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ATOMIC ABSORPTION SPECTROSCOPY (AAS) a.k.a SPEKTROSKOPI SERAPAN ATOM (SSA))

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AAS (spektroskopi serapan atom/ Atomic absorption spectroscopy) pertama kali dimanfaatkan Alan Walsh (1955). metode ini sangat tepat untuk analisis zat berkonsentrasi rendah. metode AAS berprinsip padaabsorpsi cahaya oleh atom-atom. Atom menyerap cahaya tersebut pada panjang gelombang tertentu, tergantung sifat unsurnya. Unsur-unsur yang dapat dideteksi oleh AAS/SSA adalah unsur-unsur logam, dan beberapa unsur non-logam (3 unsur).

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ATOMIC ABSORPTION SPECTROSCOPY (AAS) a.k.a SPEKTROSKOPI SERAPAN ATOM (SSA))

  1. 1. First Group A. Khaerunnisa Ha rdya nti Arki Nur Hasanah Jusm an Nurhikmah Atomic Absorption Spectrometry ICP CHEMISTRY A 2011 (AAS) FMIPA UNM 2013 Sarce Siruru Hasra Jalil
  2. 2. Contents • • • • • What is AAS Theory Instrumentations Principle of AAS Applications
  3. 3. What is AAS ? Atomic absorption spectroscopy is a quantitative method of analysis that is applicable to many metals and a few nonmetals. The technique was introduced in 1955 by Walsh in Australia (A.Walsh, Spectrochim. Acta, 1955, 7, 108) The application of atomic absorption spectra to chemical analysis Concentrations range is in the low mg/L (ppm) range.
  4. 4. Theory A much larger number of the gaseous metal atoms will normally remain in the ground state. These ground state atoms are capable of absorbing radiant energy of their own specific resonance wavelength. If light of the resonance wavelength is passed through a flame containing the atoms in question, then part of the light will be absorbed. The extend of absorption will be proportional to the number of ground state atoms present in the flame.
  5. 5. the gaseous metal atoms specific resonance wavelength extend of absorption the extend of absorption vs the number of ground state atoms present in the flame.
  6. 6. AAS Instrument
  7. 7. The simple diagram for the AAS 4. T element in the sample he will absorb some of the light, thus reducing its intensity 5. T monochromator he isolates the line of interest 3. A beam of UV light will be focused on the sample 1. W set the e instrument at certain wavelength suitable for a certain element 2. T element he in the sample will be atomized by heat 6. T detector he measures the change in intensity 7. A computer data system converts the change in intensity into an absorbance
  8. 8. Flame atomization Processes occurring during atomization
  9. 9. Nebuliser - burner To convert the test solution to gaseous atoms Nebuliser --- to produce a mist or aerosol of the test solution Vaporising chamber --Fine mist is mixed with the fuel gas and the carrier gas Larger droplets of liquid fall out from the gas stream and discharged to waste Burner head --- The flame path is about 10 –12 cm
  10. 10. 1. Nebulizer: 4. T mixture flows he immediately into the burner head. 5. It burns as a smooth, laminar flame evenly distributed along a narrow slot. 1. mixes acetylene (the fuel) and oxidant (air or nitrous oxide). 6. L iquid sample not flowing into the flame collects in the waste. 3. T result is a heterogeneous he mixture of gases (fuel + oxidant) and suspended aerosol (finely dispersed sample). 2. A negative pressure is formed at the end of the small diameter, plastic nebulizer tube→ (aspiration). Note: W hen do we use NO2 ?
  11. 11. Elements that are highlighted in pink are detectable by AAS
  12. 12. Principle of Atomic Absorption Spectrophotometer Atomized elements each absorb energy of a wavelength that is peculiar to that element. The atomic absorption method uses as its light source a hollow cathode lamp which emits light of a wavelength that is peculiar to each element. Elements within a solution are heated in a flame or electrically (2000K to 3000K) and subsequently determined using the fact that the degree of absorption will vary with its concentration. Light absorption process of atoms
