where as Fluorescence measurements are done at room temperature.

4. Phosphotimetry is more sensitive than Fluorimetry because phosphorimetry is done at low temperature the scattering of light is less at low temperature. So sensitivity is more.

5. In case of complex samples phosphorimetry is more selective than fluorimetry.

6. In phosphorimetry the re-emission of light take place after certain time While in Fluorimetry re-emission of light is instantaneous.

7. Phosphorimeters are only one type while Fluorimeters are of the two type i) Single beam and ii) double beam.

8. Phosphorimeters are more costly than Fluorimeters.

1. The studies of phosphorescence phenomenon are, more complicated, than Fluorescence.

2. Phosphorimetry has limited applications while Fluorescence has very large applications.

3. Phosphorimetry studies are done at low temperatures which are -196°C where as Fluorescence measurements are done at room temperature.

4. Phosphotimetry is more sensitive than Fluorimetry because phosphorimetry is done at low temperature the scattering of light is less at low temperature. So sensitivity is more.

5. In case of complex samples phosphorimetry is more selective than fluorimetry.

6. In phosphorimetry the re-emission of light take place after certain time While in Fluorimetry re-emission of light is instantaneous.

7. Phosphorimeters are only one type while Fluorimeters are of the two type i) Single beam and ii) double beam.

8. Phosphorimeters are more costly than Fluorimeters.

Many compounds absorb ultraviolet or visible light and undergo electronic transition from low electronic energy levels to high electronic, energy levels. The instant re-emission of the absorbed energy is called Fluorescence. That instrument with the help of which we can measure the florescence phenomenon is known as Fluorimeter.

In this case beam of light travels in a single optical path is most commonly used light from mercury vapor lamp is allowed to pass through primary filter. It allows only UV light to pass through it and absorb the visible light then UV light is incident on the sample holder which is also known as Cuvette. Here the UV light is absorbed by the sample molecules. The light which is coming out from sample holder contains fluorescent light and may contain original UV light. The emergent light from sample holder is then analyzed at the 90o from incident in order to avoid in mixing of reflected or transmitted light with the emergent light. This emergent (fluorescent) light is then allowed to pass through secondary filter. This filter will absorb any of UV light. Now the emergent light is only fluorescent light and is then incident at photocathode Digital display which gives us the intensity of fluorescent light.

First we have to standardize (Calibrate) the instrument by taking blank (solvent) in the cuvette. With the blank, we adjust the dial reading to zero with the help of calibration knob. Now the instrument is standardized and then we perform the experiment with the sample solution. For sample solution it we known dials readings then we can have quantitative analysis by plotting a graph of F (intensity of fluoresce) Vs C.

Here the UV light is absorbed by the sample molecules. The light which is coming out from sample holder contains fluorescent light and may contain original UV light. The emergent light from sample holder is then analyzed at the 90o from incident in order to avoid in mixing of reflected or transmitted light with the emergent light. This emergent (fluorescent) light is then allowed to pass through secondary filter. This filter will absorb any of UV light. Now the emergent light is only fluorescent light and is then incident at photocathode Digital display which gives us the intensity of fluorescent light.

First we have to standardize (Calibrate) the instrument by taking blank (solvent) in the cuvette. With the blank, we adjust the dial reading to zero with the help of calibration knob. Now the instrument is standardized and then we perform the experiment with the sample solution. For sample solution it we known dials readings then we can have quantitative analysis by plotting a graph of F (intensity of fluoresce) Vs C.

Applications:

1. Detection of small amount of cocaine, procaine and phenobarbital present in blood serum by phosphorimetry.

2. Determination of aspirin in blood serum with high sensitivity (0.02 to 1mg per cm3 of serum). Aspirin is strongly phosphorescent but not fluorescent. Therefore it can be detected with Phosphorimetery.

3. Alkaloids like nicotine and non-nicotine are rapidly estimated in tobacco after they are separated using thin layer or paper chromatography.

Many compounds absorb ultraviolet or visible light and undergo electronic transition from low electronic energy levels to high electronic, energy levels. The instant re-emission of the absorbed energy is called Fluorescence. That instrument with the help of which we can measure the florescence phenomenon is known as Fluorimeter.

In this case beam of light travels in a single optical path is most commonly used light from mercury vapor lamp is allowed to pass through primary filter. It allows only UV light to pass through it and absorb the visible light then UV light is incident on the sample holder which is also known as Cuvette. Here the UV light is absorbed by the sample molecules. The light which is coming out from sample holder contains fluorescent light and may contain original UV light. The emergent light from sample holder is then analyzed at the 90o from incident in order to avoid in mixing of reflected or transmitted light with the emergent light. This emergent (fluorescent) light is then allowed to pass through secondary filter. This filter will absorb any of UV light. Now the emergent light is only fluorescent light and is then incident at photocathode Digital display which gives us the intensity of fluorescent light.

First we have to standardize (Calibrate) the instrument by taking blank (solvent) in the cuvette. With the blank, we adjust the dial reading to zero with the help of calibration knob. Now the instrument is standardized and then we perform the experiment with the sample solution. For sample solution it we known dials readings then we can have quantitative analysis by plotting a graph of F (intensity of fluoresce) Vs C.

Here the UV light is absorbed by the sample molecules. The light which is coming out from sample holder contains fluorescent light and may contain original UV light. The emergent light from sample holder is then analyzed at the 90o from incident in order to avoid in mixing of reflected or transmitted light with the emergent light. This emergent (fluorescent) light is then allowed to pass through secondary filter. This filter will absorb any of UV light. Now the emergent light is only fluorescent light and is then incident at photocathode Digital display which gives us the intensity of fluorescent light.

First we have to standardize (Calibrate) the instrument by taking blank (solvent) in the cuvette. With the blank, we adjust the dial reading to zero with the help of calibration knob. Now the instrument is standardized and then we perform the experiment with the sample solution. For sample solution it we known dials readings then we can have quantitative analysis by plotting a graph of F (intensity of fluoresce) Vs C.

Applications:

1. Detection of small amount of cocaine, procaine and phenobarbital present in blood serum by phosphorimetry.

2. Determination of aspirin in blood serum with high sensitivity (0.02 to 1mg per cm3 of serum). Aspirin is strongly phosphorescent but not fluorescent. Therefore it can be detected with Phosphorimetery.

3. Alkaloids like nicotine and non-nicotine are rapidly estimated in tobacco after they are separated using thin layer or paper chromatography.

ANSWER

ANSWER

Many compounds absorb ultraviolet or visible light and undergo electronic transition from low electronic energy levels to high electronic, energy levels. The instant re-emission of the absorbed energy is called Fluorescence. That instrument with the help of which we can measure the florescence phenomenon is known as Fluorimeter.

In this case beam of light travels in a single optical path is most commonly used light from mercury vapor lamp is allowed to pass through primary filter. It allows only UV light to pass through it and absorb the visible light then UV light is incident on the sample holder which is also known as Cuvette. Here the UV light is absorbed by the sample molecules. The light which is coming out from sample holder contains fluorescent light and may contain original UV light. The emergent light from sample holder is then analyzed at the 90o from incident in order to avoid in mixing of reflected or transmitted light with the emergent light. This emergent (fluorescent) light is then allowed to pass through secondary filter. This filter will absorb any of UV light. Now the emergent light is only fluorescent light and is then incident at photocathode Digital display which gives us the intensity of fluorescent light.

