Flame emission spectroscopy

Modern pharmaceutical analytical techique

1. Flame Emission Spectroscopy Submitted By : ROHIT M.Pharmacy 1 st Year R.K.S.D COLLEGE OF PHARMACY, KAITHAL (HRY)

2. Introduction: Based on measurement of intensity of light emitted, when a metal is introduced into the flame. The wavelength of the colour tells us what the element is, and the colour's intensity tells how much the element is present. Also known as Flame Photometry, because of the use of flame to provide energy for excitation of atom.

3. Theory: The liquid sample of metallic salt is introduced into the flame and following steps takes place: Solvent is vaporised, leaving the particles of solid salt. Salt is vaporised or converted into gaseous state. Gaseous molecule get dissociated to form neutral atom or radical.

4. These neutral atoms are excited by thermal energy of flame which are unstable & emit photon & return to lower energy level & finally wavelength of emitted light is measured by- E 2 - E 1 = h ν ν = c/ λ E 2 – E 1 = hc/ λ λ = hc/(E 2 – E 1 ) The fraction of free atoms which are thermally excited is given by Boltzmann distribution eq n N*/N o = Δ e - Δ E/Kt

5. Limitation of Flame Emission Photometry: The number of excited atoms in flame is very small. It is the alkali and alkaline earth metals that can be practically determined. 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.

6. Instrumentation: Burner Mirror Slit Monochromator Filters Detector.

7. Burner:- It Requires fuel (H 2 ) or oxidant. Various types of burner are used in the spectroscopy: Mecker Burner Total C onsumption Burner Lundergarph Burner

8. Mecker Burner: Used natural gas or Oxygen. Produce Relatively low temperature and low excitation energy Generally used for the study of Alkali metals only. These days, Mecker Burner is not used.

9. Total Consumption Burner: In this burner fuel and oxidant are H 2 and O 2 gases respectively. Liquid sample is drawn into the flame from the side tubings, H 2 and O 2 are entering & both are burning at the top & produce flame. The flame is noisy and turbulent produced by it. From the liquid sample, solvent is evaporated & leaving the solid residue . It is used because all the samples that enters the capillary tube will enter the flame in form of droplets .

10. Lundergarph burner: In this, the sample must be in liquid form. Large droplets condense on the side and drain away; small droplets and vaporised sample are swept in the flame in the form of cloud. An important feature of this burner is that only 5 % of the sample reaches the flame. The rest of the droplets condense and are drained away. Other type of burner used are: Premix or Laminar Flow Burner Shielded Burner Nitrous oxide Acetylene Burner

11. Mirror: The radiation from the flame is emitted in all the direction and in order to maximize the amount of radiation, a mirror is located behind the burner to reflect the radiation back to the entrance slit. SLIT: With the best equipment, entrance and exit slits are used before and after dispersion element.

12. Entrance slit: The entrance slit cuts out most of the radiation from the surrounding and allow only radiation from the flame. Exit slit: The exit slit is placed after the monochromator and allow only selected wavelength range to pass through the detector.

13. Monochromator: Monochromator is the Prism. But in expensive models, the Grating monochromator is used. FILTERS: An optical filter may be used in place of slit and monochromator system. When filter is kept between flame and detector, the radiation of desired wavelength from the flame will be entering the detector and measured. T he remaining undesired wavelength will be absorbed by filter and not measured.

14. Detector: The radiation coming from the optical system is fell on the detector which measure the intensity of radiation falling on it. Photomultiplier Detector are used in a good Flame Photometer.

15. INTERFERENCE IN FLAME PHOTOMETRY: Spectral interference Ionisation interference Cation – Anion interference Cation – Cation interference Oxide formation interference

16. Application: Qualitative Analysis: This is only used to detect the element present in group I and group II in periodic table. i.e. Na, K, Lithium, Mg, Ca, Strontium & Barium. Quantitative Analysis: This is used for rapid quantitative determination of the elements in group I and group II of the periodic table.