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Atomic absorption spectroscopy.pptx

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Atomic absorption spectroscopy.pptx

Instrumental Method of Analysis Unit 2 (3) Atomic absorption spectroscopy/AAS/
Atomic flame Photometry
(Part -1)
Introduction- Briefing
Atomic spectroscopy involved three major techniques- Atomic emission spectroscopy,
Atomic absorption spectroscopy, and Atomic fluorescence spectroscopy

Principle, Theory of atomic Absorption spectroscopy
Interferences
Instrumentation-
Type AAS
1. Single beam atomic absorption spectrophotometer
2. Double beam atomic absorption spectrophotometer

the light source/radiation source- that emits the spectrum of the element of inetrest
the atomization system/ absorption cell- in which atoms the sample are produced (flame, graphites furnance etc
the monochromator- for light dispersion
the detection system- which measures the light intensity and amplified the signal
A read out device- that show the reading after it has been processed
Working AAS instrument (B. chopper, C. Flame atomizer - There is two types of burners in common used
1. Total consumption burner
2. Premixed burner
D. Fuel/ oxidant
E. Monochromator- Prism, gratting
F. Detectors-Photomultiplier tube
G. Recorder
Difference between Atomic Absorption Spectroscopy and Atomic Emission Spectroscopy

Advantange and limitation
Applications

Instrumental Method of Analysis Unit 2 (3) Atomic absorption spectroscopy/AAS/
Atomic flame Photometry
(Part -1)
Introduction- Briefing
Atomic spectroscopy involved three major techniques- Atomic emission spectroscopy,
Atomic absorption spectroscopy, and Atomic fluorescence spectroscopy

Principle, Theory of atomic Absorption spectroscopy
Interferences
Instrumentation-
Type AAS
1. Single beam atomic absorption spectrophotometer
2. Double beam atomic absorption spectrophotometer

the light source/radiation source- that emits the spectrum of the element of inetrest
the atomization system/ absorption cell- in which atoms the sample are produced (flame, graphites furnance etc
the monochromator- for light dispersion
the detection system- which measures the light intensity and amplified the signal
A read out device- that show the reading after it has been processed
Working AAS instrument (B. chopper, C. Flame atomizer - There is two types of burners in common used
1. Total consumption burner
2. Premixed burner
D. Fuel/ oxidant
E. Monochromator- Prism, gratting
F. Detectors-Photomultiplier tube
G. Recorder
Difference between Atomic Absorption Spectroscopy and Atomic Emission Spectroscopy

Advantange and limitation
Applications

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Atomic absorption spectroscopy.pptx

