Atomic spectroscopy (AAS & AES)

Guided by -
Prof. Dr. Vijeta Dhabre
Department of Pharmaceutical Analysis
YTIP, UNIVERSITY OF MUMBAI
Prepared by -
ROHAN JAGDALE
T. Y. B. Pharm
2020-21
Atomic
Spectroscopy
Guided by -
Prof. Dr. VIJETA DHABRE
Department of Pharmaceutical Analysis
YTIP, University Of Mumbai
Prepared by-
ROHAN JAGDALE
T. Y. B. Pharm
2020-21

CONTENTS
❖ Introduction
❖ Important terms
❖ Atomic Absorption Spectroscopy (AAS) -
Definition, overview, history, principles, steps, Instrumentation,
interferences, Applications.
❖ Atomic Emission Spectroscopy & Optical Emission Spectroscopy.
Definations, principle, plasma sources, applications
❖ Flame photometry :-- Introduction, Instrumentation,
Interferences, Applications
❖ Reference

Introduction
Spectroscopy is the study of interactions between matter and different forms
of electromagnetic radiation; when practiced to quantitative analysis, the term
spectrometry is used.Atomic spectroscopy includes the techniques of atomic
absorption spectroscopy (AAS), atomic emission spectroscopy (AES), atomic
fluorescence spectroscopy (AFS), X-ray fluorescence (XRF), and inorganic
mass spectroscopy (MS). AAS, AES, and AFS exploit interactions between
UV-visible light and the valence elec-trons of free gaseous atoms. In XRF,
high-energy charged particles collide with inner-shell electrons of atom,
initiating transitions with eventual emission of X-ray photons. For inorganic
MS, ionized analyte atoms are separated in a magnetic field according to their
mass to charge (m/z) ratio

Spectroscopy
● Spectroscopy is the branch of science that deals with the study
of interactions of electromagnetic radiations with matter i.e.
Atoms or molecules of drugs.
● Spectroscopy is of two types, Absorption spectroscopy and
Emission spectroscopy

Types of spectroscopy
Emission spectroscopy
Examples include :-
▪Fluorimetry
▪Flame spectroscopy
▪Atomic emission spectroscopy
Absorption spectroscopy
Examples include :-
▪UV/Visible spectroscopy
▪IR Spectroscopy
▪Nuclear Magnetic Resonance
Spectroscopy (NMR)
▪Atomic Absorption spectroscopy

Atomic spectroscopy
● Atomic spectroscopy is the result of phenomenon of
absorption, emission or fluorescence by atoms or
elementary ions mostly in ultraviolet region.
● technique for determing the elemental composition of an
analyte by its electromagnetic or mass spectrum.
● The spectra is obtained by converting the component into
gaseous atom or elementary ions by suitable heat
treatment

Atomic spectra
When atoms are excited they emit light of certain wavelengths
which correspond to different colors. The emitted light can be
observed as a series of colored lines with dark spaces in
between; this series of colored lines is called a line or atomic
spectra. Each element produces a unique set of spectral lines.
Since no two elements emit the same spectral lines, elements
can be identified by their line spectrum.

Atomic Absorption Spectroscopy
AAS

AAS Definition
Atomic Absorption Spectroscopy (AAS) is a technique
that deals with the absorption of electromagnetic
radiation of free gaseous atoms at a specific
wavelength. AAS allows the measurement of extremely
small amounts of elements and is extensively used
throughout the world in medicine, manufacturing, mining,
environmental monitoring, and laboratories.

Sir Alan Walsh (1916 - 1998)
1955: Australian spectroscopist Alan Walsh
(1916–1998) develops atomic absorption spectroscopy
(AAS), which has been described as "the most
significant advance in chemical analysis" in the 20th
century.
Laboratory model of an atomic absorption
spectrophotometer, demonstrated at an exhibition of
scientific instruments in Melbourne in March 1954.

