Review of Atomic Spectroscopy / Analytical Instrumentation for Tribhuvan University Nepal

1. Group D
Analytical and Instrumental
Inorganic Chemistry
By: Dr. Damodar Koirala
1
Review on Analytical Instrument

2. Chemical Analysis
Classical Methods Instrumental Methods
Gravimetric
Titrimetric Spectroscopy
Electroanalytical
Chromatography
“Chemical analysis can be performed using instrument or without using instrument”
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3. Redox titration: Uses of Potassium bromate, Ceric salts, Redox indicators
Complexometric titration: metal ion indicators
Precipitation titration: adsorption indicators
Uses of common organic reagent in chemical analysis
dmg, oxine, cupferron
A brief review on chemical analysis
PART I
3

4. Atomic absorption spectroscopy (AAS)
Atomic emission spectroscopy (AES)
Flame photometry (FP)
Atomic fluorescence spectroscopy
Plasma emission spectroscopy
Molecular luminescence
Thermal analysis: TGA and DTA
Instrumentation, working principles and applications
PART II
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5. Semester’s tentative plan
5
Day Topic
1 Introduction, basics on chemical analysis and titration
2 Redox titration
3 Complexometric titration / Precipitation titration
4 Common organic reagents
5 Spectroscopy and Optical instruments
6 Atomic Spectroscopy Introduction
7 Atomic absorption spectroscopy
8 Atomic emission spectroscopy
9 Flame photometry
10 Plasma Emission spectroscopy
11 Atomic fluorescence spectroscopy
12 Molecular luminescence
13 Thermal analysis: TGA and DTA

6. Steps in Analytical Determinations
1. Select method
2. Acquire Sample
3. Process Sample
4. Eliminate Interferences
5. Measure property
6. Calculate results
7. Evaluating Results by Estimating their Reliability
8. Presentation of data
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7. 1. Accuracy and precision required.
2. Amount of sample available.
3. Concentration range of analyte.
4. Interfering components in sample.
5. Detection method.
6. Numbers of samples to be analyzed.
7. Speed, ease, skill and const of analysis.
Selecting an Analytical Method
}Sensitivity
} Time and care
} Selectivity
} Physical and chemical properties
}Economic
In order to select an analytical method intelligently, it is essential to
define clearly the nature of the analytical problem.
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8. Electromagnetic Spectrum
Electromagnetic radiation is divided into different regions based on
frequency or wavelength called electromagnetic spectrum.
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9. Bohr Atomic Model
- Electrons occupy specific levels (orbits) and no others
- Orbits have certain energy
- Electron excited to higher level by absorbing photon
- Electron relaxes to lower level by emitting photon
- Photon energy exactly equals gap between levels
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3 2 1

10. Energy : Absorbed or Emitted ?
Ground State: Electron is in lowest energy level
Absorption: Electron absorbs photon and jumps up to an excited state of higher energy
Emission: Electron emits photon as it jumps down to a state of lower energy
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3 2 1