First we have to standardize (Calibrate) the instrument by taking blank (solvent) in the cuvette. With the blank, we adjust the dial reading to zero with the help of calibration knob. Now the instrument is standardized and then we perform the experiment with the sample solution. For sample solution it we known dials readings then we can have quantitative analysis by plotting a graph of F (intensity of fluoresce) Vs C.

Here the UV light is absorbed by the sample molecules. The light which is coming out from sample holder contains fluorescent light and may contain original UV light. The emergent light from sample holder is then analyzed at the 90o from incident in order to avoid in mixing of reflected or transmitted light with the emergent light. This emergent (fluorescent) light is then allowed to pass through secondary filter. This filter will absorb any of UV light. Now the emergent light is only fluorescent light and is then incident at photocathode Digital display which gives us the intensity of fluorescent light.

First we have to standardize (Calibrate) the instrument by taking blank (solvent) in the cuvette. With the blank, we adjust the dial reading to zero with the help of calibration knob. Now the instrument is standardized and then we perform the experiment with the sample solution. For sample solution it we known dials readings then we can have quantitative analysis by plotting a graph of F (intensity of fluoresce) Vs C.

Applications:

1. Quantitative analysis of organic, inorganic and biochemical compounds can be done with this phenomenon.

2. Boron can combine with Benzoin forming fluorescent complex. And then we can find out the amount of boron present.

3. Al, Be, Zn ions combine with 8-hydroxy quinoline forming complexes which are Fluorescent active and can be quantitatively estimated.

4. Uranium present in the sample can be determined by fluorimetry. The uranium sample is fused with sodium Fluoride to convert it into a melt containing uranium and sodium fluoride. This melt solidifies to a glass when cooled. The florescence intensity of this glass is measured in a fluorimeter. The uranium content can be determined to the order of 5 x 10^-9 gm in one (1gm) of sample.

5. Vitamin B1 (Thiamine) is non Fluorescent but its oxidation product show intense blue colour fluorescence with the help of it we can estimate the amount of Vitamin B1 in food samples.

6. Many aromatic compounds e.g. steroids and enzymes have been analyzed by using Fluorescence method.

7. There are Fluorescent indicators which are used to detect, correctly the change in colour of coloured solutions in titrimetry. E.g. Eosin shows a green fluorescence in the pH of 3 - 4.

Many compounds absorb ultraviolet or visible light and undergo electronic transition from low electronic energy levels to high electronic, energy levels. The instant re-emission of the absorbed energy is called Fluorescence. That instrument with the help of which we can measure the florescence phenomenon is known as Fluorimeter.

In this case beam of light travels in a single optical path is most commonly used light from mercury vapor lamp is allowed to pass through primary filter. It allows only UV light to pass through it and absorb the visible light then UV light is incident on the sample holder which is also known as Cuvette. Here the UV light is absorbed by the sample molecules. The light which is coming out from sample holder contains fluorescent light and may contain original UV light. The emergent light from sample holder is then analyzed at the 90o from incident in order to avoid in mixing of reflected or transmitted light with the emergent light. This emergent (fluorescent) light is then allowed to pass through secondary filter. This filter will absorb any of UV light. Now the emergent light is only fluorescent light and is then incident at photocathode Digital display which gives us the intensity of fluorescent light.

First we have to standardize (Calibrate) the instrument by taking blank (solvent) in the cuvette. With the blank, we adjust the dial reading to zero with the help of calibration knob. Now the instrument is standardized and then we perform the experiment with the sample solution. For sample solution it we known dials readings then we can have quantitative analysis by plotting a graph of F (intensity of fluoresce) Vs C.

Here the UV light is absorbed by the sample molecules. The light which is coming out from sample holder contains fluorescent light and may contain original UV light. The emergent light from sample holder is then analyzed at the 90o from incident in order to avoid in mixing of reflected or transmitted light with the emergent light. This emergent (fluorescent) light is then allowed to pass through secondary filter. This filter will absorb any of UV light. Now the emergent light is only fluorescent light and is then incident at photocathode Digital display which gives us the intensity of fluorescent light.

First we have to standardize (Calibrate) the instrument by taking blank (solvent) in the cuvette. With the blank, we adjust the dial reading to zero with the help of calibration knob. Now the instrument is standardized and then we perform the experiment with the sample solution. For sample solution it we known dials readings then we can have quantitative analysis by plotting a graph of F (intensity of fluoresce) Vs C.

Applications:

1. Quantitative analysis of organic, inorganic and biochemical compounds can be done with this phenomenon.

2. Boron can combine with Benzoin forming fluorescent complex. And then we can find out the amount of boron present.

3. Al, Be, Zn ions combine with 8-hydroxy quinoline forming complexes which are Fluorescent active and can be quantitatively estimated.

4. Uranium present in the sample can be determined by fluorimetry. The uranium sample is fused with sodium Fluoride to convert it into a melt containing uranium and sodium fluoride. This melt solidifies to a glass when cooled. The florescence intensity of this glass is measured in a fluorimeter. The uranium content can be determined to the order of 5 x 10^-9 gm in one (1gm) of sample.

5. Vitamin B1 (Thiamine) is non Fluorescent but its oxidation product show intense blue colour fluorescence with the help of it we can estimate the amount of Vitamin B1 in food samples.

6. Many aromatic compounds e.g. steroids and enzymes have been analyzed by using Fluorescence method.

7. There are Fluorescent indicators which are used to detect, correctly the change in colour of coloured solutions in titrimetry. E.g. Eosin shows a green fluorescence in the pH of 3 - 4.

The fluorescence and phosphorescence depends on following factors.

1. Fluorescence and phosphorescence depends on temperature and pH of the solution.

2. Association, Dissociation of solute with solvent will affect the fluorescence and phosphorescence.

3. Molecules with electron donating groups like -OH and –NH₂ are strongly fluorescence.

4. Electrons withdrawing groups like -COOH, -N=N-, -NO₂ and halides decreases florescence.

5. Heavy atoms like chlorine, bromine and iodine cause the un-pairing of electrons. As a result the singlet state gets converted into a triplet state and the chances of fluorescence occurring are greatly reduced.

6. Some groups like -NH₄⁺, -SO₃H and alkyl groups do not have, any affect on the fluorescence and phosphorescence phenomenon.

7. The introduction of an atom of higher atomic number, in to a \(\pi\) electron system decreases fluorescence and increases phosphorescence.

The fluorescence and phosphorescence depends on following factors.

1. Fluorescence and phosphorescence depends on temperature and pH of the solution.

2. Association, Dissociation of solute with solvent will affect the fluorescence and phosphorescence.

3. Molecules with electron donating groups like -OH and –NH₂ are strongly fluorescence.

4. Electrons withdrawing groups like -COOH, -N=N-, -NO₂ and halides decreases florescence.

5. Heavy atoms like chlorine, bromine and iodine cause the un-pairing of electrons. As a result the singlet state gets converted into a triplet state and the chances of fluorescence occurring are greatly reduced.

