Atomic Emission Spectroscopy (AES) Flame Emission Spectroscopy (FES) Instrumentation of AES Flame and Flame Profile INDUCTIVELY COUPLED PLASMA (ICP) Arc and Spark Emission Spectroscopy Comparison of AES and Atomic Absorption Spectroscopy

1. Flame Emission and Atomic
Emission Spectroscopy
(CHEM-673.1)
Dr. Sajjad Ullah

2. Course Content
(CHEM-673.1)
ATOMIC EMISSION SPECTROSCOPIC METHODS
Type of Emission Spectroscopy techniques
Flame Emission Spectroscopy
Atomic Fluorescence Spectroscopy
Plasma Emission Spectroscopy (ICP, DC)
Comparison of atomic spectroscopic techniques
Radio Chemical Methods
(will be discussed later)
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

3. Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

4. AAS
Higher number
of neutral atom (ground state)
AES
Higher number
of neutral atom (Excited state)
AFS
Higher number
of neutral atom (Excited state).
Emission measured at 90°
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

5. Atomic Emission Spectroscopy
(AES)
 AES is an analytical technique that is used to measure the
concentrations of elements in samples by quantitative
measurement of the emission from excited atoms
 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 (Flames/Plasmas) .
 The excited atoms decay back to lower levels by emitting
UV-vis light . Emissions are passed through monochromator
or filters prior to detection by photomultiplier tubes.
 Qualitative and Quantitative analysis
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

6. Types of transitions/Energy level diagram
 Atomic spectra: single external electron (Na or Mg+)
Doublet: Slightly
different in E
(LS coupling)
3p to 5s line
is weak, why?
unique λ-pattern
But depends on E o
source
λ for Mg2+ are
shorter than Na
1s2 2s2 2p6 3s1
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

7. Why a doublet for p-orbital?
When e- spin is parallel to orbital motion (L + S), E is High (repulsive interaction b/w the fields)
When e- spin is opposite to orbital motion (L - S), E is Low (attractive interaction b/w the field)
The magnitudes of such splitting for d and f orbitals are small
Both the spin and the orbital motions create magnetic fields
owing to rotation of charge carried by the electron
A doublet line is observed for species containing single e- : Na, Mg1+, Al2+
Higher no of e-, complex spectra (e.g., Fe, U have hundreds of such
electron transitions as shown in the simple Na
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

8. Atomic spectrum Mg
Singlet ground state Triplet excited stateSinglet excited state
Spins are paired
No split
Spins are unpaired
Energy splitting
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

9. 1s2 2s2 2p6 3s2
Paired spin
No splitting Three lines
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

10. Energy(eV)
Mg (2 outer electron system) Mg+ (1 outer electron system)
1s2 2s2 2p6 3s2 1s2 2s2 2p6 3s1
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

11. Excitation in flame
(Temperature Effects)
 Boltzmann equation
Boltzmann Equation relates Excited state population/Ground State
population ratios to Energy, Temperature and Degeneracy
Nj/No is exponentially related to T
 Effects on AAS and AES
)exp(
00 kT
E
g
g
N
N jj 

k= 1.38 x10-16 erg/degree
∆E btw ground and excited states
g = statistical weight factors
g= 2J+1 (J= L±S)
J is the internal atomic quantum number for the atom in
particular energetic level
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

12. Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

13. Boltzmann Distribution
All systems are more stable at lower energy. Even in the flame, most of the atoms will be in their
lowest energy state.
At 3000K, for every 7 Cs atoms available for emission, there are 1000 Cs atoms available for
absorption.
At 3000 K, for each Zn available for emission, there are approximately 1 000 000 000 Zn atoms
available for absorption.
Nj = 10-12 to 1 in most cases
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

