Atomic absorption spectroscopy (AAS).pptx

Atomic absorption spectroscopy (AAS)
Ms.Priyanka shah
M.Pharm (QA)
KPGU
1
Introduction
Atomic absorption spectrometry (AAS) is an analytical technique that
measures the concentrations of elements.
Atomic absorption is so sensitive that it can measure down to parts per billion
of a gram (µg dm–3 ) in a sample.
The technique makes use of the wavelengths of light specifically absorbed by
an element. They correspond to the energies needed to promote electrons
from one energy level to another, higher, energy level.
Atomic absorption spectrometry has many uses in different areas of
chemistry.
Clinical analysis : Analysing metals in biological fluids such as blood and urine.
Environmental analysis: Monitoring our environment – eg finding out the
levels of various elements in rivers, seawater, drinking water, air, petrol and
drinks such as wine, beer and fruit drinks.
2
Pharmaceuticals: In some pharmaceutical manufacturing processes, minute
quantities of a catalyst used in the process (usually a metal) are sometimes present
in the final product. By using AAS the amount of catalyst present can be
determined.
Atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES) is
a spectro analytical procedure for the quantitative determination of chemical
elements by free atoms in the gaseous state.
Atomic absorption spectroscopy is based on absorption of light by free metallic
ions.
In analytical chemistry the technique is used for determining the concentration of
a particular element (the analyte) in a sample to be analyzed. AAS can be used to
determine over 70 different elements in solution, or directly in solid samples via
electrothermal vaporization. 3
Principle
• The technique makes use of the atomic absorption spectrum of a sample in order to assess
the concentration of specific analytes within it. It requires standards with known analyte
content to establish the relation between the measured absorbance and the analyte
concentration and relies therefore on the [Beer–Lambert law].
• The electrons within an atom exist at various energy levels. When the atom is exposed to its
own unique wavelength, it can absorb the energy (photons) and electrons move from a
ground state to excited states.
• The radiant energy absorbed by the electrons is directly related to the transition that occurs
during this process.
• Furthermore, since the electronic structure of every element is unique, the radiation
absorbed represents a unique property of each individual element and it can be measured.
• An atomic absorption spectrometer uses these basic principles and applies them in practical
quantitative analysis
4
Atoms absorb light at a
definite wavelength depending
on the nature of chemical
elements.
Sodium is absorbed in 589 nm
Uranium is absorbed in 589 nm
Potassium is absorbed in 766.5
nm
5
Instuments:
• A typical atomic absorption spectrometer consists of four main
components:
Atomization
Light source,
Atomization system,
Monochromator &
Detection system
Schematic diagram of a typical atomic absorption
spectrometer
6
Atomization
• Atomization can be carried out either by a flame or furnace.
• Heat energy is utilized in atomic absorption spectroscopy to convert
metallic elements to atomic dissociated vapor.
• The temperature should be controlled very carefully for the
conversion of atomic vapor.
• At too high temperatures, atoms can be ionized.
• Fuel and oxidant gases are fed into a mixing chamber which passes
through baffles to the burner.
• A ribbon flame is produced in the AAS instrument. The sample is
aspirated through the air into the mixing chamber.
7
Radiation source:
1) Hallow cathode lamp
2) Electodeless discharge lamp
8
Hollow cathode lamp
We used a hollow cathode glow discharge lamp to give sharp emission
lines for a specific element in atomic absorption spectroscopy
instrumentation.
The hollow cathode lamp has two electrodes,
one is cup-shaped and
made of a specific element.
Radiation from the hollow cathode lamp should not be continuous due
to spurious radiations. Therefore, we used a chopping wheel between
the radiation or pulsed potential.
The metal which is used in the cathode is the same as that metal that
we analyzed. The lamp is filled with noble gas(Ne & Ar) at low pressure
The lamp forms a glow of emission from the hollow cathode.
