Transcript Ray of Light

ATOMIC
SPECTROSCOPY
PRESENTED BY :
GROUP 8
Page 1
ATOMIC
SPECTROscopY
PRESENTED BY:
HANEEN RASHID
Page 2
ATOMIC ABSORPTION
SPECTROSCOPY (AAS)
concerns the absorption of radiation by
the atomised analyte element in the
ground state.
• Only applicable for the detection of trace
metals.
Page 3
ATOMIC EMISSION
SPECTROSCOPY (AES)
In atomic emission spectrometry, atoms are
thermally excited so that they emit light and the
radiation emitted is measured.
• Only applicable to determination of alkali and
alkaline earth metals.
Page 4
ATOMIC SPECTRA
PRESENTED BY:
RUBINA AFZAL
Page 5
ATOMIC SPECTRA
• In an atom, electrons have specific and discrete
energies in which electron are arranged in definite
energy levels. When an electronic transitions
(‘jumps’) from one energy level to another (by an
electric arc ,temperature or flame), it emits or
absorbs light – a photon – with a discrete,
specific wavelength, the collection of all these
specific wavelengths ( spectral lines) form the
spectrum of the atom and it will be the
characteristic of particular atom…so atomic
spectra are the spectra of atoms.
Page 6
ATOMIC LINE SPECTRA ARE
CHARACTERISTIC FOR EVERY
ELEMENT
Page 7
TYPES OF ATOMIC
SPECTRA
A. Atomic absorption spectra
B. Atomic emission spectra
Page 8
ATOMIC ABSORPTION
SPECTRA
•
When an electron is excited to a higher energy
level it must absorbed energy.
• The energy absorbed as an electron jump from an
orbit of low energy to one of the higher energy is
characteristic of that transition.
• This mean that the excitation of electron in a
particular element result in energy absorption at
specific wavelength it will be the characteristic
of particular atom thus in addition to emission
spectrum every atom possess a characteristic
absorption spectrum.
Page 9
For example
• In gaseous medium, sodium atoms are
capable of absorbing radiation of
wavelength characteristic of electronic
transition from 3s state to higher excited
states, sharp absorption peaks are
observed experimentally.
Page 10
ATOMIC EMISSION SPECTRA
Page 11
For example
• When a sodium salt is heated in a flame the
outer electron in the volatilized atoms are
excited and returned to ground state with
emission of energy, which appears as a yellow
light (wavelength 589.5)
• The major line in the sodium emission
spectrum is due to an electron falling from 3p
excited state to 3s ground state.
• Common atom which give their bands in the
emission spectrum are Ca, Ba , Na, Li, k.
Page 12
TYPES OF EMISSION
SPECTRA
Continuous spectra:
• It emitted by solids
and are
characterized by the
absence of any sharp
lines as a function of
wavelength.
Band spectra
• It consists of group of
lines. Each group is
characteristic of
wavelength that
becomes closed
spaced as they
approach the end of
the band .The band
also called molecular
spectra band. Since
radiation is emitted out
by the excited
molecules.
Line spectra:
• These consist of
sharply defined and
often widely irregularly
spaced individual
lines of a single
wavelength. These
spectra are
characteristics of
elements and are duo
to the excitation of
gaseous atoms or
atomic ions. Hence,
line spectra are also
called atomic
spectra
Page 13
• Continuous emission spectrum
• Band emission spectrum
• Line emission spectrum
Page 14
COMPARISON OF
THE ABSORPTION(a) AND EMISSION
LINES (b)OF SODIUM
Page 15
PRINCIPLE OF ATOMIC
SPECTROSCOPY
PRESENTED BY:
MAHWISH MAQBOOL
Page 16
PRINCIPLE OF ATOMIC
ABSORPTION SPECTROSCOPY
• The absorption of energy by ground state
atoms in the gaseous state forms the basis
of atomic absorption spectroscopy.
