Graphite Furnace Atomic Absorption Spectroscopy

Presented By:Anuradha vermaM.Sc (1st Sem)

CONTENTSWhat is GFAASWorking of GFAASAdvantages of GFAASDisadvantages of GFAASApplications

What is GFAASGraphite furnace atomic absorption spectrometry (GFAAS) (also known as Electro thermal Atomic Absorption spectrometry (ETAAS)) is a type of spectrometry that uses a graphite-coated furnace to vaporize the sample. Instead of employing the high temperature of a flame to bring about the production of atoms from the sample and it is non-flame methods involving electrically heated graphite tubes or rods.

Working of GFAAS•Aqueous samples should be acidified (typically with nitric acid, HNO3) to a pH of 2.0 or less. Discoloration in a sample may indicate that metals are present in the sample. For example, a greenish color may indicate a high nickel content, or a bluish color may indicate a high copper content. A good rule to follow is to analyze clear (relatively dilute) samples first, and then analyze colored (relatively concentrated) samples. It may be necessary to dilute highly colored samples before they are analyzed.•After the instrument has warmed up and been calibrated, a small aliquot (usually less than 100 microliters (µL) and typically 20 µL) is placed, either manually or through an automated sampler, into the opening in the graphite tube.•The graphite furnace is an electrothermal atomizer system that can produce temperatures as high as 3,000°C. The heated graphite furnace provides the thermal energy to break chemical bonds within the sample and produce free ground-state atoms. Ground-state atoms then are capable of absorbing energy, in the form of light, and are elevated to an excited state.

Contd....

•The sample is vaporized in the heated graphite tube; the amount of light

energy absorbed in the vapour is proportional to atomic concentrations.

• The free atoms will absorb light at frequencies or wavelengths characteristic of the element of interest .• Within certain limits, the amount of light absorbed can be linearly correlated to the concentration of analyte present.

InstrumentationSchematic representation of working

Simple Schematic Working

Graphite furnace AAS

Sample holder: graphite tube

Samples are placed directly in the

graphite furnace which is then

electrically heated.

Beam of light passes through the tube

Three stages:

1. drying of sample

2. ashing of organic matter (to burn off organic species that would

interfere with the elemental analysis.

3. vaporization of analyte atoms

Flame AASDisadvantages relatively large sample

quantities required (1 – 2 mL)

less sensitivity (compared to graphite furnace)

problems with refractory elements

N.B.-Refractory elements:

Resisting the action of heat;very difficult to melt or fuse.

Advantages inexpensive (equipment,

day-to-day running) high sample throughput easy to use high precision

N.B.-Throughput:

The amount of material put through a process, esp. in manufacturing or computing. Also, processing or handling capacity.

Advantages of GFAAS

Greater sensitivity and detection limits (hundred- or thousand fold improvements in the detection limit compared with flame AAS) than other methods.Direct analysis of some types of liquid samples.Some solid sample do not require prior dissolution.Low spectral interference.Very small sample size (as low as 0.5µL).

Disadvantages of GFAAS

expensivelow precisionlow sample throughputrequires high level of operator skill

Applications of GFAAS

GFAA has been used primarily for analysis of low concentrations of metals in samples of water. The more sophisticated GFAAs have a number of lamps and therefore are capable of simultaneous and automatic determinations for more than one element.for the quantification of beryllium in blood and serum.

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