Overview of spectroscopy
Spectroscopy can be traced back to 1648, when Marcus Marci Von
Kronland, a Bohemian physicist, discussed optics, color and rainbow in his
book titled Thaumantius. Optical spectroscopy was even found in 1672 from
Newton’s description of how sunlight splits into different colors when passed
through a prism and since then the word ‘spectrum’ came into focus. In
1802, William Hyde Wollaston analyzed sunlight, which led to the discovery
of black lines in the spectrum, however, it was left uncharacterized.
Fraunhofer, starting in 1817, began to map and study the dark lines,
designating some of the more prominent ones with letters starting with “A”
at the red end of the spectrum. These black lines were later explained as a
result of the absorption of light in the sun’s atmosphere by Sir David
Brewster in 1820.

Atomic Absorption Spectroscopy (AAS) History
Robert Bunsen and Gustav Kirchhoff studied the sodium spectrum and
concluded that every element has a specific spectrum that can be used to
identify elements in their gaseous phase. Kirchoff further explained the
phenomenon that if a material emits electromagnetic radiation of a
certain wavelength, it may also absorb radiation of that wavelength.
Despite these early discoveries, AAS was mostly limited to astrophysical
studies and was virtually ignored until 1950, probably due to the high
level of difficulty of the technique and also there was a need for a very
high resolution to make quantitative measurements.

In 1952 Alan Walsh, a physicist working in the Chemical Physics
Section of the CSIRO Division of Industrial Chemistry in Melbourne,
Australia, overcame the lingering problem. This was done with the use
of a special type of atomic spectral lamp (usually a hollow cathode
lamp), which emitted a pulsed signal of very narrow spectral lines
characteristic of the element being determined, one or more of which
could be absorbed by the atoms of this element in the flame.
It was probably due to his experience in two complementary fields of
spectroscopy, i.e., in emission spectrochemical analysis and in infrared
absorption, that led him to invent the doublepass monochromator. In
1953, CSIRO filed a patent application and in March 1954, an
instrument to demonstrate the atomic absorption technique was shown
at an exhibition in Melbourne.

Principle of AAS
o "When a beam of monochromatic radiation is passed through the atoms
of an element, the rate of decrease of intensity of radiation is proportional
to the intensity of incident radiation as well as the concentration of the
solution.
o This technique basically uses the principle that free atoms (gas)
generated in an atomizer can absorb radiation at specific frequency.
o The atoms absorb UV or visible light and make transitions to higher
electronic levels. AAS quantifies the absorption of ground state atoms in
the gaseous state.
o The analyte concentration is calculated from the amount of absorption.

Steps
The steps are involved in turning a liquid sample into an
atomic gas:
Desolvation - the liquid solvent is evaporated, and the dry
sample remains.
Vaporization or Volatilization- the solid sample vaporizes to
a gas.

Instrumentation for Atomic absorption
spectroscopy
This Atomic Spectrophotometer operates in both atomic
absorption and emission modes.
The basic requirements are:-
▪A light source /radiation source
▪A sample cell and
▪a means of specific light measurement

Radiation sources
When it comes to Atomic Absorption, there are a couple important factors to note.
Absorption lines are extremely narrow, usually only ranging between 0.002 and
0.005 nm. Also, each element has its own unique electronic transition. Picking a
source is application driven, the correct source for your specific use must be
chosen. These factors must be taken into account when deciding a lamp for
analysis.
There are two categories of sources, line and continuum. Line sources emit a
narrow band of radiation, which is important because they are highly selective,
provide high sensitivity (beam power is in a narrow wavelength band) and reduce
spectral interference of other elements, molecules, atoms, or ions that have similar
spectral lines. Continuum sources are typically used for background correction, to
eliminate the matrix so only the signal of the analyte is observed.

Hallow - Cathod lamps
The most common line source used for atomic absorption spectroscopy is the
HCL. Structurally, this is an air-tight lamp filled with argon or neon and kept at
around 1 to 5 torr. The inert gas is ionized as a high voltage potential difference is
created between the tungsten anode and use-specific cylindrical cathode. Cations
of the ionized argon or neon gas dislodge metal ions from the cathode. These
produce an atomic cloud; where some of the atoms in the cloud are in an excited
state and emit an element specific radiation upon returning to ground state. There
are many commercially available models of HCLs, some can possess multiple
metal cathodes for analysis of several metals
Why the cathode is hollow? -
To allow the atoms to deposit back on the cathode, thus increasing the life time of
the lamp.