14. Intensity of Emission Line
I = A Nj hν
I = A hν No (gj/g0) exp (-∆E/kT) A = Einstein transition probability
A= 1/life time of e- in excited state
or = 1/ no. of transition per second
(A = 108 s-1)
Nj = no. of atoms in excited state
Nj = No (gj/g0) e^-∆E/kT
With increase in T, Nj increases
and Iemission increases
The line that is used for atomic absorption spectroscopy measurement
is the one for which the intensity (as predicted by above equation) is
maximum
Most intense line generally has the highest gjA values*
gjA valaues are listed in: Corliss C. H. and Bozman, Experimental transition probabilities for spectral lines of 70
elements, NBS monograph 53, NBS, Washington D.C., 1962,

15. AAS vs. AES (Effect of T)
Both occur in flame
AES: Iemission is dependent on concentration of atoms in the excited
state (↑ Nj/No)
-more dependent on T
AAS: Iabsorption is dependent on concentration of atoms in the ground
state( ↓ Nj/No)
-less dependent on T (however no of reduced atom ↑ with ↑ T
- high T, more no. of reduced atoms, more P broadening
- FWHM ↑ and peak height ↓ with ↑ in T (fast moving atoms,
Doppler Broadening)
FLAME TEMPRATURE must be CONTROLLED!
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

16. The instrumentation of AES is the same as that of atomic
absorption , but without the presence of a radiation source
Schematics of AE spectrometer
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

17. Excitation Sources in AES
Flames Plasmas Arc/Spark
- The flame ( 1700 – 3150 °C ) is most useful for elements with relatively low excitation
energies like Na, K, Ca.
- The ICP ( 6000 – 8000 °C) has a very high temperature and is useful for elements of
high excitation energies .
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

18. FES (AES with Flames)
The FLAME performs ATOMIZATION and EXCITATION
Flames: air-propane (Alkali, Alakline earth metals)
air-acetylene ( refractory compounds)
P
M
T
Filters for Na and K
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

19. Atomizer
Nebulizer Burner Flame
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

20. How to get samples into the
instruments?
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

21. How to get sample atomize?
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

22. What is a nebulizer?
(Breaks sample into fine mist)
SAMPLE
AEROSOL
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

23. Nebulizers
 Controlled droplet size distribution
 Uniform flow rate
 Easy cleaning
 No Blockage
 No chemical reaction with solution
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

24.  Pneumatic Nebulizers
 Simplest, for clear non-turbid solutions
 Break the sample solution into small droplets.
 Solvent evaporates from many of the droplets.
 Most (>99%) are collected as waste
 The small fraction that reach the flame have been de-
solvated to a great extent.
 Efficiency of Nebulizer (droplet size distribution)
depends on flow rate, viscosity, surface tension of
solvent
 A corrosion-resistant bead placed at the outlet of the
nebulizer increase efficiency by removing big droplets.
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

25. Concentric Tube
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

26. Cross-flow
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

27. Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

28. Fritted-disk
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

29. Babington
 Viscous liquids
 No Blockage

30. ULTRASONIC NEBULZIERS
 Sample is placed in a tank and ultrasound waves
are passed through it from the base.
 The dense fog formed is swept with an oxidants
into the flame.
 Particle size distribution depends on frequencyand
is independent of flow rate of oxidant
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

31. How to get sample atomize?
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

32. BURNERS
Total Consumption Burner
Premix or Laminar-flow Burner
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

33. Total Consumption Burner
 Fuel, Oxidant and Sample flow directly into the flame
 No mixing of flame gases prior to being burned in
flame (Advantage!!!)
 No risk of explosion and gases with high burning velocity
Can be used
Disadvantages:
 Turbulent flame (erratic cooling caused by large droplets
 Low (incomplete vaporization)
 Flame shape not ideal for AAS measurements (short
pathlength)
 More sample enter the flame but efficiency of atomization
is low
 TCB rarely used
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

34. Premix Burner
Turbulence decreases if large droplets are
Avoided.
Fuel is mixed with oxidant and sample (Risk!)
Only fine droplets reach the flame
Large droplets (90% sample) are drained out
(Disadvantage)
Less sample enter the flame but atomization is
efficient (advantage)
Longer pathlength (suitable burner head) (Advantage!)
Smoother burning flame results in high S/N ration (Better for Quantitative analysis!)
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

35. • Sample is “pulled” into the nebulization chamber by the flow of fuel
and oxidant.
Laminar Flow Burners
• Contains flow spoilers
(baffles) to allow only the
finest droplets to reach
the burner head.
• Burner head has a long
path length and is ideal
for atomic absorption
spectroscopy.

36. Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

37. Advantages:
1. Uniform dropsize
2. Homogeneous flame
3. Quiet flame and a long path length
Disadvantages:
1. Flash back if Vburning > Vflow
2. ~90% of sample is lost
3. Large mixing volume
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

38. FLAMES
Rich in
free atoms
The sequence of events in not the same for every drop (drop size, Fuel/Oxd flow rate,
type of flame, oxides formation tendencyDr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

39. 1. Types of Flames
Fuel / Oxidant Temperature
H-CC-H acetylene / air 2100 °C – 2400 °C (most common)
acetylene / N2O 2600 °C – 2800 °C
acetylene / O2 3050 °C – 3150 °C
• Selection of flame type depends on the volatilization temperature of
the atom of interest.
2. Flame Structure
• Interzonal region is the hottest part of the
flame and best for atomic
absorption/Emission.
• Fuel rich flames are best for atoms because
the likelihood of oxidation of the atoms is
reduced.
• Oxidation of the atoms occurs in the
secondary combustion zone where the atoms
will form molecular oxides and are dispersed
into the surroundings.

40. • A α Ɩ and A α C
C of atoms in flam can be increased by decreasing volume.
Unfortunately, increasing Ɩ increases volume.
So then?
Use a burner head that gives long but thin/narrow flame
Too thin/narrow a flame can gets easily cooled and atomic
population may decrease, Caution!
TEMPRATURE of flame depends on FUEL/OXD. Ratio
FUEL-RICH FLAME, more fuel than oxidant, reducing but low T)
LEAN FLAME: Oxidant rich flame (oxidizing but hotter)
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

41. 3. Temperature Profiles
• It is important to focus the entrance slit of the monochromator on the
same part of the flame for all calibration and sample measurements.
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

42. FLAMES
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

43. Types of Flames Used in Atomic
Spectroscopy

44. Ca Cu
K Mn
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

46. ICP
AES with Plasma
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

47. INDUCTIVELY COUPLED PLASMA
(ICP)
ICP is used as source for AAS, AES, AFS
Plasma is a type of electrical discharge
Plasma is any type of matter that contains
an appreciable amount of less than 1% of
electrons and numbers + atoms + neutral
molecules +ve ions in equal
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

48. Plasma has 2 characteristics:
i- can conduct electricity
ii- affected by magnetic fields
.Plasma is highly energetic ionized gases usually inert
ICP is the state-of-the-art plasma formed electromagnetically by the
action of RF generator and an induction coil on a stream of Ar.
Other plasmas include direct current plasma (DCP) and
microwave induced plasma (MIP)
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

49. ADVANTAGES OF THE ICP
High degree of selectivity
Capable of exciting several elements not excitable by
ordinary flames
Higher sensitivity than Flame Photometry
Simpler to operate than Arc Spark methods
Higher degree of sensitivity than Arc Spark
Lacks electrodes which gives freedom from contamination.
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

50. Up to 70 elements can be analyzed using ICP at
concentrations below 1 ppm
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

51. THE ICP DISCHARGE
The argon gas (easily ionizable, unreactive) is
directed through a torch consists of 3 concentric
tubes made of quartz
A copper coil called the Load Coil surrounds the
top end of the torch and connected to a Radio
Frequency Generator (RF)
When RF power (700 – 1500 Watts) is applied
to the load coil, an alternating current moves
back and forth within the coil or oscillates at a
rate corresponding to the frequency of the
generator (3 – 75 MHz), generally 27 MHz. That
is, the oscillating current that passes through the
induction coil from the RF generator creates an
oscillating electromagnetic fields in the area at
the top of the torch.
ICP
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

52. Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

53. With Argon gas being swirled through the torch, a spark is applied
to the gas causing some electrons to strip out from their Argon atoms
These electrons are then caught up in the magnetic field and
accelerated by them.
Adding energy to the electrons by the use of the coil in this manner
is called “Inductively Coupling”
These high-energy electrons in turn collide with other Argon atoms,
stripping off still more electrons
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

54. A Tesla discharge (a source of electrons) provides “seed” electrons
to the argon stream. The e are accelerated by the magnetic field
from the induction coil.
This collisional ionization of Argon (by electrons) continues in a
chain reaction (self-propagating) thus breaking down the gas into a
Plasma consisting of Argon atoms, electrons, and Argon ions know
as “ICP” discharge
This ICP discharge is sustained (self-propagating)
This ICP discharge appears as intense, brilliant, white and tear-drop
shaped, T= 6000-1000 K
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

55. Structure and Temperature of Plasmas
Preheating zone (PHZ): solvent evaporation, meting, vaporization of salts
Initial radiative zone (IRZ): atomization/excitation/emission
Normal analytical zone (NAZ): Ions formation (+1 and +2)
Tail (Plume): recombination of atoms, formation of polyatomic species (Interferences)
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

56. Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

57. Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

58. Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

59. General Information
Used for Qualitative Analysis
Used for Quantitative Analysis
Detection limit is in ppb range
Not possible to determine: H, N, O, C or Ar in trace levels as
they are used in solvents and plasma
Not possible to determine F, Cl and noble gases at trace levels as
they require high excitation energy
Not used for determining radioactive elements
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

60. Qualitative Analysis using FES is done by comparing the emission spectrum of
Sample with spectra of known elements using identical
measurements conditions
-at least three lines should match)
Quantitative Analysis using FES is done by comparing the intensity of emission lines
with those of a series of standard using calibration curve.
-In AES, Intensity of spectral line measured for
quantitative analysis
- Film/plates detectors difficult. Intensity of light is
proportional to amount of darkening (measured with a
densitometer)
Interferences in FES are the same encountered in AAS.
-Chemical, Spectral and Ionization interferences
- Spectral interferences are more serious (depends on band-pass of
monochromator)

61. AES with Electrical Discharges
(around 72 elements can be assayed)
An electrical Discharge between two electrodes can be used to
atomize or ionize a sample and to excite the resulting atoms/ions
Sample is coated/contained in or made into one or both electrodes.
The second electrode which does not contain the sample is called
counter electrode
Not generally applied for solution and gases though, in principle, it
can be used. ICP is ideal for gases and solutions.
Faster: Less than a minute to record spectra.
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

62. DC Arc
DC = 10-50 V
Current =1-35A
T = 4000-7000°C
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

63. Electrodes for AES
 Electrodes usually made of graphite
which is conductive and spectrally
non-interfering with most elements
 Metal or analyte/based electrodes also used
 Electrode is partially consumed during
electrical discharges
cylindrical
Narrow neck to avoid heat conduction
away from sample
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

64. Laser Microprobe
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

65. Comparison Between Atomic
Absorption and Emission
Spectroscopy
Absorption
- Measure trace metal
concentrations in
complex matrices .
- Atomic absorption
depends upon the
number of ground state
atoms .
Emission
- Measure trace metal
concentrations in
complex matrices .
- Atomic emission depends
upon the number of
excited atoms .
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar

66. Absorption
- It measures the
radiation absorbed by the
ground state atoms.
-
- Presence of a light
source ( HCL ) .
- The temperature in the
atomizer is adjusted to
atomize the analyte atoms in
the ground state only.
Emission
- It measures the
radiation emitted by the
excited atoms .
- Absence of the light
source .
- The temperature in the
atomizer is big enough to
atomize the analyte atoms
and excite them to a higher
energy level.
Dr. Sajjad Ullah, Institute of Chemical
Sciences, University of Peshawar