Flame emission spectroscopy

Flame emission spectroscopy

1. Flame Emission Spectroscopy Presented by: Mahewash A Pathan

2. Definition :- “Flame emission spectroscopy / Atomic emission spectroscopy is a method of chemical analysis that uses the intensity of light emitted from a flame at a particular wavelength to determine the quantity of an element in a sample. The wavelength of the atomic spectral lines gives the identity of an element while the intensity of the emitted light is proportional to the no. of atoms of the element”. In flame emission spectroscopy, the sample solution is nebulized and introduced into the flame where it is desolvated, vaporized, & atomized, all in rapid succession. Subsequently, atoms & molecules are raised to excited states via thermal collisions with the constituents of the partially burned flame gases. Theory and Principle

3. Upon their return to a lower or ground electronic state, the excited atoms & molecules emit radiation characteristic of the sample component. The emitted radiation passes through a monochromater that isolates the specific wavelength for the desired analysis. A photodetector measures the radiant power of the selected radiation, which is then amplified & sent to a readout device, meter, recorder or microcomputer system. The intensity of radiation emitted by these excited atoms returning to the ground state provides the basis for analytical determinations in flame emission spectroscopy.

4. Flame photometers are probably the simplest type of atomic spectrometers. They are normally designed to make measurements on up to 10 different elements, usually thus from group I & II of periodic table. This is achieved using interchangeable colored filters or diffraction gratings, which isolates an area of the spectrum containing the chosen emission line. I nstrumentation

5. Consist of 2 components: Nebulizer Burner along with air or oxygen and a fuel gas. 1.Atomizer Flame

6. It is a device used for sample introduction into the flame. The process called nebulisation. Various nebulization methods are used, some are; Pneumatic nebulisation Ultrasonic nebulisation Electro thermal vaporization Hydride generation Nebulizer

7. The following processes occur in the flame: Desolvation : dehydration by the heat of flame and solvent is evaporated. Vaporization : heat of flame vaporizes the sample constituents. No chemical change takes place at this stage. Atomization : ions are reduced to atoms. e.g. Mg++ (aq) + 2e- Mg (g) 4) Excitation : atoms at this stage are able to absorb energy from the heat of the flame. 5) Emission of radiations

8. 3.Detector Function- measure the intensity of radiations falling on it. Photoemmisive cell Photomultiplier tube 4 . Amplifier & Readout device -Meter or digital display -microprocessors controlled devices 2.Monochromator Generally a grating or prism monochromator are used.

9. Qualitative Applications :-

10. The intensity of the spectral line is directly proportional to solution concentration of the analyte. Quantitative measurement are made by reference to a previously prepared calibration line or by the method of standard addition. Quantitative application

11. In quality control where a simple and quick determination of alkali or alkali earth elements is required. Determination of Na, K,Ca & Mg in body fluids & other biological samples. Determination of calcium & iron in beer. In agriculture, the fertilizer requirement of the soil is analyzed by flame test analysis of soil. Analysis of soft drinks, fruit juices, and alcoholic beverages can also be analyzed. Other application

12. Spectral interferences When 2 elements exhibit spectra, which partially overlap, & both emit radiation at some particular wavelength. Such interference are common at flame temperatures. e.g. Fe line at 324.73nm overlaps with the Cu line at 324.75nm. When spectral lines of 2 or more elements which are close but their spectra do not overlap. Such interference can be reduced by increasing the resolution of the spectral isolation system. Due to the presence of continuous background which arises due to high concentration of salts in the samples. Interference in quantitative analysis

13. 2 . Ionization interferences :- In some cases, high temperature flame may cause ionization of some of the metal atoms. E.g. Sodium Na Na+ + e-

14. 3 . Chemical interferences :- Cation- Anion interference: presence of certain anions such as oxalate, phosphate, sulphate & aluminate in solution may affect intensity of radiation. E.g. Ca in presence of phosphate ions form a stable substance, which does not decompose easily, resulting in production of less atoms, thus Ca signals are depressed Cation-cation interference: mechanism of this interference is not well understood. e.g. Na & K , Al with Ca & Mg.

15. Simple quantitative analytical test. Inexpensive. Quite, convenient, selective and sensitive to even ppm to ppb range. Advantages

16. The conc. Of the metal ion in the solution cannot be measured accurately. A std solution with known molarities is required for determining the concentration of the ions which will corresponds to the emission spectra. It is difficult to obtain the accurate results of the ions with higher conc. The information about the molecular structure of the compound present in the sample solution can not be determined. The elements such as Carbon, hydrogen & halides can not be detected due to its non-radiating nature. Disadvantages

17. The method is selective towards detection of alkali & alkaline earth metals. The relatively low energy available from the flame leads to relatively low intensity of radiation from the metal atoms. Information about the molecular form of the metal is not obtained. Only liquid samples are used. Limitations

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