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Lecture

12ICP.pdf

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Department
Chemistry
Course
ENCH 213
Professor
Diane Beauchemin
Semester
Fall

Description
Inductively coupled plasma spectroscopy Optical emission spectroscopy (OES) Mass spectrometry (MS) Effect of temperature on atomic spectroscopy • Boltzmann distribution • relative population of different states (excited over ground) at thermal equilibrium • where: T = temperature (K), k = Boltzmann constant = 1.381 x 10 -2J/K • atom may have more than one state at a given energy • number of states at each energy called degeneracy The Boltzmann distribution describes a) the relative error of different states at thermal equilibrium. b) the relative populations of different states at thermal equilibrium. (ground and excited) c) the relative populations of different states at chemical equilibrium. Flame are not widely used for AES • flame is not efficient at exciting ground-state neutral atoms ◦ poorer detection limit than FAAS • very susceptible to change in flame temperature ◦ most atoms are in the ground state ▪ at 2600°K >99.98% Na atoms in ground state ▪ <0.02% Na atoms in excited states ▪ 4% increase in T (to 2610°K) Inductively coupled plasma (ICP) • ICP =Ar ionized at high T plasma = partiallyionized gas → at these hightemperatures, the analyte is not onlyatomized but also ionized seriumatoms emit inthe red, while ions emit inthe blue → dependingonwhat lookingfor look at different places infllame Argon plasma generation • quartz torch made of 3 concentric tubes ◦ plasma gas generates the plasma and isolates it from torch wall (12- 15 L/min) ◦ auxiliary gas positions the plasma inside the torch and prevents melting of inner tubes (0-2 L/min) ◦ nebulizer gas carries sample aerosol into heart of plasma (0.8-1.2 L/min) Fragile:made ofglass Polychromator • plasma light is first dispersed in the vertical plane • the grating then disperses light in the horizontal plane • a charge injection device allows simultaneous detection of all elements Other polychromator • concave grating • 35 charge coupled devices (CCDs) detectors • no moving part Features of ICP-OES • sample uptake = 1-3 mL/min • applied power = 1-2 kW ◦ much higher T (6,000-10,000°K) tha
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