AAS spec principles

1. Atomic Absorption
Spectroscopy, Principles and
Applications

2. What is atomic absorption spectroscopy?
• Technique for measuring the concentrations of metallic elements in
different materials.
• Involves absorbance of light by metallic atoms in the gas phase, the
light typically being sourced from a lamp specific to the
measurement of a single element.
• Determination of most metals and metalloids with this technique
offers sufficient sensitivity for many applications and is relatively
interference free.
• Metals make up around 75% of the earth’s chemical elements. Metal
content in a material is desirable, but metals can also be
contaminants (poisons).
• Used in quality control, toxicology and environmental testing.

3. Introduction
Atoms absorb light at a definite wavelength depending on the nature
of chemical elements.
• Sodium is absorbed in 589 nm
• Uranium is absorbed in 589 nm
• Potassium is absorbed in 766.5 nm
• Light at this wavelength has absorbed energy to excite another
electronic state. The electronic transition is specific to a particular
element. From the ground state of an atom is excited to a higher
energy level by absorption of energy.
• Atomic spectra are identified by sharp lines which can be
distinguished from broadband spectra associated with molecules.
Usually, lines arising from the ground state are almost important in
atomic absorption spectroscopy. These are called resonance lines.

5. Simple diagram showing atomic energy levels

7. Schematic diagram of a typical atomic
absorption spectrometer.

8. What is the principle of atomic absorption
spectroscopy?
• Firstly, all atoms or ions can absorb light at specific, unique
wavelengths. When a sample containing copper (Cu) and nickel (Ni),
for example, is exposed to light at the characteristic wavelength of
Cu, then only the Cu atoms or ions will absorb this light. The amount
of light absorbed at this wavelength is directly proportional to the
concentration of the absorbing ions or atoms.
• The electrons within an atom exist at various energy levels. When the
atom is exposed to its own unique wavelength, it can absorb the
energy (photons) and electrons move from a ground state to excited
states.
• The radiant energy absorbed by the electrons is directly related to
the transition that occurs during this process. Furthermore, since the
electronic structure of every element is unique, the radiation
absorbed represents a unique property of each individual element
and it can be measured.

9. How does an atomic absorption
spectrometer work?
• The AA spectrometer works by:
1. Creating a steady state of freely dissociated ground state atoms
using a heat source (flame)
2. Passing light of a specific wavelength through the flame. The
wavelength corresponds to the amount of energy required to
excite an electron from (typically) the ground to first excited state
for a specific element.
3. Measuring the amount of the light absorbed by the atoms as they
move to the excited state (the atomic absorption).
4. Using the measured absorbance to calculate the concentration of
the element in a solution, based on a calibration graph.

10. The electromagnetic spectrum. Atomic absorption
spectroscopy uses light in the ultraviolet-visible
range.

13. Beer-Lambert Law describes the relationship
between light absorption and concentration of
the element
• The Beer-Lambert Law defines the relationship between the
concentration and absorption of an absorbing species
•A = ε * c * l
• Where:
• A is the absorbance (Abs). Abs is measured by the AAS.
• ε is the molar absorption coefficient. This is the absorptivity of the
sample at a particular wavelength.
• c is the determined concentration of the element.
• l is the path length. For flame AAS, this is typically the path length
through the flame (along the burner) and is fixed for all
measurements.

14. Instrumentation
• Simple flame atomic absorption spectrometer includes:
1. A sample introduction system
2. The burner (flame) and its associated gas supplies: air-
acetylene or nitrous oxide-acetylene
3. A light source, the hollow cathode lamp (HCL)
4. A monochromator (the optical components inside the box in
the diagram)
5. An optical detector (photomultiplier tube or PMT)
6. Computerized instrument control, data collection, and
analysis.

17. AA spectrometer sample introduction system
• The liquid sample is transported via capillary tubing into the
nebulizer.
• The pneumatic nebulizer makes use of the Venturi effect, the
principle that fluid flows at a higher velocity through a narrower
tube, to accelerate the solution stream.
• The fluid then impacts a glass bead to create a fine spray of droplets,
known as an aerosol.
• In nebulizer the gaseous sample is broken up into a fine mist which is
then carried to the atomizer, such as a flame, by a carrier gas.

18. Atomization
• Can be carried out either by a flame or furnace.
• Atomization refers to breaking bonds in some substance to obtain its
constituent atoms in gas phase. Means by separating something into
fine particles
• Heat energy is utilized in atomic absorption spectroscopy to convert
metallic elements to atomic dissociated vapor.
• The temperature should be controlled very carefully for the
conversion of atomic vapor. At too high temperatures, atoms can be
ionized.

