ATOMIC ABSORPTION SPECTROSCOPYPreston islamabad

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Introduction

• It is very reliable and simple to use

• It can analyze over 62 elements

• It also measures the concentration of metals in sample

Atomic absorption spectroscopy is a quantitative method of analysis of any kind of

sample ; that is applicable to many metals and a few nonmetals.

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HISTORY

• The technique was introduced in 1955 by Alan Walsh in Australia ( 1916 – 1998 ).

• The first commercial atomic absorption spectrometer was introduced in 1959.

The application of atomic absorption spectra to chemical

analysis

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PRINCIPLE

• The technique uses basically the principle that free atoms ( gas ) generated in an atomizer can absorb radiation at specific frequency.

• Atomic absorption spectroscopy quantifies the absorption of ground state atoms in the gaseous state.

• The atoms absorb ultraviolet or visible light and make transitions to high electronic energy levels. The analyte concentration is determined from the amount of absorption.

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• Concentration measurements are usually determined

from a working curve after calibrating the instrument

with standards of known concentration.

• Atomic absorption is very common technique for

detecting metals and metalloids in environmental

samples. 5

INSTRUMENTATION

Atomic Absorption

Spectrometer

Hollow cathode lamp

Detector

MonochromatorAtomizer

Nebulizer

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LIGHT SOURCE

• Hollow Cathode Lamp are the most common radiation source in AAS.

• It contains a tungsten anode and a hollow cylindrical cathode made of the element to be determined.

• These are sealed in a glass tube filled with an inert gas (neon or argon ) .

• Each element has its own unique lamp which must be used for that analysis . 7

Hollow Cathode Lamp

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Hollow Cathode Lamp for Aluminum (Al)

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Sample Atomization Technique

Flame Atomization

Electro thermal Atomization

Hydride Atomization

Cold-Vapor Atomization

Atomization is separation of particles into individual molecules and breaking molecules into atoms. This is done by exposing the analyte to high temperatures in a flame or graphite furnace .

Atomization

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Flame Atomization

• Nebulizer suck up liquid samples at controlled rate.

• Create a fine aerosol spray for introduction into flame.

• Mix the aerosol and fuel and oxidant thoroughly for introduction into flame.

• An aerosol is a colloid of fine solid particles or liquid droplets, in air or another gas.

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Flame Atomization

sample

mist

Solid/gas aerosol

Gaseous molecules

Atoms

nebulization

disolvation

volatilization

dissociation

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Disadvantages of Flame Atomization

• Only 5-15% of the nebulized sample reaches the flame.

• A minimum sample volume of 0.5-1.0 ml is needed to give a reliable reading.

• Samples which are viscous require dilution with a solvent.

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Electro Thermal Atomization

• Uses a graphite coated furnace to vaporize the sample.

• ln GFAAS sample, samples are deposited in a small graphite coated tube which can then be heated to vaporize and atomize the analyte.

• The graphite tubes are heated using a high current power supply.

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Graphite Furnace Technique

Drying

Ashing Atomization

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Advantages of Graphite Furnace Technique• Small sample size

• Very little or no sample preparation is needed

• Sensitivity is enhanced

• Direct analysis of solid samples

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Disadvantages of Graphite Furnace Technique

• Analyte may be lost at the ashing stage

• The sample may not be completely atomized

• The precision is poor than flame method

• Analytical range is relatively low

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MONOCHROMATOR

• This is a very important part in an AA spectrometer. It is used to separate out all of the thousands of lines.

• A monochromator is used to select the specific wavelength of light which is absorbed by the sample, and to exclude other wavelengths.

• The selection of the specific light allows the determination of the selected element in the presence of others.

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DIFFRACTION GRATING

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the process by which a beam of light or other system of waves is spread out as a result of passing through a narrow aperture or across an edge, typically accompanied by interference between the wave forms produced

DETECTOR

• The light selected by the monochromator is directed onto a detector that is typically a photomultiplier tube , whose function is to convert the light signal into an electrical signal proportional to the light intensity.

• The processing of electrical signal is fulfilled by a signal amplifier . The signal could be displayed for readout , or further fed into a data station for printout by the requested format.

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PHOTOMULTIPLIER

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Calibration Curve• A calibration curve is used to determine the unknown

concentration of an element in a solution.

• The instrument is calibrated using several solutions of known concentrations.

• The absorbance of each known solution is measured and then a calibration curve of concentration vs absorbance is plotted.

• The sample solution is fed into the instrument, and the absorbance of the element in this solution is measured.

• The unknown concentration of the element is then calculated from the calibration curve

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Applications

1) Presence of metals as an impurity or in alloys could be done easily

2) Level of metals could be detected in tissue samples like Aluminum in blood and Copper in brain tissues

3) Due to wear and tear there are different sorts of metals which are given in the lubrication oils which could be determined for the analysis of conditions of machines

4) Determination of elements in the agricultural and food products

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THANK YOU

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