flamephotometry.pptx

This PPT tell about Flame emission spectroscopy and its instrumentation

1. FLAME PHOTOMETRY 1 BASIC CONCEPTS, INSTRUMENTATION, AND APPLICATION Mrs. Poonam Sunil Aher ( M.Pharm , PhD) Assistant Professor Sanjivani College of Pharmaceutical Education and Research (Autonomous),  Kopargaon , Ahmednagar-423603 (M.S.), INDIA Mobile: [phone]

2. INTRODUCTION: Flame photometry (more accurately called Flame Atomic Emission Spectrometry )is a branch of spectroscopy in which the species examined in the spectrometer are in the form of atoms A photoelectric flame photometer is an instrument used in inorganic chemical analysis to determine the concentration of certain metal ions among them sodium, potassium, calcium and lithium. Flame Photometry is based on measurement of intensity of the light emitted when a metal is introduced into flame. The wavelength of colour tells what the element is (qualitative) The colour's intensity tells us how much of the element present (quantitative) 2

3. 3 Flame photometer working principle: When a solution of metallic salt is sprayed as fine droplets into a flame. Due to the heat of the flame, the droplets dry leaving a fine residue of salt. This fine residue converts into neutral atoms. Due to the thermal energy of the flame, the atoms get excited and after that return to ground state. In this process of return to ground state, excited atoms emit radiation of specific wavelength. This wavelength of radiation emitted is specific for every element. This specificity of the wavelength of light emitted makes it a qualitative aspect. While the intensity of radiation depends on the concentration of element. This makes it a quantitative aspect. The process seems to be simple and applicable to all elements. But in practice, only a few elements of Group IA and group IIA  (like Li, Na, k & Ca, Mg) are only analyzed. The radiation emitted in the process is of a specific wavelength. Like for Sodium (Na) 589nm yellow radiation, Potassium 767nm range radiation.

4. The basic principle upon which Atomic Spectroscopy works is based on the fact that "Matter absorbs light at the same wavelength at which it emits light". Atoms of elements  subjected to hot flame  specific quantum of thermal energy absorbed by orbital electrons  become unstable at high energy level  release energy as photons of particular wavelength  change back to ground state. When a metal salt solution is burned, the metal provides a colored flame and each metal ion gives a different colored flame. Flame tests, therefore, can be used to test for the absence or presence of a metal ion 4

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6. 6 Events occurring in the flame:  Flame photometry employs a variety of fuels mainly air, oxygen or nitrous oxide (N 2 O) as oxidant. The temperature of the flame depends on fuel-oxidant ratio.  The various processes in the flame are discussed below:   Desolvation : The metal particles in the flame are dehydrated by the flame and hence the solvent is evaporated. Vapourisation : The metal particles in the sample are dehydrated. This also led to the evaporation of the solvent. Atomization : 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 characteristic wavelength, which is measured by the photo detector.  

7. BASIC CONCEPT: Liquid sample contaning metal salt solution is introduced into a flame, Solvent is first vaporized, leaving particles of solid salt which is then vaporised into gaseous state Gaseous molecule dissociate to give neutral atoms which can be excited (made unstable) by thermal energy of flame The unstable excited atoms emit photons while returning to lower energy state The measurement of emitted photons forms the basis of flame photometry. 7

8. The intensity of the light emitted could be described by the Scheibe-Lomakin equation: 8 I=K .C I is Intensity of emitted light K is proportionality constant C is the concentration of sample

9. Under constant and controlled conditions, the light intensity of the characteristic wavelength produced by each of the atoms is directly proportional to the number of atoms that are emitting energy, which in turn is directly proportional to the concentration of the substance of interest in the sample. Various metals emit a characteristic colour of light when heated. 9

10. Structure of Flame: As seen in the figure, the flame may be divided into the following regions or zones. Preheating zones Primary reaction zone or inner zone Internal zone Secondary reaction zone 10

11. preheating zone- In this, combustion mixture is heated to the ignition temperature by thermal conduction from the primary reaction zone. primary reaction zone- This zone is about 0.1 mm thick at atmospheric pressure There is no thermodynamic equilibrium in this zone and the concentration of ions and free radicals is very high. This region is not used for flame photometry. interconal zone – It can extend up to considerable height. The maximum temperature is achieved just above the tip of the inner zone. This zone is used for flame photometry. secondary reaction zone - In this zone, the products of the combustion processes are burnt to stable molecular species by the surrounding air. 11

12. INSTRUMENTATION: THE FLAME PHOTOMETER

13. 13 Major Components: Sample Delivery System Fuel and oxidant Source Monochromator Detector Read out device 13 Schematic Representation of the Flame Photometer

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15. 1.Sample Delivery System: There are three components for introducing liquid sample: Nebulizer – it breaks up the liquid into small droplets. Nebulization the is conversion of a sample to a mist of finely divided droplets using a jet of compressed gas. The flow carries the sample into the atomization region. Pneumatic Nebulizers: (most common) Aerosol modifier – it removes large droplets from the stream and allow only smaller droplets than a certain size to pass Flame or Atomizer – it converts the analyte into free atoms 15

16. 2.Source: A Burner used to spray the sample solution into fine droplets. The flame should possess the ability to evaporate the liquid droplets from sample solution resulting in the formation of solid residue. The flame should decompose the compounds in the solid residues and resulting in the formation of atoms The flame must have ability to excite the atoms formed and cause them to emit radiant energy 16

17. 1. Macker Burner This burner was used earlier and employed natural gas and oxygen This burner produced relatively low temp and low excitation energies therefore it was generally used for study of alkali metals only. Disadvantage: Flame produced by this burner is not homogenous chemically. Atomic excitation in the flame is differ in different region This burner is not used. 17

