ATOMIC ABSORPTION SPECTROSCOPY.pptx

Atomic absorption spectroscopy, introduction, principle, instrumentation, interferences and application.

1. ATOMIC ABSORPTION SPECTROSCOPY Presented By – SHIVAM SHARMA M Pharm (Pharmaceutical Chemistry) Department of Pharmaceutical sciences GurukulA kangri university Haridwar uk.

2. CONTENTS INTRODUCTION HISTORY OF AAS PRINCIPLE INSTRUMENTATION INTERFERENCES APPLICATIONS

3. INTRODUCTION Atomic absorption spectroscopy is a technique for measuring the concentrations of metallic elements in different materials, or we can say process of detecting metals and metalloids in sample. It is an analytical technique that measures the concentration of an element by measuring the amount of light that is absorbed at a characteristic wavelength when it passes through cloud of atoms. As the no. of atoms in the light path inc reases , the amount of light absorbed increases. It is a very simple and reliable to use. AAS is also referred to as atomic absorption spectrometry . The difference between spectroscopy and spectrometry is that spectroscopy is the study of how energy and materials interact, while spectrometry refers to how you apply this as a measuring technique.

4. HISTORY OF AAS The first atomic absorption spectrometer was built by CSIRO ( The Commonwealth Scientific and Industrial Research Organisation is an Australian Government agency responsible for scientific research) . As a phenomenon, atomic absorption spectrometry was first discovered in 1802, when the English scientist William Hyde Wollaston observed and described dark lines in the sun’s spectrum , for which further studies were done for mapping up these lines .

5. The elements highlighted in pink colour are only detected by Atomic absorption spectroscopy It is a highly sensitive method of analysis. In a given material, it can measure parts per billion of a gram. In applications such as medicine and pharmaceuticals, AAS has helped revolutionizes practices, detecting things such as trace toxins. In some sectors, this method has been able to detect elements which people were previously unaware existed in certain material, such as cobalt and molybdenum in soil.

6. PRINCIPLE The technique uses basically the principle that, free atoms (in gas) generated in an atomizer can absorb radiation at specific frequency. More the absorption = Maximum concentration of metals . Atomic-absorption spectroscopy quantifies 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 . Concentration measurements are 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.

7. INSTRUMENTATION Parts of Atomic Absorption Spectrophotometer : Light source Nebulizer Atomizer Monochromator Detector and amplifier Read out system

8. LIGHT SOURCE Hollow cathode lamp are the most common radiation source in AAS. It contains a tungsten anode and a hollow cylindrical cathode. These are sealed in a glass tube filled with an inert gas. (mainly neon or argon) Each elements has its own unique lamp which must be used for that analysis

9. 2. NEBULIZER Nebulizer suck up liquid samples at controlled rate. Create a fine aerosol spray for introduction into the flame. Mix the aerosol, fuel and oxidant thoroughly for introduction into flame. ATOMIZER Elements to be analyzed needs to in atomic state and this is done atomizer. Atomization is separation of particles into individual molecules and breaking molecules into atoms. This is done by exposing the analyte to high temperature in a flame or graphite furnace. The atomizers most commonly used nowadays are (spectroscopic) flames and electrothermal (graphite tube) atomizers.

10. MONOCHROMATOR This is very important part in an AAS , mainly prism is used . It is used to separate out all of the thousand of lines. A monochromator is used to select the specific wavelength of light which is absorbed by the sample and to remove other wavelengths. The selection of the specific light allows the determination of the selected element in the presence of others. 5. DETECTOR AND AMPLIFIER The light selected by the monochromator is directed onto a detector whose function is convert the light signal into an electrical signal. Photomultiplier tube detector is mainly used.

11. The processing of electrical signal is fulfilled by a signal amplifier. The amplified signal is then displayed on read out system or fed into a data station for printout by the requested format. 6. CALIBRATION CURVE A calibration curve is used to determine the unknown concentration of an element in a sample. The instrument is calibrated using several solutions of known concentrations. The absorbance of each known solution is measured & then a calibration curve of concentrations vs absorbance is plotted. The sample solution is fed into instrument & the absorbance of the element in the solution is measured. The unknown concentration of element is then calculated from the calibration curve.

12. 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. Spectral Interferences - affect the formation of analyte items. 2. Non Spectral Interferences : - high light absorption due to presence of absorbing species Matrix interference Chemical interference Ionization interference

13. 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. 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. 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.

14. 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. Background Absorption: Background Absorption Extends over a broad wavelength band. It is referred to as molecular absorption or non specific absorption. Background absorption is caused by light absorption due to un vaporized solvents droplets in flame. The absorption and scattering of radiation due to matrix interference give rise to sample background which becomes a problem at wavelength below 350nm.

15. Graph for determination of tin, iron, cadmium

16. Determination of small amount of metals (lead, mercury, calcium, magnesium) . AAS is widely used in metallurgy, alloys and in inorganic analysis, water analysis , determining lead in petrol . Biochemical Analysis: A number of elements present in biological samples can be analysed by AAS. These include estimated of sodium, calcium, potassium, zinc, iron, lead, mercury, etc. Pharmaceutical Analysis: Estimation of zinc in insulin preparation, calcium in calcium salt is done by using AAS. Sodium, potassium, calcium in saline and ringer solution are estimated by AAS. Analysis of ash for determining the content of sodium, potassium, calcium, magnesium and iron is done by AAS. Atomic absorption spectroscopy is used in assay of a) Intraperitoneal dialysis of fluid for calcium & magnesium. b) Activated charcoal for zinc. APPLICATIONS

17. Pharmaceutical analysis Instrumental methods Volume II by Dr. A.V. Kasture , Dr. S.G. Wadodkar , Nirali prakashan page no. 23.9 - 23.12 Instrumental methods of Chemical analysis by G.R. Chatwal, S.K. Anand, Himalaya publishing house, fifth edition page no. 2.340 - 2.360 References:

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