Chapter four

Atomic Absorption and Emission

Spectroscopy

1
 Atomic spectroscopy techniques used to determine the elemental
composition of a sample based upon the absorption or emission of
electromagnetic radiation by atomic particles
 The methods are used for the qualitative and quantitative determination
of elements and called optical spectroscopy.
 specific wavelength of the radiation (emitted or absorbed) identifies the
element where as
 the intensity of emitted (or absorbed) radiation at the specific
wavelength is proportional to the amount of the element present.
 The other types of spectrometric methods used to identify the elements
present in samples and determine their concentrations are mass
spectrometry and X-ray spectrometry
 Atomic spectroscopy are based on the direct measurement of the
fluorescence, absorption, or emission spectrum of the sample

2
 Cont…
 Typically, atomic spectroscopic methods can detect ppm to ppb
amounts, and, even smaller concentration.
 In addition, they are rapid, convenient, and usually of high
selectivity.
 Spectroscopic determination of atomic species can only be
performed on a gaseous medium in which the individual atoms
or elementary ions are well separated from one another
 Atomization is a process in w/c a sample is converted into gas-
phase atoms and ions
 It is the 1st and critical step in atomic spectroscopy
 The efficiency and reproducibility of the atomization step can
have a large influence on the sensitivity, precision, and accuracy
of the method.

3
 In atomic spectroscopy, a substance is decomposed into atoms in a
flame, furnace, or plasma.
 Each element is measured by absorption or emission of ultraviolet or
visible radiation by the gaseous atoms.
 In atomic spectroscopy, samples vaporized at high temperature and
 decompose into atoms and ions whose concentrations are measured
by emission or absorption of characteristic wavelengths of radiation.
 Atomic spectroscopy is a principal tool of analytical chemistry,
Because of
its high sensitivity,
 its ability to distinguish one element from another in a complex
sample
its ability to perform simultaneous multielement analyses and
the ease with which many samples can be automatically analyzed

4
 Classification of Atomic Spectroscopic Methods
Atomization Typical Types of Common Name and Abbreviation
Method Atomization Spectroscopy
Temperature, ºC
Inductively 6000–8000 Emission Inductively coupled plasma atomic
coupled plasma Mass emission spectroscopy, ICP- AES
Inductively coupled plasma mass
spectrometry, ICP-MS

Flame 1700–3150 Absorption Atomic absorption spectroscopy, AAS

Emission Atomic emission spectroscopy, AES
Fluorescence Atomic fluorescence spectroscopy, AFS

Electrothermal 1200–3000 Absorption Electro thermal AAS

Fluorescence Electro thermal AFS
Direct-current 5000–10,000 Emission DC plasma spectroscopy, DCP
plasma
Electric arc 1000–8000 Emission Arc-source emission spectroscopy
Electric spark Varies with time Emission Spark-source emission spectroscopy
and position Mass Spark-source mass spectroscopy 5
Atomic absorption spectroscopy (AAS): Is analytical method that use
Absorption of light or radiation to determine the concentration of gas-
phase atom or ion
 It measure the absorption of radiation / radiant energy by atoms in
the gaseous state
 atomic absorption are potentially highly specific b/c atomic
absorption lines are remarkably narrow and electronic transition
energies are unique for each element
Principles
 The basic principle of AAS involves the absorption of light by free
atoms in the gas phase, which leads to an electronic transition from a
lower energy state (ground state) to a higher energy state (excited
state).
 The absorption spectrum of each element is unique and different from the
spectrum of other elements and this is the basis of AAS.
6
1. Atomization
The sample, which contains the element of interest, is first converted into free
atoms in the gas phase. This process is called atomization.
Atomization is typically achieved using a flame or an electrically heated graphite
furnace.
The heat from these sources causes the sample to vaporize, breaking down
molecules into individual atoms.
2. Absorption of Light:
 A light source, usually a hollow cathode lamp specific to the element being
analyzed, emits light at a wavelength that corresponds to the energy
difference between the ground state and an excited state of the element's
atoms.
 When this light passes through the vaporized sample, atoms of the element of
interest absorb some of the light at this specific wavelength.
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3. Electronic Transition:
 The absorption of light causes electrons in the ground state of the atoms to jump to a
higher energy level (excited state).
 This process occurs only at specific wavelengths that match the energy difference
between the ground state and the excited state of the atom.
4. Measurement of Absorbance:
 After passing through the sample, the remaining light is directed to a detector.
 The detector measures the intensity of the light that has passed through the
sample.
 The amount of light absorbed by the sample (which is proportional to the number
of atoms that have absorbed the light) is calculated by comparing the intensity of
the light before and after passing through the sample.
 The decrease in light intensity due to absorption is used to calculate the absorbance,
which is directly related to the concentration of the element in the sample according to
Beer-Lambert's law.

