RelativeResourceManager(8) - Continuation of optical atomic...

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Continuation of optical atomic spectrometry and UV-visible molecular absorption spectrometry Chem 420 September 24, 2008
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Spectrophotometers in AA z Source modulation helps remove emission from flame z AC signal can be high pass filtered to remove low frequency background prior to amplification z Chopper or modulated source z Instrument must have narrow enough bandwidth to see specific lines. z Filters or monochromators (1Å) z Single beam instruments z Double beam instruments z Why use a double beam instrument? How?
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Interferences in AA z Spectral interferences z From source—rare with narrow hollow-cathode sources z From flame—absorption or scatter by combustion products z Matrix—absorption or scatter by components of sample z Not common with flame atomization and can be avoided ± If interfering species is known then excess can be added to dilute out amount in sample matrix ± Standard addition z Chemical interferences z More common than spectral interferences z Compounds that have low volatility are formed with anions and reduce fraction of atomized sample z Can use protective agents such as EDTA z Dissociation equilibria z Ionization equilibria z Factor in higher temperature flames—significant concentration of free electrons
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Sample prep and calibration limitations of AA z Flame spectroscopies techniques require a liquid (aqueous) phase sample z Limits applicability in soil, tissue, mineral, etc. analysis z Electrothermal atomization allow direct atomization z Samples don’t have to be liquids z Calibration challenges z Does not follow Beer’s law z Every photon of light striking the detector must have an equal chance of absorption z Atomization efficiency varies with sample matrix and concentration and path length in flames (in particular) are non-uniform z Non-linear calibration curves z In spite of these issues, over 60 metals and metalloid elements can be detected with AA—powerful technique
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Atomic fluorescence spectroscopy z Useful for quantitative determination of elements z Has not found widespread use z Due more to advantages of AA and AE than problems with AF—developed earlier z Somewhat more sensitive for some elements, less sensitive for others z ppt sensitivity for mercury—better than flame AA, ICP-AE, and ICP-MS
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Atomic emission spectroscopy z Plasma, arc, and spark emission sources operate at higher
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This note was uploaded on 04/08/2010 for the course CHEM 420 taught by Professor Bailey during the Spring '08 term at University of Illinois at Urbana–Champaign.

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RelativeResourceManager(8) - Continuation of optical atomic...

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