Working of HCL
● HCL works by the process of sputtering.
● “Sputtering occurs when the energy to be transformed into
gaseous atom and brings out an atomic cloud by shifting
some amount of metal from the cathode.
● The excited metal atoms of the atomic cloud emits the
radiation.
● Metal atoms diffuse back thus re-deposited occurs

Hollow cathode lamp Photo of a typical multielemental hollow cathode
lamp. The cathode in this lamp is fashioned from
an alloy containing Co, Cr, Cu, Fe, Mn, and Ni,
and is surrounded by a glass shield to isolate it
from the anode. The lamp is filled with Ne gas.

Position of Hollow Cathode Lamp in AAS

Electrodeless Discharge Lamps (EDLs)
EDLs are line sources that provide radiant energy that has a greater
intensity than HCL. These are sealed quartz tubes filled with inert gas at
low pressure, much like HCL. The bulb contains a small quantity of the
element of interest. An intense field of radiation provides ionization and
excitation of the metal to produce a spectrum. The line width is typically
narrower, but may require more time to analyze because it is powered by a
radio-frequency (RF) source and needs time to stabilize the RF coil. EDLs
are generally less reliable than HCLs with the exception of Se, As, Cd, and
Sb in which, better detection limits are produced.

Electrodless discharge lamp
● EDL is available for wide variety of elements. It is more efficacious
practically but expensive

Photometers
o The portion of an atomic absorption spectrometer's optical system which
conveys the light from the source to the monochromator is referred to as
the photometer.
o Types: single and double beam photometers

Nebulizer
● suck up Iiquid samples at controlled rate.
● create a fine aerosol spray for introduction into flame.
● Mix the aerosol and fuel and oxidant thoroughly for introduction into flame.

High sensitivity nebulizer
Steel nebulizer

Atomizer
● AA spectroscopy requires that the analyte atoms be in the gas
phase. lons or atoms in a sample must undergo desolvation and
vaporization in a high-temperature source such as a flame or
graphite furnace.
● Flame AA can only analyze solutions, while graphite furnace AA
can accept solutions, slurries, or solid samples.

Atomization
Atomization is 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 farnace.
Sample Atomization techniques -
● Flame atomization
● Electro thermal atomization
● Hydride atomization
● Cold - vapour atomization

Flame Atomization
● Nebulizer suck up liquid samples at controlled rate.
● Create a fine aerosol spray for introduction into flame.
● Mix the aerosol and fuel and oxidant thoroughly for introduction into flame.
● An aerosol is a colloid of fine solid particles or liquid droplets, in air or
another gas.
● Flame AA uses a slot type burner to increase the path length, and therefore to
increase the total absorbance (Beer-Lambert law). Sample solutions are
usually aspirated with the gas flow into a nebulizing /mixing chamber to form
small droplets before entering the flame.

Electro thermal/ graphite furnace atomization
● Uses a graphite coated furnace to vaporize the sample.
● In GFAAS sample, samples are deposited in a small graphite coated tube
which can then be heated to vaporize and atomize the analyte.
● The graphite tubes are heated using a high current power supply.
Uses of graphite furnace atomic absorption
● The Graphite Furnace is used for the same tests as the Flame Atomic Absorption
Spectrometer.
● The Graphite Furnace is more sensitive than the Flame AAS so it can be used for
trace metal analysis in the ppb range.
● For some metals which can cause poisoning in relatively small quantities it is vital to
test in the ppb range for their presence in food and water.

Basic Layout of a Graphite Furnace Instrument

Graphite furnace technique
It is an atomic spectroscopic technique in which a small sample is placed inside a graphite tube that is
then resistively heated to accomplish sample desolvation (for liquid samples), ashing or charring (to
decompose the sample and volatilize some of the matrix), and finally atomization.

