Flame Photometry is also called as flame emission spectroscopy. Flame Photometry is branch of atomic spectroscopy. It is used to detected certain metal ions like sodium,potassium,magenisum etc.
Sample is sprayed into a flame and it converted to droplets.Due to the thermal energy of the flame the solvent in the droplets evaporate,leaving behind fine residue, which are converted to neutral atoms. This neutral atoms are get energy form thermal energy and go exited state but they are unstable at exited state so they are return to ground state with emission of specific wave length radiation. The wavelength of the radiation emitted is characteristic of the elements and is used to identify the elements (Qualitative Analysis). The intensity of the radiation emitted depends upon the concentration of the element analysed (Quantiative Analysis).
Formation of droplets
Formation of neutral atoms
Excitation of atoms by thermal energy
Emission of radiation of specific wavelength
λ& Intensity of emitted radiation measured
The wavelength of the radiation emitted is given by the following equation :-
λ = hc/ E2-E1
h = Planks constant
c= Velocity of light
E2,E1= energy levels of exited and ground state respectively
The fraction of free atom that are thermally exited is governed by a Boltzman Distribution
N* / N = Ae–∆E/kT
• N* =is the number of exited atom
• N = is the number of atom remaining
• in the ground state
• AE = is the difference in energies levels
• k = The Boltzman constant
• T = the tempeature
INSTRUMENTATION OF A FLAME PHOTOMETER :-
COMPONENTS OF A FLAME PHOTOMETER
- Burner (With fuel and oxidant)
- Read out device
There are different burners available which are used to spray the sample solution into fine droplet mix with fuel and oxidant so that a homogenous flame of stable intensity is obtained. The most common ones are mecker burner, total consumption burner and laminar flow burner.
TOTAL CONSUMPTION BURNER
• Due to the high pressure of fuel and oxidant the sample solution is aspiratethrough capillary and burnt at the tip of burner
• Hydrogen and oxygen are generally employed as fuel and oxidant.
• The advantage over other is the entire consumption of sample,
• It’s dis advantage is the production of non uniform flame and turbulent.
• Inthis burner the sample , fuel oxidant are thoroughly mixed before aspiration and reaching to flame
• The main advantage of is the uniformity of flame produced.
• The main disadvantage is the heavy loss of mix up to 95%.
FUEL AND OXIDANTS :-
2. FILTER / MONOCHROMATOR :-
In flame photometry the wavelength as well as intensity of the radiation emitted by the elements has to be monitored. Hence a filter or monochromator is to be used. A simple flame photometer contains a filter wheel and when a particular elements has to be analysed the specific filter is selected.
The radiation emitted by the elements is mostly in the visible region. Hence conventional detectors like photo voltaic cell or photo tubes can be used. In a flame spectrophotometer, photomultiplier tube is used as detector.
4. READ OUT DEVICE :-
The signal from the detector is shown as a response in the digital read out device. The readings are displayed in an arbitrary scale (% Flame Intensity).
•To estimate sodium, potassium, calcium, lithium etc. level in sample of serum, urine, CSF and other body fluids.
•Flame photometry is useful for the determination of alkali and alkaline earth metals.
•Used in determination of lead in petrol.
•Used in the study of equilibrium constants involving in ion exchange resins.
•Used in determination of calcium and magnesium in cement.
1. Which of the following is the principle of Flame emission photometers?
a) Radiation is absorbed by non-excited atoms in vapour state and are excited to higher states
b) Medium absorbs radiation and transmitted radiation is measured
c) Colour and wavelength of the flame is measured
d) Only wavelength of the flame is measured
2. Which of the following is not an advantage of Laminar flow burner used in Flame photometry?
b) Stable flame for analysis
c) Efficient atomization of sample
d) Sample containing two or more solvents can be burned efficiently
3.Which of the following is not a detector used in Flame emission photometers?
a) Photronic cell
b) Photovoltaic cell
c) Photoemissive tube
4. If Propane and air are used in burner how many °C temp. is produced ?
5. If Hydrogen and air are used in burner how many °C temp. is produced ?
6. Which is not application of flame photometry ?
a)To estimate sodium, magnesium, calcium
b) Assay of metformin.
c)Used to determine magnesium and calcium in cement.
d) To detected metalic ions in sample.
7. BOLTZMANN Equations is
a)N* / N =R Ae–∆E/kT
b)N* / N = e–∆E/kT
c)N* / N = Ae–∆E/kT
d)N* / N = Ae–∆E/kc
8. Choose correct sequence of flame photometry ?
a) Sample residue → excited state atoms → Return in ground state → Emission of radiation
b)Sample residue → ground state → excited state → Emission of radiation
c) Emission of radiation → excited state →ground state → Sample residue
d) Sample residue → ground state → excited state → Emission of radiation
9. Which equations are used to determine wavelength of radiation ?
a)λ = hc/ E2-E1
b)N* / N = e–∆E/kT
c) λ = h/E2-E1
d)N* / N = Ae–∆E/kT
10. Which is application of flame photometry ?
a) To determine functional group
b) To study of chemical structure
c) To assay of drug
d) To estimate metalic ions like sodium, potassium, etc.
ANSWER KEY :-
TEXT BOOK OF PHARMACEUTICAL ANALYSIS THIRD EDITION DR.S.RAVI SANKAR (PG.NO. 26.1-26.13)