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Lecture 33

CHEM 212 Lecture 33: Nov 22, 2016Premium

3 pages83 viewsFall 2016

Department
Chemistry
Course Code
CHEM 212
Professor
Hamilton M.Coreen
Lecture
33

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Chem 212!
Nov. 22/ 2016!
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Resolution:!
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R= (tr)2-(tr)1/0.5(W1+W2) = delta tr/Wavg !
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Van Deemter Equation:!
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H proportional A+ B/mu + cmu!
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mu= flow rate!
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two terms are flow rate dependent!
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-every molecule has a dierent path length to get from one end of the column to the other side of the column!
#-> gives width to peak!
##- Eddy diusion in a chromatographic column!
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#########If all particles took the same amount of time!
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###########Range of path lengths gives width!
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#####time!
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-pushing them through faster does not aect therefore not flow rate dependent!
-GC does not have an A term bc there is no little p articles, its walls that are coated, therefore eddy term is very
minor is GC!
-Van deemter eqn works for both GC and liquid chromatography!
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A # Ce dp!
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B-term:!
-longitudinal diusion!
-diuse from low concentration to high concentration!
-you add broadness to the peaks if you are slow at injecting the sample, our labs have autosamplers !
-Faster flow rate the less time sample spends on column, therefore less diusion!
#--> Faster flow rates means less broadening due to eddy diusion!
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#########-slight diameter dependence on B??!
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