1. ATOMIC ABSORPTIONSPECTROPHOTOMETRYPresented By :G. Prasanth11AB1R0085VIGNAN PHARMACY COLLEGE(Approved by AICTE, PCI & Affiliated to JNTUK)VADLAMUDI, 522213.UNDER THE ESTEEMEDGUIDANCE OFMr. Ch. DEVADASU M.PharmAssistant professorDepartment of PA & QA

2. CONTENTS Introduction Principle Instrumentation1. Sharp line radiation source2. Nebulizer and Burner3. Monochromator4. Photomultiplier5. Recording system Flameless vaporization techniques1. Electro thermal atomizers2. Cold vapour systems3. Hydride generation systems7-Oct-14 Pharmaceutical Analysis 2 3. Interferences in atomic absorption spectroscopy1. Special2. Chemical Advantages Disadvantages Applications Conclusion7-Oct-14 Pharmaceutical Analysis 3 4. INTRODUCTION Atomic absorption spectroscopy technique was introduced foranalytical purpose by WALSH, ALKEMADE and MILATZ in 1956. Atomic absorption spectroscopy is an absorption spectroscopicmethod where radiation from a source is absorbed by non-excitedatoms in the vapour state. Atomic absorption spectroscopy deals with the absorption ofspecific wavelength of radiation by neutral atoms in the ground state.7-Oct-14 Pharmaceutical Analysis 4 5. PRINCIPLE OF AASLiquid sampleflameFormation ofdropletsFine residue7-Oct-14 Pharmaceutical Analysis 5 6. Formation of Neutral atomsNeutral atoms absorb specific wavelength ofradiation from hollow cathode lampMeasurement of intensity of radiation absorbed by theneutral atoms using a detector7-Oct-14 Pharmaceutical Analysis 6 7. PRINCIPLE OF AAS The extent to which radiation of a particular frequency is absorbed byan atomic vapour is related to the length of the path transversed and tothe concentration of absorbing atoms in the vapour This is analogues to the Beer Lamberts law relating to samples insamples in solution. Thus , for a collimated monochromatic beam ofradiation of incident I0 passing through an atomic vapour of thickness IIv = I0 e kvIWhereIv is the intensity of the transmitted radiationkv is absorption co efficient7-Oct-14 Pharmaceutical Analysis 7 8. The value of kv is determined by the concentration of atoms whichcan absorb at frequency v is given by the expression : kv dv = xe2 Nv fWheremcm & e are the mass and charge of the electronNv is the number of atoms per cm3 capable of absorbing radiationof frequency v ( ie., ground state atoms )f is the oscillator strength ( defined as the number of electrons peratom capable of being excited by the incident radiation ) Hence , for transitions from the ground state , integrated absorption isproportional to Nv ,which approximates to the concentration (c) of theelement in the sample7-Oct-14 Pharmaceutical Analysis 8 9. PROCESS OF ATOMIC ABSORPTION7-Oct-14 Pharmaceutical Analysis 9 10. Process Occurring DuringAtomization7-Oct-14 Pharmaceutical Analysis 10 11. INSTRUMENTATION Sharp-line radiation source (usually a hollow-cathodelamp) A solution nebulizer and burner (an electrically heatedfurnace) Monochromator Photomultiplier and Recording system7-Oct-14 Pharmaceutical Analysis 11 12. SHARP-LINE SOURCESThe absorption line width for the ground state atoms may be from0.001-0.01nm. So the light sourced must emit radiation of a linewidth less than that of the absorption line width of the elementbeing determined.This is achieved by vapour discharge lamps for certain easilyexcited elements, e.g. sodium and potassium.7-Oct-14 Pharmaceutical Analysis 12 13. HOLLOW CATHODE LAMP When a current flows between the anode and cathode in thislamps, metal atoms are sputtered from the cathode cup, andcollisions occur with the filler gas. A number of metal atoms becomeexcited and give off their characteristic radiation.7-Oct-14 Pharmaceutical Analysis 13 14. SAMPLE VAPORIZATION BY FLAMEThe production of an homogeneous atomic vapour from asample is achieved by aspirating a solution into a flame orevaporating small volumes in an electrically heated tube furnaceor from the surface of a carbon rod.In all cases, the thermal energy supplied must(a) Evaporate the solvent and(b) Dissociate the remaining solids into their constituent atomswithout causing appreciable ionization.7-Oct-14 Pharmaceutical Analysis 14 15. INSTRUMENTATION OF ATOMIC ABSORPTIONSPECTROSCOPY7-Oct-14 Pharmaceutical Analysis 15 16. BURNER WITH FUEL AND OXIDANT ( NEBULIZER ) The burner consists of a metal block containing a row ofcircular holes or one or more slots about 10 cm long. The most generally useful flame is air-acetylene, The cooler air-propanea and the Hotter nitrous oxide-acetylene flames are also used.