6. Some groups like -NH₄⁺, -SO₃H and alkyl groups do not have, any affect on the fluorescence and phosphorescence phenomenon.

7. The introduction of an atom of higher atomic number, in to a \(\pi\) electron system decreases fluorescence and increases phosphorescence.

Many compounds absorb ultraviolet or visible light and undergo electronic transition from low electronic energy levels to high electronic, energy levels. This Absorption of light requires 10^-15 sec. The instant re-emission of the absorbed energy is called Fluorescence. While delayed re-emission of the absorbed energy is called Phosphorescence.

For most molecules the electrons are paired in the ground state i.e. pair of electrons have opposite spins this is called singlet state. As the spin is paired up, they do not show any magnetic moment. But if the electrons have the same spin the magnetic moment of both the electrons gets combined and they behave like a tiny magnet. This state where the electron pair is having same spin are called as triplet state.

In molecule there are several electronic energy levels and electrons are present at the ground state in the singlet state i.e. with opposite spins. When molecule absorbs U.V. or Visible light, one electron from ground state undergoes to an excited state. Now excited state is also having several vibrational levels, so the excited electron loses its energy by intermolecular collision and it comes to the lowest vibrational level of excited state. Finally the electron from the lowest vibrational level of excited state returns to ground state by emitting the radiation or light of lower energy or higher wavelength. This overall process of absorption, intermolecular collision and emission takes 10-4 to 10-8 sec which is very small thus it looks like instant re-emission of light. But the energy of radiation emitted is always less than the energy of radiation absorbed. Or in other words wavelength of emitted radiation will be always higher than the wavelength of radiation absorbed. This is Fluorescence phenomenon.

In case of Phosphorescence the inversion of electron spin takes place. That means when the energy from the UV or visible light is absorbed the electron from the ground state jumps to excited state, at the same time the spin of the electron gets reversed and it is now in triplet state (i.e. both electrons have same spin.) In triplet state there is less chance of electron coming back to ground state because pairing of electron with same spin is not favourable. Thus it takes more time to reverse the spin and come back to ground state. The time taken by electron is from 10^-4 to several seconds. Thus, it seems that the emitted radiation is delayed. In some cases even when we turn off the light sources, radiation keeps coming.This delayed re-emission of radiation is called phosphorescence. Here again the energy of radiation emitted is always less than the energy of radiation absorbed. Or in other words wavelength of emitted radiation will be always higher than the wavelength of radiation absorbed.

Many compounds absorb ultraviolet or visible light and undergo electronic transition from low electronic energy levels to high electronic, energy levels. This Absorption of light requires 10^-15 sec. The instant re-emission of the absorbed energy is called Fluorescence. While delayed re-emission of the absorbed energy is called Phosphorescence.

For most molecules the electrons are paired in the ground state i.e. pair of electrons have opposite spins this is called singlet state. As the spin is paired up, they do not show any magnetic moment. But if the electrons have the same spin the magnetic moment of both the electrons gets combined and they behave like a tiny magnet. This state where the electron pair is having same spin are called as triplet state.

In molecule there are several electronic energy levels and electrons are present at the ground state in the singlet state i.e. with opposite spins. When molecule absorbs U.V. or Visible light, one electron from ground state undergoes to an excited state. Now excited state is also having several vibrational levels, so the excited electron loses its energy by intermolecular collision and it comes to the lowest vibrational level of excited state. Finally the electron from the lowest vibrational level of excited state returns to ground state by emitting the radiation or light of lower energy or higher wavelength. This overall process of absorption, intermolecular collision and emission takes 10-4 to 10-8 sec which is very small thus it looks like instant re-emission of light. But the energy of radiation emitted is always less than the energy of radiation absorbed. Or in other words wavelength of emitted radiation will be always higher than the wavelength of radiation absorbed. This is Fluorescence phenomenon.

In case of Phosphorescence the inversion of electron spin takes place. That means when the energy from the UV or visible light is absorbed the electron from the ground state jumps to excited state, at the same time the spin of the electron gets reversed and it is now in triplet state (i.e. both electrons have same spin.) In triplet state there is less chance of electron coming back to ground state because pairing of electron with same spin is not favourable. Thus it takes more time to reverse the spin and come back to ground state. The time taken by electron is from 10^-4 to several seconds. Thus, it seems that the emitted radiation is delayed. In some cases even when we turn off the light sources, radiation keeps coming.This delayed re-emission of radiation is called phosphorescence. Here again the energy of radiation emitted is always less than the energy of radiation absorbed. Or in other words wavelength of emitted radiation will be always higher than the wavelength of radiation absorbed.

#	Flame Photometry	Atomic Absorption Spectrometer
1	Atoms absorb the thermal energy and are excited, these excited atoms return to ground state with the emission of radiations.	The atoms which are present unexcited in the ground state absorb the radiations.
2	Intensity of emitted radiations is measured.	Intensity of absorbed radiations is measured.
3	Intensity of emission depends on no. of atoms excited.	Intensity of absorption depend on the no. of atoms unexcited present in the ground state.
4	It depends on the temp. of the flame.	It is Independent of the flame temp.
5	No separate source of radiations is needed.	The separate source of radiations is required.
6	Interference of spectral lines takes place.	No interference of spectral lines take place.
7	Beer-Lambert’s Law is not applicable.	Beer-Lambert’s Law is strictly applicable.
8	It is less expensive.	It is more expensive.

#	Flame Photometry	Atomic Absorption Spectrometer
1	Atoms absorb the thermal energy and are excited, these excited atoms return to ground state with the emission of radiations.	The atoms which are present unexcited in the ground state absorb the radiations.
2	Intensity of emitted radiations is measured.	Intensity of absorbed radiations is measured.
3	Intensity of emission depends on no. of atoms excited.	Intensity of absorption depend on the no. of atoms unexcited present in the ground state.
4	It depends on the temp. of the flame.	It is Independent of the flame temp.
5	No separate source of radiations is needed.	The separate source of radiations is required.
6	Interference of spectral lines takes place.	No interference of spectral lines take place.
7	Beer-Lambert’s Law is not applicable.	Beer-Lambert’s Law is strictly applicable.
8	It is less expensive.	It is more expensive.

A.A.S. is that branch of Analytical Chemistry with the help of which we can have quantitative analysis by knowing the amount of light absorbed by the atoms which are present in the ground state in the unexcited form. The points of superiority of A.A.S. to flame photometry are as follow:

1. If the analyst has to analyze several samples in a day it is possible with A.A.S. and is not possible with flame photometry, because A.A.S. requires less time than flame photometry.

2. The A.A.S. technique is specific as source of radiations is specific (special) Therefore; spectral interference of the lines is not taking place.

3. As the absorption of radiations is by the atoms present in the ground state, so the temperature change do not affect the absorption but in flame photometry, the temperature of the flame is very important.

4. A.A.S. is sensitive to more number of the elements. About 70 different elements can be analyzed by A.A.S. while flame photometry seems limited scope.

5. So many elements like Zn cannot be excited. For such elements the analysis by flame Photometry is not possible but A.A.S. analysis is possible. Because there is no excitation and A.A.S. depends on the absorption.