• By the help of atomic absorption
spectroscopy, one can determine the
amount of light absorbed
Page 17
In atomic absorption spectroscopy:
• Atoms of a metal are volatilized in a flame
and their absorbance of a narrow band of
radiation produced by a hollow cathode
lamp, coated with the particular metal
being determined is measured.
• Absorption will be proportional to the
density of atoms in flame.
Page 18
• Once absorption is known the concentration
of the metallic element can also be known
because absorption is proportional to
concentration of atoms in the flame.
Mathematically, the total amount of light
absorbed is given by:
Page 19
PRINCIPLE OF ATOMIC
EMISSION SPECTROSCOPY
• Atomic emission spectroscopy involves
the measurement of electromagnetic
radiation emitted from atoms.
• I n this, atoms are thermally excited so that
that emit light and the radiation emitted is
measured. Both qualitative and
quantitative data can be obtained from this
type of analysis.
Page 20
The process is as follows:
•
•
•
•
•
•
LIQUID STATE
FORMATION OF DROPLETS
FINE RESIDUE
FORMATION OF NEUTRAL ATOMS
EXCITATION OF ATOMS
EMISSSION OF RADIATION OF SPECIFIC
WAVELENGTH
• WAVELENGTH AND INTESITY OF EMITTED
RADIATION
• The intensity of emitted radiation depends upon
the proportion of thermally excited atoms, which
in turns depends upon the temperature of flame.
Page 21
Fraction of free atoms thermally excited
• The wavelength of the radiation emitted is
used to identify the element (Qualitative
Analysis). The intensity of the radiation
emitted depends upon the concentration of
element analyzed (Quantitative Analysis)
Page 22
ATOMIC ABSORPTION
SPECTROSCOPY
INSTRUMENTATION
PRESENTED BY:
FARAH HUSSAIN
Page 23
BASIC COMPONENTS
• A typical atomic absorption
spectrophotometer consists of following
components.
Radiation source
Atomic reservoir
Monochromator
Detector
Readout device
Page 24
RADIATION SOURCE
• HOLLOW CATHODE LAMP
• ELECTRODELESS DISCHARGE LAMP
Page 25
HOLLOW CATHODE LAMP
CONSTRUCTION:
• The lamp consists of thick walled glass envelope which
has a transparent window of glass and silica affixed to
one end. It consists of one anode and cup shaped cathode
which are both connected to tungsten wire. The tube is
filled with highly pure inert gas at low pressure of 1 to
2mm. The gases generally used are neon ,argon or
helium. Mica sheets are placed inside the lamp to limit
the radiation to with in the cathode. The choice of
window material depend upon the wavelength of the
resonance lines of the element concerned.
Page 26
 HOW IT WORKS:
• A potential of about 500v is applied between the
electrodes and the current of 2-30mA is used. The
filler gas becomes charged at the anode and the ions
produced are attracted to the cathode and
accelerated by the field. Bombardment of these ions
on the inner surface of cathode causes metal atom to
sputter out of the cathode cup. Further collisions
excite these metal atoms and simple, intense
characteristic spectrum of the metal is produced.
Page 27
HOLLOW CATHODE
DISCHARGE LAMP
Quartz
window
Pyrex body
Cathode
Anode
Cathode
Anode
Page 28
ELECTRODELESS DISCHARGE
LAMP
CONSTRUCTION:
• In this a small amount of the metal or salt of the
element for which the source is to be used is
sealed inside the quartz bulb. This bulb is
placed inside a small self contained RF
generator or Driver
Page 29
HOW IT WORKS:
• When power is applied to the driver, an RF field
is created. The coupled energy is vaporized and
excite the atom inside the bulb, causing them to
emit their characteristic spectrum. The emission
from an EDL is higher than that from an HCL,
and the line width is generally narrower, but
EDLs need a separate power supply and might
need a longer time to stabilize.