(It is particularly useful for samples containing refractoryelements(e.g. aluminium.)NEBULIZER7-Oct-14 Pharmaceutical Analysis 16 17. Some well known fuels with oxidants areAir Propane 2200 KOxygen Hydrogen 2450 KOxygen Acetylene 2800 KNitrous oxide Acetylene 3230 KFLAME STRUCTURE FUELS WITH OXIDANTS7-Oct-14 Pharmaceutical Analysis 17 18. POTENTIAL ADVANTAGES OF FLAMELESSVAPORIZATION:(1) The elimination of anomalous results arising from interactionsbetween the sample and components of the flame.(2) Increased sensitivity arising from a longer residence time withinthe beam of radiation from the lamp.(3) Residence times in flames are low because of strong verticalthermal currents.7-Oct-14 Pharmaceutical Analysis 18 19. (4) Increased sensitivity because of a higher proportion of theanalyte being converted to free atoms.(The conversion may be as low as 0.1% for flame atomization.)(5) The ability to handle very small samples such as clinicalspecimens.(A nebulizer, spray chamber, burner arrangement consumesseveral cm3 of sample per minute, most of which runs to waste).7-Oct-14 Pharmaceutical Analysis 19 20. FLAMELESS VAPORIZATION TECHNIQUES Electro thermal Atomizers Cold vapour systems Hydride generation systems7-Oct-14 Pharmaceutical Analysis 20 21. Electro Thermal Atomizers The most widely used Electro thermal atomizers system is agraphite tube (3-5cm long& 0.5-1cm diameter) which is heatedelectrically in a furnace containing an inert gas, e.g. argon. The sample is inserted through a hole in the centre of the tube,which is then positioned in the light path in place of flame burnerand heated according to a predetermined program as follows:7-Oct-14 Pharmaceutical Analysis 21 22. Electro thermal Atomisers: Graphite Tube7-Oct-14 Pharmaceutical Analysis 22 23. Stage 1: Drying at about 100C to remove waterStage 2: Ashing (300-500C) to remove organic constituentsStage 3: Atomisation (2000-2900C) to liberate the elements asgaseous atomsStage 4: Removal of remaining inorganic matter at themaximum operating temperature about (3000C)7-Oct-14 Pharmaceutical Analysis 23 24. ELECTRO THERMALATOMIZERSSUB TWIN ATOMIZER7-Oct-14 Pharmaceutical Analysis 24 25. Advantages Of Electro-thermal Atomisation: Only a small sample weight or sample volume is required,typically 10-20 g or l. The atomisation efficiency and the sensitivity is greater thanthat given by flame atomisation by up to 10,000 times. Chemical pretreatment of sample is not usually required. Useful for the assay of trace levels of metals & of smallquantity, e.g. blood.Disadvantage: Reduction of precision7-Oct-14 Pharmaceutical Analysis 25 26. Cold Vapour Systems Mercury is a unique metal in that it has a significant vapour pressureat room temperature. Furthermore, the vapour is monatomic andunreactive. Thus it may be entrained in a gas stream and measured bythe atomic absorption of this cold vapour. A typical analytical method first involve the use of an oxidizingmixture such as sulphuric acid and potassium permanganate to destroyorganic matter. The mercuric sulphate thus produced is then reduced with stannouschloride to produce mercury vapour, which is swept through a narrowquartz cell about 15 cm long with a diameter of about 0.75 cm.7-Oct-14 Pharmaceutical Analysis 26 27. Hydride Generation Systems A number of elements such as arsenic, tellurium and seleniummay be reduced by a suitable reagent, e.g. sodium borohydridein acidic solution, to their hydrides as follows..6BH4+ As3+ + 3H+ 3B2H6+ 3H2 + AsH37-Oct-14 Pharmaceutical Analysis 27 28. MonochromatorSome elements have a single emission line (principal line).But several elements have more than one emission line(secondary line).Hence it is necessary to isolate required absorption line from aradiation source by a grating monochromator.7-Oct-14 Pharmaceutical Analysis 28 29. VACCUM MONOCHROMATORMONOCHROMATOR7-Oct-14 Pharmaceutical Analysis 29 30. DETECTOR AND