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ATR FTIR_ Sahana

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  1. 1. ATTENUATED TOTAL REFLECTANCE-FTIR Sahana V PGD 4/20/2015 1
  2. 2. Outlook Internal Reflection Spectroscopy Infrared beam reflects from a interface via total internal reflectance. 4/20/2015 2
  3. 3. A little detail 4/20/2015 3 Incident waveReflected wave Evanescent wave
  4. 4. Edge over Traditional methods Little or no sample preparation Very thin sampling path length Depth of penetration of the IR beam into sample Sample analysis- faster (less than 1 minute for thick samples) 4/20/2015 4
  5. 5. How it works 4/20/2015 5
  6. 6. Factors Wavelength of IR radiation Refractive indexes of sample and IRE*- n(s), n(IRE) Angle of incidence of IR radiation- Depth of penetration(pathlength)- d Sample and IRE contact efficiency *Internal reflection element 4/20/2015 6
  7. 7. Instrumentation 4/20/2015 7
  8. 8. Continued 4/20/2015 8 1 2 3 4
  9. 9. CRYSTAL MATERIALS MATERIAL ATR SPECTRA RANGE REFRACTI VE INDEX DEPTH OF PENETRATI ON USES Germanium 5,500-675 4 0.66 Good for most samples. Strong absorbing samples, such as dark polymers Silicone 8,900- 1,500 and 360-120 3.4 0.85 Resistant to basic solutions AMTIR 11,000-725 2.5 1.77 Very resistant to acidic solutions ZnSe 15,000-650 2.4 2.01 General use Diamond 25,000-100 2.4 2.01 Good for most samples. Extremely caustic or harder samples. 4/20/2015 9
  10. 10. Selecting a right crystal 4/20/2015 10
  11. 11. Disadvantages 4/20/2015 11 The ATR crystal absorbs energy at lower energy levels If the sample does not have good contact with the crystal, the data will not be accurate Most ATR crystals have pH limitations
  12. 12. Applications 4/20/2015 12 Solid Analysis Liquid Analysis Powder Analysis excellent technique for measuring the composition of solids analyze non-aqueous solutions easier to run by ATR than by IR transmission, because little or no preparation is required ideal technique for measuring dark colored materials which often absorb too much energy to be measured by IR transmission Cleanup is easy and fast pure samples and mixtures that are available in powdered from films, fabrics, paper, hard polymer sheets, glass, rubber lubricants, oils, paints, glues, solvents, inks and dyes, Gels and pastes can pharmaceuticals and pigments
  13. 13. End Notes Versatile and non-destructive technique for variety of materials- soft solid materials, liquids, powders, gels, pastes, surface layers, etc. Useful for surface characterization, opaque samples Limitations: sensitivity is typically 3-4 orders less than transmission 4/20/2015 13
  14. 14. References 4/20/2015 14 http://www.azom.com/article.aspx?ArticleID=5 958 Perkin-Elmer: Technical Note SpectraTech: Technical Note