Chromatography Flashcards
what factor determines a substance’s affinity to the mobile/stationary phase
- the polarity of the substance and the stage
- polar phase attract polar substances
- non-polar phase attract non-polar substances
what are the mobile and stationary phase of thin layer chromatography (TLC)
- stationary phase = thin silica gel coating (polar)
- mobile phase = suitable liquid solvent e.g. cyclohexane (non-polar)
describe how to carry out a TLC
- draw a pencil line approx 1cm from the bottom of the plate
- place a small drop of the sample on the pencil line
- stand the plate in a beaker containing solvent that doesn’t reach the pencil line
-cover the beaker so solvent doesn’t evaporate out of beaker and allow solvent to travel up plate - remove plate from beaker, mark the solvent front and spray with ninhydrin powder to view different components
how can you make components more visible when doing chromatography
- ninhydrin powder
- Iodine stain
- UV light
how to calculate Rf value
distance travelled by spot/distance travelled by solvent front
what is a common use of TLC
- separating a mixture of amino acids
why do components separate during TLC
- components will separate because they have a differing affinity and solubility to the polar stationary phase and the non polar mobile phase.
when is two way chromatography used?
- to separate substances which have very close Rf values
what are the mobile and stationary phase of column chromatography?
- stationary phase = solid silica (polar)
- mobile phase = suitable liquid solvent e.g. cyclohexane (non-polar)
describe how to carry out column chromatography
- the mixture moves down the column and the different components travel at different speeds according to their affinity to both the stationary and mobile phase
- allows for the collection of each component in different beakers
what are the mobile and stationary phase of gas-liquid chromatography?
- stationary phase = thick viscous liquid e.g. oil (non-polar) or silica gel (non-polar) coated on the lining of the column
- mobile phase = an inert gas e.g nitrogen (it carries the components through the column)
how does gas-liquid chromatography work?
- the mixture is carried through the column and the components travel at different speeds depending on their affinity to the stationary phase
- the components are detected as they leave the column and the time it takes for them to exit is recorded as their retention time
how do you determine the number of components in a mixture after gas-liquid chromatography?
- its equal to the number of peaks on the spectrum
how do you identify a component in a gas-liquid chromatography
- its retention time can be matched to a known value using a GC-MS (gas chromatography mass spectrometer)
how do you determine the amount of each component in a mixture after gas-liquid chromatography?
- the area under the peak is proportional to the concentration of a substance in the original sample
what is the main use of gas-liquid chromatography?
- used to test the urine of athletes for doping/drugs
