chromatography Flashcards
what is chromatography
technique for the separation of a mixture by passing it in a solution or suspension through a medium in which the compounds move at different rates
what is happening in the stationary phase
the substance has affinity to the molecules in the mixture. the greater the affinity the shorter the distance it moves with the mobile phase
what is happening in the mobile phase
susbtance that allows molecules to move through the stationary phase. can be a form liquid or gas. more soluble products move further with the mobile phase
how can you visualise colourless substances
- UV light
- developing agent/ stain e.g. amino acids - ninhydrin, aromatic compounds - iodine stain
what does the Rf value show
how far the sample has run
Rf calculation
distance from start line to the middle of the ink spot/distance from the start line to the solvent front
what is thin layer chromatography
metal plate is coated with a thin layer of silica and solvent moves up the plate. this is dried in a fume cupboard to reduce toxic fumes. the chemical traces are viewed using a UV lamp. Distance travelled is measured. A developing agent can be added e.g. iodine, to allow the traces to be seen by the eye
what is column chromatography
vertical column is packed with a solid powdered substance (stationary phase). a solvent containing the mixture being analysed is added and moves down the column (mobile phase)
what does column chromatography show
Varying affinities of the molecules present mean they drain out of the column at different times, so are collected as separate samples. time taken to drain out of the column is the retention time.
what do retention times show
retention times allow the individual molecules in the mixture to be identified
what is gas chromatography
thin tube is packed with a powdered substance (stationary phase). A high-pressure gas is passed through this tube (mobile phase). this separates mixtures of volatile liquids. this is fed into the gas chromatography machine as vapours. records retention rate
what is the GC-MS
combination of gas chromatography and mass spectrometry, allowing for an advanced molecule analysis. the molecules present are separated using the gas chromatography technique. Each molecule present is fed directly into a mass spectrometer so it can be accurately identified
what are the benefits of using GC-MS
- much faster analytical process
- produces more accurate results for molecule analysis and identification
