Atomic Absorption Spectroscopy in analytical chemistry is a technique for determining the concentration of a particular
metal element within a sample. Atomic absorption spectroscopy can be used to analyze the concentration of over 62 different
metals in a solution.
Atomic absorption spectroscopy (AAS) is a spectroanalytical
procedure for the quantitative determination of chemical elements using
the absorption of optical radiation (light) by free atoms in the gaseous
state.
Although atomic absorption spectroscopy dates to the nineteenth century, the modern form was largely developed during
the 1950s by a team of Australian chemists, lead by Alan Walsh, working at the CSIRO (Commonwealth Science and Industry
Research Organization) Division of Chemical Physics, in Melbourne Australia. Typically, the technique makes use of a flame
to atomize the sample, but other atomizers such as a graphite furnace are also used. Three steps are involved in turning
a liquid sample into an atomic gas:
- Desolvation – the liquid solvent is evaporated, and the dry sample remains
- Vaporizations – the solid sample vaporizes to a gas
- Volatilization – the compounds making up the sample are broken into free atoms.
Atomic absorption spectroscopy relies on the Beer-Lambert law to
determine the concentration of a particular analyte in a sample. The
absorption spectrum and molar absorbance of the desired sample element
are known, a known amount of energy is passed through the atomized
sample, and by then measuring the quantity of light it is possible to
determine the concentration of the element being measured.
The process of atomic
absorption spectroscopy (AAS) involves two steps:
1.
Atomization
of the sample
2.
The
absorption of radiation from a light source by the free atoms
Principles
The technique makes use of absorption spectrometry to assess the
concentration of an analyte in a sample. It requires standards with
known analyte content to establish the relation between the measured
absorbance and the analyte concentration and relies therefore on the Beer-Lambert Law.
In short, the electrons of the atoms in the atomizer can be promoted
to higher orbitals (excited state) for a short period of time
(nanoseconds) by absorbing a defined quantity of energy (radiation of a
given
wavelength).
This amount of energy, i.e., wavelength, is specific to a particular
electron transition in a particular element. In general, each wavelength
corresponds to only one element, and the width of an absorption line is
only of the order of a few picometers (pm), which gives the technique
its elemental selectivity. The
radiation flux
without a sample and with a sample in the atomizer is measured using a
detector, and the ratio between the two values (the absorbance) is
converted to analyte concentration or mass using the Beer-Lambert Law.