Monochromater
● This is a very important part in an AA spectrometer. It is used to separate out
all of the thousands of lines.
● A monochromator is used to select the specific wavelength of light which is
absorbed by the sample, and to exclude other wavelengths.
● The selection of the specific light allows the determination of the selected
element in the presence of others.

Diffraction Grating
the process by which a beam of light or other system of waves is spread out as a
result of passing through a narrow aperture or across an edge, typically
accompanied by interference between the wave forms produced
Polychromatic light diffracted from a grating.

Detector
● The light selected by the monochromator is directed onto a detector that
is typically a photomultiplier tube, whose function is to convert the light
signal into an electrical signal proportional to the light intensity.
● The processing of electrical signal is fulfilled by a signal amplifier. The
signal could be displayed for readout , or further fed into a data station for
printout by the requested format.

Calibration of Spectrometer
o In the linear region, data on as little as one standard and a blank
may be sufficient for defining the relationship between
concentration and absorbance. However, additional standards are
usually used to verify calibration accuracy.
o Where the relationship becomes nonlinear, more standards are
required for which the accuracy of a calibration depends on the
number of standards and the equations used for calibration.

Data Analyzing
▪By comparing the light intensity that. has
passed through the sample with. that of
the same light after it has. passed
through a blank, the. absorbance is
measured. ▪The absorbance of
different standard. solutions of a compound of
the. element are also measured and a.
calibration curve is constructed.
▪Absorbance is plotted against.
concentration. We then use the.
calibration curve to determine the unknown concentration

Interferences in AAS
Interference is a phenomenon that leads to change (either positive or negative) in
intensity of the analyte signal in spectroscopy.

Spectral interferences
Spectral interferences are caused by presence of:
another atomic absorption line, or a molecular absorbance band close to the
spectral line of element of interest. Most common spectral interferences are
due to molecular emissions from oxides of other elements in the sample.
The main cause of background absorption is presence of undissociated
molecules of matrix that have broad band absorption spectra and tiny solid
particles, unvaporized solvent droplets or molecular species in the flame
which may scatter light over a wide wavelength region. When this type of
non-specific adsorption overlaps the atomic absorption of the analyte,
background absorption occurs.

Chemical Interferences
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 such as Ti, W, Zr, 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.
Alternatively, 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
Ionization interference is more common in hot flames. The dissociation process
does not stop at formation of ground state atoms. Excess energy of the flame can
lead to ionization of ground state atoms 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 and alkaline earths.
Ionization interference is eliminated by adding an excess of an element which is
easily ionized thereby creating a large number of free electrons in the flame and
suppressing ionization of the analyte. Salts of such elements as K, Rb and Cs are
commonly used as ionization suppressants.

Applications of AAS
● Agriculture – analyzing soil and plants for minerals necessary for growth
● Chemical – analyzing raw chemicals as well as fine chemicals
● Environmental Study – determination of heavy metals in water, soil, and
air
● Food Industry – quality assurance and testing for contamination
● Forensic’s – substance identification
● Mining – testing the concentration of valuable substances in potential
mining areas
● Nuclear Energy – monitoring potentially hazardous elements in water and
waste output
● Petrochemical – analyzing products for metals and other substances that
can have adverse affects such as oil and gas

Forensics applications
Atomic absorption spectroscopy has been utilized in the study of forensic
sciences for many years. Using this technology, forensic scientists can
perform in-depth analysis of blood samples, brain and muscle tissue, and
gunshot powder residue. This technology has vastly improved the
accuracy of toxicology reports in cases of metal poisoning. Common
causes of metal poisoning, such as mercury and lead, are easily detectable
using this technology and can be identified even in trace amounts.

Pharmaceutical Applications
▪AAS are used to help for fully characterization of the pharmaceutical
products Atomic spectrometry enables the determination of drugs with
higher sensitivity and accuracy. The method is free from interference by
excipients present in the drug formulations.
▪AAS based techniques have also been used to provide indirect
determinations of pharmaceuticals such as ciprofloxacin, amoxicillin and
diclofenac sodium. Quantification of tin in an antihelminthic powder
▪Determination of lithium in antidepressives by flame AAS, Palladium in
synthetic drugs can be done by graphite tube or furnace AAS.The material
used in the dental medicine is analyzed for the determination of zirconium
by AAS.

