Flame Photometry

1. Group D
Analytical and Instrumental
Inorganic Chemistry
By: Dr. Damodar Koirala
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Flame Photometry (FP)

2. Introduction
•Flame Photometry is based on measurement of intensity of the light emitted
when a metal is introduced into flame.
–The wavelength of color tells what the element is (qualitative)
–The color's intensity tells us how much of element is present (quantitative)
•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 (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.

3. Principle
Metals are dissociated due to the thermal energy provided by the flame source.
Due to this thermal excitation, some of the atoms are excited to a higher energy
level where they are not stable.
The subsequent loss of energy will result in the movement of excited atoms to the
low energy ground state with emission of some radiations as a wavelengths .The
emitted wavelengths are specific for specific elements.
The basic principle upon which Atomic Spectroscopy works is based on the fact
that "Matter absorbs light at the same wavelength at which it emits light".
Atoms of elements ! subjected to hot flame ! specific quantum of thermal
energy absorbed by orbital electrons ! become unstable at high energy level !
release energy as photons of particular wavelength ! change back to ground
state.
When a metal salt solution is burned, the metal provides a colored flame and each
metal ion gives a different colored flame.

4. Emitted wavelength (nm) Observed Color
Potassium (K) 766 Violet
Lithium (Li) 670 Red
Calcium (Ca) 622 Orange
Sodium (Na) 589 Yellow
Barium (Ba) 554 Lime green
Various metals emit a characteristic colour of light when heated.
Characteristic Emission

5. Sample preparation and delivery
1. Solution containing metal to be measure is first aspirated into the burner.
2. The solvent then evaporated leaving fine divided solid particles.
3. This solid particles move towards flame, where gaseous atoms are
produced.
4. Atoms absorb the energy from the flame and excite to high energy levels.
5. When the atoms return to the ground state radiation of the characteristic
element is emitted.
6. The intensity of emitted light is related to the concentration of the
element.

6. Major Components:
1. Sample Delivery System
2. Flame Source
3. Monochromator
4. Detector
5. Read out device
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Instrument Flame Photometer

7. Types of Flame
If the gas flow rate does not exceed the burning velocity, the flame
propagates back into the burner, giving flashback.
At higher flow rates, the flame rises and eventually reaches a point where it
blows off the burner.
If the flow velocity and the burning velocity are equal then this region is
where the flame is stable.
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Fuel Oxidant Temp (C)
Natural gas Air 1700-1900
Hydrogen Air 2000-2100
Acetylene Air 2100-2400
Acetylene Nitrous oxide 2600-2800
Acetylene Oxygen 3050-3150

8. Flame
The essential requirements of a burner for atomic absorption are:
●The flame must extend over a reasonable length to improve sensitivity.More of
the atoms in the long narrow band brought into the light beam.
●In order to avoid problems due to scattering of light by unburned droplets and
large sample droplets, which cannot be burned, they must be removed before
reaching the flame.

9. Temperature profile of Flame
Primary
zone
Interzonal
region
Secondary
zone
Maximum
temperature
The maximum temperature is located in the flame about 2.5 cm above the
primary combustion zone. It is important to focus the same part of the flame
on the entrance slit for all calibrations and analytical measurements.
In degree Celsius for natural gas-air flame.
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10. Flame Structure
The resulting finely divided solid particles are carried to a region
in the center of the flame called the internal region. Here, in this
hottest part of the flame, the particles are vaporized and
converted to gaseous atoms, elementary ions, and molecular
species. Excitation of atomic emission spectra also takes place in
this region.
When a nebulized sample is carried into a flame, the droplets are desolvated in the primary combustion
zone, which is located just above the tip of the burner.
Finally, the atoms, molecules, and ions are carried to the outer edge, or secondary combustion zone,
where oxidation may occur before the atomization products disperse into the atmosphere. Because the
velocity of the fuel/oxidant mixture through the flame is high, only a fraction of the sample undergoes all
these processes. Unfortunately, a flame is not a very efficient atomizer.
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11. Flame Absorption Profile
Hence, a critical step in the optimization of signal output is the adjustment
of the position of the flame with respect to the entrance slit.
•Mg
•Atomizes then oxidizes as Mg
approaches secondary combustion area
•Formation of MgO reduces absorbance
•Ag
•Does not readily oxidize
•Atomization over flame area
•Cr
•Forms oxidizes readily so that oxide is
main species in flame
Variation due to the degree of oxidation for a given element
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12. Flame Atomizer
Flame atomization is the most reproducible of all liquid-sample-introduction
methods that have been developed for atomic absorption and fluorescence
spectrometry to date.
The sampling efficiency of other atomization methods and thus the
sensitivity. however, are markedly better than in flame atomization.
There are two primary reasons for the lower sampling efficiency of the flame.
1) A large portion of the sample flows down the drain.
2) The residence time of individual atoms in the optical path in the flame is
brief (10-5s).
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13. Nebulizer – it breaks up the liquid into small droplets.
Nebulization the is conversion of a sample to a mist of finely divided droplets
using a jet of compressed gas.
The flow carries the sample into the atomization region.
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Sample Delivery System
Flame or Atomizer – it converts the analyte into free atoms
Aerosol modifier – it removes large droplets from the stream and allow only
smaller droplets than a certain size to pass
There are three components for introducing liquid sample:
Helps to transport the homogeneous solution of the substance into the
flame at a steady rate.

