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8/17/2019 Ultra Violet Spectroscopy
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M. Rashid Sarfraz Wattoo
M13-314
Ultraviolet spectroscopy
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ContextIntroduction
Types
Instrumentation
Process
Applications
Disadvantages
Research Article
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Introduction
Ultraviolet and visible (UV-Vis ) absorption spectroscopy is themeasurement of the attenuation of a beam of light after it passesthrough a sample or after reection from a sample surface.
This technique is used for :
etection of !unctional "roups.
etection of impurities.
#ualitative analysis
#uantitative analysis
$t helps us to sho% the relationship bet%een di&erent groups'it is useful to detect the conugation of the compounds
When molecules absorb energy, electronic transitions occur.
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Ultraviolet: 190~400nm.
Violet: 400 - 420 nm.
n!igo: 420 - 440 nm.
"lue: 440 - 490 nm.
#reen: 490 - $%0 nm.
&ello': $%0 - $($ nm.
)range: $($ - *20 nm.
+e!: *20 - %(0 nm.
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TYPES
ere are the tyes o/ this techniue accor!ing to the basic
henomena use! in each tye .
Absorbance :he light that interact 'ith the samle is absorbe! by it. his absorbe!
light is measure!. bsorbance sectroscoy is use! in the range o/
1*0 nm to %(0 nm.
Transmittance :3onochromatic light is /ocuse! on the samle an! the light 'hich
!ont absorbe! by it is !etecte! on the oosite si!e o/ the samle.
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Emmision :
When the molecules absorbe light, the electrons get e5cite!. When
the return to their groun! state, they relese light o/ 'avelenght eual
to that is absorbe!. n this case mostly !etectors are lace! at anangle o/ 90 !egree to the source light beam.
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UV-Visible 6ectroscoy
BEER-LAMBERT LAW
t is a uantitative relationshi to
!etermine the concentration o/
absorbing secie in solution.
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he relationshi A = εCl shows that the absorbance at acertain wavelength depends on concentration of sample.
A= Absorbance
ε = Molar Absorptivity
C = Concentration
L = path length
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#iters or Monochromators
ll monochromators contains the /ollo'ing comonents
n entrance slit .
!isersive !evice 8a rism or a grating
/ocusing lens . n e5it slit .
he /ilter or monochromator sen!s only monochromatic
light to the samle an! re/erence cell.
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ample containers *+ sample cells, variety of sample cells is available for UV region. The
choice of sample cell is based on
, path length ' shape ' sie
The transmission characteristics at the desired%avelength.
The cell holding the sample should be transparent tothe %avelength region to be recorded.
#uart or fused silica cuvettes are required forspectroscopy in UV region.
ilica te glasses can be used for the manufacture ofcuvettes for use bet%een /0 and 1000 nm. Thethic2nees of cell is generally 3 cm.
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etectors Three common types of detectors are used
i. 4arrier layer cell.
ii. 5hoto cell detectoriii. 5hotomultiplier ' photo voltic cells.
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s a m ! e
r e f e r e n c e
d e t e c t o r
I 0
I 0 I 0
I
log8I 0 I ; A
$%%&%%' nm
monochromatorbeam slitter otics
UV sources
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Process ,
or n to one o/ the t'o e5cite!
states 8= , or > .∗ ∗
(om!ounds )ith can*u"ated
doube bonds
he use/ul transitions i.e 200 nm-
400 nm are >?>@ /or the
conAugate! !ouble bon!.3oreover
n?=@ an! some >@ transitions.
+on con*u"ated com!ounds
Dienes an! lBenes usually have
absortion ma5ima belo' 200 nm.
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Process
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Remember !!!
As the number of multiple canjugated bonds in acompound increases the value of wavelenght also
increases at which the compound absorb light
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6&ect of solvent on pea2s>?>@ transitions lea!s to more olar e5cite! state that is more
easily stabiliDe! by olar associations 8 bon! . he >@ state is more
olar an! stabiliDe! more in olar solvent relative to non olar one .Eor n ;F > transition the n state is much more easily stabiliDe! by
olar solvent e//ects 8 bon! an! associations .
6o 'ith the stabiliDation o/ electronic transition the eaBs o/ sectra
also change . t means solvents can in!uce signi/icant changes in the
intensity o/ eaBs .
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Disadvantages
olvent should be
transparent to the speci7clight for sample.
amples should be insolution form.
8i9ture of substances
poses dicult toanalyse and requireprior separation.
lications
he molar bsortivity
)rganic chromosheres
bsortion by inorganic
grous
Glotting sectral !ata
Huantitative analysis
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/ Anasis of +ano (om!osite of 0##A (indrica 0(2
his bio nano comosit is a relacement to bone imlant.
t has been mo!i/ie! by calcium-carbonate to maBe a comosite o/
Ia-salt.
re!aration
t has been rein/orce! by novalac resin at 0 JI /or cross linBing.he comosite then /urther sonicate! at 40 JI /or 1 h to ro!uce "io-
nano comosites.
Weight ratio o/ Ia-carbonate to novalac resin is 1:1.
S!ectrosco! ncororation o/ resin an! carbonate ions into inner /iber sur/ace o/
bio nano comosite is con/irme! using UV sectroscoy.
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he UV- visible sectral analysis o/ all the comosites 'ere
carrie! out by UV 1*00 visible sectrometer in the 'avelength
range 200nm - (00 nm.
The s!actra
UV absortion sectrum o/ the samle sho's t'o large eaBs at
2(* nm an! $ nm 'hich sho's the resence o/ carbonate ions
in the comosite.