Page 30
ELECTRODELESS DISCHARGE
LAMP
Page 31
ATOMIZERS
• The principle of atomic absorption
requires light absorption by free atoms.
However, elements in the sample are in
a molecular form. The combination
must be broken by some means to free
the atoms. This is called
ATOMISATION. The most popular
method of atomization in AAS is flame
excitation source.
Page 32
BASIC STEPS INVOLVED IN
FLAME ATOMIZATION
Nebulisation: conversion of sample into
droplets.
Desolvation: removal of solvents.
Atomization: thermal or chemical
breakdown of solid particles.
Condensation of reaction product:
removal of residue by exhaust flame
gases.
Page 33
BURNERS
• Two major types of nebulizer
burners are used in AAS are
PREMIX NEBULISER BURNER
and TOTAL CONSUMPTION
BURNER.
• In premix type burner liquid is
sprayed into mixing chamber
where the droplets are mixed with
combustion gas and are send to
the burner.
• In the total consumption burner,
nebulizer and burners are
combined. This is also called
TURBULENT FLOW BURNER
Page 34
MONOCHROMATORS
 Important device of the optical system of AAS.
 The function of this device is to separate the spectral line of interest
from the other spectral line of different wavelength emitted by the
hollow cathode lamp. The desired spectral lines is chosen with the
preferred wavelength and bandwidth with the help of grating.
GRATING
 Wavelength dispersion is accomplished with a grating, a reflective
surface ruled with many fine parallel lines very close together.
 Reflection from this ruled surface generates interference
phenomenon known as diffraction in which different wavelength of
light diverge from grating at different angle.
Page 35
WORKING:
 Light from the source enters the monochromator
at the entrance slit and is directed to the grating
where dispersion takes place. The diverging
wavelength of light are directed towards exit slit.
By adjusting the angle of grating, a selected
emission line from the source can be allowed to
pass through exit slit and fall onto the detector
Page 36
DETECTOR
• The most commonly used in AAS is
Photomultiplier tube whose output is
fed into readout system.
• A PMT is an electronic tube that is
capable converting the photon current
into electrical signal and of amplifying
this signal.
.
Page 37
WORKING:
• It consists of photo cathode and secondary electron
multiplier. The photons impact on the cathode
surface and sputter electrons from its surface. These
electrons are accelerated in an electric field and
impact on other electrodes so called dynodes from
the surface of each impacting electron sputter
secondary electrons. This cascade effect results in
significance increase in number of electron. At the
end electron impact on an anode and flow off to the
mass. The resulting current is measured.
Page 38
READOUT SYSTEM
 It included meters, chart out device and
digital display meter.
 These days microprocessor controlled
system are commercially available where
every thing can be done by touch of button.
Page 39
INSTRUMENTATION
OF AES
PRESENTED BY :
HAFIZA RABEEA NISAR
Page 40
ATOMIC EMISSION
SPECTROMETER
Consists of three main parts:
 Emission source
 Optical system
 Detector
Page 41
EMISSION SOURCE
Atomization and excitation of sample is done
by emission source:
 Direct current plasma (DCP)
 Flame excitation source
 Inductively coupled plasma (ICP)
 Spark and arc
 Laser induced breakdown (LIB)
 Microwave induced plasma (MIP)
Page 42
1.
Direct Current Plasma Excitation
Source
 DCP is created by an
electrical discharge between
two electrodes. A plasma
support gas is necessary (Ar)
 Sample deposited on one of
the electrode.
 Solid samples, near the
discharge so that ionized gas
atoms sputter the sample into
the gas phase where the
analyte atoms are excited.
Page 43
2.
Flame Excitation Source
 The sample solution is
directly aspirated into the
flame.
 All desolvation, atomization,
and excitation occurs in the
flame.
 Flame provides a hightemperature source for
desolvating a sample.
Page 44
3.