  13. 13. Principle of Atomic Absorption Spectrophotometer Atomic Absorption Spectroscopy, AAS Excited state E1 Absorption Ground state E0 Atomic Emission Spectroscopy, AES Excited state E1 e e Emission Ground state E0 e
  14. 14. Characters of the atomic absorption spectrum Profile of the absorption line K0 - maximal absorption coefficient Δ ν - half width ν 0 - central wavelength
  15. 15. The relationship between absorbance and the concentration of atoms Beer’s law I t = I 0ν e -Kνl A = log ( I 0ν / I t ) = 0.4343 K ν l I t - intensity of the transmitted light I o – intensity of the incident light signal l – the path length through the flame (cm)
  16. 16. Types of Pretreatment Dilution Dilute the sample with purified water, dilute acid, or organic solvents. Examples: food products (e.g., dairy products), pharmaceuticals, and biological samples (e.g., blood, urine). Dry Decomposition Heat the sample to a high temperature (400 to 500°C), Decomposition is possible in a short time (a few hours) and operation is simple. Elements with low boiling points (e.g., Hg, As, Se, Te, and Sb) will vaporize Wet Decomposition Heat the sample together with acid to a low temperature (approx. 300°C). Suitable for volatile elements. A long time is required for the decomposition of organic substances. Microwave Decomposition Decompose the sample at high pressure by heating it together with acid to a temperature in the range 100 to 200°C in a sealed Teflon container. The decomposition process is sealed; there is little vaporization of elements with low boiling points; the decomposition time is short; there is little contamination from the operating environment and the reagent; and only a small amount of acid is required. Examples: Sediment, soil, dust, ceramics, living organisms, food products, etc.
  17. 17. Characters of the atomic absorption spectrum Natural broadening determined by the lifetime of the excited state and Heisenberg’s uncertainty principle ( 10-5 nm ) Doppler Broadening ( 10-3 nm ) results from the rapid motion of atoms as they emit or absorb radiation Collisional Broadening collisions between atoms and molecules in the gas phase lead to deactivation of the excited state and thus broadening the spectral lines
  18. 18. Characters of the atomic absorption spectrum Doppler Broadening ( 10-3 nm ) results from the rapid motion of atoms as they emit or absorb radiation
  19. 19. Application of AAS AAS Pretreatment (dissolution) is required for solid samples.
  20. 20. Results of Quantitative Analysis of Cd in Rice The following 2 methods can be used to analyze unpolished and polished rice decomposed using acid: Flame method Furnace method Polished rice: 0.118 ppm 0.1 ppm 0.5 ppm Unpolished rice: 0.070 ppm Polished rice : 0.118 ppm Unpolished rice : 0.073 ppm Air-C2H2 Injected amount: 10 µL Interference inhibitor: Pd 50ppm 5 µL Ashing: 400°C; Atomization: 1,800°C
  21. 21. AAS Interferences
  22. 22. AAS Advantages and Disadvantages' Advantages 1. High selectivity and sensitivity 2. Fast and simple working 3. Doesn’t need metals separation Disadvantages 1. Analysis doesn’t simultaneous 2. Fragment have to form ready measure solution 3. Limit types of cathode lamp (expensives)
  23. 23. THANK YOU 
  24. 24. Questions • • • • How could atom’s collision Sample preparation of AAS The type of sample liquid or gas Function of AAS of few nonmetals examples • What happen to the sample in flame
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AAS (spektroskopi serapan atom/ Atomic absorption spectroscopy) pertama kali dimanfaatkan Alan Walsh (1955). metode ini sangat tepat untuk analisis zat berkonsentrasi rendah. metode AAS berprinsip padaabsorpsi cahaya oleh atom-atom. Atom menyerap cahaya tersebut pada panjang gelombang tertentu, tergantung sifat unsurnya. Unsur-unsur yang dapat dideteksi oleh AAS/SSA adalah unsur-unsur logam, dan beberapa unsur non-logam (3 unsur).

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