Atomic Absorption Atomic Absorption SpectrometrySpectrometry

Dr AKM Shafiqul IslamDr AKM Shafiqul Islam

University Malaysia PerlisUniversity Malaysia Perlis

An atomic absorption spectrophotometer An atomic absorption spectrophotometer consists of a light source, a sample consists of a light source, a sample compartment and a detector.compartment and a detector.

Atomic spectroscopy is one of the major Atomic spectroscopy is one of the major tools for of trace (ppm and ppb) metallic tools for of trace (ppm and ppb) metallic elements in industrial and environmental elements in industrial and environmental laboratories. laboratories.

In these methods the solution sample is In these methods the solution sample is aspirated into a flame that is hot enough to aspirated into a flame that is hot enough to break the molecules into their atomic states. break the molecules into their atomic states.

The concentration of the analyte in the flame The concentration of the analyte in the flame may be measured by either its absorption or may be measured by either its absorption or emission of the radiation. The absorption mode emission of the radiation. The absorption mode is known as atomic absorption spectroscopy is known as atomic absorption spectroscopy (AAS) whereas emission mode as atomic (AAS) whereas emission mode as atomic emission Spectroscopy (AES)emission Spectroscopy (AES)

SensitivitySensitivity

Atomic spectroscopy is very sensitive for most Atomic spectroscopy is very sensitive for most elements.elements.

Concentrations at the ppm level may be routinely Concentrations at the ppm level may be routinely determined using flame atomisation.determined using flame atomisation.

Using electrothermal atomisation, concentrations Using electrothermal atomisation, concentrations at the ppb may be determined.at the ppb may be determined.– 1 ppm = 101 ppm = 10-6-6g/g or 1g/g or 1g/gg/g– The density of dilute aqueous solutions is The density of dilute aqueous solutions is

approximately 1.00 so that:approximately 1.00 so that:– 1 1 g/g of aqueous solution = 1g/g of aqueous solution = 1g/ml = 1 ppm g/ml = 1 ppm

1 ppm Fe = 1 x 10 1 ppm Fe = 1 x 10-6-6 g Fe/ml = 1.79 x 10 g Fe/ml = 1.79 x 10-5-5 mol dmmol dm-3-3

Both methods are used to determine the Both methods are used to determine the concentration of an element in solution.concentration of an element in solution.

Both methods use a standard curve.Both methods use a standard curve. Difference between UV and IR spectroscopy is Difference between UV and IR spectroscopy is

that sample must be atomised.that sample must be atomised. Sample may be atomised by:Sample may be atomised by:

(1) A flame(1) A flame

(2) Electrically heated furnace(2) Electrically heated furnace

(3) A Plasma(3) A Plasma

Instrumentation for an Atomic Absorption Spectrometer. The flowing fuel and air mixture provides the aspiration action drawing the solution sample into the flame.

Atomic Absorption SpectroscopyAtomic Absorption Spectroscopy

In atomic absorption spectroscopy the In atomic absorption spectroscopy the radiation of the lines of the analyte are radiation of the lines of the analyte are produced by the lamp; the presence of the produced by the lamp; the presence of the atomic state of the analyte in the flame atomic state of the analyte in the flame attenuates or reduces the intensity of the attenuates or reduces the intensity of the radiation. radiation.

The absorbance is proportional to the The absorbance is proportional to the concentration of the analyte, similar to concentration of the analyte, similar to optical spectroscopy. optical spectroscopy.

Upper Diagram is AES and the lower one is AAS. Upper Diagram is AES and the lower one is AAS. In FES the flame provides the excitation, but in In FES the flame provides the excitation, but in AAS it provides only for the atomization .AAS it provides only for the atomization .

The light source in AAS is the hollow cathode lamp (HCL). The light source in AAS is the hollow cathode lamp (HCL). The cathode is constructed of the metal or metals of the The cathode is constructed of the metal or metals of the analysis. Passage of a dc voltage through the lamp produces analysis. Passage of a dc voltage through the lamp produces the specific lines of those elements.the specific lines of those elements.

Hollow Cathode LampHollow Cathode Lamp

Atomic Absorption SpectroscopyAtomic Absorption Spectroscopy

The signal from the detector is transferred to the The signal from the detector is transferred to the computer, and the output registers on the computer, and the output registers on the monitor in a manner specified by the user.monitor in a manner specified by the user.

Spectra output of the multi-element steel hollow Spectra output of the multi-element steel hollow cathode lamp. Note the extremely sharp spectral lines.cathode lamp. Note the extremely sharp spectral lines.

Atomic Absorption SpectrometryAtomic Absorption Spectrometry

Most widely used method for determination of Most widely used method for determination of single elements in analytical chemistrysingle elements in analytical chemistry

Quantification of energy absorbed from an Quantification of energy absorbed from an incident radiation source from the promotion of incident radiation source from the promotion of elemental electrons from the ground stateelemental electrons from the ground state

Technique relies on a source of free elemental Technique relies on a source of free elemental atoms electronically excited by monochromatic atoms electronically excited by monochromatic lightlight

FlameFlame– Method of supplying atom sourceMethod of supplying atom source– Utilizes a nebulizer in conjunction with Utilizes a nebulizer in conjunction with

air/acetylene flameair/acetylene flame– Solvent evaporatesSolvent evaporates– Metal salt vaporizes and is reduced to Metal salt vaporizes and is reduced to

complete the atomization processcomplete the atomization process Radiation source is a hollow cathode lampRadiation source is a hollow cathode lamp

Sample Introduction in AASSample Introduction in AAS