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14 Cards in this Set
- Front
- Back
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Gas Chromatography
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gaseous analyte is transported through a column by a gaseous mobile phase, called a carrier gas
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Properties of an open tubular column
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1) Very high resolution
2) Very small sample size needed |
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Which variable of the van Deemter Eq is very small in open tubular columns
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A
b/c there are almost no multiple paths |
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When you decrease the diameter of a column you do what to the resolution (think van Deemter and retention times)
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You increase the resolution b/c you have decreased Cμx (less retention/equlibration time)
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how is the resolution proportional to the number of theoretical plates (formula)
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resolution is ∝√N and therefore to to the sqrt of the column length
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Why is the resolution of a longer column better?
(This is easier to answer then you think) |
There are more theoretical plates (N)
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How is stationary phase from the column prevented from bleeding into the detector?
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It's bonded to silica and crossed linked to its self
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Properties of a Pack Column
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1) broader peaks, less resolution, longer retention times
2) greater sample capacity |
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Why do you want uniform particle size in a packed column?
(think van Deemter) |
b/c you decrease the path length i.e. A in van Deemter
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Why do you want small particle size in a packed column?
(think van Deemter) |
b/c you decrease the equlibration time i.e. Cμx in van Deemter
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molecular branching does what to a molecules boiling pt?
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decreases the boiling point
(less van der Wal's interactions) |
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What does boiling point have to do with GC?
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Boiling pt is a good determinate of when molecules will come off the column.
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Kovat's retention index, I, relates the retention time, Tr, of a molecule to those of....
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linear alkanes
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Why do we use temperature programming?
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decreases the retention time
and sharpens peaks especially for late eluting peaks |