6. As the A.A.S. obeys the Beer - Lambert’s Law hence the absorbance varies in linear manner with concentration under a wide range of concentration. This is not in the case of flame photometry.

On the whole A.A.S. will always give better results, is less time consuming and have more scope. That is why the A.A.S. is superior technique to flame photometry.

A.A.S. is that branch of Analytical Chemistry with the help of which we can have quantitative analysis by knowing the amount of light absorbed by the atoms which are present in the ground state in the unexcited form. The points of superiority of A.A.S. to flame photometry are as follow:

1. If the analyst has to analyze several samples in a day it is possible with A.A.S. and is not possible with flame photometry, because A.A.S. requires less time than flame photometry.

2. The A.A.S. technique is specific as source of radiations is specific (special) Therefore; spectral interference of the lines is not taking place.

3. As the absorption of radiations is by the atoms present in the ground state, so the temperature change do not affect the absorption but in flame photometry, the temperature of the flame is very important.

4. A.A.S. is sensitive to more number of the elements. About 70 different elements can be analyzed by A.A.S. while flame photometry seems limited scope.

5. So many elements like Zn cannot be excited. For such elements the analysis by flame Photometry is not possible but A.A.S. analysis is possible. Because there is no excitation and A.A.S. depends on the absorption.

6. As the A.A.S. obeys the Beer - Lambert’s Law hence the absorbance varies in linear manner with concentration under a wide range of concentration. This is not in the case of flame photometry.

On the whole A.A.S. will always give better results, is less time consuming and have more scope. That is why the A.A.S. is superior technique to flame photometry.

The main components of AAS are:

1) Source of Radiations: It is consist of the glass jacket containing cup shaped cathode made up of the same element which is under Study. A tungsten wire (plate) Acts as anode which is arranged in the same glass jacket. The glass jacket is filled with the inert gas like Neon (Ne) or Argon (Ar) at a low pressure. When a Potential of 500-1000 volt is applied between the two electrodes from the power supply the atoms of the inert-gas is ionized. The positive charged ions moving towards cathode. These fast moving ions remove the atoms from the surface of cathode. This process is called Sputtering. These metallic atoms then collide with highly energetic gas ions and some of them are excited. These excited metal atoms emit their characteristics radiations when they return to the original state with emitting their characteristic radiations.

The cathode and anode is connected with the power supply from where we supply the potential of 500-1000 volt. The gas taken in the bulb is ionized. The cations of the gas are moving fast towards cathode and remove the atoms from the cathode. These atoms strike With the gas ions and transition take place, return to the original state with the emission of characteristic radiations which pass (penetrate) out the quartz window and are incident on rotating chopper, it produce intermittent radiations which are incident on the Unexcited atoms present in the flame of the burner. These atoms absorb the radiations. The transmitted is incident on the prism which is connected with the PMT. In PMT current is produced. PMT is connected with read out meter which gives the absorbance. Now, by applying the Beer-Lamberts Low, we can find out the conc. of solution by knowing the absorbance.

Application:

1. Quantitative Analysis can be done using Calibration Curve Method.

2. Very low concentration which is 1 ppm or less than that can also be analyzed accurately with the help of A.A.S.

3. With the help of A.A.S. we can detect the toxic elements such as Cu, Ni, Zn present in the food products.

4. The phenomenon is used to estimate Na and K present in the Blood serum.

5. How much amount of Pb (lead) is present in the Petrol can be found out with the help of A.A.S.

6. Soil extracts plant materials fertilizers have been analyzed for determination of Na, K, Cu, Mg, Mo, V etc. are present.

7. The amount of Ti and V present in the steel alloy can also be determined with the help of A.A.S.

Limitations:

1. Simultaneous analysis of many elements is not possible.

2. Metals like La, W, Si, etc. form the stable metallic oxide and so cannot be analyzed.

3. For alkali metals like Li, Na, K etc. which has low I.P. in such cases low temp. of the flame is required to minimize the ionization of the elements.

4. Each element requires the separate lamp.

5. If the sample contains the two elements which absorb the light of same Wavelength \((\lambda)\) e.g. Mn and Ga both absorb at 403nm can not be analyzed. In such case we must remove the interfering radical.

The main components of AAS are:

1) Source of Radiations: It is consist of the glass jacket containing cup shaped cathode made up of the same element which is under Study. A tungsten wire (plate) Acts as anode which is arranged in the same glass jacket. The glass jacket is filled with the inert gas like Neon (Ne) or Argon (Ar) at a low pressure. When a Potential of 500-1000 volt is applied between the two electrodes from the power supply the atoms of the inert-gas is ionized. The positive charged ions moving towards cathode. These fast moving ions remove the atoms from the surface of cathode. This process is called Sputtering. These metallic atoms then collide with highly energetic gas ions and some of them are excited. These excited metal atoms emit their characteristics radiations when they return to the original state with emitting their characteristic radiations.

The cathode and anode is connected with the power supply from where we supply the potential of 500-1000 volt. The gas taken in the bulb is ionized. The cations of the gas are moving fast towards cathode and remove the atoms from the cathode. These atoms strike With the gas ions and transition take place, return to the original state with the emission of characteristic radiations which pass (penetrate) out the quartz window and are incident on rotating chopper, it produce intermittent radiations which are incident on the Unexcited atoms present in the flame of the burner. These atoms absorb the radiations. The transmitted is incident on the prism which is connected with the PMT. In PMT current is produced. PMT is connected with read out meter which gives the absorbance. Now, by applying the Beer-Lamberts Low, we can find out the conc. of solution by knowing the absorbance.

Application:

1. Quantitative Analysis can be done using Calibration Curve Method.

2. Very low concentration which is 1 ppm or less than that can also be analyzed accurately with the help of A.A.S.

3. With the help of A.A.S. we can detect the toxic elements such as Cu, Ni, Zn present in the food products.

4. The phenomenon is used to estimate Na and K present in the Blood serum.

5. How much amount of Pb (lead) is present in the Petrol can be found out with the help of A.A.S.

6. Soil extracts plant materials fertilizers have been analyzed for determination of Na, K, Cu, Mg, Mo, V etc. are present.

7. The amount of Ti and V present in the steel alloy can also be determined with the help of A.A.S.

Limitations:

1. Simultaneous analysis of many elements is not possible.

2. Metals like La, W, Si, etc. form the stable metallic oxide and so cannot be analyzed.

3. For alkali metals like Li, Na, K etc. which has low I.P. in such cases low temp. of the flame is required to minimize the ionization of the elements.

4. Each element requires the separate lamp.

5. If the sample contains the two elements which absorb the light of same Wavelength \((\lambda)\) e.g. Mn and Ga both absorb at 403nm can not be analyzed. In such case we must remove the interfering radical.

This absorption depends on number of unexcited atoms present and hence, is independent of the flame temperature. It is possible, if the course of radiations is made up of the same element which is going to be analyzed. For e.g. if the sample solution of NaCl is to be analyzed, source of radiations must be Na Vapors.