Several types of hollow cathode lamps are available in our market. Such
types of lamps are called multi-element hollow cathode Lamps. Such
types of lamps facilitate for determination of samples without change of
lamps each time.
These types of lamps are widely used in atomic absorption spectroscopy
instruments.
9
Electodeless discharge lamp
10
CHOPPER
• Function:
• of the chopper in Atomic Absorption Spectroscopy
is to break the steady light into pulsating light.
• LOCATION:
• It is a rotating wheel placed between the flame
and the source.
11
Atomizer
In order for the sample to be analyzed, it must first be atomized. This is an extremely important
step in AAS because it determines the sensitivity of the reading. The most effective atomizers
create a large number of homogenous free atoms. There are many types of atomizers, but only
two are commonly used: flame and electrothermal atomizers.
Flame atomizer
Flame atomizers are widely used for a multitude of reasons including their simplicity, low cost,
and long length of time that they have been utilized. Flame atomizers accept an aerosol from a
nebulizer into a flame that has enough energy to both volatilize and atomize the sample. When
this happens, the sample is dried, vaporized, atomized, and ionized.
Within this category of atomizers, there are many subcategories determined by the chemical
composition of the flame. The composition of the flame is often determined based on the
sample being analyzed. The flame itself should meet several requirements including sufficient
energy, a long length, non-turbulent, and safe.
1) Total consumption burner
2) The premixed burner
12
13
14
Total consumption burner Premixed burner
Advantage
Representive sample reach flame Long path provide sensitivity
Amount of sample in flame is large
which enhance sensitivity
Only small drops reach flame
No explosive harzards. Quite operation & little tendancy to clog
Disadvantage
Short path leds to lower lower
sensitivity
Rate of sample introduce is low
Larger droplets not entirely
decomposed
Possibility of explosion in mixing
chamber
15
Non flame atomizer :
• The graphite furnace is an electro thermal atomizer system that can produce temperatures as high as 3,000°C.
• The heated graphite furnace provides the thermal energy to break chemical bonds within the sample held in a
graphite tube, and produce free ground state atoms.
• The ground-state atoms are capable of absorbing energy, in the form of light, and are elevated to an excited
state.
• The amount of light energy absorbed increases as the concentration of the selected element increases.
16
Monochromator:
A monochromator is an optical device that transmits a narrow band of wavelengths of light or other radiation from
a wider range of wavelengths.
The atoms in the AAS instrument accept the energy of excitation and emit radiation.
A desired band of lines can be isolated with a monochromator by passing a narrow band.
The spectra through a monochromator can be shown by a curve.
Detector
A detector can convert light coming from a monochromator to a simplified electrical signal.
Generally, we used a photomultiplier tube as a detector in the atomic absorption spectroscopy
instrument. A detector can be tuned to respond by a specific wavelength or frequency.
Recorder
The recorder can receive electrical signals from the detector to convert them into a readable
response. In atomic absorption spectroscopy instrumentation, today we used a computer system
with suitable software for recoding signals coming from the detector.
17
Interferences In Atomic Absorption Spectroscopy:
Interference is a phenomenon that leads to change in intensity of analyte signal in spectroscopy.
Interferences in AAS fall into two basic categories :
1. Non-Spectral Interference :
Which affect the formation of analyte Atoms
Matrix interference
Chemical interference
Ionization interference
2. Spectral Interferences :
High light absorption due to presence of absorbing species
Background absorption
Continuum source Background Correction
Others spectral interferences
18
Non-spectral Interferences:
Matrix interferences :
When a sample is more viscous or has different surface tension than the standard it result in
difference in sample uptake rate due to changes in nebulization efficiency.
Such interferences are minimized by matching the matrix composition of standard and sample.
19
Chemical Interferences
• If a sample contains a species which forms a thermally stable compound
with analyte that is not completely decomposed by the flame energy then
chemical interferences exist.
• Such interferences are minimized by using higher flame temp.
• To provide higher dissociation energy.