18. 2. Premix or laminar- flow burner. In this energy type of burner, aspirated sample, fuel and oxidant are thoroughly mixed before reaching the burner opening and then entering the flame. In this burner the gases move in non- turbulent fashion ie ., in laminar flow. An important feature of laminar-flow is that only 5 % of the sample in the form of small droplets reaches the flame and is easily decomposed. By easy in means that an efficient atomization of the sample in the flame will takes place. larger droplets from the aspirator impinge on the side of the spray chamber and are drained off. Thus in this burner 95% of the sample may be wasted, thereby, resulting in a loss of sensitivity. The flame produced by premix burner is non turbulent , noiseless and stable. 18

19. 19 Advantage: 1. easy decomposition of the sample takes place which results in an efficient atomization of the sample in the flame. 2. Premix burners can handle solutions up to several % without clogging. Disadvantages: i . Lower rate of sample introduction Possibility of selective evaporation of mixed solvents in the mixing chamber, create analytical uncertainties. ii. Mixing chamber contains a potentially explosive mixture that can flash back if the flow rates are too low.

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21. 3.Total Consumption Burner( turbulent flow burner): In this fuel and oxidant are hydrogen and oxygen gases From the tubing hydrogen and oxygen gases are entering and both are burning at the top of the burner to produce flame As soon as liquid sample is dawn into the base of the flame, the oxygen aspirates the sample solution and leaving a solid residue. Atomization and excitation of sample then follow. Entire sample is consumed. Hence its name is total consumption burner. 21

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23. 23 Advantage: introduce relatively large & representative sample into the flame. Disadvantage: 1. When the sample contains two solvents then is aspirated into the flame, the more volatile sample will evaporate in spray chamber and leaving the sample in the form of undissociated atoms in less volatile component. Thus smaller no of atoms would reach the flame. 2. Low intensity 3.A relatively short path length through flame Problems with clogging of the tip 4.Burners noisy from electronic and auditory stand point

24. 4. Lundergarph burner: For this burner sample mast be liquid form It is aspirated into spray chamber Large droplets condense on the side and drain away Small droplets and vaporised sample are swept into the base of the flame in the form of cloud. 24

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26. 26 3.Fuel and oxidants : Fuel and oxidant are required to produce the flame such that the sample converts to neutral atoms and get excited by heat energy. The temperature of flame should be stable and also ideal. If the temperature is high, the elements in sample convert into ions instead of neutral atoms. If it is too low, atoms may not go to excited state. So a combination of fuel and oxidants is used such that there is desired temperature.

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28. 4.Monochromator: Prism : Quartz material is used for making prism, as quartz is transparent over entire region Grating : it employs a grating which is essentially a series of parallel straight lines cut into a plane surface 5.Detectors: Photomultiplier tubes Photo emissive cell Photo voltaic cell Photovoltaic cell: It has a thin metallic layer coated with silver or gold which act as electrode, also has metal base plate which act as another electrode Two layers are separated by semiconductor layer of selenium, when light radiation falls on selenium layer. This creates potential diff. between the two electrode and cause flow of current. 28

29. Read-out Device: It is capable of displaying the absorption spectrum as well absorbance at specific wavelength Nowadays the instruments have microprocessor controlled electronics that provides outputs compatible with the printers and computers Thereby minimizing the possibility of operator error in transferring data. 29 Element wavelength Detection limit Element wavelength Detection limit Al 396 0.5 Pb 406 14 Ba 455 3 Li 461 0.067 Ca 423 0.07 Mg 285 1 Cu 325 0.6 Ni 355 1.6 Fe 372 2.5 Hg 254 2.5 Elements, their characteristic emission wavelengths and detection limits

30. APPLICATIONS: To estimate sodium, potassium, calcium, lithium etc. level in sample of serum, urine, CSF and other body fluids. Flame photometry is useful for the determination of alkali and alkaline earth metals. Used in determination of lead in petrol. Used in the study of equilibrium constants involving in ion exchange resins. Used in determination of calcium and magnesium in cement. 30

31. 31 Flame photometer has both quantitative and qualitative applications. to detect the presence of a particular metal in the sample. This help to determine the availability of alkali and alkaline earth metals which are critical for soil cultivation. In agriculture, the fertilizer requirement of the soil is analyzed by flame test analysis of the soil. In clinical field, Na+ and K+ ions in body fluids, muscles and heart can be determined by diluting the blood serum and aspiration into the flame. Analysis of soft drinks, fruit juices and alcoholic beverages

32. 32 Advantages: Simple quantitative analytical test based on the flame analysis. Inexpensive. The determination of elements such as alkali and alkaline earth metals is performed easily with most reliable and convenient methods. Quite quick, convenient, and selective and sensitive to even parts per million ( ppm ) to parts per billion (ppb) range.

33. 33 Disadvantages:   The concentration of the metal ion in the solution cannot be measured accurately.. A standard solution with known molarities is required for determining the concentration of the ions which will corresponds to the emission spectra. It is difficult to obtain the accurate results of ions with higher concentration. The information about the molecular structure of the compound present in the sample solution cannot be determined. The elements such as carbon, hydrogen and halides cannot be detected due to its non radiating nature.

34. 34 Limited number of elements that can be analyzed. The sample requires to be introduced as a solution into fine droplets. Many metallic salts, soil, plant and other compounds are insoluble in common solvent. Hence, they can’t be analyzed by this method. Since the sample is volatilized, if a small amount of sample is present, it is tough to analyze by this method. As some of it gets wasted by vaporization. Further, during solubilization with solvents, other impurities might mix up with the sample and may lead to errors in the spectra observed.

35. THANK YOU 35