Atomic Absorption Spectroscopy

Developed by Commonwealth Scientific and Industrial Research Organisation (CSIRO), Dr. Alan Walsh in the 1950s. a spectroanalytical procedure for the quantitative determination of chemical elements using the absorption of optical radiation (light) by free atoms in the gaseous state. Used to measure the concentration of metals in different sample. Atomic absorption methods measure the amount of energy absorbed by the sample.

TYPES OF MEASURING DEVICE

TYPES OF MEASURING DEVICE Water Sampling Rainwater Particulate Seawater Groundwater Sludges Sediments Riverwater Waste water

TYPES OF MEASURING DEVICE There are 3 steps involved in turning a liquid sample into an atomic gas: Evaporation of the liquid to leave a dry sample Vaporising the solid sample to a gas Atomisation to break down the compounds present into free atoms.

Metals that can be detected by Atomic Absorption Spectroscopy TYPES OF MEASURING DEVICE Metals that can be detected by Atomic Absorption Spectroscopy Aluminium (Al) Cadmium (Cd) Lead (Pb) Niobium (Nb) Antimony (Sb) Cobalt (Co) Lithium (Li) Ruthenium (Ru) Arsenic (As) Copper (Cu) Magnesium (Mg) Tin (Sn) Beryllium (Be) Gallium (Ga) Manganese (Mn) Tungsten (W) Barium (Ba) Hafnium (Hf) Mercury (Hg) Vanadium (V) Calcium (Ca) Indium (In) Molybdenum (Mo) Zinc (Zn) Chromium (Cr) Iron (Fe) Nickel (Ni) Zirconium (Zr)

TYPES OF MEASURING DEVICE Atomic absorption spectrometry has many uses in different areas of chemistry Analysing metals in biological fluids such as blood and urine Clinical Analysis Monitoring our environment Finding out the levels of various elements Environmental analysis Amount of catalyst present can be determined Pharmaceuticals Check that the major elements are present and toxic impurities are lower than specified Industry Amount of metals such as gold in rocks can be determined Mining

OPERATING PRINCIPLE

Principle of Atomic Absorption Spectrophotometer Principle of the Atomic Absorption Method Atomized elements each absorb energy of a wavelength that is peculiar to that element. 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. Light absorption process of atoms Lambert-beer’s Law I = I0 e-k .l .C Density C l I0 I Abs = -logI/I0 = k .l. C k : proportional constant l : path length C : density (concentration)

Flame Method Flame Atomization Method

Flameless Method (Graphite Furnace) シール Graphite cap Graphite holder Cooling block Aperture plate socket Sample inlet Seal Graphite tube Eject arm Spring Fixing knob Graphite tube

Hydride Vapor Generation Technique As, Se, Sb, Sn, Te, Bi, Hg and other metals produce a metal hydride by this method Elements Concentration (ppb) As 5~20 Sb Te Bi Se 10~40 Hg 20~80 Sn 30~90 6BH4- +As3++ 3H+ 3B2H6+3H2 +AsH3 (gas) Absorption Cell Burner Head of AAS Peristaltic Pump Manifold Gas Liquid Separator Reaction Coil Drain Sample HCl NaBH4 Carrier Gas Ar Structural Diagram of Hydride Vapor Generator

ADVANTAGES AND DISADVANTAGES

Flame Atomic Absorption Spectroscopy (F-AAS) Advantages Disadvantages Low maintenance cost is required. It can only analyse solutions. Relatively short measurement time. Sensitivity limitations. Simple. Higher initial sample volumes required. Convenient. The efficiency of atomization is poor. Short residence time of analyte in optical path.

Graphite Furnace Atomic Absorption Spectroscopy (GF-AAS) Advantages Disadvantages Small sample size. The sample may not completely atomized. Direct analysis of solid samples. Limited analytical range. Sensitivity is enhanced. It requires experienced operators. Very little or no sample preparation is needed. It is an expensive technique. The atomization process is more efficient. Low sample throughput. Analysis of liquid samples even when organic matrix is present. The precision is poor than flame method. Analysis of liquid samples with permanent inorganic matrix. High matrix interference. Low spectral interference. Slow measurement time.

Hydride Vapour Generation Atomic Absorption Spectroscopy (HVG-AAS) Advantages Disadvantages Low detection limits. The specific chemical form of the analyte is required. Quite fast measurement. High chemical interference. Most of interferences disappear when the analyte is transferred to a gaseous state. A large excess of the hydride-forming element makes determination of traces of the other one impossible.

EXAMPLE OF SAMPLE TESTING

Example of Sample Testing 1. Determination of Vanadium in Lubricating Oil Theory : High temperature corrosion and fouling can be attributed to vanadium in the fuel. During combustion, the element oxidize and form semi-liquid and low melting salts (vanadium pentoxide), which adhere to exhaust valves and turbochargers. The oil is dissolved in white spirit and the absorption of this solution is compared with the absorption of standard.

Procedure : Weight out 5g of the oil sample, dissolve in small volume of white spirit and transfer to 50ml flask. Using same solvent, make up the solution to the mark. Set up a vanadium hollow cathode lamp selecting a resonance line of wavelength 318.5nm. Adjust gas controls to give a fuel rich acetylene-nitrous oxide flame Aspirate into the flame the solvent blank, standard solutions and finally the test solution. Recording the absorbance reading. Plot the calibration curve and ascertain the vanadium content of the oil.

2. Determination of Trace Elements (Lead) in Contaminated Soil Theory : -sample of approximate 50g should be taken from specified sampling points on the site. -The sampling point should include surface soil and two further samples taken at depth, at 0.5 and 1.0m. -The exact location of these points should be noted, for it may be necessary to take further samples.

Procedures : Weight out about 1g of sieved soil and transfer to a 100ml beaker. Add 20ml of 1:1 nitric acid. Boil gently on a hot plate until the volume of nitric acid is reduced to 5ml. Add 20ml of deionised water and boil gently again until the volume is 10ml. Cool the suspension and filter through a whatman filter paper, washing the beaker and filter paper with deionised water until a volume of about 25ml is obtained. Transfer the filtrate to a 50ml flask and make up to the mark with deionised water. Setup acetylene-air flame with resonance line 217.0nm. Standard lead solutions containing 1-10mg ml-1 are suitable for measurement.

QUESTION AND ANSWER

What are the steps of turning a liquid sample into an atomic gas? Evaporation of the liquid to leave a dry sample Vaporising the solid sample to a gas Atomisation to break down the compounds present into free atoms.

List down 5 advantages and disadvantages for Graphite Furnace Atomic Absorption Spectroscopy (GF-AAS) Advantage Disadvantage - small sample size - sample may not completely atomized - low spectral interference - slow measurement time - sensitivity is enhanced - high matrix interference - the atomization process is more efficient - low sample throughout - very little or no sample preparation is needed - requires experienced operators

Atomic Absorption Spectroscopy (AAS) have many uses in different areas in chemistry. Elaborate. Clinical Analysis - analysing metals in biological fluids such as blood and urine Environmental analysis - monitoring our environment Pharmaceuticals - determine the amount of catalyst present Industry - examine the raw materials - check the toxic impurities Mining - determine the amount of metals

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