14. A Burner used to spray the sample solution into fine droplets.
Several burners and fuel+oxidant combinations have been used to produce
analytical flame including:
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Total Consumption Burner:
- Sample solution is aspirated through a capillary by high pressure of fuel
and Oxidant and burnt at the tip of burner
- Entire sample is consumed.
Source
Pre-mixed Burner:
- Widely used because uniformity in flame intensity
- Aspirated sample , fuel and oxidant are thoroughly mixed before
reaching the burner opening
A burner that provides flame and can be maintained in a constant form
and at a constant temperature.

15. – Photomultiplier tubes
– Photo emissive cell
– Photo voltaic cell
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–Prism: Quartz material is used for making prism, as quartz is transparent
over entire region.
–Grating: it employs a grating which is essentially a series of parallel
straight lines cut into a plane surface.
Detectors:
• Detects emitted light and measure the intensity of radiation emitted
• Emitted radiation is converted to an electrical signal
• Produced electrical signals are directly proportional to intensity of light
Monochromator:
Helps in isolating the wavelength to be measured from that of any other
extraneous emissions.

16. Types of FP
1. Direct type:
Standard solution of Na & K are atomized or aspirated into flame to provide a
series of meter readings in which our unknown is going to compared with.
• Any minor fluctuations in air, gas pressure might change response of
instrument and then cause errors.
• Separate analyses and separate solutions must be made for Na and K.
Disadvantages
2. Internal standard method:
Another element (Li) is added to all standards, blanks and unknowns in equal
concentration. This element has a criteria of :
* high emission intensity.
* Is absent from biological fluid.

17. Applications
• Determine the availability of alkali and alkaline earth metals which are critical
for soil cultivation.
• In agriculture, the fertilizer requirement of the soil is analyzed by flame test
analysis of the soil.
• In clinical field, Na+ and K+ ions in body fluids, muscles and heart can be
determined by diluting the blood serum and aspiration into the flame.
• Analysis of soft drinks, fruit juices and alcoholic beverages can also be
analyzed by using flame photometry.
Advantages
• Simple quantitative analytical test based on the flame analysis.
• Alkali and alkaline earth metals is easily with most reliable, inexpensive and
convenient methods.
• Quick, convenient, and selective and sensitive to even ppm to ppb range.

18. 1. Anion due to complexation (chemical interference). 2. Matrix interference.
3. Burner interference. 4. Ionisation interference. 5. Emission interference.
Interferences
FP suffer the same level of interference as AAS from:
Limitations
• Alteration of light emission because of altered flame temp.
• It needs perfect control of flame temperature.
• Interference by other elements is not easy to be eliminated.
• Heavy and transition metals , the number of absorption and emission lines is
enormous and the spectra are complex
• Differences in viscosity between standards and sample.

19. 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.
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Interferences
Ionic interferences: high temperature flame may cause ionization of metal atoms
The Na+ 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 interferents and the analyte. Includes:
Cation-anion interference: The presence of certain anions, such as oxalate,
phosphate, sulfate, in a solution may affect the intensity of radiation emitted by an
element.
Cation-cation interference: These interferences are neither spectral nor ionic in
nature
Eg. aluminum interferes with calcium and magnesium.

20. AAs vs. FP
AAs FP
Process Measured
Absorption (light absorbed
by unexcited atoms in
flames)
Emission (light emitted
excited atoms in a flame)
Use of Flame Atomization Atomization and excitation
Instrumentation Light source
No light source
(independent of flame)
Beer’ s Law Applicable
Not application
(I = kc)
Data Obtained A vs. c I vs. c