March14_2005_2pp

March14_2005_2pp - March 14, 2005 Its Pi Day! (3.14 at...

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1 March 14, 2005 ¾ It’s Pi Day! (3.14 at 1:59) ¾ Office hours: ¾ Today ¾ Until 2:15 pm ¾ A223 Cook ¾ Exam #2: Wednesday at 7 pm! 2 AAS versus AES? ± AAS: Absorbance N p ± AES: Emission Int. N q But: concentration N T For a thermal population distribution, we use the Boltzmann Equation to relate N p and N q to N T : N q = g q e -(E q /kT) N T Σ (g i e -(E i /kT) ) Where: T = absolute temp., k = Boltzmann’s constant, and g i = statistical weight of state i
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3 Impact of Boltzmann ± Population of any state is temperature dependent ± BUT: even at high temperatures, N q /N T is usually very small (~10 -3 -10 -7 @ 3000 K) ± So: N p (ground state population) N T (99+% of atoms are in the ground state) - So: absorbance N T - And: absorbance is relatively temp indep ± Also: N q /N T is very temperature sensitive, but at constant temperature: N q = N T K conc ( I) 4 Instrumentation ± Let’s start with AAS: Source Atom Cell I o I λ Selector Detector Sample -lets first look at Atom Cells and how a sample is converted to gas phase atoms
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5 Obtaining Gas Phase Atoms
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This note was uploaded on 05/15/2010 for the course CHEM 221 taught by Professor Joelgoldberg during the Spring '10 term at UVM.

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March14_2005_2pp - March 14, 2005 Its Pi Day! (3.14 at...

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