20
Ionization Interference
• It is more common in hot flames.
• The dissociation process doesn’t stop at formation of ground state atoms. Excess energy of the
flame lead to excitation of ground state atoms to ionic state by loss of electrons thereby
resulting in depletion of ground state atoms.
• Ionization interference is eliminated by an excess of an element which is easily ionized thereby
creating a large number of electrons in the flame & suppressing the ionization of the analyte.
21
Spectral Interferences :
• Atomic Spectral interferences are caused by presence of another absorption
line or a molecular absorbance band close to the spectral line of element of
interest.
• Most of these interferences are due to molecular emission from oxides of
other element is a sample.
22
Background Absorption:
• Absorption by the flame atomizer or electro thermal analyzer can cause
serious problems in atomic absorption.
• Rarely are there interferences from absorption of the analyte line by other
atoms since the hollow cathode lines are so narrow. Molecular species can
absorbs the radiation and cause radiation in atomic absorption
measurements.
• However, the total measured absorbance AT in atomic absorption is the
sum of analyte absorbance AA plus the background absorbance AB.
• AT=AA+AB
• Background correction scheme attempt to measure AB in addition to AT and
to obtain the true analyte absorbance by subtraction (AA=AT - AB)
23
CONTINUUM SOURCE BACKGROUND CORRECTION :
• A popular background correction scheme in commercial atomic absorption spectrometers is
the continuum lamp technique.
• Here a deuterium lamp and the analyte hollow cathode are directed through the atomizer at
different times. The hollow cathode lamp measures the total absorbance AT while the
deuterium lamp provides an estimates of the background absorbance AB.
• The computer system or processing electronics calculates the difference and reports the
background corrected absorbance.
• This method has limitation for elements with lines in the visible range because the D2 lamp
intensity becomes quite low in this region.
24
ZEEMAN EFFECT BACKGROUND CORRECTION
• Background correction with electro thermal atomizers can be done by
means of the Zeeman effect.
• Here a magnetic field splits normally degenerated spectral lines into
components with different polarization characteristics.
• Analyte and background absorption can be separated because of their
different magnetic and polarization behaviors
25
• The major limitations of flame AAS are as follows:
• The sample introduction system, e.g. nebulizer/expansion chamber, which is used
is inefficient and requires large volume of aqueous sample.
• The residence time, i.e. the length of time that the atom is present in the flame, is
limited due to the high burning velocity of the gases, thus leading to rather high
detection limits.
• An inability to analyze solid sample directly (solid requires dissolution prior to
analysis)
26
ADVANTAGES OF AAS :
• It does not suffer from spectral interference, which occurs in flame emission spectroscopy.
• It is independent on flame temperature.
• By atomic absorption technique , traces of one element can easily be determined in presence
of high concentration of other elements.
• It has proved very successful in the analysis of bronze and copper alloys and in the
determination of metals like platinum, gold etc.
DISADVANTAGES OF AAS
• This technique has not proved very successful for the estimation of elements like W, Si, Mo, Ti,
and Al etc. because these elements give rise to oxides in the flame.
• In aqueous solution, the predominant anion affects the signal to a negotiable degree.
• A separate lamp for each elements to be determined is required. Attempts are being made to
overcome this difficulty by using continuous source with a very high resolution Monochromator
or alternatively to produce a line source.
27
APPLICATION:
• It is used in quantitative and qualitative analysis of different drug compounds.
• Estimation of zinc in insulin preparation, oils, creams and in calamine, calcium in
number of calcium salts, lead in calcium carbonate and also as impurity in number
of chemical salts have been reported.
• Atomic absorption spectroscopy is very widely used in metallurgy, alloys and in
inorganic analysis. Almost all important metals have been analyzed by this method.
• It is especially useful to analyze ionic metal elements in blood, saliva, urine
samples like sodium, potassium, magnesium, calcium and other body fluids.
