Absorption Spectometry

The absorption of light by atoms provides a powerful analytical tool for both quantitative and qualitative analysis. Atomic absorption spectroscopy (AAS) is based upon the principle that free atoms in the ground state can absorb light of a certain wavelength. Absorption for each element is specific, no other elements absorb this wavelength.

AAS is a single-element method used for trace metal analysis of e.g., biological, metallurgical, pharmaceutical and atmospheric samples. Spectroscopic determination of atomic species can only be performed on a gasified sample in which the individual atoms such as Ag, Al, Au, Fe and Mg are well-seperated from each other.

Absorption Spectometry - Instrumentation

The most common source for atomic absorption measurements is the hollow cathode lamp. It consist of a tungsten anode and a cylindrical cathode seated in a glass tube containing inert gas, such as argon. The cathode is made of the element to be analyzed.

Absorption Spectometry - Sample

Heat is needed to gasify the sample. The heat is generated from a flame or a graphite furnace. Flame AAS can only analyze solutions, while graphite furnace AAS can analyze solutions, slurries and solid samples. A flame atomizer consists of a nebulizer which converts the sample into an aerosol that is fed into the burner. The atomization takes place in the flame commonly fed by the fuel gases acetylene and nitrous oxide.

An electrothermal atomizer gives high sensitivity because it atomizes the sample rapidly. Atomization occurs in a cylindrical graphite furnace that is open in both ends and has a central hole for the introduction of the samples. Two inert gas streams are used. The external stream prevents air to entry the furnace and the internal stream ensures that vapors generated from the sample matrix are quickly removed from the oven. The most widely used gas is argon.

Absorption Spectometry - Analyzer

To isolate a narrow band of wavelength a monochromator is used.

Absorption Spectometry - Detector

A photomultiplier converts light to electrical signals.