8
 5. Quantification:
 A calibration curve is generated by measuring the absorbance of standard solutions
with known concentrations of the element of interest.
 The absorbance of the sample is then compared to this calibration curve to
determine the concentration of the element in the sample.

A reagent blank and a set of five standards

Equation of the Line: Calibration procedure in instrumental analysis: o

y = mx + b calibration points; • test sample.
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 To analyze major constituents, the sample must be diluted.
 Trace constituents can be measured directly without pre-concentration.
 Atoms have definite energy levels in which electrons may exist.
 Normally electrons exist in the ground state energy levels.
 Electrons transition from ground state to higher energy levels need
absorption of energy equal to the energy difference b/n the two states.
ΔE = ∆Ei – Eo = hν = hc/λ
 Absorption of EMR of different wavelength by an atom gives rise to
transition of its electrons from their ground state to any of its higher
energy state.
 Each electronic transition of an atom produces absorption line & all the
transition lines of electrons of an atom constitute the absorption spectrum
of the element.
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 For example, in sodium atoms the ground state, the single valence electrons are
in the 3s orbital.
 External energy promotes the outer electrons from their ground state 3s orbitals
to 3p, 4p, or 5p excited-state orbitals.
 After a few nanoseconds, the excited atoms relax to the ground state giving up
their energy as photons of visible or ultraviolet radiation
 The absorption lines corresponding to the transition
of the single outer 3s electron of Na to the 3p & 4p orbital's .
 Not all possible transitions b/n atomic orbitals are allowed.
 For sodium the only allowed transitions are those in
which there is a change of ±l in the orbital quantum
number (l); thus transitions from s → p orbitals are allowed, and
transitions from s → d orbitals are forbidden
Fig. Origin of three sodium emission lines.11
 Fig: Atomic absorption spectrum for sodium Fig. Valence shell energy level diagram of Na.

 Na spectrum consists of a small number of discrete absorption lines corresponding

to transitions b/n the ground state 3s & the 3p & 4p.

12
 Instrumentation
 radiation source, sample holder ; wavelength selector; detector,
and signal processor and readout
 The sample holder in atomic absorption instruments is the
atomizer cell

1) Radiation source: irradiates the atomized sample.

 The sample absorbs some of the radiation, and the rest passes
through the spectrometer to a detector.
 To measure narrow light absorption with maximum sensitivity,
 it is necessary to use a line source, w/c emits radiation of the
specific wavelengths that can be absorbed by the atom.
 B /c narrow line sources provide high sensitivity and make
atomic absorption a very specific analytical technique with few
spectral interferences 13
 Hollow cathode lamps and electrodeless discharge lamps are the
most commonly used examples of line sources.
 Deuterium lamps and halogen lamps are often used for this
purpose.
 Hollow cathode lamp (HCL): It is the most common radiation source in AAS
 It contains a tungsten anode and a hollow cylindrical cathode made of
the element to be determine
 These are sealed in a glass tube filled with a low pressure of inert gas
( neon or argon)


 When a high voltage is applied across the anode and cathode; the
filler gas is ionized and the metal atoms in the cathode are in excited
state and produce the radiation that characteristic of the metal from
w/c the cathode was manufactured

