Atomic emission spectroscopy
Atomic emission spectroscopy (AES) is a method of
chemical analysis that uses the intensity of light emitted from
a flame, plasma, arc, or spark at a particular wavelength to
determine the quantity of an element in a sample. The
wavelength of the atomic spectral line in the emission
spectrum gives the identity of the element while the intensity
of the emitted light is proportional to the number of atoms of
the element. The sample may be excited by various methods.
Atomic Emission Spectroscopy allows us to measure
Inductively coupled plasma atomic
interactions between electromagnetic radiation and physical
emission spectrometer
atoms and molecules. This interaction is measured in the form
of electromagnetic waves representing the changes in energy
between atomic energy levels. When elements are burned by a flame, they emit electromagnetic radiation
that can be recorded in the form of spectral lines. Each element has its own unique spectral line due to
the fact that each element has a different atomic arrangement, so this method is an important tool for
identifying the makeup of materials. Robert Bunsen and Gustav Kirchhoff were the first to establish
atomic emission spectroscopy as a tool in chemistry.[1]
When an element is burned in a flame, its atoms move from the ground electronic state to the excited
electronic state. As atoms in the excited state move back down into the ground state, they emit light. The
Boltzmann expression is used to relate temperature to the number of atoms in the excited state where
larger temperatures indicate a larger population of excited atoms. This relationship is written as:
where nupper and nlower are the number of atoms in the higher and lower energy levels, gupper and glower
are the degeneracies in the higher and lower energy levels, and εupper and εlower are the energies of the
higher and lower energy levels. The wavelengths of this light can be dispersed and measured by a
monochromator, and the intensity of the light can be leveraged to determine the number of excited state
electrons present.[2] For atomic emission spectroscopy, the radiation emitted by atoms in the excited state
are measured specifically after they have already been excited.
Much information can be obtained from the use of atomic emission spectroscopy by interpreting the
spectral lines produced from exciting an atom. The width of spectral lines can provide information about
an atom’s kinetic temperature and electron density. Looking at the different intensities of spectral lines is
useful for determining the chemical makeup of mixtures and materials. Atomic emission spectroscopy is
mainly used for determining the makeup of mixes of molecules due to the fact that each element has its
own unique spectrum.[3]
Flame
The sample of a material (analyte) is brought into the flame as
a gas, sprayed solution, or directly inserted into the flame by
use of a small loop of wire, usually platinum. The heat from
the flame evaporates the solvent and breaks intramolecular
bonds to create free atoms. The thermal energy also excites
the atoms into excited electronic states that subsequently emit
light when they return to the ground electronic state. Each
element emits light at a characteristic wavelength, which is A flame during the assessment of calcium
ions in a flame photometer
dispersed by a grating or prism and detected in the
spectrometer.
A frequent application of the emission measurement with the flame is the
regulation of alkali metals for pharmaceutical analytics.[4]
Inductively coupled plasma
Inductively coupled plasma
atomic emission spectroscopy
(ICP-AES) uses an inductively
coupled plasma to produce
excited atoms and ions that emit
electromagnetic radiation at
wavelengths characteristic of a
Sodium atomic ions
emitting light in a flame particular element.[5][6]
displays a brilliantly Inductively coupled plasma atomic
bright yellow emission at Advantages of ICP-AES are the
emission source
588.9950 and 589.5924 excellent limit of detection and
nanometers wavelength. linear dynamic range, multi-
element capability, low chemical interference and a stable and reproducible
signal. Disadvantages are spectral interferences (many emission lines), cost
and operating expense and the fact that samples typically must be in a liquid solution. Inductively
coupled plasma (ICP) source of the emission consists of an induction coil and plasma. An induction coil
is a coil of wire that has an alternating current flowing through it. This current induces a magnetic field
inside the coil, coupling a great deal of energy to plasma contained in a quartz tube inside the coil.
Plasma is a collection of charged particles (cations and electrons) capable, by virtue of their charge, of
interacting with a magnetic field. The plasmas used in atomic emissions are formed by ionizing a flowing
stream of argon gas. Plasma's high-temperature results from resistive heating as the charged particles
move through the gas. Because plasmas operate at much higher temperatures than flames, they provide
better atomization and a higher population of excited states. The predominant form of sample matrix in
ICP-AES today is a liquid sample: acidified water or solids digested into aqueous forms. Liquid samples
are pumped into the nebulizer and sample chamber via a peristaltic pump. Then the samples pass through
a nebulizer that creates a fine mist of liquid particles. Larger water droplets condense on the sides of the
spray chamber and are removed via the drain, while finer water droplets move with the argon flow and
enter the plasma. With plasma emission, it is possible to analyze solid samples directly. These procedures
include incorporating electrothermal vaporization, laser and spark ablation, and glow-discharge
vaporization.
