instrumentation of IR spectroscopy slides ppr.

easy slides to understand the instrumentation of IR spectrometer and sample preparation for analysis at university lab level for undergraduates.

1. Instrumentation of IR spectroscopy Presentation prepared by , Muhammad Talha. .

2. IR spectroscopy , instrumentation, and General applications. Infrared spectroscopy is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functional groups in solid, liquid, or gaseous forms.

3.   Instrumentation The main parts of IR spectrometer are as follows: 1. radiation source 2. sample cells and 3. sampling of substances 4. Monochromators 5. detectors 6. recorder

4. Instrumentation of IR

5. 2 . sample cells and sampling of substances IR spectroscopy has been used for the characterization of solid, liquid or gas samples.                      i .      Solid -  Various techniques are used for preparing solid samples such as pressed pellet technique, solid run in solution, solid films, mull technique etc.                   ii.      Liquid –  samples can be held   using a liquid sample cell made of alkali halides. Aqueous solvents cannot be used as they will dissolve alkali halides. Only organic solvents like chloroform can be used.                 iii.      Gas –  sampling of gas is similar to the sampling of liquids . IR radiation sources IR instruments require a source of radiant energy which emit IR radiation which must be steady, intense enough for detection and extend over the desired wavelength . Various sources of IR radiations are as follows. a)              Nernst glower b)              Incandescent lamp c)              Mercury arc d)       Tungsten lamp

6. 4. Monochromators –  Various types of monochromators are prism, gratings and filters. Prisms are made of Potassium bromide , Sodium chloride or Caesium iodide. 5 . Filters are made up of Lithium Fluoride and Diffraction gratings are made up of alkali halides. 6. Detectors –  Detectors   are used to measure the intensity of unabsorbed infrared radiation. Detectors like thermocouples, Bolometers, thermistors, Golay cell, and pyro-electric detectors are used. 7. Recorders –  Recorders are used to record the IR spectrum.

7. Sample Preparation IR spectroscopy is used for the characterization of solid, liquid or gas samples. Material containing sample must be transparent to the IR radiation. So, the salts like NaCl, KBr are only used. 1.      Sampling of solids Various techniques used for preparing solid samples are as follows a)      Mull technique:  In this technique, the finely crushed sample is mixed with Nujol (mulling agent) in n a marble or agate mortar, with a pestle to make a thick paste. A thin film is applied onto the salt plates. This is then mounted in a path of IR beam and the spectrum is recorded. b)      Solid run in Solution –  In this technique, solid sample may be dissolved in a non-aqueous solvent provided that there is no chemical interaction with the solvent and the solvent is not absorbed in the range to be studied. A drop of solution is placed on the surface of alkali metal disc and solvent is evaporated to dryness leaving a thin film of the solute. c)      Case film technique –  If the solid is amorphous in nature then the sample is deposited on the surface of a KBr or NaCl cell by evaporation of a solution of the solid and ensured that the film is not too thick to pass the radiation. d)      Pressed pellet technique –  In this technique, a small amount of finely ground solid sample is mixed with 100 times its weight of potassium bromide and compressed into a thin transparent pellet using a hydraulic press. These pellets are transparent to IR radiation and it is used for analysis.

8. Case film method Liquid sample or solid run in solution

9. Some pellets for IR spectrophotometer

10. 2.      Sampling of liquids Liquid sample cells can be sandwiched using liquid sample cells of highly purified alkali halides, normally NaCl. Other salts such as KBr and CaF 2  can also be used. Aqueous solvents cannot be used because they cannot dissolve alkali halides. Organic solvents like chloroform can be used. The sample thickness should be selected so that the transmittance lies between 15-20%. For most liquids, the sample cell thickness is 0.01-0.05 mm. Some salt plates are highly soluble in water, so the sample and washing reagents must be anhydrous 3.      Sampling of gases The sample cell is made up of NaCl, KBr etc. and it is similar to the liquid sample cell. A sample cell with a long path length (5 – 10 cm) is needed because the gases show relatively weak absorbance. 

11. Thin-film IR Sampling Techniques Two different methods are used to prepare thin films on an IR plate. If the compound to be studied is a liquid, you need to use  thin-liquid film IR sampling technique . If it is a solid, use  thin-solid film IR sampling technique . Note: a solution of a solid compound in a solvent does  not  count as a liquid; if the compound of interest is a solid at room temperature, even if it is dissolved in a solvent like methylene chloride, the compound is a solid and must be run by the procedure for thin-solid films. Once the sample is prepared, you can  collect the spectrum  in one of the IR instruments. Other Sampling Techniques A KBr pellet is prepared by grinding the solid sample with solid potassium bromide (KBr) and applying great pressure to the dry mixture . Again, KBr is chosen because it is transparent to infrared radiation. If the pellet is prepared properly, one can actually see through it, as through a pane of glass.

12. Bad holding method Good holding method

13. Just for your knowledge to understand the IR spectrophotometry and instrumentations IR Lamp Light from quartz  tungsten halogen lamp  (QTH) lamps is emitted by a heated filament. The filament is enclosed in a quartz envelope filled with gases. The spectral distribution is close to a color temperature of approximately 3000K.  IR vs UV spectroscopy UV /vis  spectroscopy  utilizes  UV  and visible light, which has enough energy to excite molecules to a higher electronic state.  IR  light has a lower energy, and therefore only enough to excite a molecule to a 17 - 6 higher vibrational energy level.  For general knowledge Infrared heating  uses  infrared lamps , commonly called  heat lamps , to transmit  infrared  radiation to the body that is being heated. ...  Infrared heat lamps  are commonly incandescent  bulbs  which are able to produce  infrared  radiation.

14. Range of IR IR  frequencies  range  from about 300 gigahertz (GHz) up to about 400 terahertz (THz), and wavelengths are estimated to  range  between 1,000 micrometers (µm) and 760 nanometers (2.9921 inches), although these values are not definitive. The definition of infrared is  light  rays which are longer than  light  but shorter than radio waves. Electromagnetic radiation with a wavelength between . 7 and 300 micrometers is an example of infrared. A camera that can detect these wavelengths is an example of a camera that reads infrared. Most best range of IR The  most useful I.R.  region lies between 4000 - 670cm -1 . Preventions The potential hazards of infrared heat bulbs, lamps, and radiators are mainly to your  skin  and eyes. Because of the intense radiant heat emitted, prolonged exposure can result in severe  burns  to the  skin . Your eyes are very susceptible to high-intensity short-wave infrared  radiation  as well.

15. Below are the limitations of  infrared spectroscopy :- Explanation: 1 Not possible to analyze the molecular weight of any substance. 3 IR spectra of two enantiomeric compound are identical. So IR spectroscopy fails to distinguish between enantiomers. Impotent The damage done to a plate by fingerprints, pits, and cloudiness cause the IR spectrum run on the plate to have broad bands. This is because IR spectra look best when run as a thin, even films of compounds. Pits and fingerprints cause a thick and uneven film to be laid down on the plate, leading to scattering of IR radiation and to bands that are too intense; cloudiness causes scattering of IR radiation and prevent it from going through the sample, leading to broad bands and a spectrum that is less than 100% transmission.

16. Thank you Material collection typing and setting by ; Muhammad Talha KFUEIT