IA CH 28

What is gas-liquid chromatography used for?
Species that are somewhat volatile and thermally stable.
What is liquid adsoption chromatography used for?
Nonpolar low to moderate molecular mass organics and particularly isomeric organic species.
What is liquid-liquid partition chromatography used for?
Molecular species that are nonvolatile or thermally unstable
What is reversed-phase partition chromatography used for?
Most low to moderate molecular mass organic compounds that are nonvolatile or thermally unstable.
What is ion exchange chromatography used for?
Substances that are ionic or that can be derivatized to form ions.
What is gel permeation chromatography used for?
High molecular mass compounds that are soluble in nonpolar solvents
What is gas-solid chromatography used for?
Low molecular mass nonpolar gases.
What is gel filtration chromatography used for?
High molecular mass hydrophilic compounds.
What is ion-pair chromatography used for?
Small organic and inorganic ions.
Define isocratic elution
the solvent composition is held constant throughout the elution.
Define gradient elution
two or more solvents are used and the composition of the mobile phase is changed continuously or in steps as the separation proceeds.
Define stop flow injection
the flow of solvent is stopped, a fitting at the head of the column is removed, and the sample is injected directly onto the head of the column. The fitting is then replaced and pumping is resumed.
Define reveresed-phase packing
is a nonpolar packing that is used in partition chromatography with a relatively polar mobile phase.
Define normal phase packing
the stationary phase is polar and the mobile phase is relatively nonpolar.
Define ion pairing chromatography
a large organic counter-ion is added to the mobile phase as an ion-pairing reagent. Separation is achieved either through partitioning of the neutral ion-pair or as a result of electrostatic interactions between the ions in solution and charges on the stationary phase resulting from adsorption of the organic counter-ion.
Define Ion chromatography
the stationary phase is an ion-exchange resin, and detection is ordinarily accomplished by a conductivity detector.
Define bulk property detector
responds to some property of the mobile phase (such as thermal or electrical conductivity) that is altered by the presence of analytes.
Define Solute property detector
responds to some property of analytes, such as absorption or fluorescence.
Define sparging
a process for removing dissolved gases from a solution by sweeping the liquid with a stream of fine bubbles of an inert gas of low solubility.
Describe the fundamental difference between ion-exchange and size exclusion chromatography.

In size-exclusion chromatography separations are based upon the size, and to some extent the shape, of molecules with little interactions between the stationary phase and the sample components occurring.

In ion-exchange chromatography, in contrast, separations are based upon ion-exchange reactions between the stationary phase and the components of the sample in the mobile phase.

The length of the column L is the distance from:
the sample entrance to the detector
The purpose in running a non retained species on a column is to measure:
The average rate of migration of the mobile phase
As the plate count, N, increases for a column:
the column efficiency increases
Draw block diagram of a liquid chromatography system
As seen on page 819.
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