Gang Wang Instrumental_Week6&7_CH8_11-2010

Gang Wang Instrumental_Week6&7_CH8_11-2010 -...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 8: An Introduction to Optical Atomic Spectrometry Optical Atomic Spectra Atomization Methods Sample Introduction Methods - Optical Spectrometry as opposed to MS - Optics are similar to Molecular Absorption and Fluorescence Spectrometry Sample is atomized (gaseous atoms/ions) absorption or emission measured Basics Generally solution samples (sometimes solids) Aspirate sample into flame or plasma Or heat sample to atomize Observe emission from excited state (AE) Or use light source to measure atomic absorption (AA) Or use light source to generate atomic fluorescence (AF)
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Atomic spectra are line spectra Some prominent lines in the atomic spectrum of mercury (Hg) Other atomic spectra–many lines per spectra, lines are very narrow
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
λ in Å • Similar pattern between atoms but different spacing • Spectrum of ion different to atom • Separations measured in electronvolts (eV) 1eV =1.602x10 -19 C ´ 1V(J / C) = 1.602x10 -19 J = 96. 484 kJ × mol-1 • As # of electrons increases, # of levels increases Emission spectra become more complex Li 30 lines, Cs 645 lines, Cr 2277 lines Resonance fluorescence lines Others involve the ground involve a two state step process
Background image of page 4
Atomic line widths are important when considering spectral resolution, absorption experiments, etc. About 10 -5 nm or 10 -4 Å
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Doppler broadening occurs due to the observed compression and expansion of light waves as an atom moves toward or away from the radiation source
Background image of page 6
Other broadening effects include pressure or collisional broadening (10 4 Å) broadening from uncertainty effects Temperature effects from Boltzmann equation N = population of state P = statistical factor E j = energy difference k = Boltzmann constant T = temp Note similarity of spectra
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The sample must be converted to its atomic state which can be done at high temp. in a flame, furnace, plasma, arc or spark Introducing the sample to the high temperature source can be tricky
Background image of page 8
Pneumatic nebulizers a) concentric tube b) cross flow c) fritted disk d) Babington Sample introduction for solutions: 1) Pneumatic nebulizers 2) Ultrasonic nebulizers 3) Electrothermal vaporizers 4) Hydride generation 3 BH 4 + 3 H + + 4 H 3 AsO 3 Æ 3 H 3 BO 3 + 4 AsH 3 + 3 H 2 O 5) Cold vapor generation Hg 2+ + Sn 2+ Æ Hg o + Sn 4+
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Solid sample introduction: 1) Laser ablation–zap sample with laser and sweep atoms into flame/plasma 2) Direct sample insertion – place sample directly in atomizer (e.g. furnace) 3) Electrothermal atomizers – electrically heat graphite or tantalum boat 4) Arc/Spark ablation–coat sample on electrode or place in electrode well or cup 5) Glow discharge technique–see p 227 Atomic Fluorescence Spectrometry Atomic Absorption (AA) Atomic Fluorescence (AF)
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/13/2012 for the course UML 84.314 taught by Professor Ryan during the Fall '11 term at UMass Lowell.

Page1 / 50

Gang Wang Instrumental_Week6&7_CH8_11-2010 -...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online