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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Atomic absorption spectroscopy | 1/5 | https://en.wikipedia.org/wiki/Atomic_absorption_spectroscopy | reference | science, encyclopedia | 2026-05-05T10:03:45.133964+00:00 | kb-cron |
Atomic absorption spectroscopy (AAS) is an elemental analysis method for determining the concentration of metals in a given sample. The principle of AAS relies on the vaporization of metals within a sample when introduced to a flame. Every ground state metal absorbs light radiation (and excites) at a different wavelength. This uniqueness allows each metallic element to have its own absorption spectrum that corresponds to its identity. The total absorbed radiation at a specific wavelength by an element in the sample is proportional to the density of atoms of the element. The quantification of this relationship is used to determine the concentration of specific metals in the sample.
== History == The modern form of AAS was largely developed during the 1950s by a team of Australian chemists led by Sir Alan Walsh at the Commonwealth Scientific and Industrial Research Organisation, Division of Chemical Physics, in Melbourne, Australia. Alan Walsh first described AAS in an article titled "The Application of Atomic Absorption Spectra to Chemical Analysis" published in 1955 by the journal Spectrachemica Acta. In this article, Walsh emphasizes the importance of establishing a new technique that can provide an absolute method that can produce reliable chemical standards, which was not available at the time. He posits that instead of using emissive spectroscopy methods, an absorptive spectroscopic method can be used to achieve precise results. In 1960, James W. Robinson emphasizes that the main advantage of AAS is its ability to not be effected by environmental factors like other elements present in the experimental space. Before AAS, flame photometry was commonly used to determine the concentration of metal ions which can produce a wide array of results due to its sensitivity to aspects such as elements present in the air, flame temperature, and solvents. AAS circumvents these issues almost completely due to its reliance on the physical properties and interactions of atoms which are majority present in the ground state compared to the majority excited state atoms in flame photometry. Such comparisons highlight the utility of AAS as a novel technique at the time. In the early 2000s, scientists turned toward high resolution line continuum AAS (HS LC AAS) which was considered revolutionary in the field since the invention of AAS as HS LC AAS was able to overcome previous limitations. Such limitations include issues like accurate background measurement and correction. Around this time, the first commercial instrument for HS LC AAS also became available.
== Instrumentation ==
An atomic absorption spectrometer contains many components such as the radiation source, atomizer, focusing lenses, monochromator, detector, amplifier, signal processor, and finally, the sample. However, the most crucial parts of this instrument are the radiation source and atomizer.
=== Radiation sources === Radiation sources in spectrometers are what excite the atoms in the provided sample. They provide two outputs: continuum and line sources. Continuum sources are able to emit electromagnetic radiation in a wide range of wavelengths. Line sources emit electromagnetic radiation at specific wavelengths.
==== Hollow cathode lamps ==== Hollow cathode lamps (HCL) are a common radiation source used in AAS. The HCL is filled with an inert gas at low pressure. Inside, there is a hollow cup, the cathode, that contains the sample. The anode is a tungsten wire. Once a high voltage is applied across the anode and cathode, the gas begins to ionize. The gas ions accelerate towards the cathode, collide with the metal, and sputter atoms from the material. These metal ions are excited and emit specific wavelengths of radiation that allow for element identification. Often, single element lamps are used where the cathode consists predominantly of compounds with the target element. These single element lamps provide precision with specific and stable emission lines that are element specific. Multi-element lamps are available with combinations of compounds containing the target elements as the cathode but are less accurate. Multi-element lamps have slightly less sensitivity than single element lamps, so the combinations must be selected carefully to avoid spectral interference. Atomic absorption spectrometers can feature as few as 1-2 hollow cathode lamp positions or, in automated multi-element spectrometers, 8-12 lamp positions may be available. Usually, separate single element lamps are used for different elements.
==== Electrodeless discharge lamps ==== Electrodeless discharge lamps (EDL) are another radiation source used in AAS. EDL is frequently used instead of HCL when the desired sample consists of volatile metals (e.g. Arsenic) or lower sensitivity metals (e.g. Antimony). A small quantity of the metallic sample is sealed in an evacuated quartz tube filled with a low-pressure inert gas, most commonly Argon. The sealed tube is then placed into a microwave discharge cavity which allows for the gas to transform into a plasma state. The plasma state gas excites the metal atoms. The excited metal ions emit wavelengths that are then detected and organized into a spectrum. EDLs need a separate power supply and might need a longer time to stabilize.
==== Deuterium lamps ==== Deuterium HCL, hydrogen HCL, and deuterium discharge lamps are used in line source AAS for background correction. The radiation intensity emitted by these lamps decreases significantly with increasing wavelength, so that they can be only used in the wavelength range between 190 and about 320 nm.
==== Continuum sources ==== When a continuum radiation source is used for AAS, it is necessary to use a high-resolution monochromator. The lamp emits radiation of an intensity at least an order of magnitude above that of a typical HCL: wavelengths ranging from 190 nm to 900 nm. A special high-pressure xenon short arc lamp, operating in a hot-spot mode, has been developed to be used as the continuum radiation source.
=== Source Type AAS === AAS can be performed with either line source emissions or continuum source emissions.