Présentation AAS.pdf
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Transcript of Présentation AAS.pdf
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Atomic AbsorptionSpectrometry (AAS)
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Trace element Analysis
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Optical Analysis Method based on thestudy of atomic spectrum, which are rayspectra
Ray spectra = result of electronictransitions in atoms (by valenceelectrons)
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I-Denition of AAS
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II-Principle of AAS
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Energy +
ground stateatom
excited stateatom
Light radiation (through photons) brings out an atomfrom a ground state to a higher energy state
E = h.v and v = c/ !
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II-Principle of AAS
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E = h.v and v = c/ !
E = energy (Joules)h = Planck constantv = frequency (seconds)! = wavelength (nanometers)c = light celerity (or speed) (meters/seconds)
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II-Principle of AAS v frequency is characteristic of the element to
analyse and corresponds to its wavelength (as an
example!
= 213,9 nm for Zn) photon emissions is performed by a cathodic
discharge, made in rare gas atmosphere andunder very low pressure level
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III-Apparatus
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cathod lamp
Cathod
Gas : argon or neon
quartz window
Anod
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III-Apparatus Emission intensity has to be as high as possible :
the rate of ow of the photons has to be sufcientlyimportant in order the probability to meet an atom to behigh
Emission intensity has to be constant over time since quantitative measures are based on the Beer-
Lambert law, and thus necessitate a stable source
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III-Apparatus
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ame detectorsource
Abs = log I 0 /I I0 = light intensity before the ameI = light intensity after the ame
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III-Apparatus
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Abs = log I 0 /II0 = light intensity before the ame
I = light intensity after the ame
Beer-Lambert law A = elC
e = absorption coefcient, specic of the element
l = optical course length (in cm)C = concentration (mole/L)
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IV-Measure Absorbance proportional to the concentration
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Limit oflinearity
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IV-Measure
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! # $%&'()*+& , -''*).+ , (/)(..01 # /)'''*(
/
%///
&///
2///
(///
3///
-///
.///
*///
'///
%////
/ /)3 % %)3 & &)3
! " # $ % " & ' ( )
+$'()',%&-$'# .' /012
+&2."%&-$' (3%4)
Limit oflinearity
Example of Zinc
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IV Measure
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! # $%&$'$( ) *+%'%,- # +'../$0
+
1+++
*+++
/+++
&+++
$+++
%+++
0+++
+ +'* +'& +'% +'2 1 1'*
! " # $ % " & ' ( )
+$'()',%&-$'# .' /012
+&3."%&-$' (4%5) 6.,7$4, ,7) 3, 8$.',
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! # $%&'()* + &&%(',-. # '(//,/,
'
,''
&'''
&,''
0'''
0,''
%'''
%,''
$'''
$,''
,'''
' '(0 '($ '(1 '() & &(0
! " # $ % " & ' ( )
+$'()',%&-$'# .' /012
+3 +&4."%&-$' (5%6)
IV-Measure
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X
Abs X
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IV-Measure
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Control= Blank
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Detection Limit= Mean of 6 Blanks + 3 x sd
Blank1 = 0,022 mg /LBlank 2 = 0,022Blank 3 = 0,021Blank 4 = 0,023
Blank 5 = 0,023Blank 6 = 0,021
Mean = 0,022 mg/Lsd = 0,0008 mg/L
Detection Limit:0,022 +(3x0,0008) = 0,025 mg/L
Detection Limit in the tissue:0,025 mg/L x 10ml / 0,2 g = 1,28 mg/kg (ppm)
Cd
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Cd DOLT
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Cd = 24,9 mg/kg 0,6 Certied Value = 24,3 mg/kg 0,8
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Summary of DOLT values
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