DIFFERENCE BETWEEN FLAME PHOTOMETRY AND FLAME SPECTROSCOPY
The basic difference between both the techniques is of complexity with slight modification. The flame photometry is an old technique which is specific to few metals on the other hand flame spectroscopy is versatile and advance technique. The theory and basic mechanism in both the techniques is similar the slight difference comes in instrumentation.
In both the techniques the sample is introduced in the form of fine droplets. When the sample comes in contact with flame it is atomized and atoms of metal absorb the thermal energy. Some are excited to higher energy levels and some remain stable in ground state. The excitation of atoms depends on the flame intensity. More the temperature of flame more atoms will excite. When the energy is lost the atoms come to ground state by emission of energy in the form of radiations. These radiations are detected differently in both the techniques and output of both are in different forms. The emission and number of atoms are directly related to each other.
The differences between both the techniques are described in the form of table below:
Flame photometry or photoelectric flame photometry
Flame spectroscopy or flame emission spectroscopy
It is a process where emission of radiation by neutral atom is measured.
It is a type of flame photometry coupled with the simpler spectrometer.
This technique is based on the principle of flame test which is being controlled and flame intensity is analyzed by photoelectric circuitry. Principle
The determination of concentration of solution is done by measuring absorption of thermal energy by monatomic particles in gaseous state in flame.”
? Mixing chamber
? Optical filter
? Detector Instrumentation
? Prism spectrograph
Figure 1.0: Flame photometry
Figure 1.1: Flame spectroscopy
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Different types of burner are used. The burner is maintained at constant temperature. The temperature depends on fuel-oxidant ratio. Burners
The flame of air as oxidant and acetylene as fuel is most common providing the temperature of 30000C.
V. Optical filters
? Convex mirror
? Filter Prism and monohromator
The prism scatters the light from the flame source and direct it towards monochromator that allows light of specific wave length to pass reach the detector.
These are easier to calibrate and easier for unskilled workers, to Calibrations for Photometers typically need 3 to 7 samples.
Calibrations for Spectrophotometers normally need 10 to 15 samples but it can also require 200 or more samples for calibration.
VII. Elemental determination
This instrument can determine only one element at a time and it is designed to display only single reading. So its other name is single channel photometer. Elemental determination
Multichannel spectrometers have been developed for the simultaneous measurement of elements present in a sample.
It detects light from the flame the radiations are converted into electrical signals and output is in the form of electrical signals with the help of photodetector.
The detector is usually a
? Phototube or
? Photomultiplier tube depending on the quality of the instrument. Detector
It detects the light from the flame and output is in the form of spectral lines of specific metal. Complex spectra for transition metals.
Detectors used in flame photometry are
? Photomultiplier tubes
? Photo emissive cell
? Photo voltaic cell
The output is in form of electrical signals. Output
The output is being displayed as spectral lines.
? Provide selective results.
? Cannot be used for transition metals.
? The elements such C, H and halides cannot be detected.
? In case of higher concentration accurate results cannot be obtained. Demerits
? It is expensive, complex and difficult to analyze.
? Perfect control of flame is needed.
? High concentration of sample cause interference in spectral bands
DIFFERENCE BETWEEN ATOMIC ABSOPTION SPECTROSCOPY AND ATOMIC EMISSION SPECTROSCOPY
These two analytical techniques are completely different from each other. There principles, instrumentation, detection limit and application all are different. But both the analytical techniques are very useful in detection of various metals on the basis of absorption and emission phenomena.The basic differences between both are described in the form of table below:
Atomic absorption spectroscopy (AAS)
Atomic emission spectroscopy (AES)
It is a procedure based on spectral-analysis for the quantitative determination of chemical elements by using absorption of light by free atoms in the gaseous state. Definition
Atomic emission spectroscopy is a technique for analyzing the quantities of elements in the sample. This technique uses the intensity of light which is being emitted by plasma, spark, flame or arc.
Element is not excited but is only separated from its chemical bond and it is being placed in ground state. Principle
“Enough thermal energy is given to atoms of some metals so that as a result they become excited and then re-emits this energy at specific wavelength which is the characteristic of that element. The intensity of radiant energy of specific wavelength produced by the atoms in the flame is directly related to the number of atoms being excited in the flame, which is then directly proportional to the concentration of the alkali metal being present in the sample.”
III. Beers law
In AAS Beers law is followed over a wide range of concentration.
Beers law is absolutely not obeyed.
IV. Role of temperature
Absorption intensity does not depend on temperature. Role of temperature
Temperature variation influences the intensity of absorption.
? Source of light
? Detector and read out devices Instrumentation
? Photodetector and readout devices
After the atomization of sample the source of light that is cathode lamp is provided and atoms absorb the specific wavelength from the light source and gets excited. Working
The excitation of atoms occur by absorbing the heat from source then during de-excitation emit the energy in the form of light.
VII. Mechanism of excitation
? The excitation of atoms is done by source of light from cathode lamp.