11. Absorption or Emission
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12. Hydrogen Spectrum
Energy level are quantized
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13. Spectroscopy vs. Spectrometry
The term spectroscopy is normally reserved for measurements of the
electromagnetic spectrum. Words ending in -scopy mean "looking at" whereas
words in -metry mean "measurement of".
Spectroscopy:
Study of interaction between light (electromagnetic radiation) and matter.
Spectrometry:
Implies a quantitative measurement of intensity.
Atomic Absorption Spectrsocopy relies on the absorption of specific frequencies by atom
Atomic Emission Spectroscopy relies on the emission of specific frequencies by atom
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14. Basic steps on atomic spectroscopy
Formation of
Atoms
Interaction
between atoms
and EMR
Detection of
EMR
Source of EMR
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15. Energy states of chemical species
Ground state: The lowest energy state of an atom or other
particle. It is represented by Eo
Excited state: any states with higher energy than the
ground state. They are represented by E1 , E2, E3 ………..
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16. Postulate of Quantum theory
Atoms, ions, and molecules can exist only in certain discrete states,
characterized by definite amounts of energy. When a species
changes its state, it absorbs or emits an amount of energy exactly
equal to the energy difference between the states.
ΔE = E1 - E0 = h v = h c / λ
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17. Atomic Absorption
Partial energy diagram for sodium
These excitations are brought on by absorption of photons of
radiation whose energies exactly match the differences in energies
between the excited states and the 3s ground state. Transitions
between two different orbitals are termed electronic transitions.
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18. Introduction to electromagnetic
radiation
Electromagnetic radiation, or light, is a form of energy
whose behavior is described by the properties of both waves
and particles.
Wave
Reflection
Refraction
Interference
Diffraction
Particle
Absorption
Emission
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19. The oscillating electric field
Electromagnetic Wave
- It consists of oscillating electric and magnetic fields.
- These fields travel perpendicular to each other.
- In vacuum it travels with speed of light (c), 2.99792 × 108 m/s
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20. Properties of EM-Wave
Amplitude: length of the electric vector at a maximum in the wave.
Period: The time in seconds required for the passage of successive
maxima or minima through a fixed point in space
Frequency: the number of oscillations of the field per second and
is equal to 1/period.
Wavelength: linear distance between any two equivalent points.
Wavenumber: the reciprocal of the wavelength in centimeters.
Power: energy of the beam that reaches a given area per second.
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21. Effect of medium on EM-radiation
Velocity and wavelength changes when EM-wave travel through a medium.
There as energy and frequency remains the same.
In a vacuum, the velocity of radiation is independent of wavelength and is at its
maximum for all EM-radiation. 21

22. Interaction with matter
1. A transition from a lower level to a higher level with transfer of
energy from the radiation field to the atom or molecule is called
absorption.
• Absorption spectrum: A plot of the absorbance as a function of
wavelength or frequency.
• Emission spectrum: A plot of the relative power of the emitted
radiation as a function of wavelength or frequency.
2. A transition from a higher level to a lower level is called
emission if energy is transferred to the radiation field, or non-
radiative decay if no radiation is emitted.
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23. Element Detectable by AAS
Highlighted in Pink
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Atomic Absorption Spectroscopy (AAS)

24. Atomic Absorption
When a beam of polychromatic radiation passes through a
medium containing gaseous atoms, only a few frequencies
are attenuated by absorption, which when recorded is
unique for unique atom.
Detection of
EMR
Source of
EMR
Interaction
with atom
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25. Atomic Emission
When atoms absorb energy they get excited to higher
electronic state, these short-lived excited atoms relaxes to
stable ground state by emitting photons with only a few
frequencies, which when recorded is unique for unique
atom.
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Source of
energy
Detection
of energy
Excited States
Ground State

26. Atomic Absorption
Detection of
attenuated EMR
Source of
EMR
Interaction
with atom
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Detection of
emitted EMR
Source of
EMR
Interaction
with atom
Atomic Emission

