Chromatography

Mobile phase

liquid or gas solvent flowing through the column

Stationary Phase

substance that is retained in the column and performs the separation

What determines the retention time of a substance in chromatography?

how much time a species spends in the mobile phase

eluent

the mobile phase as it enters the system

Eluate

the mobile phase + analytes as it exits the system

Adsorption Chromatography

Solid stationary phase that adsorbes analytes at different strengths.
Mobile phase is liquid or gas.

Partition Chromatography

Liquid stationary phase bonded to the surface of an open column.
Analyte equilibrates between the stationary and mobile phases.

Ion-Exchange Chromatography

Solid phase: charged ions covalently attached to a resin. Oppositely charged molecules are maintained.

Mobile phase is a liquid.

Molecular (Size) Exclusion Chromatography

Solid phase forms a mesh with pores that separate molecules by size.

Mobile phase is liquid or gas.

What is the most selective type of Chromatography?

Affinity chromatography

Affinity chromatography

Specific interactions between analyte and a second molecule covalently attached to the stationary phase.

Chromatogram

a plot of detector response vs elution time or volume

Retention time (tr)

time from the injection of a mixture on the column to the appearance of a compound at the detector

Retention volume (Vr)

the volume of the mobile phase required to elute a particular compound from the column

Resolution

how far apart two bands are relative to their widths

what increases resolution?

column length

what is the minimum resolution for quantitative analysis?

1.5

What does gas chromatography separate?

volatile compounds

Gas Chromatography

Mobile phase is gas
Stationary phase is solid or liquid
Used for analytes with low boiling points

HPLC

uses high pressure to force solvent through closed columns

in HPLC what type of particles get the best resolution?

smaller particles

Normal-phase chromatography (HPLC)

uses polar stationary phase and a less polar solvent (more polar solvents have higher eluent strength)

Reversed-phase chromatography (HPLC)

stationary phase is nonpolar or weakly polar and the solvent is more polar (less polar solvents have higher eluent strength)

Gradient elution

mobile phase composition changes over time progressively eluting more solvents

Isocratic elution

solvent composition remains constant