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Atomic_Absorption_Emission.ppt
Atomic absorption spectroscopy is an analytical technique that measures the concentration of elements by using the absorption of light by ground state atoms. It works by vaporizing samples using a flame or furnace and passing light from a hollow cathode lamp of the element of interest through the vapor. The amount of light absorbed is measured and the concentration is determined using a calibration curve. Atomic emission spectroscopy similarly uses high temperatures to excite sample atoms, which then emit light of element-specific wavelengths that is measured to determine concentration. Both techniques use similar instrumentation including a light source, atomizer, monochromator, and detector.
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Atomic_Absorption_Emission.ppt
- 1. ATOMIC SPECROSCOPY (AS) Atomic AbsorptionSpectroscopy Flame Atomic Emission Spectroscopy ICP Atomic Emission Spectroscopy
- 2. 1 BASIC PRINCIPLE ATOMIC ABSORPTIONSPECTROSCOPY (AAS) is an analytical technique that measures the concentrations of elements. It makes use of the absorption of light by these elements in order to measure their concentration .
- 3. - Atomic-absorption spectroscopyquantifies the absorption of ground state atoms in the gaseous state . - The atoms absorb ultraviolet or visible light and make transitions to higher electronic energy levels . The analyte concentration is determined from the amount of absorption.
- 4. - Concentration measurementsare usually determined from a working curve after calibrating the instrument with standards of known concentration. - Atomic absorption is a very common technique for detecting metals and metalloids in environmental samples.
- 5. Elements detectable byatomic absorption are highlighted in pink in this periodic table
- 6. The Atomic AbsorptionSpectrometer • Atomic absorption spectrometers have 4 principal components 1 - A light source ( usually a hollow cathode lamp ) 2 – An atom cell ( atomizer ) 3 - A monochromator 4 - A detector , and read out device .
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- 9. 1 – LightSource • The light source is usually a hollow cathode lamp of the element that is being measured . It contains a tungsten anode and a hollow cylindrical cathode made of the element to be determined. These are sealed in a glass tube filled with an inert gas (neon or argon ) . Each element has its own unique lamp which must be used for that analysis .
- 10. Hollow cathode lamp(HCL)
- 11. How it works Applyinga potential difference between the anode and the cathode leads to the ionization of some gas atoms . These gaseous ions bombard the cathode and eject metal atoms from the cathode in a process called sputtering. Some sputtered atoms are in excited states and emit radiation characteristic of the metal as they fall back to the ground state .
- 12. Scheme of ahollow cathode lamp
- 13. The shape ofthe cathode which is hollow cylindrical concentrates the emitted radiation into a beam which passes through a quartz window all the way to the vaporized sample. Since atoms of different elements absorb characteristic wavelengths of light. Analyzing a sample to see if it contains a particular element means using light from that element .
- 14. For example withlead, a lamp containing lead emits light from excited lead atoms that produce the right mix of wavelengths to be absorbed by any lead atoms from the sample. A beam of the electromagnetic radiation emitted from excited lead atoms is passed through the vaporized sample. Some of the radiation is absorbed by the lead atoms in the sample. The greater the number of atoms there is in the vapor , the more radiation is absorbed .
- 15. 2 – Atomizer Elementsto be analyzed needs to be in atomic sate Atomization is separation of particles into individual molecules and breaking molecules into atoms .This is done by exposing the analyte to high temperatures in a flame or graphite furnace .
- 16. The role ofthe atom cell is to primarily dissolvate a liquid sample and then the solid particles are vaporized into their free gaseous ground state form . In this form atoms will be available to absorb radiation emitted from the light source and thus generate a measurable signal proportional to concentration . There are two types of atomization : Flame and Graphite furnace atomization .
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- 18. Flame • Flame AAcan only analyze solutions , where it uses a slot type burner to increase the path length, and therefore to increase the total absorbance . Sample solutions are usually introduced into a nebuliser by being sucked up by a capillary tube .In the nebuliser the sample is dispersed into tiny droplets , which can be readily broken down in the flame.
- 19. Various flame atomizationtechniques
- 20. Types of FlamesUsed in Atomic Spectroscopy
- 21. Processes that takeplace in flame
- 22. The Atomic AbsorptionSpectrometer Sample Introduction System Nebuliser Capillary Solution
- 23. • The finemist of droplets is mixed with fuel (acetylene ) , and oxidant ( nitrous oxide) and burned. The flame temperature is important because it influences the distribution of atoms. It can be manipulated by oxidant and fuel ratio.
- 24. 3- Monochromators This isa very important part in an AA spectrometer. It is used to separate out all of the thousands of lines. Without a good monochromator, detection limits are severely compromised. A monochromator is used to select the specific wavelength of light which is absorbed by the sample, and to exclude other wavelengths. The selection of the specific light allows the determination of the selected element in the presence of others.
- 25. 4 - Detectorand Read out Device The light selected by the monochromator is directed onto a detector that is typically a photomultiplier tube , whose function is to convert the light signal into an electrical signal proportional to the light intensity. The processing of electrical signal is fulfilled by a signal amplifier . The signal could be displayed for readout , or further fed into a data station for printout by the requested format.
