infra red presentation

8/17/2019 Infra Red Presentation

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INFRA RED

PRESENTATION


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INTRODUCTION

• Infrared spectroscopy (IRspectroscopy) is the subset ofspectroscopy that deals with the

infrared region of theelectromagnetic spectrum. It coversa range of techniques, the most

common being a form ofabsorption spectroscopy. As withall spectroscopic techniques, it can

be used to identify compounds or

http://en.wikipedia.org/wiki/Spectroscopyhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Electromagnetic_spectrumhttp://en.wikipedia.org/wiki/Absorption_spectroscopyhttp://en.wikipedia.org/wiki/Spectroscopyhttp://en.wikipedia.org/wiki/Spectroscopyhttp://en.wikipedia.org/wiki/Absorption_spectroscopyhttp://en.wikipedia.org/wiki/Electromagnetic_spectrumhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Spectroscopy


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• The infrared portion of theelectromagnetic spectrum is dividedinto three regions

• ear infra red!".# to $.%&m ('$#""!"""cm!')

• iddle infrared!$.% to %"&m ("""!$"")

• *ar infrared! %" to '"""&m ($"" to'")

• ostly used is from """ to +"


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• At "degrees -elvin the atoms of a moleculeare still vibrating

• ibration within infra red region

• If radiated with infra red radiation ofapprioprate wavelength energy is absorbed

• /eads to increase in vibrations and amplitude

• 0hange in dipole moments of the molecule.

• 1pectrometer then measures the energyabsorbed at di2erent wavelengths or wavenumbers to give a spectrum.


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• ibrations can result from stretchingbonds

• 0an also be by bending ordeformation of bonds.

• 1ome molecules are infrared inactiveeg. ethene.

• ost functional groups due tostretching.


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PRINCIPLE


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• I.R deals with vibrational energyinherent in a molecule.

• Increase in the vibrational energy ofeither a bond or a functional group

• *requency of vibration directlyproportional to the strength of thespring but inversely proportional tothe masses of the atoms connectedto the spring!3oo-e4s /aw


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Types of vibrational modes

• 1tretching and bending

• 1tretching can be symmetrical or assymetrical

• 5ending can either be

roc-ing,wagging,scissoring and twisting• ibrational modes should cause a change in

the dipole moment of the bond in order to beI.R active

• Intensity of the absorption bands areproportional to the change in dipole momentthat the bond undergoes when it stretches


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*actors a2ecting stretching

vibration frequencies

• 5ond strength

• ass of atoms

•

3ydrogen bonding• 6lectronegative atoms

• 0on7ugation


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Interpretation of spectrum

• 5etween 8+%"!8'""per cm,thefunctional groups 9:3 and 93appear

• Around '""per cm,the 0;: absorbsI.R radiation

• Around '+""per cm,the 0;0stretching of unsymmetrical al-enesand aromatics and carbon nitrogenstretching occurs at this

wavenumber


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PROCEDURE


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Sample preparation

• =aseous samples require little

preparation beyond puri


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• /iquid samples can be sandwiched between

two plates of a high purity salt (commonly

sodium chloride, or common salt, although a

number of other salts such as

potassium bromide or calcium ?uoride are

also used). The plates are transparent to the

infrared light and will not introduce any lines

onto the spectra. 1ome salt plates are highly

soluble in water, so the sample and washing

reagents must be anhydrous (without water).

http://en.wikipedia.org/wiki/Sodium_chloridehttp://en.wikipedia.org/wiki/Potassium_bromidehttp://en.wikipedia.org/wiki/Calcium_fluoridehttp://en.wikipedia.org/wiki/Anhydroushttp://en.wikipedia.org/wiki/Anhydroushttp://en.wikipedia.org/wiki/Calcium_fluoridehttp://en.wikipedia.org/wiki/Potassium_bromidehttp://en.wikipedia.org/wiki/Sodium_chloride


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• 1olid samples can be prepared in

four ma7or ways. The


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• The second method is to grind aquantity of the sample with aspecially puri


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• The third technique is the 0ast *ilm technique,

which is used mainly for polymeric materials.

The sample is


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• The


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• It is important to note that spectra

obtained from di2erent sample

preparation methods will loo- slightly

di2erent from each other due to

di2erences in the samplesB physical

states


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I1TRC6ITATI:

• we will be limiting our attention to

instrumentation concerned with

spectroscopy in the middle region

(""" ! $""cm!'). It is absorption in

this region which gives structural

information about a compound


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• /ight from the IR source is re?ected from a mirror, through the

reference cell, through an attenuator system and onto a second

mirror. The beam is attenuated by interposing a device that

removes a continuous, but controllable fraction of the light from

the reference beam. The attenuator usually ta-es the form of a

comb, the teeth of which are cut so that the amount of light

attenuated is linearly related to the lateral movement of thecomb through the beam. After passing through the attenuator to

the second mirror, the attenuated light passes through a chopper

to a grating, where light of a speci


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• The chopper arranges for the sensor to alternately receive light that has

been transmitted through the cell, and light that has passed through

the attenuator . The servo system of the attenuator ad7usts the light

transmission until both beams have the same intensity. The amount of

light that is absorbed is indicated by the position of the attenuator.

ore simply, the amount of light of the chosen wavelength which is

absorbed by the sample, is measured by attenuating the reference

beam until its intensity is equivalent to that of the beam transmitted

through the sample. The resolution is controlled by the width of the slit

which is ad7ustable. In the older versions of this type of IR spectrometer,

an analog plotter, mechanically associated with the attenuator,recorded the spectrum. 6ven if modi


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1:CR061

• An inert solid is electrically heated to a

temperature in the range '%""!$""" . The

heated material will then emit infra red radiation

• The Nernst glower 9 mi@ture of o@ides of

Dirconium, yttrium and thorium. Elatinum wires

are sealed to the ends, and a current passed

through the cylinder. The ernst glower canreach temperatures of $$"" .


