atomic emission spectroscopy.ppt

7/27/2019 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

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