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 The type of hollow cathode lamp tube depends on the metal
being analyzed since each element has its own unique lamp
which be used for that analysis
 The electron of the metal atoms in the atomizer can be
promoted to higher orbitals by absorbing a set quantity of
energy
 In a few cases, the quality of the analysis is impaired by
limitations of the hollow cathode lamp
 primary cases involve the more volatile elements where low
intensity and short lamp life are a problem
 The atomic absorption determination of these elements can
often be dramatically improved with the use of brighter, more
stable sources such as the electrodeless discharge lamp

15
b) Electrodeless discharge lamp (EDL): are useful sources of atomic
line spectra and provide radiant intensities usually one to two orders
of magnitude greater than hollow-cathode lamps
 It is constructed from a sealed quartz tube containing a few inert
gas such as argon and a small quantity of the metal (or its salt)
whose spectrum is of interest
 The lamp contains no electrode but instead is energized by an
intense field of radio-frequency or microwave radiation
 Ionization of the argon occurs to give ions that are accelerated by
the high-frequency component of the field until they gain
sufficient energy to excite the atoms of the metal whose spectrum
is sought
 For elements such as Se, As, Cd, & Sb, EDLs exhibit better detection limits than
do hollow-cathode lamps, due to the EDLs for these elements are more intense
than the corresponding hollow-cathode lamps

Fig. Electrodeless discharge lamp

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2) Atomizers: is the sample cell of the AAS system.
 Atomizer - is device such as a plasma, a flame, or a furnace
that produces an atomic vapor
 The atomizer must produce the ground state free gas phase
atoms necessary for the AAS process to occur.
 The analyte atoms are generally present in the sample as salts,
molecular compounds, or complexes.
 The atomizer must convert these species to the reduced, free
gas phase atomic state.
 Therefore, atomization is a process of separation particles
into individual molecules and breaking molecules into atoms
 This is done by exposing the analyte to high temperatures in a
flame or graphite furnace
 d/t temperatures required for different elements

17
 The two most common atomizers are flame atomizers and electrothermal (furnace atomizers)
i) Flame atomizer: use a premix burner, in which fuel, oxidant, and sample are mixed
before introduction into the flame.

Fig. (a) Premix burner. (b) End

view of flame. The slot in the
burner head is about 0.5 mm
wide. (c) Distribution of droplet
sizes produced by a particular
nebulizer

 In flame atomization, the sample is first converted into a fine mist consisting of small
droplets of solution in nebulizer assembly
 Sample solution is drawn (aspirated) into the nebulizer by the rapid flow of oxidant
(usually air) past the tip of the sample capillary tube.
 Liquid breaks into a fine mist as it leaves the capillary.
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 The spray is directed against a glass bead, upon which the
droplets break into smaller particles.
 The formation of small droplets is termed nebulization.
 the term “to nebulize” means to convert to a fine mist , like
a cloud.
 A fine suspension of liquid (or solid) particles in a gas is
called an aerosol.
 The nebulizer creates an aerosol from the liquid sample.
 The mist, oxidant, and fuel flow past baffles that promote
further mixing and block large droplets of liquid.
 Excess liquid collects at the bottom of the spray chamber
and flows out to a drain.
 Aerosol reaching the flame contains only about 5% of the
initial sample.
 AAS that use flame atomizer is called flame AAS (FAAS).
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 In modern commercial flame AAS, two types of flames are used.
 the air–acetylene flame, where air is the oxidant and acetylene is the
fuel .
 the nitrous oxide–acetylene flame , where nitrous oxide is the oxidant
and acetylene is the fuel when hotter flame is required to atomize high
boiling elements

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The flame consists of two principal zones or cones

The inner cone or primary reaction zone is the hottest region

just above the tip of the burner ; it is here that combustion,
atomization and thermal excitation occur

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 Common fuels and oxidants and their normal temperature ranges

General process
Sample Introduction:
 The sample solution is aspirated through a capillary into a chamber, where it is
converted into a fine mist (aerosol) by a nebulizer.
Aerosol Formation:
 The aerosol is then mixed with oxidant and fuel gas.
Flame Atomization:
 The aerosol, oxidant, and fuel are burned in a slotted burner, creating a flame that
heats the sample, causing the analyte to volatilize and atomize into free, ground-state
atoms.
 Nebulizer: Converts the sample solution into a fine mist.
 Burner: Provides the flame for atomization.
 Oxidant and Fuel Gases: Provide the necessary energy for the flame and can be
adjusted to optimize atomization for different elements.
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ii) Electrothermal atomizers (ETA)

