INFRARED SPECTROSCOPYINFRARED SPECTROSCOPY

Pn. Suryati Bt. SyafriPn. Suryati Bt. SyafriEn. Maywan HarionoEn. Maywan Hariono

20092009

What is IR light?What is IR light?Is a kind of electromagnetic radiation Is a kind of electromagnetic radiation which has wave region longer than which has wave region longer than visible light, but shorter than radio visible light, but shorter than radio wave.wave.Low energyLow energy

What is IR region?What is IR region?

The wavelength region is 2.5-25 µmThe wavelength region is 2.5-25 µmThe unit commonly used is The unit commonly used is wavenumbers (cmwavenumbers (cm-1-1 ) i.e. 4000-400 ) i.e. 4000-400 cmcm-1-1 Remember that Wavenumber is Remember that Wavenumber is proportional with energy (E) and proportional with energy (E) and frequency (v), but reciprocal with frequency (v), but reciprocal with wavelength.wavelength.

Light & Electromagnetic SpectrumLight & Electromagnetic Spectrum

IR ApplicationIR ApplicationBroadly applied in several area sort of Broadly applied in several area sort of ::

- ArmyArmy- Fire manFire man- VeterinaryVeterinary- PharmacyPharmacy- Electronic devicesElectronic devices- Remote sensingRemote sensing

IR spectrumIR spectrumDivided into 3 regionsDivided into 3 regions

1.1. Near InfraredNear Infrared2.2. Middle InfraredMiddle Infrared3. 3. Far Infrared Far Infrared

Spektrum IMSpektrum IMRangesRanges Far Far

InfraredInfraredMiddle Middle InfraredInfrared

Near Near InfraredInfrared

Wavelength Wavelength rangerange

50-1000µm50-1000µm 2.5-50µm2.5-50µm 0.8-2.5µm0.8-2.5µm

Wavelength Wavelength numbernumber

200-10cm200-10cm-1-1 4000-4000-200cm200cm-1-1

12500-4000 12500-4000 cmcm-1-1

Energy Energy rangerange

0.025-0.025-0.0012eV0.0012eV

0.5-0.025eV0.5-0.025eV 1.55-0.5eV1.55-0.5eV

PrinciplesPrinciplesWhen the certain molecules are exposed When the certain molecules are exposed to IR light, it will absorb the energy to to IR light, it will absorb the energy to make the atoms of molecules vibratingmake the atoms of molecules vibratingThe vibration frequency depend on the The vibration frequency depend on the amount of atoms and the length and the amount of atoms and the length and the strength of atomic bondingstrength of atomic bondingMolecule vibration is stimulated by Molecule vibration is stimulated by absorption radiation in the same absorption radiation in the same frequency with the frequency of its origin frequency with the frequency of its origin vibrationsvibrations

Energy TrendsEnergy TrendsEnergy follows vibration frequency of atomsEnergy follows vibration frequency of atoms-light atoms vibrate more rapidly: -CH, NH, -light atoms vibrate more rapidly: -CH, NH, OH vibrations . 2800 cmOH vibrations . 2800 cm-1-1

Multiple bonds vibrate more rapidly: Multiple bonds vibrate more rapidly: triple bonds : C≡C (2100-2200), C≡N (2240-triple bonds : C≡C (2100-2200), C≡N (2240-2280)2280)Double bonds : C=O (1680-1750), C=C Double bonds : C=O (1680-1750), C=C (1620-1680)(1620-1680)Single bond : C-O (1025-1200) Single bond : C-O (1025-1200)

Intensity TrendsIntensity TrendsFollows change in dipole caused by Follows change in dipole caused by vibrating atomsvibrating atoms– Polar bonds (strong bond dipoles) absorb Polar bonds (strong bond dipoles) absorb

stronglystronglyO-HO-HC=O, C=NC=O, C=NC-OC-O

– Nonpolar bonds absorb weaklyNonpolar bonds absorb weaklyC=C, C≡C C=C, C≡C

Follows overlapping bandsFollows overlapping bands– CH bands tend to overlapCH bands tend to overlap– Molecules contain many CHMolecules contain many CH– CH absorptions tend to be strongCH absorptions tend to be strong

PRINCIPLESPRINCIPLESFor each molecules, there is a For each molecules, there is a various kind of vibration occursvarious kind of vibration occurs

What kind of sample be able to What kind of sample be able to absorb IR radiation?absorb IR radiation?

