Download - Atomic Emission Spectroscopy.ppt
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Atomic EmissionSpectroscopy.
Chem. 331
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Introduction
Atomic absorption is the absorptionof light by free atoms. An atomicabsorption spectrophotometer is an
instrument that uses this principle toanalyze the concentration of metalsin solution. The substances in asolution are suctioned into anexcited phase where they undergovaporization, and are broken downinto small fragmented atoms bydischarge, flame or plasma.
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Atomic Emission Spectroscopy
By exposing these atoms to such
temperatures they are able to jump
to high energy levels and in return,emit light. The versatility of atomic
absorption an analytical technique
(Instrumental technique) has led to
the development of commercialinstruments. In all, a total of 68
metals can be analyzed.
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Advantages of AA
Determination of 68 metals
Ability to make ppb determinations onmajor components of a sample
Precision of measurements by flame arebetter than 1% rsd. There are few otherinstrumental methods that offer thisprecision so easily.
AA analysis is subject to little interference.
Most interference that occurs have beenwell studied and documented.
Sample preparation is simple (ofteninvolving only dissolution in an acid)
Instrument easy to tune and operate
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Flame Emission andAtomic AbsorptionSpectroscopy(3 main types) Atomic Emission (with thermal
excitation), AES
Atomic Absorption, (with optical
photon unit) AAS
Atomic Florescence, AFS
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AES experiment set-up
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Three types of high-temperature
plasmas The inductively coupled plasma
(ICP).
The direct current plasma (DCP).
The microwave induced plasma
(MIP).
The most important of theseplasmas is the inductively coupledplasma (ICP).
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The Direct Current PlasmaTechnique The direct current
plasma is createdby the electronic
release of the twoelectrodes. Thesamples are placedon an electrode. Inthe technique solid
samples are placednear the dischargeto encourage theemission of thesample by the
converted gas
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Picture of an inductively-coupled
plasma atomic emission spectrometer
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A typical inductively coupled plasma
source called a torch
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Atomic Emission Spectroscopy Qualitative analysis is done using AES in the same
manner in which it is done using FES. Thespectrum of the analyte is obtained and comparedwith the atomic and ionic spectra of possible
elements in the analyte. Generally an element isconsidered to be in the analyte if at least threeintense lines can b matched with those from thespectrum of a known element.
Quantitative analysis with a plasma can be doneusing either an atomic or an ionic line. Ionic linesare chosen for most analyses because they areusually more intense at the temperatures ofplasmas than are the atomic lines.
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AES WITH ELECTRICALDISCHARGES
An electrical discharge between two electrodes can be used toatomize or ionize a sample and to excite the resulting atoms orions. The sample can be contained in or coated on one or bothof the electrodes or the electrode(s) can be made from theanalyte. The second electrode which does not contain theanalyte is the counter electrode.
Electrical discharges can be used to assay nearly all metals andmetalloids. Approximately 72 elements can be determined usingelectrical discharges. For analyses of solutions and gases theuse of plasmas is generally preferred although electricaldischarge can be used. Solid samples are usually assayed withthe aid of electrical discharges.
Typically it is possible to assay about 30 elements in a singlesample in less than half an hour using electrical discharges. Torecord the spectrum of a sample normally requires less than aminute.
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ELECTRODES FOR AES The electrodes that are used for the various forms
of AES are usually constructed from graphite.Graphite is a good choice for an electrode materialbecause it is conductive and does not spectrally
interfere with the assay of most metals andmetalloids. In special cases metallic electrodes(often copper) or electrodes that are fabricatedfrom the analyte are used.
Regardless of the type of electrodes that are used,a portion of each of the electrodes is consumedduring the electrical discharge. The electrodematerial should be chosen so as not to spectrallyinterference during the analysis.
