Editing Atomic absorption spectroscopy (section)

=== Radiation sources ===
We have to distinguish between line source AAS (LS AAS) and continuum source AAS (CS AAS). In classical LS AAS, as it has been proposed by Alan Walsh,<ref>{{cite book|last1=Walsh|first1=Alan|last2=Becker-Ross|first2=Helmut|last3=Florek|first3=Stefan|last4=Heitmann|first4=Uwe|title=High-Resolution Continuum Source AAS|date=19 January 2006|publisher=Wiley-VCH Verlag GmbH & Co. KGaA|location=Weinheim|isbn=9783527307364|page=2}}</ref> the high spectral resolution required for AAS measurements is provided by the radiation source itself that emits the spectrum of the analyte in the form of lines that are narrower than the absorption lines. Continuum sources, such as deuterium lamps, are only used for background correction purposes. The advantage of this technique is that only a medium-resolution monochromator is necessary for measuring AAS; however, it has the disadvantage that usually a separate lamp is required for each element that has to be determined. In CS AAS, in contrast, a single lamp, emitting a continuum spectrum over the entire spectral range of interest is used for all elements. Obviously, a high-resolution monochromator is required for this technique, as will be discussed later.

[[File:Mehrelement-Hohlkathodenlampe für bessere UV-Lichtdurchlässigkeit mit eingelassenem Quarzfenster.jpg|thumb|250px|Hollow cathode lamp (HCL)]]

==== Hollow cathode lamps ====
[[Hollow cathode lamps]] (HCL) are the most common radiation source in LS AAS.{{citation needed|date=March 2016}} Inside the sealed lamp, filled with argon or neon gas at low pressure, is a cylindrical metal cathode containing the element of interest and an anode. A high voltage is applied across the anode and cathode, resulting in an ionization of the fill gas. The gas ions are accelerated towards the cathode and, upon impact on the cathode, sputter cathode material that is excited in the glow discharge to emit the radiation of the sputtered material, i.e., the element of interest. In the majority of cases single element lamps are used, where the cathode is pressed out of predominantly compounds of the target element. Multi-element lamps are available with combinations of compounds of the target elements pressed in the cathode. Multi element lamps produce slightly less sensitivity than single element lamps and the combinations of elements have to be selected carefully to avoid spectral interferences. Most multi-element lamps combine a handful of elements, e.g.: 2 - 8. Atomic Absorption Spectrometers can feature as few as 1-2 hollow cathode lamp positions or in automated multi-element spectrometers, a 8-12 lamp positions may be typically available.

==== Electrodeless discharge lamps ====
[[Electrodeless lamp|Electrodeless discharge lamps]] (EDL) contain a small quantity of the analyte as a metal or a salt in a quartz bulb together with an inert gas, typically argon gas, at low pressure. The bulb is inserted into a coil that is generating an electromagnetic radio frequency field, resulting in a low-pressure inductively coupled discharge in the lamp. The emission from an EDL is higher than that from an HCL, and the line width is generally narrower, but EDLs need a separate power supply and might need a longer time to stabilize.

==== Deuterium lamps ====
[[Deuterium arc lamp|Deuterium HCL]] or even hydrogen HCL and deuterium discharge lamps are used in LS AAS for background correction purposes.<ref>{{cite web|last1=Rakshit|first1=Amitava|title=Basics of Laboratory Safety: Common laboratory rules and regulations|url=http://www.intecol.net/pages/002_personal.php?table=blog&tb_kind=Research&id=Amitava&vvt=aa&bidx=134710|website=The International Association for Ecology|publisher=Intecol|access-date=26 September 2016|archive-url=https://web.archive.org/web/20160927115008/http://www.intecol.net/pages/002_personal.php?table=blog&tb_kind=Research&id=Amitava&vvt=aa&bidx=134710|archive-date=27 September 2016|url-status=dead}}</ref> 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&nbsp;nm.

[[File:Continuous radiation source.jpg|thumb|250px|Xenon lamp as a continuous radiation source]]

==== Continuum sources ====
When a continuum radiation source is used for AAS, it is necessary to use a high-resolution monochromator, as will be discussed later. In addition, it is necessary that the lamp emits radiation of intensity at least an order of magnitude above that of a typical HCL over the entire wavelength range from 190&nbsp;nm to 900&nbsp;nm. A special [[Xenon arc lamp|high-pressure xenon short arc lamp]], operating in a hot-spot mode has been developed to fulfill these requirements.