Only vibration which alters molecule dipole moment Only vibration which alters molecule dipole moment (electron Hanya getaran yang meyebabkan (electron Hanya getaran yang meyebabkan perubahan dipole molekul (the magnitude of positive perubahan dipole molekul (the magnitude of positive and negative charge between two bonded atoms) and and negative charge between two bonded atoms) and having the IR absorption frequency in the IR region having the IR absorption frequency in the IR region

Gas molecules such as OGas molecules such as O22, H, H22 and Cl and Cl22 don’t have a don’t have a dipole moment, means no IR absorption occursdipole moment, means no IR absorption occurs

SOSO22 dan CO dan CO22 have a dipole moment so it will give IR have a dipole moment so it will give IR absorptionabsorption

Every functional group has their own IR Every functional group has their own IR absorption absorption The more complex in molecule structure, The more complex in molecule structure, the more complex in IR absorptionthe more complex in IR absorptionIt is used to identify any functional group It is used to identify any functional group presents in a molecule structurepresents in a molecule structure

IR Spectrum DistributionIR Spectrum Distribution1.1. 4000-2500 cm4000-2500 cm-1-1, absorption of atom which , absorption of atom which

is bond to H atom, ex: C-H, O-H dan N-His bond to H atom, ex: C-H, O-H dan N-H2.2. 2500-2000 cm2500-2000 cm-1-1, triple bond, ex: C≡C , , triple bond, ex: C≡C ,

C≡NC≡N3.3. 2000-1500 cm2000-1500 cm-1-1, double bond, ex: C=O, , double bond, ex: C=O,

C=C, C=NC=C, C=N4.4. 1500-400 cm1500-400 cm-1-1, an absorption that , an absorption that

involves the deformation of other involves the deformation of other bondingsbondings

Fingerprint region (<1500 cmFingerprint region (<1500 cm-1-1))Many bands & many overlapsMany bands & many overlaps– Heavy atom stretchesHeavy atom stretches– All bends, etc.All bends, etc.– Should have simple molecule (or other Should have simple molecule (or other

evidence or structure) before intepreting evidence or structure) before intepreting bands in this regionbands in this region

Overall pattern reflects molecular Overall pattern reflects molecular structure structure – Pattern from 1400-600 = molecular Pattern from 1400-600 = molecular

fingerprintsfingerprints

ProsedureProsedure

IR light is passed through the sample, and the amount of energy which is IR light is passed through the sample, and the amount of energy which is absorbed by the sample per cm wavelength will be recorded .absorbed by the sample per cm wavelength will be recorded .The IR light desired will be selected by monochromator before exposed to The IR light desired will be selected by monochromator before exposed to the sample’ Interferometer is used for measuring all wavelength in one the sample’ Interferometer is used for measuring all wavelength in one running time.running time.The data will be translated into the graph which is plotted as wavelength The data will be translated into the graph which is plotted as wavelength vs transmisionvs transmisionThe graph might be compared to known standard referenceThe graph might be compared to known standard reference

InstrumentationInstrumentationConventional method(dispersive Conventional method(dispersive instrument)instrument)– The monochromator being used to The monochromator being used to

select frequency of one radiation in one select frequency of one radiation in one time through the sample.time through the sample.

PeralatanPeralatanSpektrometer FTIR (Fourir Transform IR)Spektrometer FTIR (Fourir Transform IR)– Semua frekuensi yang diperlukan melalui instrument sekaligusSemua frekuensi yang diperlukan melalui instrument sekaligus– Menggunakan interferometer contohnya Michelson InterferometerMenggunakan interferometer contohnya Michelson Interferometer– Teknik cepat dan pantasTeknik cepat dan pantas– Digunakan dikebanyakan makmal kimiaDigunakan dikebanyakan makmal kimia

Animation of FTIRAnimation of FTIR

IR ComponentsIR ComponentsA. IR ResourcesA. IR Resources– Quartz halogenQuartz halogenNernst Glower lamp (run at 2000Nernst Glower lamp (run at 2000ooC)C)– Globar (made from Carbide silicon, run Globar (made from Carbide silicon, run

at 1100at 1100ooC)C)

IR ComponentsIR ComponentsB. sampleB. sample1. solids1. solids– A. Nujol mullA. Nujol mull

The sample is ground using a mortar and pestle to The sample is ground using a mortar and pestle to give a very fine powdergive a very fine powderA small amount is then mixed with nujol (liquid A small amount is then mixed with nujol (liquid paraffin) togive a pasteparaffin) togive a pasteSeveral drops of this paste are then applied between Several drops of this paste are then applied between two sodium chloride plates (these do not absorb two sodium chloride plates (these do not absorb infrared in the region of interest)infrared in the region of interest)The plates are then place in the instrument sample The plates are then place in the instrument sample holder ready for scanningholder ready for scanning