Inductively-Coupled Plasma
Excitation Source
 Very high temperature excitation
source that efficiently desolvates,
vaporizes, excites, and ionizes atoms.
 Sample is nebulized and entrained in
the flow of plasma support gas (Ar).
Page 45
 The plasma torch consists of
concentric quartz tubes, with the inner
tube containing the sample aerosol and
Ar support gas and the outer tube
containing an Ar gas flow to cool the
tubes.
 An RF generator produces an
oscillating current in an induction coil
that wraps around tubes, this coil
creates an oscillating magnetic field,
which produces an oscillating magnetic
field, which in turn sets up an
oscillating current in the ions and
electrons of the support gas.
 These ions and electrons transfer
energy to other atoms by collisions to
create very high temperature plasma.
Page 46
4.
Spark and Arc
 Spark and arc excitation sources use
a current pulse (spark) or a
continuous Electrical discharge (arc)
between two electrodes to vaporize
and excite analyte atoms.
 Samples are ground with graphite
powder and placed into a cup-shaped
lower electrode.
Page 47
5.
Laser-Induced Breakdown
 High-energy laser pulse is
focused into a gas or liquid,
or onto a solid surface, it
creates hot plasma.
 The energy of the lasercreated plasma can atomize,
excite, and ionize analyte
species.
Page 48
6.
Microwave Induced Plasma
 Consists of a quartz tube
surrounded by a microwave
waveguide.
 Microwaves produced by
microwave generator fill the
waveguide or cavity and cause
the electrons in the plasma
support gas to oscillate.
 The oscillating electrons
collide with other atoms to
create and maintain a hightemperature plasma.
Page 49
OPTICAL SYSTEM
Once the sample has been introduced
into the emission source, atomized, and
excited, the emitted photons are
diffracted by an optical system
consisting of slits, mirrors, and
gratings, etc.
 It may be a Monochromators or
Diffraction grating.
Page 50
1.
Monochromators
 A Monochromators is an optical
device that transmits a mechanically
selectable narrow band of wavelengths
of light or radiation.
 Two designs are usually employed.
1. Czerny–Turner Monochromators
2. Echelle Monochromators
Page 51
Czerny–Turner
Echelle Monochromators
• Two mirrors are used to reflect • It’s made up of two dispersing
and focus the polychromatic and
elements. These elements are
diffracted beams.
arranged in series.
• As the grating rotates, a different • They have high resolution and
wavelength is focused onto the
dispersion property.
exit slit.
Page 52
2. Grating
 Gratings are reflective surfaces
containing parallel, equally spaced
lines.
 Their resolving power is proportional to
the number of lines, which in turn
depends on the line spacing.
 Diffraction gratings are used in optical
system to disperse the emitted radiation.
Page 53
DETECTORS
• Photomultiplier tube
READ OUT SYSTEM
Page 54
TYPES OF ATOMIC
SPECTROPHOTOMETERS
PRESENTED BY:
ALMAS SHAMIM
Page 55
TYPES OF ATOMIC ABSORPTION
SPECTROPHOTOMETER
• Single beam atomic absorption
spectrophotometer
• Double beam atomic absorption
spectrophotometer
Page 56
SINGLE BEAM ATOMIC ABSORPTION
SPECTROPHOTOMETER
Page 57
DOUBLE BEAM ATOMIC ABSORPTION
SPECTROPHOTOMETER
Page 58
TYPES OF ATOMIC EMISSION
SPECTROPHOTOMETER
• Sequential spectrometers
• Simultaneous spectrometers
Page 59
• The sequential and simultaneous spectrometers
are extensively used in the analytical
laboratories.
• The sequential spectrometers are less
expensive and more flexible but usually require
a higher degree of operator skill and
experience.
• On the other hand, the simultaneous
spectrometers are more precise and accurate
and are obviously more expensive.