▪HG-AAS can be used for the determination of arsenic in the commercial
samples of injectable drugs containing high concentrations of Sb (V)
▪The indirect AAS determination of active components in pharmaceutical
preparations can be achieved by continuous liquid liquid extractor coupled on
line to an atomic absorption spectrometer with substantially higher sensitivity
▪Flouroquinolone antibacterials like gatifloxacin, moxifloxacin and sparfloxacin
can be estimated accurately by AAS
▪An indirect method based on the complexation of captopril with an excess of
Pb(II) ion was used for the determination of captopril in pharmaceutical
preparation by AAS. The produced complex can be aspirated on the AAS after
resoluting on the cationic exchange resin
▪AAS can be used for the study of the presence of various proportions of
important metals along with the varied concentration of ion in the ayurvedic
preparations of the metallic ions

Atomic emission spectroscopy (AES) is a method of
chemical analysis that uses the intensity of light
emitted from a flame, plasma, arc, or spark at a
particular wavelength to determine the quantity of
an element in a sample. The wavelength of the
atomic spectral line in the emission spectrum gives
the identity of the element while the intensity of
the emitted light is proportional to the number of
atoms of the element.

Atomic Emission
spectroscopy
Optical Emission Spectroscopy (OES)

OES is often referred to as a “spark test”. It is so because it uses a sparking
process where an electrical discharge is applied to the area under analysis.
As a result of the spark, a small amount of material vaporizes which creates
a distinct chemical signature. This helps in the determination of the
elemental breakdown of the metal under consideration.
Optical Emission Spectroscopy (OES) is a widely used analytical
technique used to determine the elemental composition of a broad
range of metals. It is an extremely timeefficient and accurate method
for determining the constituents of a variety of metals and alloys.

Optical emissions are generally detected with
optical spectrometers. Thus OES is a part of
AES, and all of the technique of interest could
be called AES but since they all exclusively
measure optical emissions with optical
spectrometers the use of OES is much more
precise.

Principle of AES
● Atomic emission spectroscopy is also an analytical technique that used to
measure the concentrations of elements of samples
● It uses quantitative measurement of the emissions from excited atoms to
determine analyte concentrations.
● The analyte atoms are promoted to a higher energy level by the sufficient
energy that is provided by the high temperature of the atomization sources.
● The excited atoms decay back to lower levels by emitting light. Emissions are
passed through monochromators or filters prior to detection by
photomultiplier tubes.
● The instrumentation of atomic emission spectroscopy is the same as that of
atomic absorption, but without the presence of a radiation Source
● In atomic Emission the sample is atomized and the analyte atoms are excited
to higher energy levels.

● There are a number of different types of excitation sources used in atomic
emission spectroscopy. The primary emission sources used in atomic
emission spectroscopy today are the following
● 1. AC or DC arcs
● 2. High, medium or low voltage sparks
● 3. Glow discharges with flat or hollow cathode
● 4. Inductively coupled plasmas
● 5. Lasers
● 6. Direct Current Plasmas
● 7. Capacitively coupled microwave plasmas
● 8. Microwave induced plasmas
● 9. Furnaces
● 10. Exploding wires or foils.

Stepwise Sequence in Atomic Emission Spectroscopy

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.

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.

ICP-OES- General Instrumentation Schematic Diagram of ICP Plasma Torch

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.

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 LImin.
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.
ICP-AES Sample introduction system

Advantages of ICP-AES over Flame AES
● Temperature is two to three times higher than in a flame or furnace,
which results in higher atomization and excitation efficiencies.
● There is little chemical interference.
● Atomization in the inert (argon) atmosphere minimizes oxidation of
the analyte.
● Short optical path length minimizes the probability of self-absorption
by argon atoms in the plasma.
● Linear calibration curves can cover up to five orders of magnitude.

