4. Introduction
Basic Schematic
Atomizer
Wavelength
Selector
Detector
Scanning instruments can detect multiple elements.
Many lines detected so sometimes it is a quantitatively
difficult method.
Source can be flame, but more commonly plasma
because it is much hotter.
5. Each element emit its own characteristics line
spectrum
Quantitative analysis can be performed here by
observing what are emitted & comparing these
with various standards.
Detector permits qualitative as well as quantitative
analysis
Wavelength of emitted radiation indicates what
element is present and the radiation intensity
indicates how much of the element is present
6. Intensity of the emitted light increase with
concentration
Relationship between intensity and concentration is
usually linear
I
I = kc
Unknown concentration can
be detected by comparison
with one or a series of
standards in the same manner
for the molecular techniques
c
9. Process
Sample is sprayed by the nebulizer into the burner.
Carried into the flame
Atomized & excited
The emission from the excited atoms passes into the
monochromator where the selected wavelength is passed
through for measurement.
Intensity of the emitted wavelength is measured by the
detection system & indicated on the readout/computer.
10. Relationship Between AA and FES
Flame Emission it measures the radiation emitted by the
excited atoms that is related to concentration.
Atomic Absorption it measures the radiation absorbed by
the unexcited atoms that are determined.
Atomic absorption depends only upon the number of
unexcited atoms, the absorption intensity is not directly
affected by the temperature of the flame.
The flame emission intensity in contrast, being dependent
upon the number of excited atoms, is greatly influenced by
temperature variations.
11. Flame Emission Spectroscopy
Flame Emission Spectroscopy is based upon those particles
that are electronically excited in the medium.
The Function of Flame
To convert the constituents of liquid sample into the vapor
state.
To decompose the constituents into atoms or simple
molecules:
M+ + e- (from flame) M + hv
To electronically excite a fraction of the resulting atomic or
molecular species
M M*
12. Interference
INTERFERENCES
Spectral Chemical
interference
interference
NOTE: same interference which occur in AAS
13. Comparison btw AAS & AES
(Based on Flame)
Flame Atomic Flame Atomic
Absorption Emission
Process measured Absorption (light Emission (light
absorbed by emitted by excited
unexcited atoms in atoms in a flame)
flame)
Use of flame Atomization Atomization &
excitation
Instrumentation Light source No light source
Beer’s Law Applicable Not applicable
Data obtained A vs c I vs c
14. 2. Plasma
Plasma – highly ionized, electrically neutral gaseous
mixture of cations and electrons that approaches
temperature 10, 000 K.
There are three types of plasma sources:
a) Inductively coupled plasma (ICP)
b) Direct current plasma (DCP)
c) Microwave induced plasma (MIP)
ICP is the most common plasma source.
15. Inductively Coupled Plasma (ICP)
Constructed of three concentric quartz tube.
RF current passes through the water-cooled
Cu coil, which induces a magnetic field.
A spark generates argon ions which are held
in the magnetic field and collide with other
argon atoms to produce more ions.
Argon in outer tube swirls to keep plasma
above the tube.
The heat is produced due to the formation of
argon ions.
16. Inductively Coupled Plasma (ICP)
Plasma Appearance
a. Excitation Region
The bright, white, donut shaped region at
the top of the torch.
Radiation from this region is a continuum
with the argon line spectrum superimposed.
Temperature: 8000 – 10 000 K
b. Observation Region
The flame shaped region above the torch
with temperatures 1000 – 8000 K.
The spectrum consists of emission lines
from the analyte along with many lines from
ions in the torch.
17. Inductively Coupled Plasma (ICP)
1. Sample Introduction
a. Liquid Sample
- Nebulizer similar to FAAS
- Sample nebulized in a stream of
argon with a flow rate of 0.3 – 1.5 L/min.
- Sample aerosol enters the plasma at
the base through the central tube.
b. Solid Samples
- Sample atomized by
electrothermal atomization a and carried
into the plasma by a flow of argon gas.
18. Advantage of ICP-AES over
Flame AES
1. Temperature is two to three times higher than
in a flame or furnace, which results in higher
atomization and excitation efficiencies.
2. There is little chemical interference.
3. Atomization in the inert (argon) atmosphere
minimizes oxidation of the analyte.
4. Short optical path length minimizes the
probability of self-absorption by argon atoms
in the plasma.
5. Linear calibration curves can cover up to five
orders of magnitude.
19. ICP-AES over Flame AES
Much lower detection limit because:
Higher temperature with the plasma will increase
the population of excited state atoms.
The plasma environment is relatively chemically
inert due to the higher population of electrons which
will minimize the interference of ionization.
20. AAS and AES
Both methods use atomization of a sample and therefore
determine the concentrations of elements.
For AAS, absorption of radiation of a defined wavelength is
passed through a sample and the absorption of the
radiation is determined. The absorption is defined by the
electronic transition for a given element and is specific for
a given element. The concentration is proportional to the
absorbed radiation.
In AES, the element is excited. A rapid relaxation is
accompanied by emission of UV or visible radiation is used
to identify the element. The intensity of the emitted
photon is proportional to element concentration.