  1. 1. Mrs Vandana Sharma Assistant Proffesor
  2. 2.  Principle  Interferences  Instrumentation  Applications
  3. 3.  Describe the principle, instrumentation and applications of following:  AAS  Nepheloturbidometry.- 10  Short note on- various interference in AAS. How they are corrected.-8  Explain the difference between Atomic absorption spectroscopy and flame photometry. 8  Discuss various types of interferences involved in atomic absorption spectroscopy. 8  What is the principle of AAS and explain briefly its instrumentation. 8  Explain the theory, applications and instrumentation of Atomic absorption spectroscopy.-16
  4. 4.  Allan walsh in 1955- Introduced AAS  Used for quantitative determination of trace metals in liquids of completely of different nature for example  Ca+2, Mg+2, Na+, and K+ = ions in blood serum  Ni+2 ions = in edible oils  Cu+ ions = in beer sample  Pb+2 ions = in gasoline (petrol)  Se+4 ions= in Urine etc  Ca+2, Mg+2, Na+ ions = in hard water  sodium and potassium, = in alkali drinking water  calcium, = in our bones  It can measure from ppm to ppb.  These are units indicating concentration, similar to percent.  In ppm- 'm' stand for million and ppb- 'b' stand for billion.  1% means 1/100, ppm means 1/million and ppb means 1/billion. To illustrate simply, 1% would mean one person in 100 people,  while 1 ppm would be one person in one million people.
  5. 5.  AAS accomplished either  by using a flame, whereby the sample solution is aspirated directly into a flame or  by using an electrothermal device, where by the sample solution is first evaporated and then ignited on a hot surface.  Advantage-  AAS facilitates the estimation of a particular element in the presence of many other element from the rest Means  There is no necessity to separate the test element from the rest, thereby not only saving a great deal of time but also eliminating the possibility of various sources of error incurred by these process.  In addition AAS may be used for estimation of both aqueous and nonaqueous solutions
  6. 6.  Atomic absorption spectroscopy involves the study of the absorption of radiation by neutral atom in gaseous state.  For this the sample is first converted into atomic vapour and then absorption of atomic vapour is measured at the selected wavelength which is characteristic of each element under study.  For quantitative studies  the measured absorption ά the concentration of element in vapour state.  Since, the techniques involves spraying of a solution into a flame, it is also called atomic flame Photometry  This technique appears similar to flame photometry.  Difference between AAS and flame photometry- AAS is based on the absorption from the flame rather than emission into the flame.  In the technique of atomic absorption, the solution of sample in a suitable solvent is--- sprayed in a form of fine mist--- into a flame  Due to high temperature of flame, the element to be determined is reduced to element state in a vapour form.
  7. 7.  A suitable source of radiation ---is allowed to fall and pass through flame to the detector.  Absorption of energy occurs by the vapour phase of element in flame and remainder is transmitted to the detector.  The flame not only serves to convert element into its gaseous atomic form but also act as a cell in usual type of spectrophotometer.  In the absorption process by the gaseous atomic form, a series of well defined lines occurs due to electronic transition of outer most shell electrons of the element.  In the absorption process the number of atoms capable of absorbing any transmitted light of characteristic wavelength of ά [concentration of atoms in flame X path length in flame].  In most determinations, concentration of sample solution, wavelength of radiation used for absorption studies, the temperature and height of flame is so adjusted to give accurate and quantitative results
  8. 8.  Atomic emission spectroscopy  Atomic absorption spectroscopy  Atomic fluorescence spectroscopy
  9. 9.  The basic principles of AAS can be expressed as follows.  Firstly, all atoms or ions can absorb light at specific, unique wavelengths.  When a sample containing copper (Cu) and nickel (Ni), for example, is exposed to light at the characteristic wavelength of Cu, then only the Cu atoms or ions will absorb this light.  The amount of light absorbed at this wavelength ά to the concentration of the absorbing ions or atoms.  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.
  10. 10.  The amount of light absorbed can be determined as:  Total amount of light absorbed (at ‫ט‬ ) = (Πe2/mc) * Nf  ‫=ט‬ Frequency of the light path  e= Charge on the electron  m= Mass of the electron  N= Total number of atoms which can absorb at ‫ט‬  f= Ability for each atom to absorb at ‫ט‬  Π, e, m and c= Constant K  Total amount of light absorbed= K x N x f
  11. 11.  The process of atomic absorption is illustrated in next slide  The ground state atom absorbs light energy of specific wavelength ---as it enters the excited state  As the number of atoms in the light path increases,--- the amount of light absorbed also increases.  By measuring the amount of light absorbed, ----a quantitative determination of the amount of analyte can be made.  Use of special light sources and careful selection of wavelength - --allow the specific determination of individual elements.  When the solution of metallic salt is sprayed on the flame, ---the fine droplets are formed.  Due to the thermal energy of flame, ---the solvent in the droplets evaporate,---- leaving a fine residue, ----which are converted into neutral atoms.  These neutral atoms absorb radiation of specific wavelength, emitted by hollow cathode lamp (HCL)  Very important note-This lamp is filled with the vapour of
