Chromatography Flashcards
What is chromatography used for
It is used to separate out mixtures
What is the stationary phase in chromatgrophy
It is either paper chromatography which is made out of cellulose or a thin layer chromatography plate (a sheet of plastic coated with a thin layer of silica gel.)
What is the mobile phase
It is the solvent (often water for polar molecules and ethanol for non polar molecules)
What does the mobile phase do to the stationary phase
It flows across the stationary phase carrying the biological molecules with it.
What is the thin layer chromatography plate made pout of
It is a glass slide covered by a layer of a substance such as SiO2 (silicon dioxide), which acts as a stationary phase. This is adsorbent and substances tend to accumulate on its surface.
Where is the line draw on the TLC and with what and what is the vertical line for
A line is drawn near the bottom of the plate using a pencil. The vertical line is added to indicate where the sample should be placed.
Where is the sample placed and with what
The sample is placed by dipping a small glass tube into the sample and lightly touching it to the plate at the vertical line.
What happens once the tlc plate has had the sample added
It is placed in the solvent jar and the lid secured on, to perevent evaporation of the solution
What is it important to make sure that (pencil line)
That the level of the solvent is below the pencil line
What happens as the solvent rises
Substances are carried along and adsorb to the stationary phase to different extents. Some substances bind strongly whereas others bind weakly and are carried further.
What is the formula for Rf
Distance travelled by pigment/ distance travelled by solvent front
What determines how quickly the molecules travel across the stationary phase
Solubility in the solvent - the more soluble molecules travel further
Polarity - due to the exposed OH groups in the paper plate, highly polar solutes tend to stick to the surface and move slowly whereas non-polar solutes will travel quickly
Size (paper chromatography only)
