2. BC ILN Atomic Absorption Spectroscopy (AAS) 1 Thompson Rivers University

3. BC ILN 2 Atomic Absorption Spectroscopy (AAS) Introduction to AAS AAS Block Diagram o Lamp o Burner o Flame o Nebulizer o Monochromator o Detector Interferences Summary

4. BC ILN 3 Atomic Absorption Spectroscopy (AAS) AAS is an instrumental method of quantitative and qualitative analysis  Quantitative analysis refers to determining the amount of analyte in a sample  Qualitative analysis refers to determining whether an analyte is present in a sample It is used to identify elements present in a wide variety of substances Uses the characteristic absorption spectrum associated with each element

5. BC ILN Atomic Absorption Spectroscopy 4

6. BC ILN 5 Atomic Absorption Spectrophotometer

7. BC ILN Lamp The most popular design is the Hollow Cathode Lamp An Ar or Ne gas filled tube with a cathode made from the element undergoing analysis Emits narrow spectral lines at wavelengths characteristic of the element undergoing analysis 6

8. BC ILN Burner Produces the flame which evaporates the solvent and atomizes the sample Produces analyte atoms in their ground state Ground state atoms are then capable of absorbing the spectral lines emitted by the lamp This promotes an electron to a higher energy level and results in the atom being in an excited state 7

9. BC ILN Flame The most common and affordable atomic absorption instruments use flame as the method of sample atomization A variety of such flame burners are available: o An air/acetylene mixture is the most common oxidant/fuel used o A nitrous oxide/acetylene mixture is used if hotter flame is required The sample undergoing analysis is aspirated (drawn) into the instrument and then sprayed into the flame The flame heat supplies the energy to dissociate the sample into atoms 8

10. BC ILN Nebulizer 9 A device which disperses the sample uniformly throughout the flame by transforming the liquid sample into fine droplets The sample is mixed with oxidant and fuel in a mixing chamber before being dispersed into the flame The nebulizer and burner usually form an integral unit

11. BC ILN Monochromator The purpose is to select and filter the spectral lines emerging from the lamp 10

12. BC ILN 11 Detector Any photosensitive device may be used as a detector provided that it is: o Responsive to the characteristic wavelength o Sensitive enough to measure the change in radiant energy caused by any absorption of the sample The most common detector in AAS is either a phototube or a photomultiplier The detector is connected to a computer which acts as an amplifier and read-out device producing a value in terms of absorbance “units”

13. BC ILN Spectral Caused by background radiation from flame emission lines or molecular combustion products The atomization process may create particulates which scatter the lamp radiation Signals due to other elements or molecules overlap the signal of the sample element 12

14. BC ILN Chemical Caused by incomplete volatilization or dissociation of other compounds in the flame Ionization Results from the flame temperature being too high Causes a number of the vaporized atoms to become ionized by the flame and absorb at a different wavelengths All three types of interferences should be considered during any AAS analytical technique 13

15. BC ILN Atomic Absorption Spectroscopy (AAS) AAS is an instrumental method of quantitative and qualitative analysis Uses an Atomic Absorption Spectrophotometer Uses the characteristic absorption spectrum associated with each element Identifies elements present in a wide variety of substances Atomic Absorption Spectrophotometer The lamp, most commonly a Hollow Cathode Lamp (HCL) consisting of an Ar or Ne gas filled tube with a cathode made from the element undergoing analysis, emits narrow spectral lines at wavelengths characteristic of the element being analyzed The burner, produces the flame which evaporates the solvent and atomizes the sample producing ground state atoms which are capable of absorbing the spectral lines emitted by the lamp promoting electrons to a higher energy level and resulting in the production of excited state atoms The monochromator selects and filters the spectral lines emerging from the lamp due to a prism or grating that is set at such an angle to allow only the wavelength chosen for measurement, based on the element undergoing analysis, to pass through the exit slit to the detector Any photosensitive device may be used as a detector provided that: It is responsive to the characteristic wavelength being used It is sensitive enough to measure the change in radiant energy caused by any absorption by the sample in the flame The most common detector in AAS is either a phototube or a photomultiplier 14 The computer is connected to the detector and acts as the amplifier and read out device displaying the results in terms of absorbance “units”