Chromatography Flashcards
Chromatography
a method for separating mixtures composed of two or more compounds
What are the phases in chromatography? (2)
- stationary phase
- mobile phase
Stationary Phase
remains fixed in place
Mobile Phase (2)
- moves along the stationary phase
- carries the components of the mixture along the stationary phase
What is the movement of components in chromatography controlled by? (2)
- the strength of their interactions with the stationary and mobile phase
- the difference in polarity
Adsorption
the adhesion of atoms or molecules onto a surface
What are examples of adsorption chromatography? (3)
- thin layer chromatography
- column chromatography
- gas chromatography
Thin Layer Chromatography
consists of a stationary phase coated on a glass or plastic plate and a mobile phase
What is the stationary phase in thin layer chromatography?
a thin layer of solid silica gel or alumina
What type of solvent is used as a developing solvent?
a volatile solvent
Why is a volatile solvent used as a developing solvent?
it dries faster, so the plate can be visualized sooner
How is thin-layer chromatography carried out? (4)
- the samples are spotted on the edge of the plate
- the plate is placed in a jar with a developing solvent
- the solvent moves up via capillary action
- the components travel up the plate at various speeds
Rf Value
a ratio of how far a compound has traveled up the TLC plate relative to how far the solvent has traveled
Is Rf value an intrinsic property?
no
Silica gel (2)
- granular porous form of silica
- has high polarity and strong affinity towards polar compounds
What is TLC used for? (2)
- identification
- determining the number of compounds present in a mixture
Column Chromatography (2)
- similar to TLC, but the stationary phase is packed in a long glass column
- a large amount of sample can be separated
What do polar compounds typically do in chromatography?
adsorb to the stationary phase, resulting in a low Rf value
What do nonpolar compounds typically do in chromatography?
travel with the mobile phase, resulting in a high Rf value
What are the steps of column chromatography? (5)
1) solid absorbent is packed into a class column that has a small amount of glass wool at the bottom
2) The liquid sample is loaded onto the column of silica
3) Eluant flows down the column either by gravity or an applied external pressure
4) Components in the sample mixture are eluted along with the eluant
5) The eluate can be collected as separate fractions