- 26. Calibration Curve A calibrationcurve is used to determine the unknown concentration of an element in a solution. The instrument is calibrated using several solutions of known concentrations. The absorbance of each known solution is measured and then a calibration curve of concentration vs absorbance is plotted. The sample solution is fed into the instrument, and the absorbance of the element in this solution is measured .The unknown concentration of the element is then calculated from the calibration curve
- 27. Calibration Curve A 1.0- b 0.9 - S 0.8 - . o 0.7 - . r 0.6 - . b 0.5 - . . a 0.4 - . n 0.3 - . c 0.2 - e 0.1 - 10 20 30 40 50 60 70 80 90 100 Concentration ( g/ml )
- 28. Determining concentration from CalibrationCurve A 1.0 - absorbance measured b 0.9 - S 0.8 - . o 0.7 - . r 0.6 - . b 0.5 - . . a 0.4 - . n 0.3 - . concentration calculated c 0.2 - e 0.1 - 10 20 30 40 50 60 70 80 90 100 Concentration ( mg/l )
- 29. A life-saving technique •Japan: From 1932 to 1968, AAS was used to identify the reason why over 3,000 residents who lives near the Minimata Bay started showing neurogical problems and pregnant women starts giving birth to impaired children. Scientist starts taking samples and performing AAS process; AAS results shows a very high concentration of mercury in their blood. This result on stopping the company, Chisso corporation who dumped approximately 27 tones of mercury in the bay.
- 30. Interferences The concentration ofthe analyte element is considered to be proportional to the ground state atom population in the flame ,any factor that affects the ground state atom population can be classified as an interference . Factors that may affect the ability of the instrument to read this parameter can also be classified as an interference .
- 31. The different interferencesthat are encountered in atomic absorption spectroscopy are : - Absorption of Source Radiation : Element other than the one of interest may absorb the wavelength being used. - Ionization Interference : the formation of ions rather than atoms causes lower absorption of radiation .This problem is overcome by adding ionization suppressors. - Self Absorption : the atoms of the same kind that are absorbing radiation will absorb more at the center of the line than at the wings and thus resulting in the change of shape of the line as well as its intensity .
- 32. - Back groundAbsorption of Source Radiation : This is caused by the presence of a particle from incomplete atomization .This problem is overcome by increasing the flame temperature . - Transport Interference : Rate of aspiration, nebulization, or transport of the sample ( e g viscosity, surface tension, vapor pressure , and density ) .
- 33. 2 Atomic Emission Spectroscopy Atomic emissionspectroscopy is also an analytical technique that is used to measure the concentrations of elements in samples . It uses quantitative measurement of the emission from excited atoms to determine analyte concentration .
- 34. The analyte atomsare promoted to a higher energy level by the sufficient energy that is provided by the high temperature of the atomization sources . The excited atoms decay back to lower levels by emitting light . Emissions are passed through monochromators or filters prior to detection by photomultiplier tubes.
- 35. The instrumentation ofatomic emission spectroscopy is the same as that of atomic absorption ,but without the presence of a radiation source . In atomic Emission the sample is atomized and the analyte atoms are excited to higher energy levels all in the atomizer .
- 36. Schematic Diagram ofan Atomic Emission spectrometer
- 37. The source ofenergy in Atomic Emission could be a flame like the one used in atomic absorption ,or an inductively coupled plasma ( ICP ) . - The flame ( 1700 – 3150 oC ) is most useful for elements with relatively low excitation energies like sodium potassium and calcium . - The ICP ( 6000 – 8000 oC) has a very high temperature and is useful for elements of high excitation energies .
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- 39. Similar to anatomic absorption spectrometer ,the monochromator is simply a wavelength selector that separates all different wave lengths and select the desired one . The selected wave length is passed on to a detector that converts the light signal into an electrical signal .
- 40. Comparison Between AtomicAbsorption and Emission Spectroscopy Absorption - Measure trace metal concentrations in complex matrices . - Atomic absorption depends upon the number of ground state atoms . Emission - Measure trace metal concentrations in complex matrices . - Atomic emission depends upon the number of excited atoms .
- 41. 3 AAS APPLICATIONS The aremany applications for atomic absorption: - Clinical analysis : Analyzing metals in biological fluids such as blood and urine. - Environmental analysis : Monitoring our environment – e g finding out the levels of various elements in rivers, seawater, drinking water, air, and petrol.
- 42. - Pharmaceuticals. - Insome 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.
- 43. - Industry :Many raw materials are examined and AAS is widely used to check that the major elements are present and that toxic impurities are lower than specified – e g in concrete, where calcium is a major constituent, the lead level should be low because it is toxic.
- 44. - Mining: Byusing AAS the amount of metals such as gold in rocks can be determined to see whether it is worth mining the rocks to extract the gold . - Trace elements in food analysis - Trace element analysis of cosmetics - Trace element analysis of hair
- 45. Advantages of AAS •very sensitive: can detect concentrations as small as a few parts to g / Litre (parts per million) • generally very specific: set wavelength is strongly absorbed by the particular metal ion being analysed (and not by other components)