19. Atomizing techniques - flame atomic
absorption spectroscopy (FAAS)
• FAAS is mainly used to determine the concentration of metals in
solution in parts per million (ppm) or parts per billion (ppb) ranges.
• The metal ions are nebulized as a fine spray into a high-temperature
flame where they are reduced to their atoms and subsequently
absorb light from an element-specific hollow cathode lamp.
• Robust technique for routine metal determinations.
• But, it has limited sensitivity because of the spectral noise created by
the flame. Can only measure one metal at a time and as different
lamps are required for each element, the lamp must be changed each
time you want to analyze for something different. Also, a large part of
the sample is lost in the flame (up to 90%) in FAAS, further
influencing the sensitivity.

20. The atomization process in FAAS.

21. Fuels and Oxidants Used for Flame
Combustion
fuel oxidant temperature range (o
C)
natural gas air 1700–1900
hydrogen air 2000–2100
acetylene air 2100–2400
acetylene nitrous oxide 2600–2800
acetylene oxygen 3050–3150

22. Advantages and Disadvantages of Flame
Atomization
• Advantage ; reproducibility with which the sample is introduced into
the spectrophotometer;
• Disadvantage ;
• efficiency of atomization is quite poor. There are two reasons for
poor atomization efficiency. First, the majority of the aerosol droplets
produced during nebulization are too large to be carried to the flame
by the combustion gases. Consequently, as much as 95% of the
sample never reaches the flame, which is the reason for the waste
line shown at the bottom of the spray chamber. Second reason for
poor atomization efficiency is that the large volume of combustion
gases significantly dilutes the sample.

23. Atomizing techniques - graphite furnace
atomic absorption spectroscopy (GFAAS)
• In GFAAS, a type of electrothermal atomization, a sample is placed in
a hollow graphite tube which is heated until the sample is completely
vaporized.
• GFAAS is much more sensitive than FAAS and can detect very low
concentrations of metals (less than 1 ppb) in smaller samples.
• Using electricity to heat the narrow graphite tube ensures that all of
the sample is atomized in a period of a few milliseconds to seconds.
• The absorption of the atomic vapor is then measured in the region
immediately above the heated surface. Naturally, the detection unit
does not have to contend with spectral noise, leading to improved
sensitivity.

24. Typical graphite tube atomization process.

25. Atomization Method

26. Comparison of standard burner and high
temperature burner
Standard burner High temperature burner
Gas system
Air-acetylene: 2000°C
Air-hydrogen: 2000°C
Argon hydrogen: 1600°C
Dinitrogen oxide-
acetylene: 2900°C
Tip size 0.5 mm x 100 mm 0.4 mm x 50 mm
Measured elements
Pb Cd Fe Cu Mn Cr Au K
Ag Zn Na Ca Mg etc.
Al B Ba Be Ge Si Ti V W
etc.

27. LIGHT SOURCE
• Hollow cathode lamp (HCL) is used as the light source.
• It consists of a cylindrical hollow cathode made up of the same
element under consideration. The anode is made up of tungsten.
Both anode and cathode are enclosed in a glass tube with a quartz
window.
• The metal which is used in the cathode is the same as that metal that
we analyzed. The lamp is filled with noble gas at low pressure. The
lamp forms a glow of emission from the hollow cathode.

29. Monochromator
• An optical device that transmits a narrow band of wavelengths of light
or other radiation from a wider range of wavelengths. The atoms in the
AAS instrument accept the energy of excitation and emit radiation.
• A desired band of lines can be isolated with a monochromator by
passing a narrow band. The spectra through a monochromator can be
shown by a curve.
• Types of monochromators ;
1. Prism
2. Diffraction gratings
• Dispersion from the grating is more uniform than dispersion from the
prism. So, the grating can maintain a higher resolution over a longer
range of wavelengths.

30. AAS Monochromator

31. Detector
• Detector can convert light coming from a monochromator to a
simplified electrical signal.
• Photomultiplier tubes are the most commonly used detectors in
atomic absorption spectroscopy. These are used to convert
electromagnetic waves into electric currents.
• They are made up of photoemissive cathodes and dynodes. These
dynodes provide electron multiplications.
• Photodiode array detectors
• These detectors convert the transmitted light signals into an electric
pulse.

32. Photomultiplier tube (PMT)

33. Computerized instrument control/Recorder
• Recorder can receive electrical signals from the detector to
convert them into a readable response.
• In atomic absorption spectroscopy instrumentation, today
we used a computer system with suitable software for
recoding signals coming from the detector.
• Modern AA spectrometers contain a network of sensors and
use sophisticated algorithms to monitor and control their
operating conditions. They notify the user when there is a
problem with the system and ensure safety of operation.

