Flame emission spectroscopy and atomic absorption spectroscopy ppt

Presented By: Facilitated To:
Sachin.J.Gaddimath Dr. B.S.Kittur
M.Pharm 1st year HOD & PROFESSOR
Dept. of Pharmaceutics Dept. of ph. Chemistry
HSKCOP, BAGALKOT HSKCOP, BAGALKOT

Contents
 Flame Emission Spectroscopy and Atomic Absorption
Spectroscopy:
 Principle
 Instrumentation
 Interferences
 Applications

 Desolvation: The metal particles in the flame are
dehydrated by the flame and hence the solvent is
evaporated.
 Vaporisation: The metal particles in the flame are
dehydrated. This also led to the evaporation of the
solvent.
 Atomisation: Reduction of metal ions in the solvent to
metal atoms by the flame heat.
 Excitation: The electrostatic force of attraction
between the electrons and nucleus of the atom helps
them to absorb a particular amount of energy. The
atoms then jump to the exited energy state.
 Emission process: Since the higher energy state is
unstable the atoms jump back to the stable low energy
state with the emission of energy in the form of
radiation of characteristics wavelength, which is
measured by the photo detector

 The basic components of Flame Emission
Spectroscopy are:
 Burners
 Atomiser
 Monochromators
 Detector
Burners:
1.The flame should have ability to evaporate the liquid
droplets from the sample solution in the formation of
solid residue.
2. The flame should decompose the compounds in the
solid residue resulting in the formation of atoms.
3. The flame must have the capacity to excite the
atoms formed and cause them to emit radiant energy

 FLAMES IN FES
Name of the element
emitted
Wavelength range(nm) Colour observed in the
flame
Potassium(K) 766 Violet
Lithium(Li) 670 Red
Calcium(Ca) 622 Orange
Sodium(Na) 589 Yellow
Barium(Ba) 554 Lime green

 Types of burners:
 1. Mecker burner.
 2. Total consumption burner.
 3. Laminar flow burner.
 4. Lundergraph burner.
 5. Shielded burner.
 6. Nitrous oxide- Acytelene flame.

Mecker burner:
1. This burner employed natural gas and oxygen.
2. Produces relatively low temperature and low excitation
energies.
3. These are best used for alkali metals only.

Total consumption burner:
 1. In this burner the fuel and oxidant used are
hydrogen and oxygen gas.
 2.In this sample, solution is aspirated through a
capillary by the high pressure. the fuel and oxidant
are burnt at the tip of burner.
 3.The name “total consumption burner” is used
becoz all the sample that enters the capillary will
enter into flame of the droplet size.

CONSUMPTION BURNER
Advantage:
This design is very simple and the whole/entire sample is
consumed by this process.
Disadvantage:
Uniform & homogenous flame is not obtained. Since the
droplet size vary, leading to fluctuations in the flame
intensity.

Laminar flow burner:
 In this type of burner, aspirated sample, fuel and oxidant
are thoroughly mixed before reaching the burner opening
and then entering the flame.
 Important feature of this is that only a small portion (about
5%) of the sample reaches the flame in the form of small
droplets and is easily decompose.

Advantages:
 Burner is non-turbulent, noiseless, stable.
 Easy decomposition which leads to high atomisation.
 It can handle the solution up to several % without
clogging.
Disadvantages:
 When it contains 2 solvents, more volume will
evaporate and lesser will remain undissociated.
Monochromators and filters:
 In simple FES, monochromators is the prism.
 QUARTZ is the material most commonly used for
making prisms becoz quartz is transparent over entire
region.

Filters:
 It is made up of such material which is transparent
over a narrow spectral range.
 When a filter is kept between flame detector, the
radiation of the desired wavelength from the flame
will be entering the detector and be measured. The
remaining undesired wavelength will be absorbed by
the filter and not measured.
 In FES, the wavelength as well as intensity of radiation
emitted by the element has to be monitored. Hence a
filter or monochromator is used.
DETECTORS:
 Photovoltic cell
 Phototubes
 Photomultiplier tubes

 Applications:
 FES has found wide application in agricultural and
environmental analysis, industrial analysis of ferrous
metals and alloys as well as glasses, ceramic materials,
and clinical analysis of body fluids.
 FES can be easily automated to handle a large number
of samples. Array detectors interfaced to a
microcomputer system permit simultaneous analyses
of several elements in a single sample.
 They are also used to determine the metals present in
chemicals, soil, cements, plant materials, water, air
pollutants.
 Used in clinical laboratory to determine
concentrations of sodium and potassium in biological
fluids like serum, urine.

INTERFERENCES:
 Matrix Interference
 Chemical Interference
 Ionization Interference
 Spectral Interference
Matrix Interference:
 When a sample is more viscous or has different
surface tension than the standard, it can result in
differences in sample uptake rate due to changes in
nebulisation efficiency.
 Such interferences are minimized by matching as
closely as possible the matrix composition of standard
sample.

Chemical interference:
 If a sample contains a species which forms a thermally
stable compound with the analyte that is not completely
decomposed by the energy available in the flame then
chemical interference exists.
 Refractory elements(Ti, W, Mo and Al) may combine with
oxygen to form thermally stable oxides.
 Analysis of such elements can be carried out at higher
flame temperatures using nitrous oxide- acetylene flame
instead of air acetylene to provide higher dissociation
energy.
 Alternately an excess of another element or compound can
be added e.g Ca in presence of phosphate produces stable
calcium phosphate which reduces absorption due to Ca
ion.
 If an excess of lanthanum is added it forms a thermally
stable compound with phosphate and calcium absorption
is not affected.

