chapter 9 atomic absorption and atomic fluorescence spectrometry

Chapter 9

Atomic Absorption and Atomic Fluorescence Spectrometry

Atomic SpectroscopyAtomization is by

far the most critical step in atomic spectroscopy.

In AAS and AFS there are two factors involved.

The intensity of light source.

The probability of transition.

Flame Atomization

Flame Structure

Flame Atomizer

Flame Atomizer

Electrothermal AtomizersGraphite furnace atomic absorption spectrometry (GFAAS) is also

known by various other acronyms, including electrothermal atomic absorption spectrometry (ETAAS).

An ideal graphite furnace should fulfill the following requirements: A constant temperature in time and space during the interval in

which free atoms are produced Quantitative atom formation regardless of the sample

composition Separate control of the volatilization and atomization processes High sensitivity and good detection limits

A minimum of spectral interferences

Specialized Atomization Techniques

Glow Discharge Atomization Hydride Atomization Cold-Vapor Atomization

Flame Atomic Absorption Spectroscopy

Radiation Sources Doppler Broadening Pressure BroadeningElectrodeless Discharge Lamps Source Modulation Hollow Cathode Lamps:

Spectrophotometers In general, the instrument must contain: Narrow bandwidth to isolate the line chosen for measurement Sufficient glass filter Interchangeable interference filters Good-quality ultraviolet/visible monochromators Photomultiplier tubes

SpectrophotometersSingle-BeamDouble-Beam

Spectral Interferences The Two-Line Correction Method The Continuum-Source Correction

Method Background Correction Based on the

Zeeman EffectBackground Correction Based on the

Source Self-Reversal

Chemical Interference

The equilibria of principle interest include:Formation of Compounds of Low

VolatilityDissociation Reactions Ionization

Calibration CurvesShould follow Beer’s Law

Standard Addition Method

InstrumentationSources: Hollow Cathode Lamp- only

observed the fluorescent signal during pulses

Electrodeless Discharge Lamp- produced intensities that exceed those of hollow cathode lamps

Lasers- ideal source with high intensities and narrow bandwidths

InstrumentationDispersive Instruments- They are made up of a

modulated source, an atomizer, a monochromator or an interference filter system, a detector, and a signal processor and readout.

 Nondispersive Instruments- They ideally are made up of a source, an atomizer, and a detector.

Advantages: Simplicity and low-cost instrumentation Ready adaptability to multi-element analysis High-energy throughput and thus high sensitivity Simultaneous collection of energy from multiple lines,

enhancing sensitivity

References www.anachemumu.se.htm www.aurora-instr.com/right.htm www.anachem.umu.se/jumpstation.htm www.anachem.umu.se/cgi/jumpstation.exe?AtomicSpectroscopy 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/

References www.dq.fct.unl.pt/QOF/Chroma.html www-ssg.chem.utas.edu.au/ www.yahoo.com/science/chemistry/chromatography/ www.onlinegc.com http://www.scimedia.com/chem-ed/analytic/ac-meth.htm http://www.scimedia.com/chem-ed/spec/atomic/aa.htm http://www.scimedia.com/chem-ed/spec/atomic/afs.htm http://www.cee.vt.edu/program_areas/environmental/teach/smprimer/aa/

aa.html#Features http://www.anachem.umu.se/aas/gfaas.htm http://www.agsci.ubc.ca/fnh/courses/food302/atomic/

aatomic03.htm#electro http://www.scpscience.com/products/AA/hollowlamps.asp http://las.perkinelmer.com/catalog/Product.aspx?ProductId=N3050691 http://elchem.kaist.ac.kr/vt/chem-ed/spec/atomic/aa.htm