• To detect heavy metals in herbal drugs and synthetic drugs.
• To determine metal elements in the food industry.
• To estimate Lead in petroleum products.
28
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Atomic absorption spectroscopy (AAS).pptx

  • 1. Atomic absorption spectroscopy (AAS) Ms.Priyanka shah M.Pharm (QA) KPGU 1
  • 2. Introduction Atomic absorption spectrometry (AAS) is an analytical technique that measures the concentrations of elements. Atomic absorption is so sensitive that it can measure down to parts per billion of a gram (µg dm–3 ) in a sample. The technique makes use of the wavelengths of light specifically absorbed by an element. They correspond to the energies needed to promote electrons from one energy level to another, higher, energy level. Atomic absorption spectrometry has many uses in different areas of chemistry. Clinical analysis : Analysing metals in biological fluids such as blood and urine. Environmental analysis: Monitoring our environment – eg finding out the levels of various elements in rivers, seawater, drinking water, air, petrol and drinks such as wine, beer and fruit drinks. 2
  • 3. Pharmaceuticals: In some pharmaceutical manufacturing processes, minute quantities of a catalyst used in the process (usually a metal) are sometimes present in the final product. By using AAS the amount of catalyst present can be determined. Atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES) is a spectro analytical procedure for the quantitative determination of chemical elements by free atoms in the gaseous state. Atomic absorption spectroscopy is based on absorption of light by free metallic ions. In analytical chemistry the technique is used for determining the concentration of a particular element (the analyte) in a sample to be analyzed. AAS can be used to determine over 70 different elements in solution, or directly in solid samples via electrothermal vaporization. 3
  • 4. Principle • The technique makes use of the atomic absorption spectrum of a sample in order to assess the concentration of specific analytes within it. It requires standards with known analyte content to establish the relation between the measured absorbance and the analyte concentration and relies therefore on the [Beer–Lambert law]. • The electrons within an atom exist at various energy levels. When the atom is exposed to its own unique wavelength, it can absorb the energy (photons) and electrons move from a ground state to excited states. • The radiant energy absorbed by the electrons is directly related to the transition that occurs during this process. • Furthermore, since the electronic structure of every element is unique, the radiation absorbed represents a unique property of each individual element and it can be measured. • An atomic absorption spectrometer uses these basic principles and applies them in practical quantitative analysis 4
  • 5. Atoms absorb light at a definite wavelength depending on the nature of chemical elements. Sodium is absorbed in 589 nm Uranium is absorbed in 589 nm Potassium is absorbed in 766.5 nm 5
  • 6. Instuments: • A typical atomic absorption spectrometer consists of four main components: Atomization Light source, Atomization system, Monochromator & Detection system Schematic diagram of a typical atomic absorption spectrometer 6
  • 7. Atomization • Atomization can be carried out either by a flame or furnace. • Heat energy is utilized in atomic absorption spectroscopy to convert metallic elements to atomic dissociated vapor. • The temperature should be controlled very carefully for the conversion of atomic vapor. • At too high temperatures, atoms can be ionized. • Fuel and oxidant gases are fed into a mixing chamber which passes through baffles to the burner. • A ribbon flame is produced in the AAS instrument. The sample is aspirated through the air into the mixing chamber. 7
  • 8. Radiation source: 1) Hallow cathode lamp 2) Electodeless discharge lamp 8
  • 9. Hollow cathode lamp We used a hollow cathode glow discharge lamp to give sharp emission lines for a specific element in atomic absorption spectroscopy instrumentation. The hollow cathode lamp has two electrodes, one is cup-shaped and made of a specific element. Radiation from the hollow cathode lamp should not be continuous due to spurious radiations. Therefore, we used a chopping wheel between the radiation or pulsed potential. The metal which is used in the cathode is the same as that metal that we analyzed. The lamp is filled with noble gas(Ne & Ar) at low pressure The lamp forms a glow of emission from the hollow cathode. Several types of hollow cathode lamps are available in our market. Such types of lamps are called multi-element hollow cathode Lamps. Such types of lamps facilitate for determination of samples without change of lamps each time. These types of lamps are widely used in atomic absorption spectroscopy instruments. 9
