ATOMIC ABSORPTION SPECTROSCOPY

AAS DETECTION TECHNIQUE OF HEAVY METALS,

1. ATOMIC ABSORPTION SPECTROSCOPY - BY SUBHASISH DAS M.PHARM 1 ST YEAR ROLL- 19320712001 REG. NO-121932310012 OF 2012-2013 CLASS ROLL – 13 .

2. INTRODUCTION Atomic absorption spectroscopy was introduced in mid 1950’s by “Alan Walsh”. Most powerful technique to determine trace metals in liquid quantitatively In a sentence “Atomic Absorption Spectroscopy (AAS) “ is a method of elemental analysis , particularly useful for determination of trace metals in liquid and is almost independent of the molecular form of the metal in sample.

3. MERITS The atomic absorption technique is specific because the atoms of a particular element can only absorb radiation of their own characteristic wavelength Some element possess higher detection limits by atomic absorption like Ag , As , Au etc. Independent of flame temperature.

4. THEORY Atomic absorption spectroscopy deals with absorption of specific wave length of radiation by neutral atoms in the ground state. When a light of this wavelength is allowed to pass through a flame having atoms of the metallic species , part of the light will be proportional to the density of the atoms in the flame.

5. EQUATIONS At , υ the total amount of light absorbed = (e 2 /mc)* Nf Where, e = charge on electron. m = mass of electron. c = speed of light. N = total number of atoms that can absorb frequency ν in the light path. f = the oscillator strength or ability for each atom to absorb at frequency ν . contd..

6. Contd.. As ,e, m, c are constant equation becomes Total amount of light absorbed = constant * N * f

7. GROTRIAN DIAGRAMME Walter Robert Wilhelm Grotrian  (21/4/1890 - 3/3/ 1954) was a German   astronomer and astrophysicist . Grotrian studied the  emission  line from the  solar corona  in the  green  region of the  spectrum ; this emission line could not be attributed to any known  chemical element  and was thought to be a new element (which scientists named " coronium "). Grotrian and  Bengt Edlén from  Sweden  demonstrated that the two observed emission lines arise from  iron   atoms  that have lost about half their 26  electrons .

8. Atomic Absorption Transitions

9. EFFECT OF FLAME TEMPERATURE Effect of flame temperature : Since flame is at high temperature might have an effect on fraction of atoms in excited state. Boltzmann's equation describes effect of flame temperature: where

10. Where, N u is the number of atoms in excited state g u the number of degenerated orbitals on this energy level. N o and g o refers to the same figures at ground state. k is Boltzmann constant and T is the temperature . E is energy difference between two orbitals Therefore, an increase in temperature results in an increase of the number of excited atoms, which is equivalent to a lowering in absorption

11. PRINCIPLE DETECTOR SIGNAL RECORDER

12. A light beam is passed through the flame, Radiation is absorbed, transforming the ground state atoms to an exited state.

13. WORKING PRINCIPLE Liquid sample → formation of droplet → fine residue ↓ neutral atom ← Formation of neutral atom absorbs specific Wavelength of radiation from hollow cathode lamp. ↓ Measurement of intensity of radiation absorbed by using photometric detectors.

14. Atomic Absorption Instrumentations

15. INSTRUMENTATION SINGLE BEAM DOUBLE BEAM

16. MAJOR PARTS OF INSTRUMENT HOLLOW CATHODE LAMP - The cathode is made up of specific element or alloys of elements or coating of elements on cathode , as current is applied between anode & cathode , metal atoms emerge from hollow cup and collides with filler glass . Due to the collision, number of metal atoms are excited and emit their characteristic radiation , this is absorbed by neutral atoms of same element in ground state , occur in the flame , when sample solution is sprayed. Band width-0.001to 0.01 nm.

17. Contd … ATOMISER ASSEMBLY– Assembly used as atomizer and nebulizer. Premix type Total consumption Graphite furnace

18. INTERFERENCES A. PHYSICAL – Due to sample matrix or flame or scattering or similar alkali halides , termed as Background absorption. remedy- use background corrector

19. Contd.. B. CHEMICAL – In complete dissociation of compound , remedy – 1. use high temperature flame 2. chemical means are applied. C. IONISATION – Due to too high flame temperature. remedy – addition of more easily ionisable element. D. SCATTERING EFFECTS – Due to presence of high concentration of interfering element. remedy – using a continuum source.

20. APPLICATIONS Estimation of trace elements in biological fluid. Estimation of Copper ,Zinc, Nickel in food products. Estimation of Zinc in Zinc insulin injection Estimation of lead in Calcium Carbonate, petrol. Estimation of elements in soil ,water, effluents, ceramic etc. ELEMENT Λ (nm) ppm SODIUM 589 0.01 POTASSIUM 766.5 0.01 CALCIUM 442.7 0.05 LEAD 217 0.01

21. DETECTION LIMIT AND SENSITIVITY The concentration of element present in the sample solution which produces 1% absorption. Sensitivity , expressed in terms of μ g/ml for 1% absorption. C 1% =(C 0.1 *0.0044)/0.1 Where, C 1% = the concentration give rise to 1% absorption. C 0.1 = the concentration give rise to an absorbance of 0.1

22. DEMERITS A separate lamp for each element to be determined is required. Elements produce oxides in flame may not be successfully determined quantitatively. In aqueous solution , the predominant anions affects the signal to a negotiable degree.

23. CONCLUSION ATOMIC ABSORPTION SPECTROSCOPY mainly used to determine trace element in soil samples, waters, petrol etc ; not just qualitatively, mainly quantitative determination of metals are done . In case of isolation and purification of herbal drugs or phytochemical form crude form AAS helps as a support to determine the amount of trace material present , so as an analytical tool it is very use full.

24. REFERENCES 1. G. R. Chatwal , S. K. Anand (2010) , Instrumental Methods Of Chemical Analysis , Himalaya Publishing house , Ch – 13 , Pg. no. - 2.340 – 2.366 . 2 . A. H. Beckett , J. B. Stenlake , (2007) , Practical Pharmaceutical Chemistry , CBS Publishers & Distributors Pvt. Ltd. , 4 th ed. , part two, Ch – 8 , Pg. no .- 346 – 357. CBS Pubs ISBN : 81-239-0514-9 , Athlone ISBN : 0-485-11323-8 3. Hobart H. Williard , Lynne L . Merritt, jr . , John A. Dean , Frank A. Settle, jr . , Instrumental Methods Of Analysis , (2006), CBS Publishers & Distributors Pvt. Ltd. , 7 th ed. , Ch – 9 , Pg no – 243- 255 , ISBN : 81-239-0943-8