  12. 12. element, which gives specific wavelength of radiation.  For the determination of every element , hallow cathode lamp is selected, which contains vapour of the element to be analysed.  Although this appears to be demerit of AAS, specificity can be achieved only by the use of HCL  The intensity of light absorbed by neutral atom ά to the concentration obeys Beer,s law over a wide concentration range.  The intensity of radiation absorbed by neutral atom ---- is measured using photometric detectors ( photo tube or photomultiplier tube)  Very important note--In AAS, the flame temperature is not critical, since ----the thermal energy of flame is used just to--- atomise the sample solution into fine droplets,---- to form a fine residue and later to neutral atoms.  Very important Note- Excitation of neutral atoms is brought about only by radiation from hollow cathode lamp and not by the thermal energy of the flame.
  13. 13. Additional information to getting more clear view
  14. 14. a
  15. 15.  An atomic absorption spectrometer uses these basic principles and applies them in practical quantitative analysis.  A typical atomic absorption spectrometer consists of four main components:  the light source/radiation source- that emits the spectrum of the element of inetrest  the atomization system/ absorption cell- in which atoms the sample are produced (flame, graphites furnance etc  the monochromator- for light dispersion  the detection system- which measures the light intensity and amplified the signal  A read out device- that show the reading after it has been processed  Type AAS  1. Single beam atomic absorption spectrophotometer  2. Double beam atomic absorption spectrophotometer
  16. 16. 1. Radiation/light source A. Hollow cathode lamp-For most elements, the hollow cathode lamp is satisfactory source for atomic absorption.  In a few cases, however, the quality of analysis is impaired by limitations of hollow cathode lamp.  Limitation- The primary cases involve the more volatile elements where low intensity and short lamp life are a problem. B. Electrode –less discharge lamp -The Atomic absorption determination of these elements can be improved with the use of electrode –less discharge lamp which is a brighter and more stable source.  Construction of Hollow Cathode lamp (HCL)  Consists of a hollow cup containing the element to be determined (in this case the element is sodium).  The anode - tungsten wire- containg (+) charge  The 2 electrodes are housed in a tube contaning an inert gas.  The lamp window is of quartz, silica, or glass. The exact material is used depends upon the wavelength to be determine
  17. 17. When a potential is applied between the two electrodes a current in the milliampere range arises the inert gas charged (+) at the anode (tungsten wire) The charged gas (+) is attracted at the high velocity to the cathode ( - ) The impact with the cathode vaporise some of the sodium atoms The vaporised some sodium atom are excited and return to the ground state give rise to the Sodium emission spectrum. Working
  18. 18. Tungsten wire And Eg- sodium-element to be determine Lamp window eg. Quartz, silica or glass (+) (-) The impact with the cathode vaporise some of the sodium atoms The vaporised some sodium atom are excited and return to the ground state give rise to the Sodium emission spectrum.
  19. 19. ( - ) ( + )
  20. 20.  B. Electrode –less discharge lamp  In a few cases, however, the quality of analysis is impaired by limitations of hollow cathode lamp.  Limitation- The primary cases involve the more volatile elements where low intensity and short lamp life are a problem.  The Atomic absorption determination of these elements can be improved with the use of electrode –less discharge lamp . This lamp is a brighter and more stable source.
  21. 21. A small amount of the metal or salt of the element for which the source is to be used---is sealed inside a quartz bulb, which is placed inside a small, self- contained RF generator or “driver” When power is applied (1)to the driver An RF field (2) is created The coupled energy will vaporise and excite the atoms inside the bulb Causing them to emit their characteristic spectrum. Electrode-less Discharge lamp: Construction Working
  22. 22. Electrode-less Discharge lamp (Radio frequency generator coil) Note-An accessory power supply is required to operate and EDL NOTE-“RF generator” radio frequency generators are used for testing components etc
  23. 23. 2. Chopper  A rotating wheel, Known as chopper, is interposed or set or situated b/w the hollow cathode lamp and the flame.  The rotating wheel is interposed to break the steady light from the lamp into an intermittent or discontinuously or pulsating light  This gives a pulsating current in the photocell.  Note- There is also a steady current is caused by light which is emitted by a flame.  But only the pulsating (or alternating) current is amplified and recorded and  Advantage of chopper-thus, the absorption of light will be measured without interference from the light emitted by the flame itself
  24. 24. 3. Flame atomizers  Flame is used for converting the liquid sample into the gaseous state and----- also converting the molecular entities into an atomic vapour.  There is two types of burners in common used  Total consumption burner  Premixed burner –  Premixed burner- The sample is nebulized and mixed with the fuel and oxidant prior to introduction into the flame, with the used of a series of buffles  Sample is drawn from the sample container via vacuum created by rushing the fuel and oxidant (Aspiration)  Advantage of is the uniformity of flame produced.  Uses-Premixed burner is very suitable for the atomic absorption studies of metals of 1A, 1B, and IIB group together with Ga, In, Ti, Pb, Te, Mn, Ni, and Pd.
  25. 25. Sample or 1 2 3 4
