Atomic Absorption Spectrometry

Abstract

The basis of atomic absorption spectrometry (AAS) is the absorption of discrete wavelengths of light by ground-state, gas-phase free atoms. Free atoms in the gas phase are formed from the sample by an “atomizer” at high temperature. AAS was developed in the 1950s by Alan Walsh and rapidly became a widely used analytical tool. AAS is an elemental analysis technique capable of providing quantitative information on ∼70 elements in almost any type of sample. As an elemental analysis technique, it has the signicant advantage in many (but not all) cases of being practically independent of the chemical form of the element in the sample. A determination of cadmium in a water sample is a determination of the total cadmium concentration. It does not matter whether the cadmium exists as the chloride, sulfate, or nitrate, or even if it exists as a complex or an organometallic compound, if the proper analysis conditions are used. Concentrations as low as ppt levels of some elements in solution can be determined and AAS is used routinely to determine ppb and ppm concentrations of most metal elements. Another principal advantage is that a given element can be determined in the presence of other elements, which do not interfere by absorption of the analyte wavelength. Therefore, it is not necessary to separate the analyte from the rest of the sample (the matrix). This results in rapid analysis times and eliminates some sources of error. This is not to say that AAS measurements are completely free from interferences; both chemical and spectral interferences do occur and must be compensated for, as will be discussed. The major disadvantages of AAS are that no information is obtained on the chemical form of the analyte (no “speciation”) and that often only one element can be determined at a time. The latter makes AAS of very limited use for qualitative analysis. AAS is used almost exclusively for quantitative analysis of elements, hence the use of the term “spectrometry” in the name of the technique instead of “spectroscopy.”