A brief overview of the process:

1. The solvent is first evaporated leaving fine divided solid particles.

2. This solid particles move towards the flame, where the gaseous atoms and ions are produced.

3. Some of the ions absorb the energy from the flame and excited to high energy levels. Remaining ions will be excited from the external source.

4. So the decrease in intensity of radiation is measured.

5. The decrease in intensity of transmitted light is related to the concentration of the unexcited atoms.

The absorption of radiations follows the Beer-Lamberts Law. As each element absorb the radiations of its own characteristics therefore separate source of radiations is required for each element. $$ \log { \frac { { I }_{ t } }{ { I }_{ 0 } } } =KL{ N }_{ 0 } $$ Where, \({ I }_{ 0 }\) = Intensity of radiations incident.
\({ I }_{ t }\) = Intensity of radiations transmitted.
\(K\) = Characteristics Constant
\(L\) = Path length of flame in cm.
\({ N }_{ 0 }\) = No of atoms in the ground state.

This absorption depends on number of unexcited atoms present and hence, is independent of the flame temperature. It is possible, if the course of radiations is made up of the same element which is going to be analyzed. For e.g. if the sample solution of NaCl is to be analyzed, source of radiations must be Na Vapors.

A brief overview of the process:

1. The solvent is first evaporated leaving fine divided solid particles.

2. This solid particles move towards the flame, where the gaseous atoms and ions are produced.

3. Some of the ions absorb the energy from the flame and excited to high energy levels. Remaining ions will be excited from the external source.

4. So the decrease in intensity of radiation is measured.

5. The decrease in intensity of transmitted light is related to the concentration of the unexcited atoms.

The absorption of radiations follows the Beer-Lamberts Law. As each element absorb the radiations of its own characteristics therefore separate source of radiations is required for each element. $$ \log { \frac { { I }_{ t } }{ { I }_{ 0 } } } =KL{ N }_{ 0 } $$ Where, \({ I }_{ 0 }\) = Intensity of radiations incident.
\({ I }_{ t }\) = Intensity of radiations transmitted.
\(K\) = Characteristics Constant
\(L\) = Path length of flame in cm.
\({ N }_{ 0 }\) = No of atoms in the ground state.

(1) Calibration Curve Method:

We take some known concentration of the given solution and find the intensity of the emitted light.

Conc.	O.D.
5 ppm	50
10 ppm	100
15 ppm	150
20 ppm	200
25 ppm	250
30 ppm	300
Unknown	125

A graph of intensity measured Vs Conc is plotted. Now the intensity of the test solution is measured.

Take this value on the intensity axis and draw the line parallel to the X-axis where it cuts the standard curve, from there draw the perpendicular to the conc axis which will give the concentration.

(2) Standard Addition Method:

In this method the intensity of the light of the test solution is measured with reference to the blank. Now known increasing amount of the element to be determined are then added to a number of the test solutions and the solutions are diluted to the same volume in each case.

Conc.	O.D.
x + 0 ppm	150
x + 5 ppm	200
x + 10 ppm	250
x + 15 ppm	300
x + 20 ppm	350
x + 25 ppm	400
x + 30 ppm	450

Intensity of the light of each solution is determined. A graph of readings Vs slandered conc added is plotted the graph will be straight line this line is extrapolated on conc axis which gives the concentration.

(1) Calibration Curve Method:

We take some known concentration of the given solution and find the intensity of the emitted light.

Conc.	O.D.
5 ppm	50
10 ppm	100
15 ppm	150
20 ppm	200
25 ppm	250
30 ppm	300
Unknown	125

A graph of intensity measured Vs Conc is plotted. Now the intensity of the test solution is measured.

Take this value on the intensity axis and draw the line parallel to the X-axis where it cuts the standard curve, from there draw the perpendicular to the conc axis which will give the concentration.

(2) Standard Addition Method:

In this method the intensity of the light of the test solution is measured with reference to the blank. Now known increasing amount of the element to be determined are then added to a number of the test solutions and the solutions are diluted to the same volume in each case.

Conc.	O.D.
x + 0 ppm	150
x + 5 ppm	200
x + 10 ppm	250
x + 15 ppm	300
x + 20 ppm	350
x + 25 ppm	400
x + 30 ppm	450

Intensity of the light of each solution is determined. A graph of readings Vs slandered conc added is plotted the graph will be straight line this line is extrapolated on conc axis which gives the concentration.

The main components are :

(1) BURNER: The temp. of the burner must be more then 2000 K. Burners used are of the two types: (i) Total Consumption Burner, and (ii) Premix Burner.

Total Consumption Burner: As the Sample Solution is completely burnt so it is known as total consumption burners. The fuel which are used in this case are C2H2, C3H8 or H2. The fuel is oxidized by oxidizer which are either air or nitrous oxide or oxygen diluted with N2. When the fuel and oxidizer are burnt at the tip of the burner. The large amount of heat is produced, so the air present In the capillary expand creating a partial vacuum in the capillary, because of vacuum the sample solution is rushed to the tip of the burner.

Now, the principle start, the sample is broken into the fine spray at the upper tip of the capillary and then mixed with the gases and are burnt. This process is known as Nebulization. In the principle, some of the gaseous metallic atoms absorb the heat energy so transition take place return to original state with emission of radiations which are obtained in the form of the flame.

Merits and demerits of the burners:a) The flame obtained is turbulent.
b) It is noisy.
c) It has small area of cross-section
d) Used for most types of the flame.

Premix Burner: In this case sample solution fuel and oxidizer are well mixed with the help of axle having the baffles. In this case only a small droplet of sample can reach to the flame and large droplets of the sample is collected at the bottom in drain. Only 5% of the sample is burnt where as 95% is Condensed and drained.

Merits and Demerits:a) Flame produced is non-turbulent.
b) The flame is noiseless and stable,
c) It has large area of cross-section.
d) 5% of the sample is burnt while 95% is drained.

(2) CONCAVE MIRROR: All the radiations which are emitted by the exited atoms are collected by the Concave-mirror and are passed to monochromator.

(3) MONOCHROMATOR: The radiations are dispersed into the different wavelengths by rotating the Prism (monochromator). The radiations of one value of wavelength are incident at a time on photo-cell.

(4) PHOTOCELL: A beam from monochromator falls on photocathode of photo cell. The current is recorded. The magnitude of electric current is directly proportional to the concentration of the solution. The photo cell used Is P.M.T. (Photo-multiplier tube)

(5) READ-OUT METER: This meter gives us directly the Intensity of radiation which is emitted by the excited atoms when they return to the ground state.

Working:

When the fuel is burnt at the tip of burner the sample sol n. rushes upward then tile solvent is vaporized. Solid molecules and then gaseous atoms are formed. Some of the gaseous metallic atoms absorb heat energy and jump to the excited state and instantaneously returned to the ground state with emission of radiations which are collected by concave mirror and are incident after passing through monochromator (prism). The current is produced in the photocell and it is connected with read-out meter which give us directly the intensity of radiations emitted by the excited atoms. From this Intensity, we can have the quantitative analysis.