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WAVELENGTH SELECTION ANDDETECTION FOR AES
Arc and spark instruments normallycontain non scanningmonochromators. Either a series ofslits is cut in the focal plane of themonochromator and aphotomultiplier tube is placed behindeach slit that corresponds to the
wavelength of a line that is to bemeasured, or one or morephotographic plates or pieces of filmare placed on the focal of the
monochromator.
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QUALITATIVE ANALYSIS WITH ARC ANDSPARK AES
Qualitative analysis is performed by
comparing the wavelengths of the
intense lines from the sample withthose for known elements. It is
generally agreed that at least three
intense lines of a sample must be
matched within a known element inorder to conclude that the sample
contains the element
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QUANTITATIVE ANALYSIS WITHARC AND SPARK AES.
Regardless of the type of detection usedfor the assay, the precision of the resultscan be improved by matrix-matching thestandards with the sample. Use of theinternal-standard method also improvesprecision. Usually a working curve isprepared by plotting the ratio or logarithmof the ratio of intensity of the standard'sline to the internal standard's line as a
function of the logarithm of theconcentration of the standard. Thecorresponding ratio for the analyte isobtained and the concentration determinedfrom the working curve.
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References www.anachem.umu.se/jumpstation.htm www.anachem.umu.se/cgi/jumpstation.exe?Atomic
Spectroscopy
www.anachem.umu.se/cgi/jumpstation.exe?OpticalMolecularSpectroscopy
www.minyos.its.rmit.edu.au/~rcmfa/mstheory.html
http://science.widener.edu/sub/ftir/intro_it.html
http://www.s-a-s.org/
http://www.chemsw.com
http://www.scimedia.com/chem-ed/spec/atomic/aa.htm
http://nercdg.org http://www.analyticon.com
www.lcgmag.com/
www.lcms.com/
www.dq.fct.unl.pt/QOF/Chroma.html
www-ssg.chem.utas.edu.au/
http://science.widener.edu/sub/ftir/intro_it.htmlhttp://science.widener.edu/sub/ftir/intro_it.html -
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References (Contd.) www.yahoo.com/science/chemistry/chromatograph
y/
www.onlinegc.com
http://www.aurora-instr.com
http://www.chem.ufl.edu/~itl/3417_s98/spectroscopy
/aes.htm http://www.rohan.sdsu.edu/staff/drjackm/chemistry/
chemlink/analytic/analyt1.html
http://www.cofc.edu/~deavorj/521/jpd521.htm
http://www.scimedia.com/chem-
ed/spec/atomic/aes.htm http://elchem.kaist.ac.kr/vt/chem-
ed/spec/atomic/aes.htm
http://www.chemistry.adelaide.edu.au/external/soc-rel/content/icp.htm
http://employees.oneonta.edu/schaumjc/chm361/iron.doc
http://www.scimedia.com/chem-ed/spec/atomic/aes.htmhttp://www.scimedia.com/chem-ed/spec/atomic/aes.htmhttp://www.scimedia.com/chem-ed/spec/atomic/aes.htmhttp://www.chemistry.adelaide.edu.au/external/soc-rel/content/icp.htmhttp://www.chemistry.adelaide.edu.au/external/soc-rel/content/icp.htmhttp://www.chemistry.adelaide.edu.au/external/soc-rel/content/icp.htmhttp://www.chemistry.adelaide.edu.au/external/soc-rel/content/icp.htmhttp://www.chemistry.adelaide.edu.au/external/soc-rel/content/icp.htmhttp://www.chemistry.adelaide.edu.au/external/soc-rel/content/icp.htmhttp://www.chemistry.adelaide.edu.au/external/soc-rel/content/icp.htmhttp://www.chemistry.adelaide.edu.au/external/soc-rel/content/icp.htmhttp://www.scimedia.com/chem-ed/spec/atomic/aes.htmhttp://www.scimedia.com/chem-ed/spec/atomic/aes.htmhttp://www.scimedia.com/chem-ed/spec/atomic/aes.htmhttp://www.scimedia.com/chem-ed/spec/atomic/aes.htm