Ionization Interference:
 It is more common in hot flames. The dissociation
process does not stop at formation of ground state
atoms.
 Excess energy of flame can lead to excitation of
ground state atoms to ionic state by loss of electrons
thereby resulting in depletion of ground state atoms.
 In cooler flames such interference is encountered with
easily ionized elements such as alkali metals, alkaline
earths.
 Salts of such elements as K, RB, and Cs are commonly
used as ionization suppressants.

Atomic Absorption Spectroscopy
 AAS is a technique for determining the concentration
of a particular metal element in a sample. And it can
be used to analyse the concentration over a 62 different
metals in a solution.

Principle:
 The principle of Atomic Absorption Spectroscopy is
based on the free atoms (gas) generated in an atomiser
which can absorb radiation at specific frequency.
 It quantifies the absorption of ground state atoms in
the gaseous state.
 This absorbs UV or visible light and make transitions
to higher electronic energy levels. The analyte
concentration is determined from the amount of
absorption.
 Concentration measurements are usually determined
from a working curve after calibrating the instrument
with standards of known concentration.
 It is very common technique for detecting metals and
metalloids in environment samples.

Light Source:
 Hollow cathode lamp are the most common radiation
source in AAS.
 It contains a tungsten anode and a hollow cylindrical
cathode.
 These are sealed in a glass tube filled with an inert
gas(mainly neon or argon).
 Each elements has its own unique lamp which must be
used for that analysis.

Nebulizer:
 Nebulizer suck up liquid samples at controlled rate.
 Creates a fine aerosol spray for introduction into the
flame.
 Mix the aerosol, fuel and oxidant thoroughly for
introduction into flame.
Atomizer:
 Elements to be analysed needs to in atomic state and
this is done by means of atomizer.
 Atomization is a separation of particles into individual
molecules and breaking molecules into atoms.
 This is done by exposing the analyte to high
temperature in flame or graphite furnace.
 The atomizers most commonly used nowadays
are(spectroscopic) flames and electro thermal
(graphite tube) atomizers.

Types of Atomizers:
Flame atomization:
 Nebulizer suck up in liquid sample at controlled rate and
creates a fine aerosol spray for introduction into flame.
 To creat flame, we need to mix an oxidant gas and a fuel
gas.
 In most of the cases air-acetylene flame or nitrous oxide
acetylene flame is used.
 Liquids or dissolved samples are typically used with flame
atomizer.

Elecrto Thermal Atomization:
 It uses a graphite coated furnace to vaporize the sample.
 Samples are deposited in a small graphite coated tube
which then heated to vaporize and atomize the analyte.
 The graphite tubes are heated using a high current power
supply.
 Steps used in electro thermal atomization:
Drying, Pyrolysis, Atomization, Cleaning
Monochromators:
 It is used to separate out all of the thousand of lines.
 It is used to select the specific wavelength of light which is
absorbed by the sample and to remove other wavelengths.
 The selection of the specific light allows the determination
of the selected element in the presence of others.

Detector and Amplifier:
 The light selected by the monochromator is directed
onto a detector whose function converts the light
signal into an electrical signal.
 Photomultiplier tube detector is mainly used.
 The processing of electrical signal is fulfilled by a
signal amplifier.
 The amplified signal is then displayed on read out
system or fed into a data station for printout by the
requested format.

Calibration Curve:
 It is used to determine the unknown concentration of
an element in a sample.
 The instrument is calibrated using several solutions of
known concentrations.
 The absorbance of each solution is measured & then
calibration curve of concentration vs absorbance is
plotted.
 The sample solution is fed into instrument & the abs
of the element in the solution is measured.
 The unknown concentration of element is then
calculated from the calibration curve.

Interferences in AAS:
 Analyte interference:
 It changes the magnitude of the analyte signal itself.
Such interferences are usually not spectral in nature
but rather physical or chemical effects.
 Physical interference:
 It can alter the aspiration, nebulisation, desolvation,
and volatilization processes.
 Substances in the sample that change the solution
viscosity.(EX- It can alter the flow rate and efficiency
of the nebulisation process.)
 Combustible constituents, such as organic solvents,
can change the atomiser temperature and thus affects
the atomization efficiency indirectly.

 Chemical interference:
 They occur in the conversion of solid or molten
particle after desolvation into free atoms or elementary
ions.
 Constituents that influences the volatilization of
analyte particle causes this type of interferences and
are often called solute volatilization interferences.
 For example, can alter in some flames the presence of
phosphate in the sample can alter the atomic
concentration of calcium in the flame owing to the
formation of relately non-volatile complexes.
 Such effects can sometimes be eliminated or
moderated by the use of higher temperatures.

 Spectral interference:
 The elements that absorb at analyte wavelength are
rare in atomic absorption.
 Molecular constituents and radiation scattering can
cause interference.
 These are often corrected by background correction
scheme.
 In some case, if the source of interference is known, an
excess of the interferent can be added to both the
sample and the standards. The added substance is
sometimes called as radiation buffer.

Applications:
 Determination of even small amounts of metals(lead,
mercury, calcium, magnesium)
 Environmental studies: drinking water, ocean water,
soil.
 Food industry
 Pharmaceutical industry.
 Presence of metals as an impurity or in alloys could be
done easily.
 It is used in qualitative & quantitative analysis of
different drug compounds
 To detect heavy metals elements in the herbal drugs
and synthetic drugs.
 To estimate lead in petroleum products.

Reference:
 Analytical chemistry by Gary D Christian
 Principles of instrumental analysis Skoog
 Instrumental method of analysis by Willard Merritt
 Spectroscopy by B K Sharma
 Instrumental method of analysis by Gurdeep chatwal
 www.google.com

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