DCP
Direct-current plasma (DCP) is a type of plasma source used for
atomic emission spectroscopy that utilizes three electrodes to produce
a plasma stream. The most common three-electrode DCP apparatus
consists of two graphite anode blocks and a tungsten cathode block
arranged in an inverted-Y arrangement. An argon gas source is
situated between the anode blocks and argon gas flows through the
anode blocks. The plasma stream is produced by briefly contacting the
cathode with the anodes. Temperatures at the arc core exceed 8000 K.

Applications of DCP
● The applications of DCP are comparable to inductively coupled
plasma (ICP). Some applications include, but are not limited to:
● identification of boron in tissues and cells
● analysis of trace metals in cows
● synthesis of carbon nanofibers.

Comparison to inductively coupled plasma (ICP)
DCP incurs several key disadvantages in comparison to ICP. In addition to the
lower sensitivity, spectra generated by DCP generally present fewer spectral lines.
DCP samples are often incompletely volatilized due to the relatively short amount
of time spent in the hottest region of the plasma. Furthermore, DCP requires more
regular upkeep than ICP, because the graphite electrodes wear out after a few
hours and must be exchanged
However, DCP is not without a few advantages over ICP. The amount of argon
needed for DCP is much less than that needed for ICP. Also, DCP can analyze
samples that have a higher percentage of solid in solution than can be handled by
ICP

Applications of AES and OES
● Metallurgy :- OES offers rapid elemental analysis of solid metal
samples, making it indispensable for quality control in steel
making and aluminum metallurgy processes.
● Rare Earth Analysis:- (Bastnasite) Bastnasite is a mineral of
lanthanide rare earth type. Two of the major challenges of
analyzing rareearth with atomic absorption spectrophotometers are
(a) the difficulty to obtain a light source lamp and (b) difficulty of
atomization due to oxides generated from rare earth. These
problems are eliminated with Inductively Coupled Plasma OES (ICP
OES).
● Plasma Manufacturing Systems

● Human Hair & Fingernail Analysis:- Research has revealed that
the metabolism of several trace elements present in human
hair and fingernails have specific roles in the pathogenesis of
diseases such as Diabetes mellitus and Hypertension. OES can
help in the detection of such trace elements in the human
body and, thereby, aid in proper diagnosis.
● High Current Proton Sources :-OES is a very reliable technique
for carrying out noninvasive measurements of plasma density
and plasma temperature. It can also characterize the different
populations of neutrals and ionized particles constituting the
plasma.
● Realtime Tissue Differentiation

A schematic digram of flame photometry

▪Flame photometry (more accurately called Flame Atomic
Emission Spectrometry)is a branch of spectroscopy in which
the species examined in the spectrometer are in the form of
atoms.
▪A photoelectric flame photometer is an instrument used in
inorganic chemical analysis to determine the concentration
of certain metal ions among them sodium, potassium,
calcium and lithium.
▪Flame Photometry is based on measurement of intensity of
the light emitted when a metal is introduced into flame.
- The wavelength of colour tells what the element is
(qualitative)
-The colour's intensity tells us how much of the element present
(quantitative)

Instrumentation
● Flame atomizer
● Monochromator
● Detector
● Amplifier and readout device.

Flame atomizer
The role of atomizer is to generate the vapors of analyte which get excited by
thee thermal energy of the flame and then emit characteristic radiation that is
measured.
The flame atomizer assembly consists of two components. The prior is a
nebulizer where the sample in the form ofa solution is drawn in and converted
into a fine mist or an aerosol.
It is then passed onto the second component i.e. the burner along with air or
oxygen and a fuel gas. In the flame a number of processes occur that convert
the analyte into excited species.

a. Nebulizer
It is a device used for sample introduction into the flame. The process is called
nebulisation and consists of thermal vaporization and dissociation of aerosol
particles at high temperatures producing small particle size with high residence
time. A number of nebulisation methods are available. A few are listed below.
▪Pneumatic nebulisation
▪.Ultrasonic nebulisation
▪Electro thermal vaporization
▪Hydride generation (used for certain elements only).

