Principle & app and instrumentaton of IR

INSTRUMENTAL METHODS OF ANALYSIS, B.PHARM 7TH SEM. AND FOR BSC,MSC CHEMISTRY. Principle & app and instrumentaton of IR. This is Geeta prasad kashyap (Asst. Professor), SVITS, Bilaspur (C.G) 495001

1. Presented by : Mr. G.P Kashyap ( Asst. Prof )
M.Pharm(Q.A)
SiddhiVinayaka Inst. of Technology & Sciences
(Bilaspur, C.G)

2. PrincipleofInfrared(IR)Spectroscopy
➢InfraredSpectroscopyistheanalysisofinfraredlightinteracting
withamolecule.
➢Theportionoftheinfraredregionmostusefulforanalysisof
organiccompoundshaveawavelengthrangefrom2,500to16,000
nm,withacorrespondingfrequencyrangefrom1.9*1013to
1.2*1014Hz.
➢Photonenergiesassociatedwiththispartoftheinfrared(from1
to15kcal/mole)arenotlargeenoughtoexciteelectrons,butmay
inducevibrationalexcitationofcovalentlybondedatomsand
groups.

3. Contn….
•It is known that in addition to the facile rotation of groups about
single bonds, molecules experience a wide variety of vibrational
motions, characteristic of their component atoms.
•Consequently, virtually all organic compounds will absorb infrared
radiation that corresponds in energy to these vibrations.
•Infrared spectrometers, similar in principle to other spectrometer,
permit chemists to obtain absorption spectra of compounds that
are a unique reflection of their molecular structure.

4. Cont….
•Thefundamentalmeasurementobtainedininfrared
spectroscopyisaninfraredspectrum,whichisaplotof
measuredinfraredintensityversuswavelength(or
frequency)oflight.
•IRSpectroscopymeasuresthevibrationsofatoms,and
basedonthisitispossibletodeterminethefunctional
groups.
•Generally,strongerbondsandlightatomswillvibrateata
highstretchingfrequency(wavenumber).

5. InstrumentationofInfrared(IR)Spectroscopy
ThemainpartsofIRspectrometerareasfollows:
•Radiationsource
•Samplecellsandsamplingofsubstances
•Monochromators
•Detectors
•Recorder
•

7. 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.
•Nernst glower
•Mercury arc
•Tungsten lamp
•Globersource
•carbon dioxide laser

8. The Nernst glower
•TheNernstglowerisconstructedofrareearthoxidesin
theformofahollowcylinder.
•Platinumleadsattheendsofthecylinderpermitthe
passageofelectricity.
•Nernstglowersarefragile.
•Theyhavealargenegativetemperaturecoefficientof
electricalresistanceandmustbepreheatedtobe
conductive.

10. THE GLOBAR SOURCE
•Aglobarisarodofsiliconcarbide(5mm
diameter,50mmlong)whichiselectrically
heatedtoabout1,500K.
•Watercoolingoftheelectricalcontactsisneeded
topreventarcing.
•Thespectraloutputiscomparablewiththe
Nernstglower,execeptatshortwavelengths(less
than5mm)whereit'soutputbecomeslarger.

12. The carbon dioxide laser
A tuneablecarbon dioxide laser is used as an
infrared source for monitoring certain
atmospheric pollutants and for determining
absorbing species in aqueous solutions.