  • 11. CHOPPER • Function: • of the chopper in Atomic Absorption Spectroscopy is to break the steady light into pulsating light. • LOCATION: • It is a rotating wheel placed between the flame and the source. 11
  • 12. Atomizer In order for the sample to be analyzed, it must first be atomized. This is an extremely important step in AAS because it determines the sensitivity of the reading. The most effective atomizers create a large number of homogenous free atoms. There are many types of atomizers, but only two are commonly used: flame and electrothermal atomizers. Flame atomizer Flame atomizers are widely used for a multitude of reasons including their simplicity, low cost, and long length of time that they have been utilized. Flame atomizers accept an aerosol from a nebulizer into a flame that has enough energy to both volatilize and atomize the sample. When this happens, the sample is dried, vaporized, atomized, and ionized. Within this category of atomizers, there are many subcategories determined by the chemical composition of the flame. The composition of the flame is often determined based on the sample being analyzed. The flame itself should meet several requirements including sufficient energy, a long length, non-turbulent, and safe. 1) Total consumption burner 2) The premixed burner 12
  • 13. 13
  • 14. 14
  • 15. Total consumption burner Premixed burner Advantage Representive sample reach flame Long path provide sensitivity Amount of sample in flame is large which enhance sensitivity Only small drops reach flame No explosive harzards. Quite operation & little tendancy to clog Disadvantage Short path leds to lower lower sensitivity Rate of sample introduce is low Larger droplets not entirely decomposed Possibility of explosion in mixing chamber 15
  • 16. Non flame atomizer : • The graphite furnace is an electro thermal atomizer system that can produce temperatures as high as 3,000°C. • The heated graphite furnace provides the thermal energy to break chemical bonds within the sample held in a graphite tube, and produce free ground state atoms. • The ground-state atoms are capable of absorbing energy, in the form of light, and are elevated to an excited state. • The amount of light energy absorbed increases as the concentration of the selected element increases. 16
  • 17. Monochromator: A monochromator is an optical device that transmits a narrow band of wavelengths of light or other radiation from a wider range of wavelengths. The atoms in the AAS instrument accept the energy of excitation and emit radiation. A desired band of lines can be isolated with a monochromator by passing a narrow band. The spectra through a monochromator can be shown by a curve. Detector A detector can convert light coming from a monochromator to a simplified electrical signal. Generally, we used a photomultiplier tube as a detector in the atomic absorption spectroscopy instrument. A detector can be tuned to respond by a specific wavelength or frequency. Recorder The recorder can receive electrical signals from the detector to convert them into a readable response. In atomic absorption spectroscopy instrumentation, today we used a computer system with suitable software for recoding signals coming from the detector. 17
  • 18. Interferences In Atomic Absorption Spectroscopy: Interference is a phenomenon that leads to change in intensity of analyte signal in spectroscopy. Interferences in AAS fall into two basic categories : 1. Non-Spectral Interference : Which affect the formation of analyte Atoms Matrix interference Chemical interference Ionization interference 2. Spectral Interferences : High light absorption due to presence of absorbing species Background absorption Continuum source Background Correction Others spectral interferences 18
  • 19. Non-spectral Interferences: Matrix interferences : When a sample is more viscous or has different surface tension than the standard it result in difference in sample uptake rate due to changes in nebulization efficiency. Such interferences are minimized by matching the matrix composition of standard and sample. 19
  • 20. Chemical Interferences • If a sample contains a species which forms a thermally stable compound with analyte that is not completely decomposed by the flame energy then chemical interferences exist. • Such interferences are minimized by using higher flame temp. • To provide higher dissociation energy. 20