  26. 26.  In this burner, a mixture of the sample (liquid) and premixed gases (C2H2 +O2) is allowed to enter the base.  From the base, the gases enter a region, from where unburn hydrocarbon gaseous mixture [premixed gases (C2H2 +O2)] and liquid droplets are allowed to enter a region which is of free heating and about 1mm in thickness.  In this region, the liquid is evaporated leaving a residue.  Heating in this region is done by the heat obtained by conduction and convection and by diffusion of radicals into it which initiate the combustion.  After this the sample residue is burnt to produce atoms  Production of atoms is initiated in one region and is completed in another region
  27. 27. Total consumption burner  It consist of inlets for fuel and oxidants at the base of the apparatus  Sample is also kept at the base to be aspirated.  Acetylene -commonly used as fuel and air -used oxidant are forced, under pressure, into the flame  The sample is drawn into the flame by aspiration by vacuum created because of movement of fuel and oxidant.  The aspirated sample reaches-- the burner head with a nebulizing effect.  This sample is mixed with fuels and oxidant at the base of the flame.  Advantage over other is the entire consumption of sample,  Limitation  The resulting flame is turbulent and not homogeneous Acetylene air
  28. 28. 5. Monochromator-  In atomic absorption measurement – the most common monochromators are Prism and gratings  Function of monochromator is to select a given absorbing line from spectral lines emitted from the Hollow cathode lamp Collimating mirror Focusing mirror gratings Entrance slit Exit slit
  29. 29. 6. Detectors  Photomultiplier tube-  For AAS – most suitable detector  It has good stability if used with a stable power supply  In photomultiplier tubes- contains a photocathode, a series of electrodes called dynodes, and an anode.  The photocathode is fixed to the power supply terminal
  30. 30. Construction and working Photomultiplier tube In a vacuum tube, A primary Photo- cathode is fixed which receives radiation form the sample 8 to 10 dynodes are fixed Each with increasing potential about 90V. Near the last dynode is fixed an anode/ electron collector electrode A high voltage is maintained between the cathode and anode The light received by cathode releases electrons which through series of dynodes produce more electrons (+) (-) e- Vacuum (Coming from sample) (Electron collector electrode)
  31. 31. 7. 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.
  32. 32. Difference between AAS and AES
  33. 33.  Advantages  Today, the atomic absorption spectroscopy technique is the most powerful tool in analytical chemistry, forensic science, environmental analysis, and food industries. It is popular for analysts due to several advantages.  The most important advantage is the speed of analysis. It can analyze various samples within a day.  Secondly, it is possible to determine all elements at trace concentration.  Thirdly, it is not always essential to separate the element before analysis because AAS can be used to determine one element in presence of another.  The atomic absorption spectroscopy principle or instrumentation can be used to analyze sixty-seven metals and several nonmetals such as phosphorus and boron
  34. 34. Advantages Limitations Low cost per analysis Cannot detect non-metals Easy to operate New equipment is quite expensive High sensitivity (up to ppb detection) More geared towards analysis of liquids High accuracy Sample is destroyed Mostly free from inter- element interference Wide applications across many industries
  35. 35. 1. AAS is widely used in metallurgy, alloy and in inorganic analysis  Almost all important metals have been analysed by this method  It is an ideal method for analysis of many ores, minerals and alloys 2. Biological analysis- A number of elements present in biological sample can be analyzed by atomic absorption method. These include estimation of Sodium, potassium, lead, zinc, mercury, cadmium, magnesium and iron. 3. Pharmaceutical analysis : estimation of zinc in insulin preparations, oils, creams and in calamine, calcium in number of calcium salts, lead in calcium carbonate and also as impurities in number of chemical salt have been reported 4. Sodium, potassium, and calcium in saline and ringer solutions are estimated by this method 5. In petroleum industry, metallic impurities in petrol, lubricating oils have been determined
  36. 36. 6. Analysis of ash for determining the contents of sodium, potassium, magnesium, calcium and iron is carried out in boiler deposits 7. In cement industry, estimation of sodium potassium, calcium, magnesium is carried out to determine the quality of cement 8. AAS find various applications in various industries like agriculture, soil, forestry, oceanography, fertilizer etc 9. Atomic absorption spectroscopy is used in the assay of (a) Intraperitonial dialysis fluid (for Calcium, magnesium) (b) Activated charcoal (for Zinc) (c ) Cisplatin (for silver) Brief
  37. 37.  APPLICATIONS OF ATOMIC ABSORPTION SPECTROSCOPY  Atomic absorption is the most widely used technique for the determination of metals at trace and ultra-trace levels in a solution.  It is used to analyze metals in biological fluids such as blood, hair, and urine.  Atomic absorption is used to find out the number of various metals in the environment.  It is used in pharmaceutical industries for quantitative analysis of metals in samples for example, in multivitamins tablets.  Atomic absorption is used to find the concentration of metals (Ca, Mg, Fe, Si, Al, ) analysis of water.  Atomic absorption is used to determine the amount of catalyst.  It is used for the analysis of crude oil, and petroleum.  Atomic absorption is used for the analysis of soil samples. For example, minerals inland before cultivation are tested to get maximum yields.  It is used for trace element analysis of cosmetics.  Atomic absorption is used to find the amount of metals such as gold in rocks.  It is used to determine the amount of various metals (Mn, Fe, Cu, Zn) in foodstuff.  It is used for the analysis of additives (Ba, Ca, Na, Li, Mg) in lubricating oils and grease.

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