 It is also called graphite furnace atomizer

 uses electrically heated graphite furnace

(GF) for atomization,

AAS that use GF atomizer is called GFAAS

 GF atomizer consists of

 a graphite tube, approximately 6 mm in diameter and 25–30 mm long,

 the electrical contacts required to heat the tube,

 a system for water-cooling the electrical contacts at each end of the tube,
and inert purge gas controls to remove air from the furnace.
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 A small sample is placed as a drop (usually 10-50 µL) in a heated,
electrically conductive element (e.g., a graphite tube or rod).
 The element is heated, typically in a stepwise manner, to progressively
dry, ash (remove organic matter), and then atomize the sample.
 The resulting gaseous atoms are then passed through a light source, and
the absorption or emission of light at specific wavelengths is measured.
 Drying: using a current that raises the temperature of the graphite tube
to about 110 °C. This leaves the sample as a solid residue.
 Ashing: using a current that raises the temperature to 350–1200 °C, and
at these temperatures, any organic material in the sample is converted to
CO2 and H2O, and volatile inorganic materials are vaporized. These
gases are removed by the inert gas flow.
 Atomization: the sample is atomized by rapidly increasing the
temperature to 2000–3000 °C.
 Cleanout: waste is blown out with a blast of Argon gas. (quick ramp
up to 3500 ºC )
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3. Monochromator
 A monochromator is required to separate the absorption line of
interest from other spectral lines emitted from the HCL and other
elements in the atomizer that are also emitting their spectra. Because
the radiation source produces such narrow lines
 The most common dispersion element used in AAS is a diffraction
grating.
 The grating disperses different wavelengths of light at different
angles
 The grating can be rotated to select the wavelength that will pass
through the exit slit to the detector. All other wavelengths are blocked
from reaching the detector
 The more lines on the grating, the higher is the dispersion. Higher
dispersion means greater separation between adjacent lines
 The analytically useful wavelength range for commercial AAS is
from 190 to 850 nm.
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4. Detectors
 The common detector for AAS is the photomultiplier tube (PMT).
 Solid-state single and multichannel detectors such as photodiode arrays
(PDAs) and charge-coupled devices (CCDs) are increasingly being used
in AAS
5. Signal Processor and Readout Device:
The electrical signal generated by the detector is processed to amplify it and
reduce any noise.
The processed signal is then converted into a readable format, usually as a digital
display or on a computer screen, representing the absorbance or concentration of
the element.
Readout devices can be digital displays, chart recorders, or computerized systems
that allow for data storage, processing, and analysis.
26
The workflow diagram of the instrumentation used in AAS

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Interference
 Interference is any effect that changes the signal while analyte
concentration remains unchanged.
 Interferences are physical or chemical processes that cause the
signal from the analyte in the sample to be higher or lower than
the signal from an equivalent standard.
 Interferences can cause either positive or negative errors in
quantitative analysis.
 It can be corrected by removing the source of interference or
by preparing standards that exhibit the same interference
 There are two major classes of interferences in AAS
spectral interferences and non-spectral interferences
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i)Spectral interferences cause the amount of light absorbed to be
erroneously high due to absorption by a species other than the analyte atom.
 Or unwanted signals overlapping analyte signal
 AAS is less susceptible to spectral interferences b/c specific
radiation sources (line sources) are used.
ii) Non-spectral interferences: affect the formation of analyte free atoms.
 chemical interference ,
 ionization interference ,and
 solvent effects (or matrix interference)
a)Chemical Interference

 Chemical interference occurs when some species in the sample affects

the atomization efficiency of the sample compared with the standard
solution.

 It is the serious source of interferences.

 It either enhance or depress the analyte signal from the sample.

29
 The effect is commonly associated with the anions present in the sample.

 Anions affect the stability of the metal compound in which the analyte is

bound, & thus, affects also the efficiency with which the atomizer produces

metal atoms.

