Atomic Absorption Spectroscopy (AAS)

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:

1. Desolvation – the liquid solvent is evaporated, and the dry sample remains
2. Vaporizations – the solid sample vaporizes to a gas
3. 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.