Atomic Absorption Spectrometer (AAS)

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The main components of the instrumentation used are as follow;
1) Source of Radiations: It is a hollow cathode sup. It is consist of the glass jacket containing cup shaped cathode made up of the same element which is under Study. A tungsten wire (plate) Acts as anode which is arranged in the same glass jacket. The glass jacket is filled with the inert gas like Neon (Ne) or Argon (Ar) at a low pressure. When a Potential of 500-1000 volt is applied between the two electrodes from the power supply the atoms of the inert-gas is ionized.
The positive charged ions ace moving towards cathode. These fast moving ions remove the atoms from the surface of cathode. This process is called Sputtering. These metallic atoms then collide with highly energetic gas ions and some of them are excited. These excited metal atoms emit their characteristics radiations when they return to the original state with emitting their characteristic radiations.
2) Rotating Chopper: A rotating wheal brooks the beam of light coming from cathode lamp and produce intermittent light.
3) Burner: The flame is produced by burning the fuel with the oxidizer and the sample is burnt. Burners used are of the two types: i) Total Consumption Burners and ii) Pro-mix Burners.
4) Monochromator: Either prisms or diffraction gratings are used as monochromator. The transmitted beam from the flame enters, the monochromator which is allowed to fall only one wave length at a time on P.M.T.
5) P.M.T: The transmitted light from the monochromator when falls on P.M.T. the currant is produced. This currant is proportional to the light incident on the photo cathode of P.M.T.
6) Read out meter: This dial will give us the amount of radiations absorbed by unexcited atoms present in the ground state in terms of the absorbance.
The cathode and anode is connected with the power supply from where we supply the potential of 500-1000 volt. The gas taken in the bulb is ionized. The cations of the gas are moving fast towards cathode and remove the atoms from the cathode. These atoms strike With the gas ions and transition take place, return to the original state with the emission of characteristic radiations which pass (penetrate) out the mica wall and are incident on rotating chopper, it produce intermittent radiations which are incident on the Unexcited atoms present in the flame of the burner. These atoms absorb the radiations. The transmitted is incident on the prism which is connected with the PMT. In PMT current is produced. PMT is connected with read out meter which gives the absorbance. Now, by applying the Beer-Lambert's Law, we can find out the conc. of solution by knowing the absorbance.
Applications:
1. Quantitative analysis can be done using calibration curve method.
2. Very low concentration, which is 1ppm or less than that, can also be analysed accurately with the help of A.A.S.
3. With the help of A.A.S. we can detect the toxic elements such as Copper, Nickel, Zinc present in food products.
4. The phenomenon is used to estimate sodium and potassium present in Blood serum.
5. How much amount of lead is present in the petrol can be found out with the help of A.A.S.
6. Soli extracts, plant materials, fertilises have been analysed for determination of sodium, potassium, Magnesium, Molybdenum, Vanadium etc.
7. The amount of Titanium and vanadium present in the steel alloy can also be determined with the help of A.A.S.
Limitations:
1. Simultaneous analysis of many elements is not possible.
2. Metals like Lanthanum, tungsten, Silicon etc form the stable metallic oxide and so cannot be analysed.
3. For alkali metals like lithium, Sodium, potassium etc, which has low ionisation potential. In such cases low temperature of flame is required to minimise the ionisation of the elements.
4. Each element requires the separate lamp.
5. If the sample contains two elements which absorb the light of same wavelength. for example Manganese and gallium both absorbs at 403nm cannot be analysed. In such case we must remove the interfering radical.
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