Transcript Principle of Spectroscopy

Atomic Absorption Spectroscopy
(AAS)I
Mentor :
Prof. Kuniyuki KITAGAWA
Assistant:
Dr. Eng.Nelfa Desmira
Visible and Ultraviolet Light
Uv-Vis Spectrometer Double Beam
Light Source UV
(Deuterium/D2)
1a
2
Mirror 1
Slit 1
Slit 2
1b
Light Source Vis (Tungsten)
3
Detector-2
Filter
Reference
Beam
6a
Reference
Cuvette
7a
I
Lens 1
Half Mirror
5
4
Detector-1
6b
Sample
Beam
Sample
Cuvette
7b
Lens 2
I
0
Uv-Vis Spectrometer Double Beam
•
•
•
•
•
•
•
•
No 1a and 1 b
– The UV-Visible spectrophotometer uses two light sources, a deuterium (D2) lamp for
ultraviolet light and a tungsten (W) lamp for visible light. Two light sources hit Mirror 1
one pass through slit 1 go to diffraction grating (no.2)
No 2
– The grating is able to rotated so a specific wavelength is selectable. From diffraction
grating goes to slit 2 and filter (No. 3)
No 3
– A filter is used to remove unwanted higher orders of diffraction.
No 4
– The light beam hits a second mirror
No 5
– splited by a half mirror to 6a and 6b
No 6a and 6b
– Half of the light is reflected (6a), the other half passes through (6b)
No 7a
– One of the beams is allowed to pass through a reference cuvette.
No 7b
– the other passes through the sample cuvette. The intensities of the light beams are then
measured at the end
Beer-Lambert Law
• The Beer-Lambert law is the linear relationship between
absorbance and concentration of an absorbing species.
• Experimental measurements are usually made in terms of
transmittance (T), which is defined as:
T = I / Io
where I is the light intensity after it passes through the sample
and Io is the initial light intensity.
• The relation between A and T is:
A = -log T = - log (I / Io)
where A is the measured absorbance
Transmittance
The relationship between absorbance and transmittance is illustrated in
the following diagram:
Assignment
• Calculate the transmission for absorbance A
0.6 and 0.06
• How to make correction for background
absorption caused by sample matrices
using a one-beam spectrophotometer?
• Explain the system of single beam Uv-Vis
Spectrometer
Atomic Absorption Spectroscopy
(AAS) II
Mentor :
Prof. Kuniyuki Kitagawa
Assistant :
Dr. Eng. Nelfa Desmira
Atomic Spectroscopy
• A method to analyze the elemental composition
using atomic absorption or emission
• Energy transition electrons of atoms
E1
E2
E3
Ground State
E0
Emission
Excited State
Excited State
Absorption
E1
E2
E3
Ground State
h = Ei– E0
h = Ej – Ei
i = 1.2 and 3
i = 1.2 and 3
Ej
v1
1
v2
2
v3
3
1 2 3

Atomic Absorption Spectroscopy
Ej
I0
E0
Beer Lambert Law :
I
Where :
A = absorbance/Emission
T = Transmitance
Atomic Absorption Spectroscopy :
The term used when the radiation absorbed by atoms is measured
E0 and Ej : energy levels where Ej higher than E0.
Arrow line: Absorption
Atomic Absorption Spectrometry
Radiation
Source
Lens
Atomized
Sample
(Flame)
Lens
Monochromator
Detector
Output
Flame Atomic Absorption Spectrometry
AAS consist of two type: Flame AAS and Graphite-furnace AAS.
Please open this link :
http://www.cee.vt.edu/ewr/environmental/teach/smprimer/aa/aadiag.gif
Atomic Absorption Spectrometry
• Radiation Source
– Hollow-Cathode Lamp
• Atomization Sample
– AAS analyzes atoms in gas phase so atoms in a
sample must heated/vaporized in a hightemperature source such as a flame or graphite
furnace. Flame AA is suitable to analyze solutions,
while graphite furnace AA is able to analyze
solutions, slurries, or solid samples.
Atomic Absorption Spectrometry
• Monochromator and Detector
– AA spectrometers use monochromators and
detectors for UV and visible light.
– Monochromator is used to isolate the absorption
line from background light due to interferences.
Assignment
• Explain the detail of flame atomization
absorption spectrometry (FAAS)
• Explain the detail of graphite furnace atomization
absorption spectrometry (GAAS)
• Compare the detection limits of FAAS and GAAS and
mention their applications respectively