34. Atomic Absorption Spectrometer
Model: AAnalyst 100 and PinAAcle 900F
Manufacturer: Perkin Elmer

35. Calibration
• The instrument must be calibrated before analysis for better
results.
• There must be five standard solutions containing a known
concentration of metals to be analyzed for calibration of the
instrument and of the same concentration as the sample
solutions.
• Calibrating solution is generally prepared as a sample of salt
dissolved in water or dilute acid.

37. Strengths and limitations of atomic
absorption spectroscopy (AAS)
Advantages Limitations
Low cost per analysis Cannot detect non-metals
Easy to operate New equipment is quite
expensive
High sensitivity (up to ppb
detection)
More geared towards analysis
of liquids
High accuracy Sample is destroyed
Mostly free from inter-element
interference
Wide applications across many
industries

38. What are the benefits of Atomic Absorption
Spectroscopy?
• Despite being one of the first elemental analytical techniques on the
market, Atomic Absorption Spectroscopy (AAS) is still in widespread use
across many industries. This is largely because the benefits of AAS are
simplicity, reliability, and low cost while still delivering precise, accurate
results.

39. The benefits of flame AAS
• Flame atomic absorption spectrometry (FAAS) is an entry-level
spectroscopy technique that is ideally suited to labs in which a small
number of elements are routinely measured.
• Compared with other atomic spectroscopic techniques, flame AAS:
1. Has the lowest capital cost, making it a more affordable option
2. Is a good technique for those new to spectroscopic analysis, due to
the simplicity of operation
3. Can deliver excellent sample throughput for a single element
analysis
4. Can measure samples over a wide concentration range, from low
ppm to percent levels, without the need to dilute the sample
5. Delivers accurate results
6. Can easily be operated manually or can be automated with an
additional autosampler

40. The benefits of graphite furnace AAS
• In contrast to FAAS, Graphite Furnace Atomic Absorption
Spectroscopy (GFAAS) is a highly sensitive technique that allows labs
to achieve ultra-trace analysis down to low ppb levels.
• Other benefits of GFAAS include:
1. Robust technique capable of handling samples with high total
dissolved solids (TDS)
2. Cost-effective trace element analysis option
3. Can be operated without constant supervision, as no flammable
gases are required
4. Ideal option for labs with trace detection limit requirements and
small numbers of samples
5. Ideal when a very small volume of sample is available
6. Suitable for a limited budget where ICP-MS is out of reach or
unnecessary

41. What are the applications of atomic
absorption spectroscopy?
• Today, the atomic absorption spectroscopy technique is the most
powerful tool in analytical chemistry, forensic science, environmental
analysis, and food industries. It is popular for analysts due to several
advantages ;
1. Speed of analysis. It can analyze various samples within a day.
2. Possible to determine all elements at trace concentration.
3. Not always essential to separate the element before analysis
because AAS can be used to determine one element in presence of
another.
4. The atomic absorption spectroscopy principle or instrumentation
can be used to analyze sixty-seven metals and several nonmetals
such as phosphorus and boron.

42. APPLICATIONS OF ATOMIC ABSORPTION
SPECTROSCOPY
Atomic absorption is the most widely used technique for the
determination of metals at trace and ultra-trace levels in a solution.
It is used to analyze metals in biological fluids such as blood, hair,
and urine.
Atomic absorption is used to find out the number of various metals
in the environment.
It is used in pharmaceutical industries for quantitative analysis of
metals in samples for example, in multivitamins tablets.
Atomic absorption is used to find the concentration of metals (Ca,
Mg, Fe, Si, Al, ) analysis of water.
Atomic absorption is used to determine the amount of catalyst.

43. Application of atomic absorption
spectroscopy…
It is used for the analysis of crude oil, and petroleum.
Atomic absorption is used for the analysis of soil samples. For
example, minerals inland before cultivation are tested to get
maximum yields.
It is used for trace element analysis of cosmetics.
Atomic absorption is used to find the amount of metals such as gold
in rocks.
It is used to determine the amount of various metals (Mn, Fe, Cu, Zn)
in foodstuff.
It is used for the analysis of additives (Ba, Ca, Na, Li, Mg) in
lubricating oils and grease.

44. References
• Atomic Absorption Spectroscopy, Principles and Applications
• https://www.technologynetworks.com/analysis/articles/atomic-
absorption-spectroscopy-principles-and-applications-356829
• Atomic Absorption Spectroscopy
• https://psiberg.com/atomic-absorption-spectroscopy/
• Atomic Absorption Spectroscopy
• https://www.priyamstudycentre.com/2021/11/atomic-absorption-
spectroscopy.html