Atomic absorption spectroscopy

AAS

1. ATOMIC ABSORPTION SPECTROSCOPY PRESENTED BY, DEVIPRIYA P V M PHARM Department of Pharmaceutical Analysis

2. Atomic absorption spectroscopy “The absorption of specific wavelength of radiation by neutral atoms in the ground state”. 2

3. AAS is a very common technique for detecting metals and metalloids in sample. It is very reliable and simple to use. It can analyze over 62 elements. It can also measure the concentration of metals in the sample. The atoms absorb UV or visible light and make transitions to higher electronic energy levels. The analyte concentration is determined from the amount of absorption. 3

4. principle Liquid sample Formation of droplet formation of neutral atoms fine residue Neutral atoms absorb specific wavelength of radiation from Hollow cathode lamp Measurement of intensity of radiation absorbed by using photometric detector 4

5. instrumentation 5

6. Components of aas Radiation source :Hollow cathode lamp :Electrodeless discharge lamp Chopper Atomizers :flame atomizer :Non flame atomizer Nebulisation of the liquid sample Monochromator Detector Amplifier Read out device 6

7. Hollow cathode lamp Source of light in AAS Tungsten anode. Hollow cylindrical cathode made of elements to be determined These are sealed in a glass tube filled with inert gas (Ne or Ar ). Lamp window is constructed of either quartz, silica, or glass. 7

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9. Electrodeless discharge lamp Evacuated tube with metal of interest. The is filled with Ar at low P and sealed. The sealed tube is then placed in a microwave discharge cavity. High intensity. 9

10. chopper Rotating wheel interposed between the hollow cathode lamp and the flame. Produces pulsating current which is amplified and recorded 10

11. atomizers Elements to be analyzed needs to be in the atomic state Flame atomizer: total consumption burner :premixed burner 11

12. Mixing of gas and sample within the flame. Flame is hot enough for molecular dissociations needed. Rate of sample introduction depends on viscosity. No explosive hazards. Consume entire sample. Gases are mixed and sample is atomized before burned. Uniformity of flame Less tendency to clog. Quiet operation. Possibility of explosion in the mixing chamber. Total consumption burner Premixed burner 12

13. Monochromator Prisms and gratings To select a given absorbing line from spectral line emitted from HCL Good resolution of 1nm or less is used. 13

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15. detector Photomultiplier tubes. Convert radiant energy into an electrical signal. Evacuated envelope with a : photocathode : a series of electrodes called dynodes : anode Photocathode is fixed to the terminal of power supply. 15

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17. amplifier Lock-in amplifiers are preferred. READ OUT DEVICES : Chart recorders or digital devices are used. 17

18. Single beam aas All measurements are based on the varying intensity of a single beam of light in a single optical path. It consists of several hollow cathode sources, a chopper or a pulsed power supply, an atomizer, and a simple grating spectrophotometer with a photomultiplier transducer. Blank is replaced by sample. Low stability. 18

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20. Double beam instrument The beam from the HCL is split by a mirror chopper, one half passing through the flame and the half around it. Sample beam : focused to sample cell Reference beam : focused around the sample cell. The 2 beams are then recombined . 20

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