organic - chromatography Flashcards
how does basic paper chromatography work
-components in a mixture are dissolved in a fluid - solvent
-will have different affinities for either the stationary phase or the mobile phase
what is the stationary phase
-attracted to the paper so will move the least
what is the mobile phase
-attracted to the liquid solvent - so will move the furthest
what is retention factor
distance moved by compound / distance moved by solvent
what is thin layer chromatography
-analyse small samples via separation
-often amino acids
what is the stationary phase in TLC
-often the thin metal sheet coated in alumina or silica
-solute molecules adsorb on the surface
-depending on the strength of interactions with the stationary phase, the separated components will travel particular distances through the plate
-the more they interact with the stationary phase the more they will stick to it
what is the mobile phase of TLC
-flows over the stationary phase
-it is a polar or non-polar solvent that carries components of the compound being investigated
-polar solvents -water or alcohol
-non-polar - alkanes
-separate by relative solubility
what can be used to locate the spots in TLC
If the sample components are not coloured, then we can locate the spots on the chromatogram and draw around them in pencil
To locate the spots we can use:
-UV light
-Ninhydrin (carcinogenic)
-Iodine vapour
what is the standrad method for TLC
a) Wearing gloves, draw a pencil line 1 cm above the bottom of a TLC plate and mark spots for each sample, equally spaced along line.
b) Use a capillary tube to add a tiny drop of each solution to a different spot and allow the plate to air dry.
c) Add solvent to a chamber or large beaker with a lid so that is no more than 1cm in depth
d) Place the TLC plate into the chamber, making sure that the level of the solvent is below the pencil line. Replace the lid to get a tight seal.
e) When the level of the solvent reaches about 1 cm from the top of the plate, remove the plate and mark the solvent level with a pencil. Allow the plate to dry in the fume cupboard.
f) Place the plate under a UV lamp in order to see the spots. Draw around them lightly in pencil.
g) Calculate the Rf values of the observed spots.
why is the line drawn in pencil on the TLC
-will not dissolve in the solvent
why are gloves worn when conducting TLC
-prevent contamination on the paper
-hands are made of proteins
how dos the depth of the solvent affect the TLC
- if the solvent is too deep then it will dissolve the sample spots from the plate
why is a lid used in TLC
-to prevent evaporation of the toxic solvent
how do you get more accurate results
-if the solvent is allowed to rise to the top of the plate #-the Rf value can be calculated if the solvent front does not reach the top of the plate
what is column chromatography
-long vertical glass tube or lab burette is used
-inert solid is the stationary phase which is placed in the column
-a liquid solvent phase - mobile phase - is added to the column until it is saturated with solvent
-sample mixture is dissolved in the solvent and introduced at the top of the column - pipette often used to carefully add the solvent
-more solvent is addded
how does polarity affect how far the compounds move
-if the solvent is more polar the SiO2 then polar molecules are more attracted to the solvent - if move faster
-if ore slower then non-polar ad are more attracted to the SiO2
if the solvent is less polar than SiO2 then non-polar molecules move fastest and are attracted to the solvent
-if they are slower then will move less as non-polar molecules would be attracted to the SiO2
-more polar to TLC - move less
-non-polar/less polar to tlc move more
