Flame emission spectroscopy and atomic absorption spectroscopy ppt

spectroscopy

1. Flame Emission Spectroscopy And Atomic Absorption Spectroscopy Presented By: Facilitated To: Sachin.J.Gaddimath Dr. B.S.Kittur M.Pharm 1 st year HOD & PROFESSOR Dept. of Pharmaceutics Dept. of ph. Chemistry HSKCOP, BAGALKOT HSKCOP, BAGALKOT

2. Contents Flame Emission Spectroscopy and Atomic Absorption Spectroscopy: Principle Instrumentation Interferences Applications

3. Principle:

4. Desolvation: The metal particles in the flame are dehydrated by the flame and hence the solvent is evaporated. Vaporisation : The metal particles in the flame are dehydrated. This also led to the evaporation of the solvent. Atomisation : Reduction of metal ions in the solvent to metal atoms by the flame heat. Excitation : The electrostatic force of attraction between the electrons and nucleus of the atom helps them to absorb a particular amount of energy. The atoms then jump to the exited energy state. Emission process : Since the higher energy state is unstable the atoms jump back to the stable low energy state with the emission of energy in the form of radiation of characteristics wavelength, which is measured by the photo detector

5. Instrumentation:

6. The basic components of Flame Emission Spectroscopy are: Burners Atomiser Monochromators Detector Burners: 1.The flame should have ability to evaporate the liquid droplets from the sample solution in the formation of solid residue. 2. The flame should decompose the compounds in the solid residue resulting in the formation of atoms. 3. The flame must have the capacity to excite the atoms formed and cause them to emit radiant energy

7. FLAMES IN FES Name of the element emitted Wavelength range(nm) Colour observed in the flame Potassium(K) 766 Violet Lithium(Li) 670 Red Calcium(Ca) 622 Orange Sodium(Na) 589 Yellow Barium( Ba ) 554 Lime green

8. Types of burners: 1. Mecker burner. 2. Total consumption burner. 3. Laminar flow burner. 4. Lundergraph burner. 5. Shielded burner. 6. Nitrous oxide- Acytelene flame.

9. Mecker burner: 1. This burner employed natural gas and oxygen. 2. Produces relatively low temperature and low excitation energies. 3. These are best used for alkali metals only.

10. Total consumption burner: 1. In this burner the fuel and oxidant used are hydrogen and oxygen gas. 2.In this sample, solution is aspirated through a capillary by the high pressure. the fuel and oxidant are burnt at the tip of burner. 3.The name “total consumption burner” is used becoz all the sample that enters the capillary will enter into flame of the droplet size.

11. CONSUMPTION BURNER Advantage: This design is very simple and the whole/entire sample is consumed by this process. Disadvantage: Uniform & homogenous flame is not obtained. Since the droplet size vary, leading to fluctuations in the flame intensity .

12. Laminar flow burner: In this type of burner, aspirated sample, fuel and oxidant are thoroughly mixed before reaching the burner opening and then entering the flame. Important feature of this is that only a small portion (about 5%) of the sample reaches the flame in the form of small droplets and is easily decompose.

13. Advantages: Burner is non-turbulent, noiseless, stable. Easy decomposition which leads to high atomisation. It can handle the solution up to several % without clogging. Disadvantages: When it contains 2 solvents, more volume will evaporate and lesser will remain undissociated. Monochromators and filters: In simple FES, monochromators is the prism. QUARTZ is the material most commonly used for making prisms becoz quartz is transparent over entire region.

14. Filters: It is made up of such material which is transparent over a narrow spectral range. When a filter is kept between flame detector, the radiation of the desired wavelength from the flame will be entering the detector and be measured. The remaining undesired wavelength will be absorbed by the filter and not measured. In FES, the wavelength as well as intensity of radiation emitted by the element has to be monitored. Hence a filter or monochromator is used.   DETECTORS: Photovoltic cell Phototubes Photomultiplier tubes

15. Applications: FES has found wide application in agricultural and environmental analysis, industrial analysis of ferrous metals and alloys as well as glasses, ceramic materials, and clinical analysis of body fluids. FES can be easily automated to handle a large number of samples. Array detectors interfaced to a microcomputer system permit simultaneous analyses of several elements in a single sample. They are also used to determine the metals present in chemicals, soil, cements, plant materials, water, air pollutants. Used in clinical laboratory to determine concentrations of sodium and potassium in biological fluids like serum, urine.

16. INTERFERENCES: Matrix Interference Chemical Interference Ionization Interference Spectral Interference Matrix Interference: When a sample is more viscous or has different surface tension than the standard, it can result in differences in sample uptake rate due to changes in nebulisation efficiency. Such interferences are minimized by matching as closely as possible the matrix composition of standard sample.

