irinstruction

8/7/2019 IRInstruction

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InfraredInfrared

SpectroscopySpectroscopy

Department of Natural SciencesDepartment of Natural Sciences

UMUM--DearbornDearborn

Written by Bette KreuzWritten by Bette Kreuz

Produced by Ruth DusenberyProduced by Ruth Dusenbery

20002000



Info Slide 1Info Slide 1

Infrared spectroscopy is anInfrared spectroscopy is an

instrumental method of instrumental method of

analysis that can be used toanalysis that can be used toidentify and quantifyidentify and quantify

samples ranging fromsamples ranging from

pharmaceuticals to dieselpharmaceuticals to diesel

emissions.emissions.



Slide 1Slide 1IntroductionIntroduction




All modern instruments areAll modern instruments are

Fourier TransformFourier Transform

instruments.instruments.

In all transmissionIn all transmissionexperiments radiation fromexperiments radiation from

a source is directeda source is directed

through the sample to athrough the sample to adetector.detector.



Slide 2Slide 2

SampleSample

CompartmentCompartment

IR SourceIR Source DetectorDetector




The measurement of theThe measurement of the

type and amount of light type and amount of light

transmitted by the sampletransmitted by the sample

gives information about thegives information about the

structure of the moleculesstructure of the molecules

comprising the sample.comprising the sample.



Slide 3Slide 3

InfraredInfrared

SourceSource

DetectorDetector

SampleSample

CompartmentCompartment




In the IR region of theIn the IR region of the

electromagnetic spectrum,electromagnetic spectrum,

the absorption of radiationthe absorption of radiationby a sample is due toby a sample is due to

changes in the vibrationalchanges in the vibrational

energy states of a molecule.energy states of a molecule.



Slide 4Slide 4




The pattern of absorptionThe pattern of absorption

as a function of wavelengthas a function of wavelength

is called an IR spectrum.is called an IR spectrum.



Slide 5Slide 5




To obtain an IR spectrum,To obtain an IR spectrum,the sample must be placedthe sample must be placed

in a ´containerµ or cell that in a ´containerµ or cell that

is transparent in the IRis transparent in the IRregion of the spectrum.region of the spectrum.

Sodium chloride or salt Sodium chloride or salt

plates are a common meansplates are a common means

of placing the sample in theof placing the sample in the

light beam of thelight beam of the

instrument.instrument.



Slide 6Slide 6

IR transparent Salt PlatesIR transparent Salt Plates




These plates are made of These plates are made of

salt and must be stored in asalt and must be stored in a

water freewater free environment environment such as the dessicatorsuch as the dessicator

shown here.shown here.



Slide 7Slide 7

DessicatorDessicator

WaterWater--freefree

EnvironmentEnvironment

forfor

WaterWater--sensitivesensitive

Salt Plates.Salt Plates.




The plates must also beThe plates must also be

handled with gloves tohandled with gloves to

avoid contact of the plateavoid contact of the platewith moisture from one·swith moisture from one·s

hands.hands.



Slide 8Slide 8




To run an IR spectrum of aTo run an IR spectrum of a

liquid sample, a drop or twoliquid sample, a drop or two

of the liquid sample isof the liquid sample isapplied to a salt plate.applied to a salt plate.



Slide 9Slide 9




A second salt plate isA second salt plate is

placed on top of the first placed on top of the first

one such that the liquidone such that the liquidforms a thin filmforms a thin film

´sandwichedµ between the´sandwichedµ between the

two plates.two plates.



Slide 10Slide 10




The two plates are thenThe two plates are then

secured in a sample holdersecured in a sample holder

that is compatible with thethat is compatible with theparticular instrument beingparticular instrument being

used.used.



Slide 11Slide 11



The cell holder is thenThe cell holder is then

placed in the beam of theplaced in the beam of the

instrument.instrument.




Slide 12Slide 12



The light beam traversesThe light beam traverses

the sample compartment,the sample compartment,

as illustrated by the redas illustrated by the redline.line.




Slide 13Slide 13

Light PathLight Path(shown by red line)(shown by red line)



Info Side 14Info Side 14

The sample is then scannedThe sample is then scanned

by the instrument utilizingby the instrument utilizing

predesignated parameters.predesignated parameters.

A relevant background scanA relevant background scan

should already have beenshould already have been

taken.taken.



Slide 14Slide 14

Click Here to Start ScanClick Here to Start Scan




A satisfactory spectrum hasA satisfactory spectrum haswell defined peakswell defined peaks--but not but not so intense as to causeso intense as to cause

flattening on the bottom of flattening on the bottom of the peaks.the peaks.

Major peaks can be labeledMajor peaks can be labeled

using the peak function of using the peak function of the softwarethe software



Slide 15Slide 15

WellWell--defineddefined

peaks arepeaks are

labeled with thelabeled with theWavenumbersWavenumbers

of theof the

AbsorptionAbsorption

Maxima.Maxima.




The spectrum can then beThe spectrum can then be

printed using the print printed using the print

function of the software.function of the software.



Slide 16Slide 16




A sample of a printout of A sample of a printout of

an IR spectrum.an IR spectrum.



Slide 17Slide 17

Sample of aSample of aprintout of printout of

an IR an IR

spectrum.spectrum.




The salt plates are cleanedThe salt plates are cleanedby rinsing into a wasteby rinsing into a wastecontainer with a suitablecontainer with a suitable

organic solvent organic solvent--commonlycommonlycyclohexane.cyclohexane.

NEVER WATER!NEVER WATER!



Slide 18Slide 18

CYCLOHEXANECYCLOHEXANE

SolventSolvent




Cloudy plates must beCloudy plates must be

polished to return them to apolished to return them to a

transparent condition.transparent condition.

To polish cloudy windows,To polish cloudy windows,

rotate salt plate onrotate salt plate on

polishing cloth.polishing cloth.



Slide 19Slide 19




The clean plates and cellThe clean plates and cell

holder are stored in theholder are stored in the

moisture free atmospheremoisture free atmosphereof a dessicator.of a dessicator.



Slide 20Slide 20

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