What Does Atomic Absorption Spectroscopy (AAS) Mean?
Atomic absorption spectroscopy (AAS) is a spectroscopic analysis technique that determines the concentration of a particular element in a sample by atomizing the contents of the sample and measuring the absorbance of a wavelength specific to that particular element in the gaseous state. Atomic absorption lines of free atoms are very narrow, with absorption ranges of only a few picometers (1 picometer = 0.001 nanometer). Further, these absorption lines typically do not overlap with those of different elements, making the technique specific.
AAS is performed using an atomic absorption spectrometer, which is composed of an atomizer that prepares the sample for analysis, a lamp for radiation and a detector. Two types of atomic absorption spectrometers are available, depending on the lamp type: line source (LS) AAS and continuum source (CS) AAS.
LS AAS uses a single lamp for a single element of interest, while CS AAS uses a lamp that can measure many different elements. While CS AAS may sound more appealing, they require a more expensive high-resolution monochromator for wavelength selection.
AAS is used across many disciplines such as chemistry, biology, pharmaceuticals, material analysis and water quality evaluation to determine the presence and concentration of a particular atom of interest, such as a toxic metal atom such as lead. More than 70 elements, mainly metals, can be analyzed with AAS.
Corrosionpedia Explains Atomic Absorption Spectroscopy (AAS)
AAS starts with specialized sample preparation to release the element’s atoms into solution. Certain metals require harsh acids such as nitric acid (HNO3) to ensure that any bonds to other atoms are broken in order to be atomized into the gas phase as a free atom. If these bonds are not broken, a portion of the metal may not be detected. Various atomizers are available:
- Flame atomizers
- Electrothermal atomizers
- Glow-discharge atomizers
- Hydride atomizers
- Cold-vapor atomizers
The atomic absorption lines of these metals lie between 200-700 nanometers. For LS AAS, hollow cathode lamps and electrodeless discharge lamps are used to create a specific wavelength radiation for the absorption line of a specific element in question. For CS AAS, other sources such as a xenon arc lamp are used. The radiation from the lamps will only interact with a free metal atom at a specific wavelength because at that wavelength of energy, the atom is able to undergo an electronic state change from its ground state to an excited state. Any energy absorbed by an atom will not be detected after passing through the sample, indicating the presence of that atom.
As with any absorption experiment, the amount of absorption of a particular wavelength is measured with the sample. The absorbance that relates to the concentration of the element in question is based on the Beer-Lambert law. Accurate values require calibration and concentration values that lie within the linear Beer-Lambert relationship. Background absorption correction is necessary to remove further error in the AAS measurement. Correction techniques include:
- Deuterium background correction
- Smith-Hieftje background correction
- Zeeman-effect background correction