Definition of Flame Photometry:
Flame photometry, or flame atomic emission spectrometry (FAES), is used to determine alkali and alkaline earth metals by analyzing the light emitted when a sample is introduced into a flame.
Principle:
Excitation: Metal atoms in the flame get vaporized and excited to higher energy levels.
Emission: On returning to the ground state, they emit light at specific wavelengths unique to the element.
Theoretical Basis:
Boltzmann's Distribution: Relates the ratio of atoms in ground vs. excited states at a given temperature.
Bohr's Theory: Describes energy transitions:
Procedure:
Sample Preparation: Dissolve the sample in water or a suitable solvent.
Introduction to Flame: Atomized sample produces light emissions.
Emission: Excited atoms emit characteristic radiation.
Detection: A monochromator isolates the wavelength of interest; a photodetector measures intensity.
Calibration: Emission intensity is compared against a standard calibration curve for quantification.
Flame Colors of Common Elements:
Element | Element | Flame Color |
Lithium (Li) | Lithium (Li) | Crimson/Red |
Sodium (Na) | Sodium (Na) | Bright Yellow |
Potassium (K) | Potassium (K) | Lilac/Purple |
Calcium (Ca) | Calcium (Ca) | Orange-Red |
Strontium (Sr) | Strontium (Sr) | Crimson/Red |
Barium (Ba) | Barium (Ba) | Apple Green |
Copper (Cu) | Copper (Cu) | Blue-Green |
Advantages:
Simple and cost-effective.
High sensitivity for alkali and alkaline earth metals.
Limitations:
Limited to elements that can atomize and emit in the visible/UV spectrum.
Results can be affected by flame interferences.