Atomic Absorption Spectrometry (AAS) ICP CHEMISTRY A 2011 FMIPA UNM 2013 Contents • • • • • What is AAS Theory Instrumentations Principle of AAS Applications 7. Spectrochim.Walsh. The technique was introduced in 1955 by Walsh in Australia (A.What is AAS ? Atomic absorption spectroscopy is a quantitative method of analysis that is applicable to many metals and a few nonmetals. 108) The application of atomic absorption spectra to chemical analysis Concentrations range is in the low mg/L (ppm) range. Acta. 1955. . The extend of absorption will be proportional to the number of ground state atoms present in the flame. These ground state atoms are capable of absorbing radiant energy of their own specific resonance wavelength.Theory A much larger number of the gaseous metal atoms will normally remain in the ground state. then part of the light will be absorbed. . If light of the resonance wavelength is passed through a flame containing the atoms in question. .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. AAS Instrument . The element in the sample will be atomized by heat 6. The detector measures the change in intensity 7. The monochromator isolates the line of interest 1.The simple diagram for the AAS 4. thus reducing its intensity 3. A computer data system converts the change in intensity into an absorbance . The element in the sample will absorb some of the light. We set the instrument at certain wavelength suitable for a certain element 2. A beam of UV light will be focused on the sample 5. Flame atomization Processes occurring during atomization . The flame path is about 10 –12 cm .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 --.Nebuliser . It burns as a smooth. The mixture flows immediately into the burner head. Nebulizer: 4. 2. 5. 1. mixes acetylene (the fuel) and oxidant (air or nitrous oxide). 3. Liquid sample not flowing into the flame collects in the waste.1. A negative pressure is formed at the end of the small diameter. plastic nebulizer tube (aspiration). 6. The result is a heterogeneous mixture of gases (fuel + oxidant) and suspended aerosol (finely dispersed sample). laminar flame evenly distributed along a narrow slot. Note: When do we use NO2 ? . Elements that are highlighted in pink are detectable by AAS . 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.Principle of Atomic Absorption Spectrophotometer Atomized elements each absorb energy of a wavelength that is peculiar to that element. Light absorption process of atoms . AES Excited state E1 Emission e Ground state E0 .Principle of Atomic Absorption Spectrophotometer Atomic Absorption Spectroscopy. AAS Excited state E1 Absorption e Ground state E0 e Atomic Emission Spectroscopy. central wavelength .maximal absorption coefficient Δ .Characters of the atomic absorption spectrum Profile of the absorption line K0 .half width 0 . intensity of the transmitted light Io – intensity of the incident light signal l – the path length through the flame (cm) .4343 K l It .The relationship between absorbance and the concentration of atoms Beer’s law It = I0νe -Kνl A = log （ I0ν/ It）= 0. there is little vaporization of elements with low boiling points. Examples: Sediment. Suitable for volatile elements. dairy products). Te. Microwave Decomposition .. ceramics. the decomposition time is short. Decomposition is possible in a short time (a few hours) and operation is simple.. pharmaceuticals. A long time is required for the decomposition of organic substances. Elements with low boiling points (e. soil. and biological samples (e. etc.. Decompose the sample at high pressure by heating it together with acid to a temperature in the range 100 to 200C in a sealed Teflon container. or organic solvents. food products. dust. urine).g. and only a small amount of acid is required. Dry Decomposition Heat the sample to a high temperature (400 to 500C).g. Se.g. Hg. The decomposition process is sealed. dilute acid. 300C). living organisms. As. Examples: food products (e. and Sb) will vaporize Wet Decomposition Heat the sample together with acid to a low temperature (approx. blood.Types of Pretreatment Dilution Dilute the sample with purified water. there is little contamination from the operating environment and the reagent. 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 . Characters of the atomic absorption spectrum Doppler Broadening （10-3 nm） results from the rapid motion of atoms as they emit or absorb radiation . Application of AAS AAS Pretreatment (dissolution) is required for solid samples. . 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: 0.073 ppm Air-C2H2 Injected amount: 10 µL Interference inhibitor: Pd 50ppm 5 µL Ashing: 400C.800C .070 ppm Unpolished rice : 0.5 ppm Polished rice : 0. Atomization: 1.1 ppm 0.118 ppm Unpolished rice: 0.118 ppm 0. AAS Interferences Spectral interferences Chemical interferences Physical interferences . AAS Advantages and Disadvantages' Advantages 1. Limit types of cathode lamp (expensives) . Fragment have to form ready measure solution 3. Doesn’t need metals separation Disadvantages 1. High selectivity and sensitivity 2. Fast and simple working 3. Analysis doesn’t simultaneous 2. THANK YOU . 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 .