Application:

1. Flame photometry is specially used in accurate analysis of alkali and alkaline earth metals.
2. The process of analysis is very simple, fast and reliable.
3. The flame photometry is used in the quantitative analysis by using standard Curve method.
4. The amount of metals present in the waste water (especially alkali and alkaline earth metals) can be detected.
5. With the help of flame photometry we can determine the hardness of water.
6. It is used to determine Na, K, Ca, Zn present in the cement.
7. It is used in the determination of lead present in the petrol.
8. The phenomenon is used in the determination of tetra ethyl lead (TEL) and Manganese present In the gasoline stock.
9. We can determine the amount of baron present in an organic compound.
10. Detection of Na⁺, K⁺, Ca⁺², Al⁺³, Fe⁺² and Co⁺³ present in biological fluids and tissues can be done with the help of flame photometry.

Limitations:

1. It gives the total metal content present in the soln It does no give any idea about the molecular conditions of metals.
2. It is used for analysis of alkali and alkaline earth metal, specially.
3. Non-radiating elements like carbon, hydrogen and halogens cannot be detected by this method.
4. Only solutions can be analyzed.
5. For alkali and alkaline earth metals low temp. of the flame is required, because their I.P. is low so at higher temp. those metals are ionized. This ionization decrease the intensity of light emitted, so low temp. is required.

The main components are :

(1) BURNER: The temp. of the burner must be more then 2000 K. Burners used are of the two types: (i) Total Consumption Burner, and (ii) Premix Burner.

Total Consumption Burner: As the Sample Solution is completely burnt so it is known as total consumption burners. The fuel which are used in this case are C2H2, C3H8 or H2. The fuel is oxidized by oxidizer which are either air or nitrous oxide or oxygen diluted with N2. When the fuel and oxidizer are burnt at the tip of the burner. The large amount of heat is produced, so the air present In the capillary expand creating a partial vacuum in the capillary, because of vacuum the sample solution is rushed to the tip of the burner.

Now, the principle start, the sample is broken into the fine spray at the upper tip of the capillary and then mixed with the gases and are burnt. This process is known as Nebulization. In the principle, some of the gaseous metallic atoms absorb the heat energy so transition take place return to original state with emission of radiations which are obtained in the form of the flame.

Merits and demerits of the burners:a) The flame obtained is turbulent.
b) It is noisy.
c) It has small area of cross-section
d) Used for most types of the flame.

Premix Burner: In this case sample solution fuel and oxidizer are well mixed with the help of axle having the baffles. In this case only a small droplet of sample can reach to the flame and large droplets of the sample is collected at the bottom in drain. Only 5% of the sample is burnt where as 95% is Condensed and drained.

Merits and Demerits:a) Flame produced is non-turbulent.
b) The flame is noiseless and stable,
c) It has large area of cross-section.
d) 5% of the sample is burnt while 95% is drained.

(2) CONCAVE MIRROR: All the radiations which are emitted by the exited atoms are collected by the Concave-mirror and are passed to monochromator.

(3) MONOCHROMATOR: The radiations are dispersed into the different wavelengths by rotating the Prism (monochromator). The radiations of one value of wavelength are incident at a time on photo-cell.

(4) PHOTOCELL: A beam from monochromator falls on photocathode of photo cell. The current is recorded. The magnitude of electric current is directly proportional to the concentration of the solution. The photo cell used Is P.M.T. (Photo-multiplier tube)

(5) READ-OUT METER: This meter gives us directly the Intensity of radiation which is emitted by the excited atoms when they return to the ground state.

Working:

When the fuel is burnt at the tip of burner the sample sol n. rushes upward then tile solvent is vaporized. Solid molecules and then gaseous atoms are formed. Some of the gaseous metallic atoms absorb heat energy and jump to the excited state and instantaneously returned to the ground state with emission of radiations which are collected by concave mirror and are incident after passing through monochromator (prism). The current is produced in the photocell and it is connected with read-out meter which give us directly the intensity of radiations emitted by the excited atoms. From this Intensity, we can have the quantitative analysis.

Application:

1. Flame photometry is specially used in accurate analysis of alkali and alkaline earth metals.
2. The process of analysis is very simple, fast and reliable.
3. The flame photometry is used in the quantitative analysis by using standard Curve method.
4. The amount of metals present in the waste water (especially alkali and alkaline earth metals) can be detected.
5. With the help of flame photometry we can determine the hardness of water.
6. It is used to determine Na, K, Ca, Zn present in the cement.
7. It is used in the determination of lead present in the petrol.
8. The phenomenon is used in the determination of tetra ethyl lead (TEL) and Manganese present In the gasoline stock.
9. We can determine the amount of baron present in an organic compound.
10. Detection of Na⁺, K⁺, Ca⁺², Al⁺³, Fe⁺² and Co⁺³ present in biological fluids and tissues can be done with the help of flame photometry.

Limitations:

1. It gives the total metal content present in the soln It does no give any idea about the molecular conditions of metals.
2. It is used for analysis of alkali and alkaline earth metal, specially.
3. Non-radiating elements like carbon, hydrogen and halogens cannot be detected by this method.
4. Only solutions can be analyzed.
5. For alkali and alkaline earth metals low temp. of the flame is required, because their I.P. is low so at higher temp. those metals are ionized. This ionization decrease the intensity of light emitted, so low temp. is required.

Whenever any sample salt solution is introduced into the flame, the solvent is vaporized leaving behind tiny particle of solute solid molecules which further on heating are converted into gaseous molecules. These gaseous molecules are then decomposed into the gaseous atoms, some of the gaseous metallic atoms absorb the heat energy from flame and got excited.

The transition of the atoms takes place to higher energy state. Those atoms return to the ground state by emitting the radiations. If we know the amount of radiations emitted and the wavelength of the emitted radiations we can have quantitative and qualitative analysis,

A brief overview of the process:

1. The solvent is first evaporated leaving fine divided solid particles.

2. This solid particles move towards the flame, where the gaseous atoms and ions are produced.

3. The ions absorb the energy from the flame and excited to high energy levels.

4. When the atoms return to the ground state radiation of the characteristic element is emitted.

5. The intensity of emitted light is related to the concentration of the element.

The temperature of the flame must be 2000 K or above. The fraction of the number of the atoms which are excited is given by Boltzmann equation: $$ \frac { { N }_{ 1 } }{ { N }_{ 0 } } =A { e }^{ \left( \frac { -\Delta E }{ kT } \right) } $$ Where, \( { N }_{ 1 } \) = no. of the atoms in the-excited state
\( { N }_{ 0 } \) = no. of the atoms in the ground State.
\( \Delta E \) = \( { E }_{ excited } - { E }_{ ground } \) (Energy of Activation)
\(K\) = Baltzman Constant
\(T\) = Temperature in dag. K
\(A\) = characteristic constant.

Whenever any sample salt solution is introduced into the flame, the solvent is vaporized leaving behind tiny particle of solute solid molecules which further on heating are converted into gaseous molecules. These gaseous molecules are then decomposed into the gaseous atoms, some of the gaseous metallic atoms absorb the heat energy from flame and got excited.