 Ex., a solution of CaCl2 , when atomized in an air –acetylene flame,

decomposes to Ca atoms more readily than a solution of Ca3 (PO4 )2 .

 Ca3 (PO4 )2 is more thermally stable than CaCl2 .

 A solution of CaCl2 containing 10 ppm Ca will give a higher absorbance

than a solution of Ca3 (PO4 )2 containing 10 ppm Ca.

 If PO4 -3 ion is added to a solution of CaCl2 , the absorbance due to Ca will

decrease as the concentration of phosphate increases. This is a chemical

interference. 30
 Chemical interference is a result of having insufficient energy in the flame or
furnace to break the chemical bonds in molecules to form free atoms.
Chemical interferences can be compensated in three ways
1) To use matrix matching, (i.e., to match the matrix of the standards and
samples)
 To have the same anion(s) present in the same concentrations in the working
standards as in the samples being analyzed.
 Used for samples that have been thoroughly characterized and that their
composition is known and constant.
2) To add another metal ion (or releasing agent) that forms more stable
compound with the interfering anion than that of the analyte ion
 Releasing agent frees the analyte from forming a compound with the anion
and permits it to atomize.
 Ex., Lanthanum (La) forms a very thermally stable phosphate, more stable
than Ca3 (PO4 )2 .
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 To determine Ca in solutions that contain an unknown or variable amount of
phosphate, such as those from biological samples, La (as the chloride, LaCl3
or nitrate, La (NO3 )3 salt) is added to all standards and samples.
 The La “ties up” the phosphate by forming LaPO4 .
3) To eliminate the chemical interference by switching to a higher-
temperature flame.
Ex., when a nitrous oxide - acetylene flame is used, there is no chemical
interference on Ca from phosphate, because the flame has sufficient energy to
decompose the Ca3 (PO4 )2 molecules.
b) Matrix Interference
 The sample matrix and the solvent used for making the sample solution are
other potential sources of interference.
 Sample matrix is anything in the sample other than the analyte.
 Some sample matrices are quite complex.
Ex., determination of Ca in milk presents matrix effects that are not found when
determining Ca in drinking water

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 The presence of matrix interference can be determined by comparing the
slopes of an external calibration curve with the slope of an method of
standard additions curve.
 If the slopes of the two calibrations are the same (parallel to each other) there
is no matrix interference;
 If the slopes are different (not parallel), interference exists and must be
corrected for.
 The solvent may interfere in the atomization process.
 Ex. Organic solvents such as a ketone, alcohol, ether, and hydrocarbon can
evaporate rapidly and also burn, thus increasing the flame temperature.
 The atomization process is more efficient in a hotter flame.
 Organic solvents produce more free atoms and thus higher absorbance signals
than from aqueous solutions

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c) Ionization Interference:
 Occurs when the flame is hot enough to cause significant excitation &
ionization of the atoms.
 The absorbance is decreased b/c of the decreased population of ground state
atoms as a result of ionization and excitation.
 Ionization interferences are commonly found for the easily ionized alkali
metal and alkaline earth elements, even in cool flames. Ionization
interferences for other elements may occur in the hotter N2O-C2H2 .
 Ionization interference can be eliminated by adding excess suppressant
(easily ionized element) such as K, Rb, & Cs to all standard and sample
solutions.
 The ionization suppression agent is also called an ionization buffer.
 This addition creates a large number of free electrons in the flame, which can
be captured by the analyte ions and convert them back to atoms.
 Ex. in the determination of Na by AAS, it is common to add a large excess of
K to all samples and standards.
 K is more easily ionized than Na.
 The K ionizes preferentially and the free electrons from the ionization of K
suppress the ionization of Na.
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Application of AAS
i) Qualitative application
 Atomic absorption spectroscopy finds wide application in fields that vary from
mining to pharmaceuticals, environmental control and agriculture.
 The wavelength of absorption maxima is characteristic of a particular element.
 That means, the maxima indicate the type of element that generate the spectrum.
 AAS is used for the determination of metal and metalloid elements in samples of
different origins such as food, water, soil, plants, minerals, oil, cosmetics,
pharmaceuticals, etc.
 AAS is essentially a single-element technique, so it is not well suited for
qualitative analysis of unknowns.
ii) Quantitative analysis
 Absorption intensity (A) is proportional to the population of ground state atoms.
Aαc
 In AAS quantitative determination can be made in two ways.
(a) Direct determination using Beer’s Law;
A = εbc
b) Comparing absorbance of solutions
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Advantage AAS:

 Less affected with spectral interferences

 Sensitivity and Specificity

 Versatile Sample Types

Limitations of AAS:

 Individual radiation source is required for each element.