27. Case of Sodium
Partial Absorption spectrum for sodium vapor
*Note that the wavelengths of the absorption and emission lines for sodium are identical.
The absorption and emission spectra for sodium are relatively simple and consist of only a few
lines. For elements that have several outer electrons that can be excited, absorption and emission
spectra may be much more complex.
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28. Optical instruments for analysis
A communication device between the system under study and the
investigator.
Block diagram showing process of instrument measurement.
Non-electric Domain Electric Domain Non-electric Domain
Electrical Signal : Voltage, current, charge
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29. Five Basic Component of Optical Instrument
1) Source - A stable source of radiant energy at the desired wavelength (or λ
range).
2) Sample Holder - A transparent container used to hold the sample (cells,
cuvettes, etc.).
3). Wavelength Selector - A device that isolates a restricted region of the EM
spectrum used for measurement (monochromators, prisms, & filters).
4). Photoelectric Transducer - (Detector) Converts the radiant energy into a
useable signal (usually electrical).
5). Signal Processor & Readout - Amplifies or attenuates the transduced signal
and sends it to a readout device such as a meter, digital readout, chart recorder,
computer, etc.
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30. Component of Optical Instrument
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31. General Design of optical instrument
Absorption
Emission
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32. I. Source of energy
A. Sources of Electromagnetic Radiation:
- It must provide an output that is both intense and stable in the desired region
of the electromagnetic spectrum.
- Classification
- Continuum source emits radiation over a wide range of wavelengths
- Line source emits radiation at a few selected, narrow wavelength ranges.
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33. B. Sources of Thermal Energy:
- Flames and plasmas are common source.
- Flame sources use the combustion of a fuel and an oxidant such as acetylene
and air, to achieve temperatures of 2000–3400 K.
- Plasmas are hot, ionized gases, provide temperatures of 6000–10,000 K.
I. Source of energy
C. Chemical Sources of Energy:
- Exothermic reactions can serve as a source of energy.
- In chemiluminescence the analyte is raised to a higher-energy state by means
of a chemical reaction, emitting characteristic radiation when it returns to a
lower-energy state.
- When the chemical reaction results from a biological or enzymatic reaction,
the emission of radiation is called bioluminescence.
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34. • Wavelength selectors output a limited, narrow, continuous group
of wavelengths called a band.
II. WAVELENGTH SELECTORS
1) Interference Filters: transmit or reflect range of wavelengths
2) Absorption Filters: blocks(absorbs) unwanted wavelengths
A. Filters
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35. II. WAVELENGTH SELECTORS
B. Monochromator
• Wavelength selector that can continuously scan a broad range of
wavelengths
• Used in most scanning spectrometers including UV, visible, and IR
instruments.
35 https://www.shimadzu.com/an/uv/support/fundamentals/monochromators.html

36. III. RADIATION TRANSDUCERS (DETECTORS)
- Early detectors were the human eye, photographic plates or films.
- Modern instruments contain devices that convert radiation to electrical signal.
A. Photon Detectors
1. Vacuum phototubes 2. Photomultiplier tubes
3. Photovoltaic cells 4. Silicon photodiodes
• Commonly useful in ultraviolet, visible, and near infrared instruments. eg.
36 https://study.com/academy/lesson/how-photomultiplier-tubes-array-detectors-work.html
Figure: Working principle of
photomultiplier tube

37. III. RADIATION TRANSDUCERS (DETECTORS)
B. Thermal Detectors
• Three types of thermal detectors :
1. Thermocouples 2.Bolometers 3.Pyroelectric transducers
• Used for infrared spectroscopy because photons in the IR region lack the
energy to cause photoemission of electrons.
• They are based on a temperature change of the element through
the absorption of electromagnetic radiation.
• The change in temperature causes a change in a temperature-dependent
property of the thermal detector, which is evaluated electrically and is a
measure of the absorbed energy.
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https://www.optris.global/thermal-detector

38. III. RADIATION TRANSDUCERS (DETECTORS)
Characteristics
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39. ■ Sample containers, usually called cells or cuvettes must have windows that
are transparent in the spectral region of interest.
■ There are few types of cuvettes:
- quartz or fused silica
- silicate glass
- crystalline sodium chloride
Quartz OR Fused silica
- Required for UV and may be for visible region.
Silicate glass
- Cheaper compared to Quartz, used in UV
Crystalline sodium chloride
- Used in IR
IV. SAMPLE HOLDER (CONTAINER)
cuvette
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40. SUMMARY
REGION SOURCE SAMPLE
HOLDER
DETECTOR
Ultraviolet Deuterium lamp Quartz/fused silica Phototube, PM tube,
diode array
Visible Tungsten lamp Glass/quartz Phototube, PM tube,
diode array
Infrared Nernst glower (rare earth
oxides or silicon carbide
glowers)
Salt crystals e.g.
crystalline sodium
chloride
Thermocouples,
bolometers
Types of source, sample holder and detector for
various EM region
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