ATOMIC EMISSION SPECTROSCOPYSPECTROSCOPY

Dr. Anshumala VaniS.S. in Chemistry & BiochemistryV. U. Ujjain

• In atomic emission small part of sample is vaporized forms free atom that attain is vaporized forms free atom that attain energy form excitation source results in transition from lower to higher energy state on returning back emit a photon of radiationradiation

• Ancient: atomic emission was only based on flame , arc or spark excitationsources.

• Modern era: advancement is made by the introduction of non combustion plasma sources

• Consist of discrete irregularlyspaced lines

• Spectra obtained from plasma ,arc or spark excitation source are often highly complex

Principle

• The electrons of an atom moves from higher energy • The electrons of an atom moves from higher energy level to lower energy level, they emit extra amount of

energy in the form of light which is consist of photons.

Instrumentation

Comprises on:

• Source &Sample• Source &Sample

• Atomizer

• Monochromator

• Detector & readout device

Schematic Diagram of Instrumentation

1. Light source

a. Inductively coupled plasma(ICP)a. Inductively coupled plasma(ICP)

b. Direct current plasma (DCP)

c. Flame

d. Arc and spark

Plasma Source

“ Plasma is defined as a neutral gas “ Plasma is defined as a neutral gas containing significant number of both

positive and negative ions or freeelectrons”

Mechanism Of Inductively Coupled Plasma

� The inductively coupled plasma torch consist of 3

concentric silica quartz tube.

� Argon streamthat carries the sample in the formof

an aerosol, passes through the central tube.

� Plasmais initiatedby a sparkfrom a tesla coil. Argon� Plasmais initiatedby a sparkfrom a tesla coil. Argon

gas ionized and emission is measured.

Flame Source

Mechanism:• It consist of total consumptionburner in which• It consist of total consumptionburner in which

sample is drawn through a capillary tube whichinjected directly into flame and flame is hightemperature source that is used to desolvate andvaporize a sample and generate free atomforspectroscopic study.

Spark source

Mechanism:

• It consist of the primary circuit a voltage of• It consist of the primary circuit a voltage of

110-220V is maintained. The high voltage is

obtained fromsetup transformer which convert the

line power to 15000-40000V which then charge the

capacitor. When energy stored in the capacitor,

synchronous trigger the spark between the

electrodes.

Light source

� Arc and spark

� Laser induced breakdown

� Laser induced plasma

� Microwave induced plasma

Laser Induced Plasma

� In this source highly energetic laser pulse used togenerated optical sample excitation.

� When laser beamfocused on the small spot on asample(liquid, solid and gases).

� The temperature of heated region is rise rapidly thatvaporized the sample material & induced plasmaformed.formed.

� Vaporized material excited & emit radiation.

Laser Beam Excitation

Microwave Induced Plasma

� Used for multi-analytic determination of major to minor

elements.

� Employed microwave energy to produced plasma.

� MIP generated fromfew hundred watts of radiation source

� Atomized sample pass through plasma & promote electron� Atomized sample pass through plasma & promote electron

excitation .

Atomizer

• Elements to be analyzed needs to be in atomic state.

• Atomization; Conversion of sample (maybe; solid or liquid)

into free gaseous atom.

• Atomizer; Device used for atomization

TYPES OFATOMIZER

FLAMEATOMIZER ELECTRO-THERMAL ATOMIZER

CONTINUOUS DISCRETE

1. Flame Atomizer

• To produce flame, required oxidant gas and flamegas.and flamegas.

• Mostly the air-acetylene flame or nitrous oxide- acetylene flame is used.

• Liquid or dissolved samples are typically • Liquid or dissolved samples are typically used with flame atomizer.

Flame Atomization

Sub-types Of Flame Atomization

a. Continuous Atomization; sample penetrate

the atomizer at constantspeed.the atomizer at constantspeed.

a. not used for dissolved solid.*

b. Discrete Atomization; measured amountof b. Discrete Atomization; measured amountof

sample enters atomizer.

– effective when sample volume islimited.

2. Electro-thermalAtomizer

� Also known as “Graphite Furnace Atomizer”

� More convenient to uses a non-flame method i.e.

electrically heated graphite tube.

Construction

• Serves as a sample cellGraphite Tube

• Metal jacket by which the water is circulated

• Made of quartz allow light to pass throughthe tube

Enclosed Water Cooled Housing

Transparent Window

• Protect graphite tube from oxidationInert Pure Gas Control

• Heating of graphite tubeElectrical Contact

Atomization Of Sample

• drying of sample into solid deposit.

• by heating

DRYING ASHING

• conversion of organic matter in CO2 and H2O &volatilization of inorganic

ATOMIZATION

• leads to gaseous atom

• by raising the • by heating

graphite tube at 110 ºC.

of inorganic matter.

• by heating graphite tube at 350-1200 ºC.

• by raising the temperature up to 2000-3000 ºC.

Sample Handling

• The droplets of sample introduced in atomizer should

beof constantsize.beof constantsize.

• The temperature should be maintained to obtain good

reproducibility.

• The speed of introducing sample must be equal to certain

permissiblebandvalues.permissiblebandvalues.

• Sufficient sample volume should be available for

maximumefficiency

Monochromator

• It is a device use to transmit narrowband of wavelengthwhich is chosenfrom wavelengthof wider rangeavailable.which is chosenfrom wavelengthof wider rangeavailable.

Types of monochromator:• PrismMonochromator

• Grating Monochromator

a. Prism

� When the light pass through prism it emerges out in form of

two lines orbeam.two lines orbeam.

� To overcome this drawback two half prism are placed.

� When light pass through first prism it splits into two beams, when it reaches second half prism recombines two beam into single beam

b. Diffraction grating

• It gives better result and resolution.• It replacedprismgive lineardispersion.• It replacedprismgive lineardispersion.

• Problem occurred during the identification ofwavelength of emission lines on photographic platesolved through grating monochromator.

• Once we identify known reference line and other

linesidentifiedautomatically.linesidentifiedautomatically.

Phototube (Photo Electric Cell)

• Glass filled or vacuumtube

• Sensitive to light

• Depend on frequency and intensity of incoming photon

• Need amplifier. But are replaced by photomultiplier detectors.

Photo Multiplier Detector

• Vacuumphototubes, are extremely sensitive detectors of light inthe ultra violet, visible, and near-infrared region ranges of theelectromagnetic spectrum.

Atomic Emission Spectrometers

� Sensitivity is limited by noise.

� High luminosity and high resolution monochromators

necessary to isolate spectral lines.

� Concave and plane grating use as dispersive element.

� Echelle grating system use for high resolutionspectrograph.� Echelle grating system use for high resolutionspectrograph.

Echelle Grating

• Provide excellent dispersion and resolution.

• Longest wavelength of lowest order appear at bottomhigherorderat top.orderat top.

• Two dimension permits high dispersion as compare to onedimension.

• Spectral interference eliminated by echelle grating.

• Special camera attach to instrument and they providewidespreadapplicationof multi elementanalysis.widespreadapplicationof multi elementanalysis.

Applications

� It is used for rapid analysis of multi-component pharmaceuticaltablet.

� It is used for elemental analysis.� It is used primarily for the identification and determination of � It is used primarily for the identification and determination of

metals in traces amount.� It is used for determination of mineral composition of igneous

and metamorphic rock.� It is used for routine analysis of wear metals in lubricating

oils.� It is used for the analysis of sodium, potassium and

lithium.lithium.