Atomic Absorption Notes

Less signal variation due to temperature e ff ects

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less signal variation due to temperature e ff ects for a graphite furnace, it confines the sample to light path for longer times giving enhanced signal, greater sensitivity, less sample requirements Atomic Emission (AES) AES is more expensive ICP instrumentation somewhat more complicated to operate AES require less sample preparation and gives simultaneous analysis doesn't require di ff erent lamps( light sources). Uses PDA or a series of detectors to monitor di ff erent wavelengths (di ff erent element ID's) Interferences in Atomic Absorption Spectroscopy The detection limit is the concentration of an element that gives a signal equal to twice the peak-to-peak noise level of the baseline. Interference is any e ff ect that changes the signal when analyte concentration remains unchanged. Types of Interferences 1. Spectral – unwanted signals overlapping analyte signal 2. Chemical – chemical reactions decreasing the concentration of analyte atoms 3. Ionization – ionization of analyte atoms decreases the concentration of neutral atoms
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What about interferences? How do we over come interferences? Chemical interference -- most common in AA, due to a thermally stable compound present, which influences the analyte's energy absorption. Two ways of controlling: use hotter flame or add a releasing agent (something that ties up the competing species). Ionization interference- - flame too hot causes ionization of analyte. Add alkali metals, which have lower ionization potentials to suppress analyte ionization. Matrix interferences -- due to nature of sample, the junk in it! Dilute the sample if possible to reduce e ff ects or use "method of standard addition", the sample is spiked with a standard, readings plotted and the concentration is extrapolated from plot.
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  • Fall '11
  • Tarr
  • Atom, pH, atomic absorption, atomic absorption spectroscopy, atomic absorption spectrometry, graphite furnace

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