Exam 2: Gas and Liquid Chromatography Flashcards
(122 cards)
What is gas chromatography?
gaseous analyte is transported through the column by a gaseous mobile phase.
A gaseous mobile phase is also referred to as _________ ____.
carrier gas
Describe the GC process.
1) a volatile liquid or gas sample is injected through a septum into the heated port
2) Sample evaporates and is pulled through the column with a carrier gas
3) the column is heated to provide sufficient vapor pressure to elute analytes
4) analytes separately flow through a heated detection for observation.
The mobile phase in GC is usually a (solid/liquid/gas).
gas
What is usually the stationary phase in GC?
nonvolatile liquid, but sometimes a solid.
What is the usually the analyte in GC?
gas or volatile liquid
Name the three different carrier gasses.
- He
- N2
- H2
What does the choice of carrier gas depend on?
the detector and the desired separation efficiency and speed
What are the advantages of using open tubular column rather than packed columns?
- higher resolution
- shorter analysis time
- greater sensitivity
- lower sample capacity
Name the three types of open tubular columns.
- Wall-coated open tubular column (WCOT)
- Support coated open tubular column (SCOT)
- Porous-layer open tubular column (PLOT)
Describe a wall-coated open tubular column (WCOT)
A 0.1 -5 µm film of liquid stationary phase on the inside wall of the column

Describe a support-coated open tubular column
(SCOT)
solid particles coated with liquid stationary phase and attached to the inner wall.

Describe a porous-layer open tubular column (PLOT)
solid particles are the active stationary phase on inside wall of column

(narrow/wider) columns provide higher resolution than (narrow/wider) columns.
narrower; wider
what are the disadvantages of a narrower column?
require higher operating pressure and have less sample capacity.
What are the two types of columns?
1) Open Tubular Column
2) Packed Column
What is the range of a open tubular columns inner diameter, length, and thickness of stationary phase?
diameter: 0.10 to 0.53 mm
length: 10-100 mm
thickness: 0.1 -5 µm thick
Diameters greater than ____ mm tend to overload the vacuum system of a mass spectrometer.
0.32
what does increasing the thickness of the stationary phase of an open tubular column do at a constant linear velocity.
increases the retention time and sample capacity and increases resolution of early eluting peaks with a retention factor of k ≤ 5
Thick films of staionary phase can _______ tailing.
reduce
thick films of staionary phase can __________ bleed (decomposition and evaporation)
increase
List the three different types of open tubular columns in order of increasing surface area.
WCOT < SCOT < PLOT
List the three different types of open tubular columns in order of greater separation efficiency.
PLOT < SCOT < WCOT
For an Open tubular column, Rs increases with a ________ column
longer