The transition of the atoms takes place to higher energy state. Those atoms return to the ground state by emitting the radiations. If we know the amount of radiations emitted and the wavelength of the emitted radiations we can have quantitative and qualitative analysis,

A brief overview of the process:

1. The solvent is first evaporated leaving fine divided solid particles.

2. This solid particles move towards the flame, where the gaseous atoms and ions are produced.

3. The ions absorb the energy from the flame and excited to high energy levels.

4. When the atoms return to the ground state radiation of the characteristic element is emitted.

5. The intensity of emitted light is related to the concentration of the element.

The temperature of the flame must be 2000 K or above. The fraction of the number of the atoms which are excited is given by Boltzmann equation: $$ \frac { { N }_{ 1 } }{ { N }_{ 0 } } =A { e }^{ \left( \frac { -\Delta E }{ kT } \right) } $$ Where, \( { N }_{ 1 } \) = no. of the atoms in the-excited state
\( { N }_{ 0 } \) = no. of the atoms in the ground State.
\( \Delta E \) = \( { E }_{ excited } - { E }_{ ground } \) (Energy of Activation)
\(K\) = Baltzman Constant
\(T\) = Temperature in dag. K
\(A\) = characteristic constant.

Those titration in which absorbance of the solution is used to determine the end point are called photometric titrations. The method is based on the fact that the absorbance of the solution is directly proportional to concentration.

During the course of titration the concentration of the solution being titrated changes. So the absorbance of the solution changes. The end point is obtained from the graph by plotting Absorbance Vs volume of titrant added.

1. If titrand is the absorber while titrant and products do not absorb then O.D. decreases during the titration and remain constant after the end point is reached.

2. If the titrant is capable to absorb then O.D. initially remain constant but increases once the end point is reached as excess titrant is added.

3. When the products are capable to absorb the radiations while titrand and titran cannot absorb. Thus as the titrant is added to titrand the product formation take place, so the absorbance increases up to the equivalence point and after that it remain constant.

4. When the titrant and titrand are capable to absorb and the products cannot, initially absorbance decreases as titrand diminishes and after the equivalence point, again the absorbance increases due to presence of excess of titrant.

Those titration in which absorbance of the solution is used to determine the end point are called photometric titrations. The method is based on the fact that the absorbance of the solution is directly proportional to concentration.

During the course of titration the concentration of the solution being titrated changes. So the absorbance of the solution changes. The end point is obtained from the graph by plotting Absorbance Vs volume of titrant added.

1. If titrand is the absorber while titrant and products do not absorb then O.D. decreases during the titration and remain constant after the end point is reached.

2. If the titrant is capable to absorb then O.D. initially remain constant but increases once the end point is reached as excess titrant is added.

3. When the products are capable to absorb the radiations while titrand and titran cannot absorb. Thus as the titrant is added to titrand the product formation take place, so the absorbance increases up to the equivalence point and after that it remain constant.

4. When the titrant and titrand are capable to absorb and the products cannot, initially absorbance decreases as titrand diminishes and after the equivalence point, again the absorbance increases due to presence of excess of titrant.

1. Quantitative Analysis: The metal salt solutions which are coloured for e.g. Cu (II), Fe (III), Ni (II) etc and some organic coloured compounds can be easily analyzed quantitatively by using Beer Lambert’s Law. Thus, from OD we can calculate the concentration of the solution.

2. Identification of functional group (Qualitative analysis): The spectrophotometers are the instruments working on the principle of \({ \lambda }_{ max }\). This \({ \lambda }_{ max }\) is constant for each functional group. If we know λmax for the particular sample, we can decide the type of functional group present in it, as \({ \lambda }_{ max }\) is characteristic property.

3. Distinguish between geometrical isomer: Each geometrical isomer have its own characteristic \({ \lambda }_{ max }\), therefore from \({ \lambda }_{ max }\) we identify geometrical isomers. E.g. Cinnamic acid exists in Cis and Trans form.

4. Chemical Analysis: With the help of spectrophotometer we can find out the rate constant (K) of any chemical reaction. As we know the first order reaction. $$ K = \frac { 2.303 }{ t } \log { \left( \frac { a }{ a-x } \right) } $$ Where a is initial concentration and (a - x) is final concentration.

We will take some ester and keep in the instrument and find out the absorbance then with the help of Beer-Lamberts Law we can find out the concentration.

Now add some reagent the reaction will take place at the time t. Now we will find out the O.D. of the solution in the cuvette which is (a-x) then by using the above eqn. for first order we can find out the K (rate constant).

Similarly we can find out the K for zero order, second order and so on by using its expression.

5. Determination and estimation of tautomers: Keto and Enol form are present in equilibrium which can be determined by spectrophotometer. E.g. Acetoacetic ester exists in two tautomeric forms which show different \({ \lambda }_{ max }\) values.

1. Quantitative Analysis: The metal salt solutions which are coloured for e.g. Cu (II), Fe (III), Ni (II) etc and some organic coloured compounds can be easily analyzed quantitatively by using Beer Lambert’s Law. Thus, from OD we can calculate the concentration of the solution.

2. Identification of functional group (Qualitative analysis): The spectrophotometers are the instruments working on the principle of \({ \lambda }_{ max }\). This \({ \lambda }_{ max }\) is constant for each functional group. If we know λmax for the particular sample, we can decide the type of functional group present in it, as \({ \lambda }_{ max }\) is characteristic property.

3. Distinguish between geometrical isomer: Each geometrical isomer have its own characteristic \({ \lambda }_{ max }\), therefore from \({ \lambda }_{ max }\) we identify geometrical isomers. E.g. Cinnamic acid exists in Cis and Trans form.

4. Chemical Analysis: With the help of spectrophotometer we can find out the rate constant (K) of any chemical reaction. As we know the first order reaction. $$ K = \frac { 2.303 }{ t } \log { \left( \frac { a }{ a-x } \right) } $$ Where a is initial concentration and (a - x) is final concentration.

We will take some ester and keep in the instrument and find out the absorbance then with the help of Beer-Lamberts Law we can find out the concentration.

Now add some reagent the reaction will take place at the time t. Now we will find out the O.D. of the solution in the cuvette which is (a-x) then by using the above eqn. for first order we can find out the K (rate constant).

Similarly we can find out the K for zero order, second order and so on by using its expression.

5. Determination and estimation of tautomers: Keto and Enol form are present in equilibrium which can be determined by spectrophotometer. E.g. Acetoacetic ester exists in two tautomeric forms which show different \({ \lambda }_{ max }\) values.

Spectrophotometers are the instruments which are working at a wavelength where the absorbance is maximum. Such wavelength of the radiations whose absorbance is maximum is called \({ \lambda }_{ max }\).

With the help of spectrophotometers we can have qualitative as well as quantitative analysis of any type of sample it may be solid, liquid or gas. It may be coloured or colourless.

The spectrophotometers are of two types;

(i) Single Beam Spectrophotometers,

(ii) Double Beam Spectrophotometers.

The following are the main components of a Double Beam Spectrophotometers:

1. Source of radiations: It may be U.V-light, visible light or I.R. light. U.V. Light can be obtained by heating the filament which is filled with either H2 gas or deuterium. Visible Radiations can be obtained by incandescent lamp with tungsten filament and I.R. Radiations can be obtained by heating Newtons glower at the temp. of 1500-2000 ℃. Newtons glower is metallic oxide of Yettrium, Erbium and Zirconium. I.R. radiations can also be obtained by heating glow bar which is Silicon carbide SiC (Carborandum) at the temp. of 1300-1700 ℃.