READOUT DEVICE:The intensity of radiation absorbed by elements, in the UV orvisible region(190-900nm) can be detected using photometricdetector like photomultiplier tube.The readout device is capable of displaying the absorptionspectrum as well as the absorbance at a specified wavelength.7-Oct-14 Pharmaceutical Analysis 30 31. INTERFERENCES IN ATOMIC ABSORPTIONSPECTROSCOPY Interferences in atomic absorption measurements can arise fromspectral chemical and physical sources SPECIAL INTERFACE resulting from the overlap of absorptionlines is rare because of the simplicity and the sharpness of the lines However , broadband by molecular species can lead to significantbackground interface. Correction for this may be made by matrix matching of samples andstandards , or by use of a standard addition method7-Oct-14 Pharmaceutical Analysis 31 32. 7-Oct-14 Pharmaceutical Analysis 32 33. CHEMICAL INTERFERANCE include stable compoundformation and ionization , both of which decrease thepopulation of free atoms in the sample vapour and therebylower the measured absorbance Ex: Reactions between alkaline earth metals and oxyanionssuch as aluminum , vanadium ,boron etc7-Oct-14 Pharmaceutical Analysis 33 34. ADVANTAGES OF AAS Solutions, slurries and solid samples can be analysed. Much more efficient atomization Greater sensitivity Smaller quantities of sample (typically 5 50 L) Provides a reducing environment for easily oxidized7-OEct-1l4ements Pharmaceutical Analysis 34 35. DISADVANTAGES Expensive Low precision Low sample throughput Requires high level of operator skill Sample must be in solution or at least volatile Individual source lamps required foreach element7-Oct-14 Pharmaceutical Analysis 35 36. APPLICATIONS OF AAS Atomic absorption spectroscopy is one of the most widely usedtechniques for the determination of metals at trace levels in solution Its popularity as compared with that of flame emission is due to itsrelative freedom from interferences by inter element effects and itsrelative insensitivity to various in flame temperature Only for the routine determination of alkali and alkaline earth metals ,is flame photometry usually preferred7-Oct-14 Pharmaceutical Analysis 36 37. Over sixty elements can be determined in almost in any matrixby atomic absorption .Ex: 1. Heavy metals in body fluids2. Polluted waters3. Food stuffs4. Soft drinks and beer5. Analysis of metallurgical and geochemicalsamples6. Determination of many metals in soils , crude oils, petroleum products and plastics etcPURIFICATION OF WATER PETROLEUM PRODUCTS FOOD STUFF7-Oct-14 Pharmaceutical Analysis 37 38. Detection limits generally lie in the range 100- 0.1 ppb but thesecan be improved by chemical pre concentration proceduresinvolving solvent extraction or ion exchangePeak Peaknoise curve Currently a balance seems to have reached in the use of varioustechniques for the determination of metals at trace levels In its modern form AAS remains important and competativewhere small ranges of elemants need to be determined in samples7-Oct-14 Pharmaceutical Analysis 38 39. CONCLUSION Atoms of a metal are volatilized in a flame and there absorption ofa narrow band of radiation produced by a hallow cathode lamp,coated with particular metal being determined is measured. More sensitive than atomic emission spectrometer. A highly specific method of analysis useful in some aspects ofquality control. Determination of metal residues remaining from the manufacturingprocess in drugs.7-Oct-14 Pharmaceutical Analysis 39 40. Skoog, Holler, Crouch s (2nd Edition) InstrumentalAnalysis.(p.g no 272-287) Chatwals Instrumental Analysis(p.g no.340-2.366) Vogels (6th Edition) p.g No 562-586. A.H Beckett & J.B Stenlake Part 2 PracticalPharmaceutical Chemiatry(4th Edition)p.g No 346-357. David. G. Watsons Pharmaceutical Analysis (p.g 142-148).7-Oct-14 Pharmaceutical Analysis 40 41. Acknowledgement I like to thank my guide Ch. DEVADSU sir for hisconstant support & guidance to achieve my seminartopic. I also thank our principal sir P. SRINIVASA BABUgaru & seminar committee for giving me thiswonderful opportunity. Thank you guys for being patience.7-Oct-14 Pharmaceutical Analysis 41 42. 7-Oct-14 Pharmaceutical Analysis 42