 AAS primarily analyzes metals and metalloids, not other types of elements.

 Not a Multi-Element Technique:

 Traditionally, AAS was not a multi-element technique, meaning it could only measure one
element at a time.

 AAS can be affected by matrix interferences, which can lead to inaccurate results.

 AAS is not suitable for screening tests, and some prior knowledge of the elements
expected is desirable.
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 Atomic Emission Spectroscopy (AES)
 Is measure the intensity of emitted radiation by gaseous atoms or ions
of the elements of interest at specific wavelengths
 An atom in its excited state reverts to either of its lower energy states or
to its ground state by emitting the absorbed energy in the form of
radiation.
 Emission gives spectral line.
 Each spectral line represents a particular electronic transition from
higher to lower energy level.
 The emission lines of an atom constitute and form emission spectrum.
Notice: The emission spectrum of an atom is unique and is different from
the spectrum of other elements and this is the basis of AES.

37
Atomic Emission Spectroscopy (AES)

38
Principle
 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 return back to lower levels by emitting
light.
 Emissions are passed through monochromators or filters
prior to detection by detector.
 By analyzing the wavelengths and intensities of the emitted
light, AES can be used for both qualitative (identifying
elements) and quantitative (measuring concentrations)
analysis.
 The intensity of the emitted light is directly proportional
to the concentration of the element in the sample.

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 Principle
 A sample containing the elements to be analyzed is introduced into a
high-temperature environment (flame, plasma, arc, or spark).
 Atomization: The sample is converted into free atoms in the gas
phase.
 Excitation: The free atoms or ions are then excited to higher energy
levels by absorbing energy from the atomization-excitation source.
 Emission: When excited atoms return to lower energy levels, they emit
light at specific wavelengths, characteristic of the element.
 Each element emits light at specific wavelengths, creating a unique
emission spectrum.
 Measurement and Analysis:. The emitted light is then passed through
a monochromator or filter to isolate specific wavelengths.
 A detector, such as a photomultiplier tube, measures the intensity of the
light at those wavelengths.
 The intensity of the emitted light is directly proportional to the
concentration of the element in the sample.
 By analyzing the wavelengths and intensities of the emitted light, AES
can be used for both qualitative (identifying elements) and quantitative
(measuring concentrations) analysis.

40
 Atomic emission is usually carried out with an inductively coupled
plasma, whose temperature is more stable than that of a flame.

 Plasma is normally used for emission, not absorption, because it is

so hot that there is a substantial population of excited-state atoms
and ions.

 Two additional commercially available atomizers are

 the cold vapor AAS (CVAAS) technique for determination of the

element mercury, Hg, and

 the hydride generation AAS (HGAAS) technique for several

elements that form volatile hydrides, including As, Se, and Sb

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Flame atomic emission spectroscopy (FAES): it is also called flame photometry.

 It is based on the measurement of the emission spectrum produced when a solution

containing metals or some nonmetals including halides, sulfur, or phosphorus is
introduced into a flame.

 In early experiments, the detector used was the analyst’s eye.

 Elements that emitted visible light, particularly alkali and alkaline-earth metals, could
be identified qualitatively.

 Flame tests were used to confirm the presence of certain elements in the sample.

 Flame AES is particularly useful for the determination of the elements in the first two
groups of the

periodic table, including

Na, K, Li, Ca, Mg,

Sr, and Ba.

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 Replacing the human eye with a spectrometer and photon detector permits
more accurate identification of the elements present because the exact
wavelengths emitted by the sample can be determined.

 The use of a photon detector also permits quantitative analysis of the

sample.

 The wavelength of the radiation indicates what element is present, and the
radiation intensity indicates how much of the element is present.