  • 21. Ionization Interference • It is more common in hot flames. • The dissociation process doesn’t stop at formation of ground state atoms. Excess energy of the flame lead to excitation of ground state atoms to ionic state by loss of electrons thereby resulting in depletion of ground state atoms. • Ionization interference is eliminated by an excess of an element which is easily ionized thereby creating a large number of electrons in the flame & suppressing the ionization of the analyte. 21
  • 22. Spectral Interferences : • Atomic Spectral interferences are caused by presence of another absorption line or a molecular absorbance band close to the spectral line of element of interest. • Most of these interferences are due to molecular emission from oxides of other element is a sample. 22
  • 23. Background Absorption: • Absorption by the flame atomizer or electro thermal analyzer can cause serious problems in atomic absorption. • Rarely are there interferences from absorption of the analyte line by other atoms since the hollow cathode lines are so narrow. Molecular species can absorbs the radiation and cause radiation in atomic absorption measurements. • However, the total measured absorbance AT in atomic absorption is the sum of analyte absorbance AA plus the background absorbance AB. • AT=AA+AB • Background correction scheme attempt to measure AB in addition to AT and to obtain the true analyte absorbance by subtraction (AA=AT - AB) 23
  • 24. CONTINUUM SOURCE BACKGROUND CORRECTION : • A popular background correction scheme in commercial atomic absorption spectrometers is the continuum lamp technique. • Here a deuterium lamp and the analyte hollow cathode are directed through the atomizer at different times. The hollow cathode lamp measures the total absorbance AT while the deuterium lamp provides an estimates of the background absorbance AB. • The computer system or processing electronics calculates the difference and reports the background corrected absorbance. • This method has limitation for elements with lines in the visible range because the D2 lamp intensity becomes quite low in this region. 24
  • 25. ZEEMAN EFFECT BACKGROUND CORRECTION • Background correction with electro thermal atomizers can be done by means of the Zeeman effect. • Here a magnetic field splits normally degenerated spectral lines into components with different polarization characteristics. • Analyte and background absorption can be separated because of their different magnetic and polarization behaviors 25
  • 26. • The major limitations of flame AAS are as follows: • The sample introduction system, e.g. nebulizer/expansion chamber, which is used is inefficient and requires large volume of aqueous sample. • The residence time, i.e. the length of time that the atom is present in the flame, is limited due to the high burning velocity of the gases, thus leading to rather high detection limits. • An inability to analyze solid sample directly (solid requires dissolution prior to analysis) 26
  • 27. ADVANTAGES OF AAS : • It does not suffer from spectral interference, which occurs in flame emission spectroscopy. • It is independent on flame temperature. • By atomic absorption technique , traces of one element can easily be determined in presence of high concentration of other elements. • It has proved very successful in the analysis of bronze and copper alloys and in the determination of metals like platinum, gold etc. DISADVANTAGES OF AAS • This technique has not proved very successful for the estimation of elements like W, Si, Mo, Ti, and Al etc. because these elements give rise to oxides in the flame. • In aqueous solution, the predominant anion affects the signal to a negotiable degree. • A separate lamp for each elements to be determined is required. Attempts are being made to overcome this difficulty by using continuous source with a very high resolution Monochromator or alternatively to produce a line source. 27
  • 28. APPLICATION: • It is used in quantitative and qualitative analysis of different drug compounds. • Estimation of zinc in insulin preparation, oils, creams and in calamine, calcium in number of calcium salts, lead in calcium carbonate and also as impurity in number of chemical salts have been reported. • Atomic absorption spectroscopy is very widely used in metallurgy, alloys and in inorganic analysis. Almost all important metals have been analyzed by this method. • It is especially useful to analyze ionic metal elements in blood, saliva, urine samples like sodium, potassium, magnesium, calcium and other body fluids. • To detect heavy metals in herbal drugs and synthetic drugs. • To determine metal elements in the food industry. • To estimate Lead in petroleum products. 28