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• The Globar source- a small rod of silicon carbide

which is electrically heated to about '%"" . Fater

cooling of the electrical contacts is needed toprevent arcing. The spectral output is comparable

with the ernst glower, e@ecept at short

wavelengths (less than % mm) where itBs outputbecomes larger.

• The incandescent wire source is a tightly wound

coil of nichrome wire, electrically heated to ''"" .It produces a lower intensity of radiation than the

ernst or =lobar sources, but has a longer wor-ing

life.


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G6T60T:R1•

Thermocouples consist of a pair of 7unctions ofdi2erent metalsH for e@ample, two pieces of

bismuth fused to either end of a piece of

antimony

• Pyroelectric detectors made from a single

crystalline wafer of a pyroelectric material, such

as triglycerine slp!ate. ost developed

detector and have a fast response time. They are

used in most *ourier transform IR instruments.


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• Photoelectric detectors- mercury

cadmium telluride detector , lead

sulphide photon detector. These

detectors have better response

characteristics than pyroelectric

detectors and are used in *T!IR

instruments


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::03R:AT:R1

• ay be either a prism or grating.ost common prisms material isa0l (transparent from """!+%"cm!

'). 1u2ers from low resolution• 5r may be used (e@tends range to

"")

• :ther 9 0s5r, 0sI


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• "ratings are now pre2ered as they

give better resolution at high

frequency than prisms. If used


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types

• Dispersi#e infra red spectop!otometers These are often double!beam recordinginstruments, employing di2raction gratings fordispersion of radiation.

• Radiation from the source is ?ic-ed between thereference and sample paths. :ften, an optical null system is used. This is when the detector onlyresponds if the intensity of the two beams is

unequal. If the intensities are unequal, a lightattenuator restores equality by moving in or out ofthe reference beam. The recording pen is attachedto this attenuator


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• Forier transform infrared $FTIR%spectrop!otometer is a measurementtechnique for collecting infrared spectra.Instead of recording the amount ofenergy absorbed when the frequency ofthe infra!red light is varied

(monochromator), the IR light is guidedthrough an interferometer. After passingthrough the sample, the measured signalis the interferogram. Eerforming a

mathematical *ourier transform on thissignal results in a spectrum identical tothat from conventional (dispersive)infrared spectroscopy.

http://en.wikipedia.org/wiki/Interferometerhttp://en.wikipedia.org/wiki/Fourier_transformhttp://en.wikipedia.org/wiki/Fourier_transformhttp://en.wikipedia.org/wiki/Interferometer


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Adv.

• Improved frequency resolution

• Improved frequency reproducibility (olderdispersive instruments must be recalibrated foreach session of use)

• 3igher energy throughput

• *aster operation

• 0omputer based (allowing storage of spectra andfacilities for processing spectra)

• 6asily adapted for remote use (such as divertingthe beam to pass through an e@ternal cell anddetector, as in =0 ! *T!IR)


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:G6R AGA066T


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T36R: I0:/6T 6C1 +" *TIR 1pectrometer


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6C1 +" *TIR 1pectrometer with Thermo!icolet microscope


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:CT=A1 + *TIR


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The %"" Juic- 1can I.R

1pectrophotometer


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APPLICATION

• IG6TITK

• 1ubstances that give the same IR 1pectra are

identical,however although IR 1pectrum is

unique for any given chemical compound,there

is the e@ception of optical isomers,which have

identical spectra.


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• A collection of reference spectra for

use with monographs as published in

the 5ritish Eharmacopoeia(5E)helps

in verifying identity of drugs or drug

products


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0:*IRAT: :* IG6TITK

• ost IR 1pectra especially in the


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Getection of IECRITI61

• IR may prove to be useful if only the

impurity absorbs strongly in a

regionwhere the main component is

reasonably transparent eg.

• Adrenalone in adrenaline

R iti f f ti l


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Recognition of functionalgroups

• The IR 1pectrum is capable of yielding

considerable information about the

bonds present in a molecule.

• 1ince functional groups have vibrational

groups,within well de


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Recog cont

• This ma-es IR1pectrum the

1IE/61T,most RAEIG and often most

R6/IA5/6 means for assigning a

compound its class,thus contributing to

structure elucidation of organic molecules.


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JCATITATI6 AA/K1I1

• The application of IR for quantitative

analysis has diminished with the

advent of newer techniques such as

=as 0hromatography,3E/0,R and

1pectro?uorimetry.


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Juantitative cont

• The quantitative analysis is based on

the fact that the intensity or depth of

an absorption band in a substances

is re?ected to the concentration of

the material associated with that

band

JCATITATI6 AA/K1I1


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JCATITATI6 AA/K1I10:T4G

• *or solutions (of drug formulations)

the 5eer /ambert4s law holds and

since the IR 1pectrophotometers

measures band intensities linearly in

LT and therefor log.in Absorbance,A.


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cont

• A plot of Absorbance against concentration

for a series of standards using a calibration

curve, the absorbance of the un-nown canbe measured and the curve used to read

the concentration and vice versa.eg

determination of amount of

phenobarbitone in phenobarbitone tablets.


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JCATITATI6 0:TR:/ :*036I0A/ R AG 16EARATI:

• IR provides a convenient and simple methodfor chec-ing each stage of synthesis or formonitoring 0hromatographic 1eparation orprogress of organic reactions especially ifthey involve suitable spectral changeseg.include the o@idation of a secondaryalcohol(8%"cm!') to -etone ('$%cm!')and

chromatographic separation of a %!membered!ring -etone('%"cm!')and a +!memberedisomer('%"cm!')

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