b. Atomisers Burner Flame Photometry
The sample is introduced in the form of a fine spray at a controlled rate into the
flame of burner with the help of nebuliser. In the burner, the analyte undergoes
a number of processes as mentioned earlier
The following processes occur in the flame.
1.Desolvation - The sample containing metal particles is dehydrated by heat of
the flame.
2.Vapourization - The heat of the flame vapouriser the sample constituents.
3. Atomisation - At this stage the metal ions that were in the solvent are
reduced

4. Excitation - The atoms at this stage are able to absorb energy from
the heat.
5. Emission of radiation - Electrons in the excited state are very
unstable and move back down to ground state or a lower energy state
quite quickly.
▪Two types of of atomisation burner have been used in flame
photometry -
1.Pre-mix or Lundegårh burner
2.Total consumption burner

Types of flames used
The most common instruments use air as the oxidant. The temperature of the
flames produced is relatively low so the technique is only suitable for elements
that are easily excited such as alkali and alkali earth elements. When oxygen or
nitrous oxide is used a much higher temperature can be obtained.
o Different temperatures required for different elements
o Air-Acetylene flame
.Preferred flame for 35 elements
Temperature of 2300 C
o Nitrous Oxide-Acetylene flame
Temperature of 2900 C

Name of the element Emitted wavelength range (nm). Observed colour
Potassium (K) 766 Violet
Lithium (Li). 670. Red
Calcium (Ca) 622. Orange
Sodium (Na) 589. Yellow
Barium (Ba). 554. Lime green

Structure of flame
Flames are not uniform in composition, length or cross section. The structure of
a premixed flame, supported as a laminar flow
the flame may be divided into the following regions or zones.
i) Preheating zones
ii) Primary reaction zone or inner zone
iii) Internal zone
iv) Secondary reaction zone

Interferences
1.Spectral Interferences:
occurs when the emission lines of two elements cannot
be resolved or arises from the background of flame itself.
They are either too close, or overlap, or occur due to high
concentration of salts in the sample
2. lonic Interferences:
high temperature flame may cause ionisation of some of
the metal atoms.
e.g.sodium.
The Nat ion possesses an emission spectrum of its own
with frequencies, which are different from those of
atomic spectrum of the Na atom.

Chemical Interferences
The chemical interferences arise out of the reaction between different interferences
and the analyte Includes:
Cation-Anaion Interference:
The presence of certain anions, such as oxalate, phosphate,
sulfate, in a solution may affect the intensity of radiation
emitted by an element.
E.g, calcium + phosphate ion forms a stable substance, as
Ca3(P04)2 which does not decompose easily, resulting in the
production of lesser atoms
Cation-Cation Interference:
These interferences are neither spectral nor ionic in nature
Eg. aluminum interferes with calcium and magnesium

Applications of flame photometry
Qualitative applications:
- Used for the determination of alkali and the alkaline earth metals in
samples which are easily prepared as aqueous solutions.
- Example: Sodium produces yellow flame.
- Non-radiating element such as carbon, hydrogen and halides cannot be
detected.

Quantitative applications :-
1. The concentration of various alkali and alkaline earth metals is important
in determining the suitability of the soil for cultivation.
2. Used for the determination of the concentration of Sodium and potassium
ions in body fluids since their ratio controls the action of muscles including
the heart.
3. Analysis of water from various sources is carried out to determine its
suitability for drinking, washing, agricultural and industrial purposes.
4. Used for determination of lead in petrol.

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 thee 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.

Reference
https://www.researchgate.net/publication/336582088_Atomic_Spectroscopy
https://www.spectroscopyonline.com/view/timeline-atomic-spectroscopy
https://www.azom.com/
https://www.sas.upenn.edu/~seanjw/ICP-AES%20Index.html
https://blogs.maryville.edu/aas/source/
Wikipedia
ResearchGate
Google

Atomic spectroscopy (AAS & AES)

Atomic spectroscopy (AAS & AES)

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