Spark and arc
Spark or arc atomic emission spectroscopy is used for the analysis of metallic elements in solid samples.
For non-conductive materials, the sample is ground with graphite powder to make it conductive. In
traditional arc spectroscopy methods, a sample of the solid was commonly ground up and destroyed
during analysis. An electric arc or spark is passed through the sample, heating it to a high temperature to
excite the atoms within it. The excited analyte atoms emit light at characteristic wavelengths that can be
dispersed with a monochromator and detected. In the past, the spark or arc conditions were typically not
well controlled, the analysis for the elements in the sample were qualitative. However, modern spark
sources with controlled discharges can be considered quantitative. Both qualitative and quantitative spark
analysis are widely used for production quality control in foundry and metal casting facilities.
See also
Atomic absorption spectroscopy
Atomic spectroscopy
Inductively coupled plasma atomic emission spectroscopy
Laser-induced breakdown spectroscopy
References
1. Thakur, Surya N. (2020-01-01), Singh, Jagdish P.; Thakur, Surya N. (eds.), "Chapter 2 -
Atomic emission spectroscopy" (https://linkinghub.elsevier.com/retrieve/pii/B9780128188293
000022), Laser-Induced Breakdown Spectroscopy (Second Edition), Amsterdam: Elsevier,
pp. 23–40, doi:10.1016/b978-0-12-818829-3.00002-2 (https://doi.org/10.1016%2Fb978-0-12
-818829-3.00002-2), ISBN 978-0-12-818829-3, retrieved 2024-11-13
2. Engel, Thomas; Hehre, Warren J.; Angerhofer, Alex (2019). Quantum chemistry and
spectroscopy: physical chemistry (Fourth ed.). New York: Pearson. ISBN 978-0-13-480459-
0.
3. Lajunen, Lauri H.; Perämäki, P.; Lajunen, Lauri H. J. (2004). Spectrochemical analysis by
atomic absorption and emission. Royal Society of Chemistry (2. ed.). Cambridge: Royal
Society of Chemistry. ISBN 978-0-85404-624-9.
4. Stáhlavská A (April 1973). "[The use of spectrum analytical methods in drug analysis. 1.
Determination of alkaline metals using emission flame photometry]". Pharmazie (in
German). 28 (4): 238–9. PMID 4716605 (https://pubmed.ncbi.nlm.nih.gov/4716605).
5. Stefánsson A, Gunnarsson I, Giroud N (2007). "New methods for the direct determination of
dissolved inorganic, organic and total carbon in natural waters by Reagent-Free Ion
Chromatography and inductively coupled plasma atomic emission spectrometry". Anal.
Chim. Acta. 582 (1): 69–74. doi:10.1016/j.aca.2006.09.001 (https://doi.org/10.1016%2Fj.ac
a.2006.09.001). PMID 17386476 (https://pubmed.ncbi.nlm.nih.gov/17386476).
6. Mermet, J. M. (2005). "Is it still possible, necessary and beneficial to perform research in
ICP-atomic emission spectrometry?". J. Anal. At. Spectrom. 20: 11–16.
doi:10.1039/b416511j (https://doi.org/10.1039%2Fb416511
j).|url=http://www.rsc.org/publishing/journals/JA/article.asp?
doi=b416511j%7Cformat=%7Caccessdate=2007-08-31
Bibliography
Reynolds, R. J.; Thompson, K. C. (1978). Atomic absorption, fluorescence, and flame
emission spectroscopy: a practical approach. New York: Wiley. ISBN 0-470-26478-0.
Uden, Peter C. (1992). Element-specific chromatographic detection by atomic emission
spectroscopy. Columbus, OH: American Chemical Society. ISBN 0-8412-2174-X.
External links
"Atomic Emission Spectroscopy Tutorial" (https://web.archive.org/web/20060501014235/htt
p://www.chem.vt.edu/chem-ed/spec/atomic/aes.html). Archived from the original (http://www.
chem.vt.edu/chem-ed/spec/atomic/aes.html) on 2006-05-01.
Media related to Atomic emission spectroscopy at Wikimedia Commons
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