1. Infrared Radiation 780 nm - 1000 m Near, Mid and Far
Most used m
IR spectra contain qualitative information, can also be used for quantitative analysis.

2. Energy Level Diagram

3. Types of Molecular Vibrations
Vibration must result in net change of dipole moment for it to be “IR active”

4. IR spectrum of CO2

5. Laser (red) to maintain alignment and keep detector calibrated
FT- IR Instrument
IR Sources:
Nernst Glower or
Nichrome Wire
Or Globar
No optics other than mirrors, due to interferometer (Jacquinot Advantage)
Thermal Detectors:
Thermocouple or
Pyroelectric cell

6. Fourier Transform of the Interferogram

7. Sample preparation
No good solvents transparent in this region - best to do pure substances.
Gas - use special gas cell
Liquid - neat, 0.01mm thickness between two salt plates
Solid - particles must be <  to avoid scattering radiation.

8. More Sample Preparation
Pellet - grind sample with KBr powder, then press into a transparent disc.
Mull - analyte is dispersed into a mineral oil (Nujol) or a fluorinated polymer

9. Reflectance measurements
DRIFTS - Diffuse Reflectance Infrared FT Spectroscopy
ATR -Atenuated Total Reflectance

10. ATR - Golden Gate
IR beam focused on sample through germanium crystal, onto sample which is held down with diamond anvil.
IR beam reflects off sample, some of the wave penetrates into surface so reflected light is comparable to what would be transmitted through a sample cuvette.

11. ATR Evanescent Wave  for Ge is ~ 4
 for your sample will be different, so reflection will take place at the interface

12. Qualitative Analysis - Spectral Interpretation
Group Frequency range cm-1
Fingerprint region cm-1
Spectral Libraries are available for matching your results to known spectra.
Forensics – ex, single strands of fiber
Surface Studies

13. FT-IR Quantitative Analysis
Not common, because of overlapping signals from mixed compounds.
Also, deviations from Beer’s Law happen at these wavelengths.

14. Near Infrared Spectroscopy
770 nm-2500 nm
Quantitative, not qualitative
Liquids or Solids (DRIFTS)

15. Applications of NIR Pharmaceutical Powders
Process Analytical Technology (PAT) - online in situ process monitoring