Presentation is loading. Please wait.

Presentation is loading. Please wait.

Applications of IR spectroscopy

Similar presentations

Presentation on theme: "Applications of IR spectroscopy"— Presentation transcript:

1 Applications of IR spectroscopy
Yongsik Lee

2 IR spectrum

3 Sample handling Most time-consuming part is sample preparation
Gases fill gas cell transparent windows (NaCl/KBr) long path length (10 cm) - few molecules Liquids fill liquid cell solute in transparent solvent Not in water (attacks windows) short path length ( mm) - solvents absorb

4 Solution sample Solvents Water, alcohols – NO
Check the background absorption

5 Demountable IR cell for liquid
Cells 0.01 – 1.0 mm path length Narrower than UV/VIS Sample concentration 0.1 – 10% Demountable cells with Teflon spacers Variation in path length

6 Determination of cell thickness
Determination of thickness(b) Empty cell in the light path Interference fringe 2b/N = l Number if interference fringes DN between two known wavelengths DN = 2b/l1 – 2b/l2 b = DN /2(n1-n2)

7 Solid sample Solid samples make semi-transparent pellet with KBr
Halide salts get transparent when pressured grind and mix with Nujol (hydrocarbon oil) to form mull Grind size < the radiation wavelength 1-2 drop(s) between NaCl plates.

8 Qualitative Analysis Step One : Identify functional groups (group frequency region) cm-1 Step Two : Compare with standard spectra containing these functional groups fingerprint region – sensitive to the structure 600 – 1200 cm-1

9 Group frequency and fingerprint region

10 Group frequencies Approximately calculated from masses and spring constants Variations due to coupling Compared to correlation charts/databases Bond force constant

11 Group frequecy table for organic groups

12 Correlation chart

13 Computer search system
Spectra pattern search Position Relative magnitude Sadtler IR collection (1980) Over 130,000 spectra Spectra coding Algorithm Location of its strongest abs peak Then each additional strong band in 10 regions 40 second for 25,000 compound search

14 Quantitative Analysis
IR more difficult than UV-Vis because narrow bands (variation in e) complex spectra weak incident beam low transducer sensitivity solvent absorption IR mostly used for rapid qualitative but not quantitative analysis Beer’s law failure Long optical path-length required Regular FT-IR is worse than UV-VIS Exception - Tunable IR laser, quantum cascade laser, OPO

15 Reflectance spectroscopy
Types Specular reflection Diffuse reflection Internal reflection Attenuated total reflection

16 DRIFTS Diffuse reflectance IR FT spectroscopy Analysis
Fine powder sample Specular reflections from all randomly oriented surfaces of the powder The intensity of the reflection is roughly independent of the viewing angle Analysis Using mathematical models Kubelka and Munk Fuller and Griffiths

17 Instrumentation of DRIFTS
Adaptor in cell compartment Reference sample Finely grounded KBr Mirror ABS vs. DRIFTS Peak locations are same Relative intensities are different Figure 17-10

18 ATR Attenuated total reflection Sample – wide variety of types
solids of limited solubility Films Threads Pastes Adhesives Powers Principles of the method At a certain angle, total reflection can occur Depth of penetration when reflected (< l) Evanescent wave can be absorbed by the sample

19 ATR instrumentation Figure 17-11 High refrative index ATR crystal
Thallium bromide Thallium iodide Germanium and ZeSe plate Adjustment of incident angle ATR crystal can be dipped into the liquid

20 Applications of ATR

21 17C Photoacoustic IR Spectroscopy
History 1880 Alexander Graham Bell Photo absorption effect Chopped Photon -> sample -> microphone

22 Photoacoutstic (PA) IR
Advantages Scattered & reflected light = no microphone signal FT method is possible CO2 laser PA IR spectroscopy Tunable CO2 laser source PA cell 10 gases (sensitivity 1 ppb) in 5 minutes

23 17D Near IR Spectrum Disadvantages Application 770-2500 nm
13000 – 4000 cm-1 Overtone or combination of fundamental stretching modes C-H, N-H, O-H Weaker absorption than fundamental bands Disadvantages Low molar absorption coefficient Detection limit 0.1% Application Mostly qualitative analysis Water, protein, low mw carbohydrates, food, petro

24 17G IR microspectrometry
Introduced in 1980s IR ABS or reflection spectra Sample dimensions in mm Instrument Ordinary optical microsocpe FT-IR with small IR beam size LN2 MCT (mercury/cadmium/telluride) PC

25 Nicolet Magna 760 with Nic-Plan IR Microscope

26 Tabletop Optical Module (foreground),
Nicolet Magna 550 spectrometer, Right Auxiliary Experimental Module Olympus IX70 inverted microscope 

Download ppt "Applications of IR spectroscopy"

Similar presentations

Ads by Google