FLAME EMISSION SPECTROSCOPY

1. INTRODUCTION

2. PRINCIPLE

3. INSTRUMENTATION

4. INTERFERENCES

5. APPLICATIONS

1. 1 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 1 FLAME EMISSION SPECTROSCOPY PRESENTED BY : PATIL ABHISHEK SHARAD DEPARTMENT OF PHARMACEUTICS RAJARAMBAPU COLLEGE OF PHARMACY, KASEGAON

2. CONTENTS : 1. INTRODUCTION 2. PRINCIPLE 3. INSTRUMENTATION 4. INTERFERENCES 5. APPLICATIONS 02-Aug-21 2 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI

3. INTRODUCTION : “The determination of elemental composition by its electromagnetic or mass spectrum.” Atomic Spectroscopy is assumed to be the oldest instrumental method for the determination of elements. These techniques are introduced in the mid of 19th Century, when Bunsen and Kirchhoff showed that the radiation emitted from the flames depends on the characteristic element present in the flame. 02-Aug-21 3 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI

4. TYPES OF ATOMIC SPECTROSCOPY : 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 4

5. WHAT IS FLAME PHOTOMETRY ? 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 5 • 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).

6. 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 6 • 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.

7. PRINCIPLE : 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 7 • 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.

8. 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 8 • 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.

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11. Structure of Flame: 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 11 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

12. 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 12 • 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.

13. INSTRUMENTATION: 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 13

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15. Major Components: 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 15 1. Sample Delivery System 2. Source 3. Monochromator 4. Detector 5. Read out device

16. 1. Sample Delivery System: 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 16 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.

17. 2. Source: 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 17 • A Burner used to spray the sample solution into fine droplets. • Several burners and fuel+oxidant combinations have been used to produce analytical flame including: Premixed, Mecker , Total consumption, Lundergarh , Shielded burner, and Nitrous oxideacetylene flames • Pre-mixed Burner: – widely used because uniformity in flame intensity – In this energy type of burner , aspirated sample , fuel and oxidant are thoroughly mixed before reaching the burner opening.

18. 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 18 • Total Consumption Burner: – In this fuel and oxidant are hydrogen and oxygen gases – Sample solution is aspirated through a capillary by high pressure of fuel and Oxidant and burnt at the tip of burner – Entire sample is consumed. Pre-mixed burner Total Consumption Burner

19. MECKER BURNER: 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 19 This burner was used earlier and employed natural gas and oxygen. Produces relatively low temp. and low excitation energies. This are best used for ALKALI metals only. Now-a-days it is not used.

20. LUNDERGRAPH BURNER : 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 20 In this sample and air is mixed in a chamber, this mixed composition is send to fuel nozzle where it is atomized. Here the sample reaches the flame is only about 5%.

21. SHIELDED BURNERS : 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 21 In this flame was shielded from the ambient atmosphere by a stream of inert gas. Shielding is done to get better analytical sensitivity and quieter flame.

22. NITROUS OXIDE ACETYLENE FLAME: 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 22 These flames were superior to other flames for effectively producing free atoms. The drawback of it is the high temperature reduces its usefulness for the determination of alkali metals as they are easily ionized and Intense background emission, which makes the measurement of metal emission very difficult

23. 3. MONOCHROMATOR : 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 23 1. MIRRORS : The radiation from the flame is emitted in all the directions in space. Much of the radiation is lost and loss of signal results. A mirror is located behind the burner to reflect the radiation back to the entrance slit of the monochromator. The reflecting surface of the mirror is front-faced.

24. 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 24 2. SLITS : The entrance and exit slits are used before and after the dispersion elements.  The entrance slit cuts off most if radiation from the surroundings and allows only the radiation from the flame and the mirror reflection of flame to enter the optical system.  The exit slit is placed after the monochromator and allows only the selected wavelength range to pass through the detector.

25. 4. DETECTORS : 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 25 1. PHOTOMULTIPLIER TUBE :  The third major type of light detector is the photomultiplier (PM) tube, which detects and amplifies radiant energy.  Incident light strikes the coated cathode, emitting electrons. The electrons are attracted to a series of anodes, known as dynodes,each having a successively higher positive voltage These dynodes are of a material that gives off many secondary electrons when hit by single electrons. Initial electron emission at the cathode triggers a multiple cascade of electrons within the PM tube itself. Because of this amplification, the PM tube is 200 times more sensitive than the phototube.

26. 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 26  PM tubes are used in instruments designed to be extremely sensitive to very low light levels and light flashes of very short duration.  The accumulation of electrons striking the anode produces a current signal, measured in amperes, that is proportional to the initial intensity of the light. The analog signal is converted first to a voltage and then to a digital signal through the use of an analog to- digital (A/D) converter. Digital signals are processed electronically to produce absorbance readings.

27. 5. READ OUT DEVICES : 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 27 In the past nearly all spectrophotometer used ammeters or galvanometers. Newer digital devices and printers have now replaced these, and many instruments relay their electrical output directly to computer circuits where calculations are performed, allowing direct reporting of sample concentration. Microprocessor and recorders.

28. INTERFERENCES : 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 28 • In determining the amount of a particular element present, other elements can also affect the result. Such interference may be of 3 kinds: 1. Spectral interferences: Occurs when the emission lines of two elements cannot be resolved or arises from the background of flame itself. – They are either too close, or overlap, or occur due to high concentration of salts in the sample 2. Ionic interferences: High temperature flame may cause ionisation of some of the metal atoms, e.g. sodium. – The Na+ ion possesses an emission spectrum of its own with frequencies, which are different from those of atomic spectrum of the Na atom.

29. 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 29 3. Chemical interferences : The chemical interferences arise out of the reaction between different interferents and the analyte. Includes: • Cation -anion interference: – The presence of certain anions, such as oxalate, phosphate, sulfate, in a solution may affect the intensity of radiation emitted by an element. E.g., – calcium + phosphate ion forms a stable substance, as Ca3(PO4)2 which does not decompose easily, resulting in the production of lesser atoms. • Cation-cation interference: – These interferences are neither spectral nor ionic in nature – Eg. aluminum interferes with calcium and magnesium.

30. APPLICATIONS: 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 30 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.

31. ADVANTAGES: 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 31 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, convenient, selective and sensitive to even parts per million ( ppm ) to parts per billion (ppb) range.

32. DISADVANTAGES: 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 32 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.

33. LIMITATION : 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 33 Limited number of elements that can be analyzed. The sample requires to be introduced as solution into fine droplets. Many metallic salts, soil, plant and other compounds are insoluble in common solvents. Hence, they can’t be analyzed by this method. Since sample is volatilized, if small amount of sample is present, it is tough to analyze by this method. As some of it gets wasted by vaporization. Further during solubilisation with solvents, other impurities might mix up with sample and may lead to errors in the spectra observed.

34. REFERENCES: 02-Aug-21 RAJARAMBAPU COLLEGE OF PHARMACY, SANGLI 34 Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Basic Clinical Biochemistry Practice, second edition, editied by O. A. Afonja. College Analytical Chemistry, Himalaya Publishing House, 19th Edition (2011), By K.B.Baliga et al. Chapter 4 - Optical Methods, Pages : 135-148. http://www.hindawi.com/journals/chem/2013/4658 25/ Practical Biochemistry, Principles & Techniques, Cambridge lowprice editions, 5th Edition, Edited By Keith Wilson & John Walker, Chapter: Spectroscopic Techniques, Pages : 486-490.

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