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ATTENUATED TOTAL REFLECTION SPECTROSCOPY

ATTENUATED TOTAL REFLECTION SPECTROSCOPY. Outline . Introduction to ATR technology Evanescent Waves Crystal Composition Data Collection Advantages & Disadvantages Sample Analysis Challenges Future Applications Conclusion.

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ATTENUATED TOTAL REFLECTION SPECTROSCOPY

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  1. ATTENUATED TOTAL REFLECTION SPECTROSCOPY

  2. Outline • Introduction to ATR technology • Evanescent Waves • Crystal Composition • Data Collection • Advantages & Disadvantages • Sample Analysis • Challenges • Future Applications • Conclusion

  3. Attenuated total reflection (ATR) spectroscopy is a versatile and powerful technique for infrared sampling

  4. How an ATR accessory works • Internal reflection spectroscopy passes infrared radiation through an infrared-transmitting crystal of high refractive index, allowing the radiation to reflect in the crystal one or more times • An attenuated total reflection accessory measures the totally reflected infrared beam when the beam comes in contact with a sample • In this way, an evanescent wave penetrates into the sample in contact with the crystal, producing a spectrum of the sample

  5. Evanescent Waves • The infrared radiation interacts with the sample through a series of standing waves, called evanescent waves • An evanescent wave is a penetrating electromagnetic field whose intensity quickly decays as it moves away from its source

  6. ATR Data Collection • When collecting ATR data, samples are run as % Reflectance or log (1/R) • % Reflectance is equivalent to % Transmittance • Log (1/R) is equivalent to Absorbance • In summary, % Reflectance is similar to Absorbance

  7. DisadvantagesATR vs. Transmission • 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

  8. Crystal Composition • Crystals are typically made of: • Zinc Selenide (ZnSe) • Germanium (Ge) • Zinc Sulfide (ZnS) • Silicon (Si) • Diamond • AMTIR: Germanium, Arsenic, Selenium (GeAsSe)

  9. Advantages ATR vs. Transmission • When an ATR accessory is used, most samples can be run “neat”, which means “in their natural state” • ATR sampling is fast and easy because little or no sample preparation is required • Other techniques, such as infrared transmission, often require the sample to be heated, pressed or ground in order to collect the spectrum

  10. Solid analysis • ATR is an excellent technique for measuring the composition of solids • Some examples of solids are films, fabrics, paper, hard polymer sheets, glass, rubber • ATR is an ideal technique for measuring dark colored materials which often absorb too much energy to be measured by IR transmission

  11. Liquid Analysis • ATR is an ideal technique for analyzing liquids • Sample preparation is minimal • Cleanup is easy and fast

  12. Liquid Analysis • ATR can be used to analyze non-aqueous solutions such a lubricants, oils, paints, glues, solvents, inks and dyes • Gels and pastes can also be analyzed

  13. Powder Analysis • Powders are easier to run by ATR than by IR transmission, because little or no preparation is required • This category includes pure samples and mixtures that are available in powdered from • Some examples of pure samples and mixtures are pharmaceuticals and pigments

  14. Challenges • Alignment of the beamsplitter • Technique will change with sample type

  15. Future Applications • Forensic Investigation • Biomedical applications

  16. Conclusion • Attenuated Total Reflectance is an easy-to-use, fast, and versatile technique for infrared sampling • Solids, pastes, gels, liquids and powders can be analyzed with little or no preparation

  17. References • Thermo Electron Corporation • http://www.brukeroptics.com/applications/microscopy.html

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