H 2 2100 2900 2900 hc ch 2200 3100 3200 ch 4 1800

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H 2 2100 2900 2900 HC CH 2200 3100 3200 CH 4 1800 2700 N/A (Flame temperatures are in degrees Centigrade) Hotter flames are needed for refractory elements (those with high vaporization temperatures) or to decompose species such as metal oxides or hydroxides. When a hotter flame is required, the acetylene–nitrous oxide combination is usually used (flame temp: 2900–3100K) 2) Graphite furnace cell path— Graphite furnace o ff ers greater sensitivity than a flame and requires a smaller volume of sample. A graphite furnace (at ~2000K) confines the atomized sample in the optical path for a residence time of several seconds resulting in high sensitivity. Data Treatment: Calibration Curve: Usually make a "best fit" plot using di ff erent concentrations of standards and their absorbances. For example: Copper in sample: using standards and linear regression curve. Standards Std1 1.0 ppm Abs 0.046 Std2 3.0 ppm Abs 0.168 Std3 5.0 ppm Abs 0.281 Std4 7.5 ppm Abs 0.401 Std5 10 ppm Abs 0.529 unknown reading : Abs= 0.156 Conc = ? What if we had taken an absorbance reading of 0.769?
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(ii) Atomic emission spectroscopy (AES): overview Similar to AAS but no light source (HC) is needed. Some of the atomized atoms are promoted to excited electronic states by collisions with other atoms. The excited atoms emit their characteristic radiation as they return to their ground state. an emission technique Allows simultaneous analysis of di ff erent species. Several methods of excitation are possible: flame, a spark, or Inductively coupled Plasma (ICP). The other methods for excitation are not as e ffi cient in exciting the analyte (atoms) as ICP. The analyte signal increases as the number of same excited atoms increases. As According to the Boltzman Distribution: N * /N o = (g * /g o ) e - Δ E/RT COMPARISON OF AAS vs AES Atomic absorption (AAS) an absorption technique one analyte at a time cheaper analysis than AES requires analyte specific HC lamp source can use a flame or graphite furnace to heat sample works with metals and a few metalloids some matrix e ff ects
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  • Fall '11
  • Tarr
  • Atom, pH, atomic absorption, atomic absorption spectroscopy, atomic absorption spectrometry, graphite furnace

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