? The gaseous ions of atoms after atomization hit the cathode and cause ejection of atoms from cathode.
? Some of them get excited and some fall to ground state. Mechanism of excitation
In this different sources of energy are used to excite the atoms:
? Flame that provides temperature from 1700-31500C. It provides relatively low energy.
? Plasma provides temperature from 6000-80000C and is used to provide high excitation energy. It is more efficient.
In this technique metals along with metalloids are detected in environmental samples. Detection
In this technique some metals are detected. Such as alkali metals.
Figure-1.3: Atomic absorption spectroscopy Figure-1.4: Atomic emission spectroscopy
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IX. It depends on the number of atoms in ground state. It depends on the number of atoms in excited state.
X. There is a light source present. There is no light source present.
XI. It is measure of radiations that are absorbed by atoms in ground state. It is measure of radiations that are emtted by the atoms that are in excited state.
? High precision
? Easy to handle
? Sensitive Advantages
? Fine spectral lines
? High resolution
? Multi elemental analysis is possible
? ICP-AES has become the technique of choice for metal analysis.
? More costly and less widely applicable
? Intended for metallic or metaloid atomic species and nor for non metallic
? Not easy for solids Disadvantages
? initial cost of ICP instumentation
? continuing cost of operation(Ar required)
? Used for analysis of enviornmental samples.
? It is used to determine amount of gold in rocks.
? Determination of small amount of metals like lead mercury calcium magnesium etc
? Food industry
? Pharmaceutical industry
? Agriculture Applications
? It used for the regulation of alkali metals in the pharmaceutical processes.
? Trace metals are detected by this technique.
? It is applicable in the smelting process of ores, in the process of extraction of metals.
? It helps in the detection of elements in the given sample and hence for structure elucidation.
? Motor oils are also analyzed by this process.
DIFFERECE BETWEEN THE FLAME PHOTOMETER, ATOMIC ABSORPTION SPECTROPHOTOMETER AND ATOMIC EMISSION SPECTROPHOTOMETER
Major difference between photometer and spectrophotometer is given as
? Photometer: Photometer basically measures the single wavelength of the light source.
? Spectrophotometer: A spectrophotometer on the other hand would measure complete spectral of the same light source. So spectrophotometer would give a detailed information about behavior of light on to the spectral band.
Flame photometer Atomic absorption spectrophotometer Atomic emission spectrophotometer
It is a device which has been used in inorganic chemical analysis to check the concentration of some specific metal ions such as sodium, potassium, lithium and calcium. Introduction
It is a device which has been used to analyze element’s concentration present in a liquid sample depending on the energy which is absorbed from the specific wavelength of light. Introduction
It is an instrument use for which is being used to measure the emission spectra of elements.
When some of the elements are oxidizes on flame would release energy in form of the light. Every element generate energy at distinctive and measureable wavelength means colors obtained in visible region. And these colored emissions can be detected with the help of flame photometer. Principle
It atomized the elements that can absorb the energy of the wavelength which would be distinctive to that element. It uses a light source such as cathode lamp that has the ability to emit the light of specific wavelength distinctive to that element. Principle
When a molecule gets the energy in the form of either light or heat it get excited and go to high energy level as the molecule is unstable in this state and would come back to lower energy level by emitting equal amount of radiation in the form of photon. Wavelength of these emitted photons is emitted by spectrophotometer.
III. Parts of flame photometer
Flame photometer includes
? source of flame,
? mixing chamber,
? optical system
? Photo detector. Parts of absorption spectrophotometer
? light source
? flame burner,
? Photodetector. Parts of emission spectrophotometer
? source which itself is a analyzer,
IV. Use of filter
It involve the use of filter. Use of monochromator
Instead of using filter it involves the use of monochromator. Use of monochromator
It also uses monochromator.
Flame is use as source in flame photometer. Source
Hollow cathode lamp is use as source in it. Source
Hollow cathode lamp is use in AES.
Atomic Absorption Spectrophotometer Figure-1.7:
Atomic emission spectrophotometer
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? Can detect alkali and alkaline earth metals.
? Helpful in studying electrolyte balance in clinical analysis.
? In determining lead in petrol. Advantages
? Helpful in water analysis.
? Food analysis
? Analysis of soil
? Best for analyzing animal feed stuffs
? Clinical analysis. Advantages
? Could be used in clinical laboratory to check concentration of sodium and potassium in biological fluids.
? Serum lithium level-therapeutic
? Concentration of metal present in solution cannot be measured correctly.
? For higher concentration accurate result is difficult to obtain.
? Due to non-radiating nature carbon, hydrogen and halides cannot be detected.
? Limited to only Hg as no other element has possibility to convert into volatile free atomic state.
? Theoretical limit is imposed by the background as well as contamination level in Hg in hardware. Limitation
? Very expensive.
? Procedures are very complicated than absorption spectrophotometer.
? More operating cost.