17. Chemical interference: If a sample contains a species which forms a thermally stable compound with the analyte that is not completely decomposed by the energy available in the flame then chemical interference exists. Refractory elements(Ti, W, Mo and Al) may combine with oxygen to form thermally stable oxides. Analysis of such elements can be carried out at higher flame temperatures using nitrous oxide- acetylene flame instead of air acetylene to provide higher dissociation energy. Alternately an excess of another element or compound can be added e.g Ca in presence of phosphate produces stable calcium phosphate which reduces absorption due to Ca ion. If an excess of lanthanum is added it forms a thermally stable compound with phosphate and calcium absorption is not affected.

18. Ionization Interference: It is more common in hot flames. The dissociation process does not stop at formation of ground state atoms. Excess energy of flame can lead to excitation of ground state atoms to ionic state by loss of electrons thereby resulting in depletion of ground state atoms. In cooler flames such interference is encountered with easily ionized elements such as alkali metals, alkaline earths. Salts of such elements as K, RB, and Cs are commonly used as ionization suppressants.

19. Atomic Absorption Spectroscopy AAS is a technique for determining the concentration of a particular metal element in a sample. And it can be used to analyse the concentration over a 62 different metals in a solution.

20. Principle: The principle of Atomic Absorption Spectroscopy is based on the free atoms (gas) generated in an atomiser which can absorb radiation at specific frequency. It quantifies the absorption of ground state atoms in the gaseous state. This absorbs UV 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. It is very common technique for detecting metals and metalloids in environment samples.

21. INSTRUMENTATION:

22. 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.

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

24. Types of Atomizers: Flame atomization: Nebulizer suck up in liquid sample at controlled rate and creates a fine aerosol spray for introduction into flame. To creat flame, we need to mix an oxidant gas and a fuel gas. In most of the cases air-acetylene flame or nitrous oxide acetylene flame is used. Liquids or dissolved samples are typically used with flame atomizer.

25. Elecrto Thermal Atomization: It uses a graphite coated furnace to vaporize the sample. Samples are deposited in a small graphite coated tube which then heated to vaporize and atomize the analyte. The graphite tubes are heated using a high current power supply. Steps used in electro thermal atomization: Drying, Pyrolysis, Atomization, Cleaning Monochromators: It is used to separate out all of the thousand of lines. It 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.

26. Detector and Amplifier: The light selected by the monochromator is directed onto a detector whose function converts the light signal into an electrical signal. Photomultiplier tube detector is mainly used. 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.

27. Calibration Curve: It 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 solution is measured & then calibration curve of concentration vs absorbance is plotted. The sample solution is fed into instrument & the abs of the element in the solution is measured. The unknown concentration of element is then calculated from the calibration curve.

28. Interferences in AAS: Analyte interference: It changes the magnitude of the analyte signal itself. Such interferences are usually not spectral in nature but rather physical or chemical effects. Physical interference: It can alter the aspiration, nebulisation, desolvation, and volatilization processes. Substances in the sample that change the solution viscosity.(EX- It can alter the flow rate and efficiency of the nebulisation process.) Combustible constituents, such as organic solvents, can change the atomiser temperature and thus affects the atomization efficiency indirectly.

29. Chemical interference: They occur in the conversion of solid or molten particle after desolvation into free atoms or elementary ions. Constituents that influences the volatilization of analyte particle causes this type of interferences and are often called solute volatilization interferences. For example, can alter in some flames the presence of phosphate in the sample can alter the atomic concentration of calcium in the flame owing to the formation of relately non-volatile complexes. Such effects can sometimes be eliminated or moderated by the use of higher temperatures.

30. Spectral interference: The elements that absorb at analyte wavelength are rare in atomic absorption. Molecular constituents and radiation scattering can cause interference. These are often corrected by background correction scheme. In some case, if the source of interference is known, an excess of the interferent can be added to both the sample and the standards. The added substance is sometimes called as radiation buffer.

31. Applications: Determination of even small amounts of metals(lead, mercury, calcium, magnesium) Environmental studies: drinking water, ocean water, soil. Food industry Pharmaceutical industry. Presence of metals as an impurity or in alloys could be done easily. It is used in qualitative & quantitative analysis of different drug compounds To detect heavy metals elements in the herbal drugs and synthetic drugs. To estimate lead in petroleum products.

32. Reference: Analytical chemistry by Gary D Christian Principles of instrumental analysis Skoog Instrumental method of analysis by Willard Merritt Spectroscopy by B K Sharma Instrumental method of analysis by Gurdeep chatwal www.google.com

33. THANK YOU