Atomic absorption spectroscopy (AAS).pptx

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

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.
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
A typical atomic absorption spectrometer consists of four main components:
Atomization
Light source,
Atomization system,
Monochromator &
Detection system
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

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. P rinciple 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, M onochromator & 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) E lectodeless 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 & A r ) 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

10. Electodeless discharge lamp 10

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 a re 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 . Total consumption burner The premixed burner 12

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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. I nterferences 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