Sampling Techniques in IR Spectroscopy

In this slide contains principle of IR spectroscopy and sampling techniques.
Presented by: R.Banuteja (Department of pharmaceutical analysis).
RIPER, anantpur.

1. 1 Presented by R. BHANUTEJA (Reg. No: 20L81S0702) Under the guidance of Dr. P. Ramalingam, M. Pharm., PhD Director – R&D Division & Professor of Pharmaceutical Analysis and Medicinal Chemistry, President – IPA Local Branch – Anantapuramu . Sampling techniques in IR Spectroscopy A seminar as a part of curricular requirement for 1 st year M. Pharm 1 st semester

2. 2 Basic principle of IR absorption About IR Spectra Sampling techniques in IR Spectroscopy Solid run in solutions Solid films Mull technique Sampling of liquids Sampling of Gas References Contents

3. 3 IR spectroscopy refers broadly to that region of electromagnetic spectrum which lies between visible and microwave regions . This region is divided into different sections Region Energy (Kj/mol) Wave number (cm ¯¹) Wavelength ( µm ) Near IR 150-50 12,800-4000 0.78-2.5 Mid IR 50-2.5 4000-200 2.5-50 Far IR 2.5-0.1 200-10 50-1000 Basic principle of IR Absorption

4. 4 In IR spectroscopy detects the absorption of light by a compound, in the IR region of the electromagnetic spectrum . To absorb light a molecule must have a bond within its structure that can exhibit what is referred to as a dipole moment which means electrons within a bond are not shared equally . Applications Identification of functional groups and structural elucidation. Study of covalent bonds in molecule. Detection of impurities in a compound. Biomedical studies of human hair.

5. 5 About IR Spectra Graph plots:- X-axis–wave number Y-axis-transmittance

6. 6

7. 7 IR spectrum of ethanol

8. 8 Sampling in solids Solid run in solution Solid films Mull technique Pressed pellet technique Sampling in liquids Sampling in gases Sampling techniques in IR spectroscopy

9. 9 Solid is dissolved in non-aqueous inert solution A drop of this solution is placed on alkali metal disc Allow to evaporate & leaving a thin film of solute Allow the thin film in spectrometer Some solvents used are chloroform, carbon tetra chloride, Acetone, cyclohexane etc. SOLID RUN IN SOLUTIONS

10. 10 If sample is polymer resins and amorphous solids Dissolve the sample in a suitable (or) reasonable volatile solvent Solution is mounted on rock salt plate (Nacl or KBR) Evaporate by gentle heat SOLID FILMS

11. 11 Small quantity of sample is thoroughly grind in a clean mortar until fine powder. The mulling agent(mineral oil (or) nujol) is introduced in a small quantity just sufficient to powder grind ,the powder & mulling agent approximately the consistency of paste . Mixture transferred to mull plates and squeezed together to adjust the thickness of sample between IR transmitting window. This is then mounted in path of ir beam and spectrum is run. Although Nujol is transparent throughout IR region, it has absorption maxima at 2915, 1462, 1376 & 719 cm− ¹ Mull techniques

12. Mull technique

13. 13 A small amount of finely ground solid sample is mixed with 100 times its weight of KBR in a vibrating ball mill. This finely ground mixture is then pressed under very high pressure (5000-10000 psi) in a mini press to form a small pellet. The powder (sample + KBR) is introduced in between the 2 bolts and the upper screw A is tightened until the powder is compressed to thin disc. After compressing the sample bolts A&A1 are removed and a steel cylinder with pellet inside it is placed in path of the beam of IR spectrometer and A blank KBR pellet of identical thickness is kept in the path of reference beam. Pressed pellet technique

14. 14 Pressed pellet technique Hydraulic press

15. 15 Advantages The use of KBR eliminates the problem of bands which appear in IR spectrum. Kbr pellets can be stored for long periods of time The resolution of spectrum in KBR is superior than any other Disadvantages The high pressure involved during the formation of pellets may bring polymorphic changes in crystalinity in sample . In some cases the substitution of ligand by bromide may be possible in organic complexes The method not successful for some polymers which are difficult to grind with kbr

16. Liquid sample cells can be sandwiched using highly purified alkali halides such as Nacl ,kbr ,caf2. The sample thickness should be selected so that the transmittance lies between 15-20%. For most of liquids the sample cell thickness is 0.01 -0.05 mm. Aqueous solvents cannot be used instead use organic solvents like chloroform, Acetone, cyclohexane . Sampling of liquids

17. 17 The IR radiation passes through a sample and chemical vapours in sample will absorb the IR energy at different wave lengths. The gas cell is made up of Nacl and for low concentrated gases long path length is required. Multi reflections can be used to make effective path length as long as 40 cm so that constitutions of gas can be determined All compounds in the vapour will give unique fingerprints of absorbance features which will compared to library of spectra. Sampling of gases

18. 18 Gurudeep.R.chatwal & sharm.K.Anand , Instrumental methods of chemical analysis, 5 th edition, pg.no.2.29. Willard,merritt,dean&settle , Instrumental methods of analysis,7 th edition,pg.no.305-310 . B.K.Sharma , Insrumental methods of chemical analysis,26 th edition,pg.no.262-264. https://www.pharmatutor.org https://chem.libretexts.org References

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