2. Collimating Convex Lens: The function is to collect all the rays coming from the source.

3. Diaphragm: To set the 100% transmittance.

4. Monochromators: To obtain the radiation of one wavelength. The Monochromators may be prism or diffraction gratings.

5. Cuvette or Sample Holder: For U.V. light it should be made up of quartz, for visible light it should be made up of glass and for I.R. light it must be that of rock salts for eg. NaCl.
a) If the sample is gas or volatile liquid having low B.P. must be taken in the closed container.
b) If it is liquid, one drop of the liquid must be placed between two parallel plates for U-V. the plates must be quartz and for visible it must be glass and for I.R. it is rock salt.
c) If it is solutions the solvent used for the preparation of solution must be Cyclohexane, methyl alcohol, ethyl alcohol or any other suitable solvent which is not capable to absorb the radiations incident on it.
d) If it is solids then we take about 1mg. of it and is mixed in 100-200 mg. of KBr - prepare slurry. It is cut into smaller circular discs (just like bindle) called pellets. They are dried and placed in the place of cuvette. The diameter of pellets is 10mm. and thickness is 1mm.

6. The Focusing Convex Lens: Its function is to collect all the transmitted light from cuvette and is focused at a point where photo cathode of the photo-cell is placed.

7. Photo-Cell: The transmitted light is incident on it photo cathode converts these radiations into current. It can be amplified using the amplifier if needed.

8. Read out meter or dial: The current is converted into OD or Absorbance in read out meter and by knowing OD we can find out the concentration of the solution i.e. quantitative analysis is possible by applying Beer Lamberts Law.

Working:

First of all the source of radiations from U.V. light to visible light to I.R. radiations is started. The light from the source is collected by Collimating convex lens and allowed to fall on monochromator. For each radiations incident on monochromator we are getting the radiations of one wave length only i.e. \( \lambda \), the monochromatic light is then separated in two beams with the help of two mirrors. One beam is passed through one cuvette containing blank (solvent) and the other through the other cuvette containing sample solution and both are finally incident on detectors. These may be photo calls or thermocouples. Where the heat is produced which is then converted to current and finally O.D. or Absorbance (A).

The signal generated is platted O D Vs \(\lambda\). From the graph we can find out \({ \lambda }_{ max }\) and we can have the qualitative analysis. From O.D. or Absorbance we can have the quantitative analysis.

Value of the wavelength where the absorbance is maximum is known as \({ \lambda }_{ max }\) which is characteristic property of the compound and gives the qualitative analysis of sample.While knowing the value of absorbance we can find out the concentration of solution using beer lambert’s law. Thus quantitative analysis is possible.

Double beam Spectrophotometer have following advantages:

1. As the two beams of radiations are passed simultaneously from sample solution and Blank Therefore any fluctuation in voltage can be compensated (cancelled).

2. As the two beams are passed from Blank and Sample solution any impurities present in the solvent will not affect the absorbance.

3. Accuracy is more than single beam spectrophotometer.

4. The main disadvantage is the instrument is costly.

Spectrophotometers are the instruments which are working at a wavelength where the absorbance is maximum. Such wavelength of the radiations whose absorbance is maximum is called \({ \lambda }_{ max }\).

With the help of spectrophotometers we can have qualitative as well as quantitative analysis of any type of sample it may be solid, liquid or gas. It may be coloured or colourless.

The spectrophotometers are of two types;

(i) Single Beam Spectrophotometers,

(ii) Double Beam Spectrophotometers.

The following are the main components of a Double Beam Spectrophotometers:

1. Source of radiations: It may be U.V-light, visible light or I.R. light. U.V. Light can be obtained by heating the filament which is filled with either H2 gas or deuterium. Visible Radiations can be obtained by incandescent lamp with tungsten filament and I.R. Radiations can be obtained by heating Newtons glower at the temp. of 1500-2000 ℃. Newtons glower is metallic oxide of Yettrium, Erbium and Zirconium. I.R. radiations can also be obtained by heating glow bar which is Silicon carbide SiC (Carborandum) at the temp. of 1300-1700 ℃.

2. Collimating Convex Lens: The function is to collect all the rays coming from the source.

3. Diaphragm: To set the 100% transmittance.

4. Monochromators: To obtain the radiation of one wavelength. The Monochromators may be prism or diffraction gratings.

5. Cuvette or Sample Holder: For U.V. light it should be made up of quartz, for visible light it should be made up of glass and for I.R. light it must be that of rock salts for eg. NaCl.
a) If the sample is gas or volatile liquid having low B.P. must be taken in the closed container.
b) If it is liquid, one drop of the liquid must be placed between two parallel plates for U-V. the plates must be quartz and for visible it must be glass and for I.R. it is rock salt.
c) If it is solutions the solvent used for the preparation of solution must be Cyclohexane, methyl alcohol, ethyl alcohol or any other suitable solvent which is not capable to absorb the radiations incident on it.
d) If it is solids then we take about 1mg. of it and is mixed in 100-200 mg. of KBr - prepare slurry. It is cut into smaller circular discs (just like bindle) called pellets. They are dried and placed in the place of cuvette. The diameter of pellets is 10mm. and thickness is 1mm.

6. The Focusing Convex Lens: Its function is to collect all the transmitted light from cuvette and is focused at a point where photo cathode of the photo-cell is placed.

7. Photo-Cell: The transmitted light is incident on it photo cathode converts these radiations into current. It can be amplified using the amplifier if needed.

8. Read out meter or dial: The current is converted into OD or Absorbance in read out meter and by knowing OD we can find out the concentration of the solution i.e. quantitative analysis is possible by applying Beer Lamberts Law.

Working:

First of all the source of radiations from U.V. light to visible light to I.R. radiations is started. The light from the source is collected by Collimating convex lens and allowed to fall on monochromator. For each radiations incident on monochromator we are getting the radiations of one wave length only i.e. \( \lambda \), the monochromatic light is then separated in two beams with the help of two mirrors. One beam is passed through one cuvette containing blank (solvent) and the other through the other cuvette containing sample solution and both are finally incident on detectors. These may be photo calls or thermocouples. Where the heat is produced which is then converted to current and finally O.D. or Absorbance (A).

The signal generated is platted O D Vs \(\lambda\). From the graph we can find out \({ \lambda }_{ max }\) and we can have the qualitative analysis. From O.D. or Absorbance we can have the quantitative analysis.

Value of the wavelength where the absorbance is maximum is known as \({ \lambda }_{ max }\) which is characteristic property of the compound and gives the qualitative analysis of sample.While knowing the value of absorbance we can find out the concentration of solution using beer lambert’s law. Thus quantitative analysis is possible.

Double beam Spectrophotometer have following advantages:

1. As the two beams of radiations are passed simultaneously from sample solution and Blank Therefore any fluctuation in voltage can be compensated (cancelled).

2. As the two beams are passed from Blank and Sample solution any impurities present in the solvent will not affect the absorbance.

3. Accuracy is more than single beam spectrophotometer.

4. The main disadvantage is the instrument is costly.