 FAES is particularly useful for the determination of alkali and alkaline-

earth metals.

Notice: the term spectrometry is used for quantitative analysis by the

measurement of radiation intensity.

43
 Cont…
Instrumentation : AES uses the same configuration as that of AAS.
 The instrumentation of atomic emission spectroscopy is the same as that
of atomic absorption.
 In atomic Emission the sample is atomized and the analyte atoms are
excited to higher energy levels all in the atomizer.
 Emission spectrometer consists an atomizer, (sample nebulizer), grating
monochromatic, photomultiplier detection system and microprocessor
controller

44
Cont…

45
 Cont…
Sample Atomizer/Excitation Source
 The sample is first prepared, often by dissolving it in a suitable
solvent, and then introduced into an atomization-excitation
source.
 This is the component that converts the sample into a gaseous
state and excites the atoms.
 Common sources include flames, electrical arcs, electrical sparks,
and inductively coupled plasmas (ICPs).
 ICPs are widely used due to their ability to analyze a wide range
of elements simultaneously.
 plasmas are at least twice as hot as flames or furnaces
 Its common temperature is 6000-10000 K w/c hot enough to
excite most elements and prevent the formation of most
interferences, break down oxides and eliminate most molecular
spectral interferences
 Plasma - is an electrical conducting gaseous mixture containing a
significant concentration of cations and electrons.
 Argon gas, is one of the most widely used plasma species

46
 Cont…
 Three types of plasma source for atomic emission spectroscopy:
 Inductively coupled plasma (ICP)
 Direct current plasma (DCP)
 Microwave induced plasma (MIP)
 ICP is the most common plasma source
 typical plasma source construction, consists three concentric quartz
tubes
An aerosol of the sample solution is injected into the plasma through
the central tube in a stream of argon
 So, inner tube contains the sample aerosol and Argon support gas
A higher flow of argon is injected b/n the second and outer tubes
 Therefore, outer tube contains flowing gas to keep the tubes cool
Radiofrequency (RF) generator produces an oscillating current in an
induction coil that wraps around the tubes
 Induction coil creates an oscillating magnetic field, w/c produces an
oscillating magnetic field, the magnetic field in turn sets up an
oscillating current in the ions and electrons of the support gas (argon)

47
INSTRUMENTATION

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 Cont…
Monochromator: This device separates the
emitted light into its constituent wavelengths.
 prism or grating-based, are used to select
and isolate specific wavelengths of light
emitted by the sample for analysis.
Detector: This component measures the
intensity of the light at specific wavelengths.
 In Atomic Emission Spectroscopy (AES),
common detectors include photomultiplier
tubes (PMTs) & photodiode arrays

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APPLICATION
a) Qualitative analysis: the emission spectra (wavelength of
emission maxima) are characteristics of elements.
b) Quantitative analysis: the intensity of the emitted radiation (I)
is directly proportional to the number of atoms being excited.
 Either external calibration or method standard addition curves is used
for quantitative analysis).
 Pharmaceutical and Metals Analysis: Identifying and quantifying
metals in pharmaceutical products and alloys.
 Environmental Monitoring: Analyzing metal concentrations in water
and soil samples.
 Geochemistry: Determining the elemental composition of rocks and
minerals.
 Material Science: Analyzing the composition of various materials.

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 Comparison between AAS and AES
Absorption Emission
Measure trace metal Measure trace metal
concentrations in complex concentrations in complex
matrices . matrices .
Atomic absorption depends upon Atomic emission depends upon
the number of ground state atoms the number of excited atoms .
It measures the radiation It measures the radiation emitted
absorbed by the ground state by the excited atoms .
atoms.
Presence of a light source ( HCL ) Absence of the light source .
The temperature in the atomizer The temperature in the atomizer
is adjusted to atomize the analyte is big enough to atomize the
atoms in the ground state only. analyte atoms and excite them to
a higher energy level.
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1. Explain why simultaneous multielemental determination
by ICP-AES is easier compared to that by AAS.
2. Explain the difference between atomic emission and
atomic absorption spectrometry
3. Explain the principle of AAS and AES.

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