3. INTRODUCTION
• Flame emission spectroscopy is so named
because of the use of a flame to provide the
energy of excitation to atoms introduced into
the flame.
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4. HISTORY
Early- detect the presence of metal elements in samples aspirated
into a flame.
Modern analytical FES- Lundegardh- 1934,
(flame- air-acetylene, Prism spectrograph, densitometer for
spectral line )
First "flame photometer" -1945- Barnes.(Na, K detection, Poor
detection of Ca, Mg)-Meeker burner
1948- total-consumption burner.
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6. Desolvation: The metal particles in the flame are dehydrated by the
flame and hence the solvent is evaporated
Vapourisation: The metal particles in the sample are dehydrated. This
also led to the evaporation of the solvent.
Atomization: Reduction of metal ions in the solvent to metal atoms by
the flame heat.
Excitation: The electrostatic force of attraction between the electrons
and nucleus of the atom helps them to absorb a particular amount of
energy. The atoms then jump to the exited energy state.
Emission process: Since the higher energy state is unstable the atoms
jump back to the stable low energy state with the emission of energy in
the form of radiation of characteristic wavelength, which is measured
by the photo detector.
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7. The basic components for flame photometer are as follows
Burner(source)
Atomizer
Monochromators
Detector
Read out device
INSTRUMENTATION
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8. BURNERS
The FLAME used in the flame photometer should possess following
functions:
The flame should have ability to evaporate the liquid droplets from
the sample solution in the formation of solid residue
The flame should decompose the compounds in the solid residue
resulting in the formation of atoms.
The flame must have the capacity to excite the atoms formed and
cause them to emit radiant energy.
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9. FLMES IN FES
Name of the element
Emitted
wavelength range
(nm)
Observed colour of
the flame
Potassium (K) 766 Violet
Lithium (Li) 670 Red
Calcium (Ca) 622 Orange
Sodium (Na) 589 Yellow
Barium (Ba) 554 Lime green
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10. TYPES OF BURNERS
Mecker Burner
Total Consumption Burner
Laminar Flow (premix) Burner
Lundergraph Burner.
Shielded Burner
Nitrous Oxide –Acytelene Flame.
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11. MECKER BURNER
1
This burner employed natural gas and
oxygen.
Produces relatively low temp. and
low excitation energies.
This are best used for ALKALI
metals only.
Nowadays it is not used.
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12. Total consumption burner
In this burner the fuel and
oxidant are hydrogen and
oxygen gas respectively.
In this the sample solution is
aspirated through a capillary by
the high pressure. fuel and
oxidant are burnt at the tip of
the burner.
The name “total consumption
burner” is used because all the
sample that enters the capillary
will enter the flame regardless
of the droplet size.
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13. Advantage
Design is simple and entire sample is consumed.
Disadvantage
Uniform and homogeneous flame is not obtained. Since
droplet size vary, leading to fluctuations in the flame
intensity.
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15. LAMINAR FLOW (PREMIX) BURNER.
In this type of the burner, aspirated sample, fuel and oxidant are
thoroughly mixed before reaching the burner opening and then
entering the flame.
Important feature of this is that only a small portion (about 5%) of the
sample reaches the flame in the form of small droplets and is easily
decompose.
ADVANTAGES:
Premix burner is non-turbulent ,noiseless and stable.
Easy decomposition which leads to high atomization.
Can handle solution up to several % without clogging.
DEMERITS
When it contains 2 solvents, the more vol. will evaporate and lesser
will remain undissociated.
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16. MONOCHROMATORS AND FILTERS
In simple flame photometers, the monochromators is the prism.
QUARTZ is the material most commonly used for making prisms
because quartz is transparent over entire region .
FILTERS: the filter is made up of such material which is
transparent over a narrow spectral range.
When a filter is kept between the flame detector, the radiation of
the desired wavelength from the flame will be entering the
detector and be measured. The remaining undesired wavelength
will be absorbed by the filter and not measured.
In flame photometry, the wavelength as well as intensity of
radiation emitted by the element has to be monitored. Hence a
filter or monochromatore is used.
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18. APPLICATIONS
FES has found wide application in agricultural and
environmental analysis, industrial analyses of ferrous metals and
alloys as well as glasses and ceramic materials, and clinical
analyses of body fluids.
FES can be easily automated to handle a large number of
samples. Array detectors interfaced to a microcomputer system
permit simultaneous analyses of several elements in a single
sample
They are also used to determine the metals present in Chemicals,
Soil, Cements, Plant materials, Water, Air pollutants and
Oceanography
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19. INTERFERENCES
Matrix interference
Chemical interference
Ionization interference
Spectral Interferences
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20. Matrix interference
When a sample is more viscous or has different surface tension
than the standard it can result in differences in sample uptake rate
due to changes in nebulization efficiency.
Such interferences are minimized by matching as closely as
possible the matrix composition of standard and sample.
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21. Chemical interference
If a sample contains a species which forms a thermally stable
compound with the analyte that is not completely decomposed by
the energy available in the flame then chemical interference
exists.
Refractory elements (Ti, W, Zr, Mo and Al) may combine with
oxygen to form thermally stable oxides.
Analysis of such elements can be carried out at higher flame
temperatures using nitrous oxide – acetylene flame instead of air-
acetylene to provide higher dissociation energy.
Alternately an excess of another element or compound can be
added e.g. Ca in presence of phosphate produces stable calcium
phosphate which reduces absorption due to Ca ion.
If an excess of lanthanum is added it forms a thermally stable
compound with phosphate and calcium absorption is not affected.
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22. Ionization interference
Ionization interference is more common in hot flames. The
dissociation process does not stop at formation of ground state
atoms.
Excess energy of the flame can lead to excitation of ground state
atoms to ionic state by loss of electrons thereby resulting in
depletion of ground state atoms.
In cooler flames such interference is encountered with easily
ionized elements such as alkali metals and alkaline earths.
Ionisation interference is eliminated by adding an excess of an
element which is easily ionized thereby creating a large number
of free electrons in the flame and suppressing ionization of the
analyte.
Salts of such elements as K, Rb and Cs are commonly used as
ionization suppressants.
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