Infrared spectroscopy. Siriphorn Laomanacharoen Bureau of Drug and Narcotic Department of Medical Sciences 2 March 2012

Transcription

1 Siriphorn Laomanacharoen Bureau of Drug and Narcotic Department of Medical Sciences 2 March

2 Infrared region 2

3 Infrared region below red in the visible region at wavelengths between µm more common units are wavenumbers, or cm -1, reciprocal to the wavelength in centimeters, proportional to the frequency of the wave. 3

4 Infrared region Infrared light far infrared cm -1 mid infrared cm -1 near infrared cm -1 4

5 Molecular vibrations 2 types of molecular vibrations stretching movement along the bond axis, interatomic distance is increasing or decreasing bending change in bond angle 5

6 Molecular vibrations: Stretching 6

7 Molecular vibrations: Bending 7

8 Molecular vibrations The vibrations that change the dipole moment of the molecule are IR active. 8

9 Fingerprint Infrared spectroscopy No two molecules will give exactly the same IR spectrum (except enantiomers). Complex vibrations: cm -1, called the fingerprint region 9

10 Infrared spectroscopy chemical analytical technique which measures the infrared intensity versus wavenumber of light detects the vibration characteristics of chemical function groups in a sample 10

11 Instrument Dispersive 11

12 Instrument Fourier Transform 12

13 Instrument Fourier Transform 13

14 Instrument Infrared spectroscopy Fourier Transform high sensitivity high resolution completes a scan in 1-2 seconds takes several scans and averages them 14

15 Sample preparation (transmission) Solid sample Pellet method transparent disk - finely ground mixture of dry KBr (IR grade) and sample and compacted under pressure 15

16 Sample preparation (transmission) Solid sample Pellet method - sample 1-2 mg mix with about mg of dry, powdered KBr (dry at 250 C for 1 hr; BP2012, 105 C for 12 hr; USP34) - the mixture is pressed under a pressure of 800 MPa. 16

17 Sample preparation (transmission) Solid sample Pellet method - KBr is extremely hygroscopic. Bands near 3440 and 1630 cm -1,resulting from moisture, frequently appear in the spectra. - It is difficult to make a good pellet. Mini-Press or Handi-Press affords a simple procedure. 17

18 Sample preparation (transmission) Solid sample Pellet method : Handi-Press 18

19 Sample preparation (transmission) Solid sample Pellet method : Mini-Press 19

20 Sample preparation (transmission) Solid sample Mull method dispersion of finely ground solid in a mulling agent and placed between two cell windows (as a thin film) in a demountable cell 20

21 Sample preparation (transmission) Solid sample Mull method - mulling agent has a high viscosity which helps to maintain the dispersion. Nujol (liquid paraffin) Fluorolube - strong absorption peaks of Nujol at and cm -1 21

22 Sample preparation (transmission) Liquid sample Demountable cell (neat liquid cell) placing a thin film of pure liquid between two windows windows : highly polished salt plate NaCl, AgCl, KBr 22

23 Sample preparation (transmission) Liquid sample Demountable cell (neat liquid cell) - the thickness of the film cannot be determined and is slightly different at each time of sample preparation. - volatile liquid evaporate to some extent causing a decrease in the intensity while the spectrum is being run. 23

24 Sample preparation (transmission) Liquid sample Demountable cell (neat liquid cell) 24

25 Sample preparation (transmission) Liquid sample Liquid sealed cell filling liquid sample in a permanently mounted windows which separated by a thin spacer of known thickness 25

26 Sample preparation (transmission) Liquid sample Liquid sealed cell - the solvent must be dry. - the common used solvent : CCl 4, CHCl 3, CS 2 - the solvent gives strong peaks. 26

27 Sample preparation (Transmission) Liquid sample Liquid sealed cell 27

28 Sample preparation (Diffuse reflectance) Diffuse reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) 28

29 Sample preparation (Diffuse reflectance) - it is fast and easy because no sample preparation is required. - fill the micro-cup with the mixture of powder and KBr (5% of sample) - the sample should be ground to the particles size of 5 microns or less. 29

30 Sample preparation (Diffuse reflectance) 30

31 Sample preparation (Diffuse reflectance) 31

32 Interpretation of spectra Requirement for interpretation Spectrum must be adequately resolved and of adequate intensity. Spectrum should be that of a reasonably pure compound. Spectrophotometer should be calibrated. Method of sample handling must be specified. 32

33 Interpretation of spectra Alkane 33

34 Interpretation of spectra Alkene 34

35 Interpretation of spectra Alkyne 35

36 Interpretation of spectra Alcohol 36

37 Interpretation of spectra Amine 37

38 Interpretation of spectra Ketone 38

39 Interpretation of spectra Background 39

40 Interpretation of spectra Air 40

41 Interpretation of spectra 41

42 Interpretation of spectra Nujol 42

43 Limitation Infrared spectroscopy IR alone cannot determine a structure. Some signals may be ambiguous. The absence of a signal is definite proof that the functional group is absent. Correspondence with a known sample s IR spectrum confirms the identity of the compound. 43

44 Calibration Infrared spectroscopy Calibration can be made with reliable standards such as polystyrene film. Test : Wavenumber accuracy Wavenumber precision 44

45 Polystyrene film 45

46 Factors that affect the IR spectra - Humidity - Carbondioxide - Solvent effect - Temperature 46

47 Application Identification - compare with reference compound - compare with reference spectra Structure investigation Quatitative analysis 47

48 Reference Organic Chemistry, L.G. Wade,Jr. Spectrometric Identification of Organic Compounds, Robert M. Silverstein and Francis X. Webster British Pharmacopoeia 2012 ค ม อการใช งาน Jasco FTIR