IR ComponentsIR ComponentsB. Potassium Bromide diskB. Potassium Bromide disk– A verry small amount of the solid A verry small amount of the solid

(approximately 1-2 mg) is added to pure (approximately 1-2 mg) is added to pure potassium bromide powder (approximately 200 potassium bromide powder (approximately 200 mg) and ground up as fine as possiblemg) and ground up as fine as possible

– This is then placed in a small die and put under This is then placed in a small die and put under pressure mechanically. The pressure is pressure mechanically. The pressure is maintained for several minutes before maintained for several minutes before removing the die and the KBr disk formedremoving the die and the KBr disk formed

– The disk is then placed in a sample holder The disk is then placed in a sample holder ready scanningready scanning

Sample preparationSample preparation

Sample preparationSample preparation2. thin films2. thin films– The infrared spectrum of thin film can be easily obtained The infrared spectrum of thin film can be easily obtained

by placing a sample in a suitable holder, such as a card by placing a sample in a suitable holder, such as a card with a slot cut for the sample windowwith a slot cut for the sample window

– This method is often used for checking the calibration of This method is often used for checking the calibration of an instrument with a polystrirene sample as the band an instrument with a polystrirene sample as the band produced by this material are accurately knownproduced by this material are accurately known

3. liquids3. liquids– This is possibly the simplest and the common method This is possibly the simplest and the common method

for sample preparationfor sample preparation– A drop of the sample is placed between two potassium A drop of the sample is placed between two potassium

bromide or sodium chloride circular plates to produce a bromide or sodium chloride circular plates to produce a thin capillary filmthin capillary film

– The plates are then placed in a holder ready for analysisThe plates are then placed in a holder ready for analysis

Sample preparationSample preparation4. gases4. gases– To obtaine an infrared spectrum of a gas To obtaine an infrared spectrum of a gas

requires the use of a cylindrical gas cell requires the use of a cylindrical gas cell with windows at each end composed of with windows at each end composed of an infrared inactive material such as an infrared inactive material such as KBr, NaCl or CaFKBr, NaCl or CaF22

– The cell usually has an inlet and outlet The cell usually has an inlet and outlet port with atap to enable the cell to be port with atap to enable the cell to be easilly filled with the gas to be analyzedeasilly filled with the gas to be analyzed

instrumentationinstrumentationC. monochromator/interferometerC. monochromator/interferometer– Break down the radiation of light to the Break down the radiation of light to the

different wave region in one time different wave region in one time running process.running process.

D. detectorD. detector– CCD (charge couple device)CCD (charge couple device)– InGaAs (Indium Gallium Arsen)InGaAs (Indium Gallium Arsen)– Pbs (Lead sulfide)Pbs (Lead sulfide)

InstrumentationInstrumentationDisplayDisplay– Exhibit the collected dataExhibit the collected data– Translate the data to the graphTranslate the data to the graph– The graph is plotted as transmision vs The graph is plotted as transmision vs

frequnecy (wavenumbers)frequnecy (wavenumbers)

AdvantagesAdvantagesProvide the fingerprint for the sample Provide the fingerprint for the sample being analyzedbeing analyzedThe installation of instrument to the The installation of instrument to the computer allows the comparison of computer allows the comparison of sample spectrum and standard sample spectrum and standard reference can be run simultaneouslyreference can be run simultaneously

DisadvantagesDisadvantagesRarely used for quantitative purpose Rarely used for quantitative purpose since the spectrum produced is too since the spectrum produced is too complicated to determine one by onecomplicated to determine one by oneThe sample preaparation is quite The sample preaparation is quite difficult, needs the skill to handle it.difficult, needs the skill to handle it.

anilineaniline

phenolphenol

Salycilic acidSalycilic acid

ethanolethanol

Contoh spektrumContoh spektrumallopurinolallopurinol

phenytoinphenytoin

References References David G. watson (2005). David G. watson (2005). Pharmaceuthical Analysis. Second Pharmaceuthical Analysis. Second edition. Pp:115-128edition. Pp:115-128http://en. Wikipedia.org./wiki/Infrared http://en. Wikipedia.org./wiki/Infrared spectroscopyspectroscopyhttp://www.chem.ualberta.ca/http://www.chem.ualberta.ca/~orglabs/procedures/Infrared ~orglabs/procedures/Infrared Spectroscopy/ir/IR%20Main.htmlSpectroscopy/ir/IR%20Main.html