Page 60
SEQUENTIAL SPECTROMETER
Page 61
SIMULTANEOUS SPECTROMETER
1. Polychromators
2. Solid state array based spectrometers
Page 62
POLYCHROMATORS
Page 63
SOLID STATE ARRAY BASED
SPECTROMETERS
Page 64
INTERFERENCES
PRESENTED BY:
HANEEN RASHID
Page 65
INTERFERENCES IN
ATOMIC
ABSORPTION
SPECTROPHOTOMETRY
Page 66
1. Spectral Interferences
The presence of another atomic absorption line or a
molecular absorption band close to the spectral
line of the analyte element being monitored.
• This may be corrected by modulation of the
radiation source and the detection system.
.
Page 67
2. Chemical interferences
These include interferences due to ionisation,
formation of low volatility compounds, etc
• Such interferences can be avoided by increasing
the flame temperature.
Page 68
3. Physical interferences
These may be due to variations in the gas flow rates,
changes in the solution viscosity which may finally
change the atomic concentration in the flame.
• This can be avoided by matching the matrix and by
performing frequent calibrations.
Page 69
INTERFERENCES IN
ATOMIC
EMISSION
SPECTROPHOTOMETRY
Page 70
1. Spectral Interferences
involves the overlap of the spectral lines of two or
more elements in the matrix emitting radiation at
the same wavelength.
• These can be minimized by using a high
resolution dispersion system.
Page 71
2. Chemical interferences
The chemical interferences include molecular
compound formation and ionization effects.
• These can be minimized by carefully controlling
the operating conditions.
Page 72
3. Physical interferences
These interferences are associated with the
processes of sample nebulisation and transport.
• The physical interferences can be reduced by
diluting the sample.
Page 73
APPLICATIONS
PRESENTED BY
KIRAN ILLAHI
Page 74
Page 75
Page 76
Page 77
Page 78
Page 79
Page 80
Page 81
ADVANTAGES AND
DISADVANTAGES
PRESENTED BY:
MADIHA KHALID
Page 82
ADVANTAGES OF AAS
 The atomic absorption technique is specific
because the atom of a particular elements
can only absorb radiation of their own
characteristic wavelength i.e. the light of a
particular frequency can easily be absorbed
by the specific element to which it is
characteristic.
 Atomic absorption spectroscopy is
independent of flame temperature.
Page 83
DISADVANTAGES OF
AAS
 A separate lamp for each element is
required.
 This technique is unsuccessful for
estimation of elements like Al, Mo;
vanadium because, these elements give rise
to red metallic oxidizes in the flame.
 In aqueous solution the signal is affected
by predominant anion.
Page 84
ADVANTAGES OF
AES
 It is very specific; the unique character of the
wavelength pattern produced by each element is the
reason of its specificity.
 The method is extremely sensitive, with this
technique all metallic elements can be detected even
if they are present in very low concentration
(0.0001%). Even metalloids (arsenic, silicon, and
selenium) have been identified.
 The method can be used for qualitative analysis as
well as to determine concentration as low as 1 ppm.
Page 85
 The analysis has the advantage of
providing results rapidly because there are
situation (e.g. in industrial processes)
where time is more important than the
high levels of accuracy. If automated, time
required is just 30 seconds to a minute.
 A very small amount of sample
(1-10mg) is sufficient for analysis.
Page 86
DISADVANTAGES OF
AES
 The equipment is costly and wide experience is
required for its successful handling and
interpretation of spectra.
 The spectrograph is essentially a comparator, for
quantitative analysis, standards (usually similar
composition to the material under analysis) are
necessary. For quantitative results, therefore, a
problem is often posed for unknown samples.
 The sample is destroyed in the process of analysis.
Page 87
 This method is not recommended for
elements present to a greater extent than 3
percent since for quantities greater than 2-5
percent of the method does not offer
accuracy as in gravimetric, titrimetric and
some spectrophotometric measurements.
 The method is limited to the analysis
of elements.
Page 88
Page 89