Chromatography
• Chromatography is used in separating mixtures
• Examples of chromatography are thin-layer chromatography and paper chromatography
• Mobile Phase- Where the molecule can move, this is often a liquid
• Stationary Phase- where the molecules cannot move, in paper chromatography the stationary phase is chromatography paper
• All types of chromatography works using the same basic principle:

o The mobile phase moves through/over the stationary phase
o The different components of the mixtures require different amounts of time in the mobile phase and stationary phase
o The component which spend a greater amount of time in the mobile phase travel faster or further
o It is the different times which separate out the components of a mixture
Investigating the Pigment in Leaves
• All plants contain multiple different photosynthetic pigments in their leaves
• Each pigment absorbs a different wavelength of light, therefore having multiple different kinds of pigment enables a wider spectrum of wavelengths that can be absorbed
• Some plants also have additional pigments that allow the plants to have different characteristics, for example a pigment which allows the leaves survive excessive UV radiation
• Different species of plant have different proportions and mixtures of these pigments
• A sample of pigments can be extracted from the leaves of a plant and separated using paper of thin layer chromatography
• Pigments found in the mixture can be determined by their Rf value where the value is the distance of a substance which has moved through the stationary phase in relation to the solvent
Rf = Distance Moved by substance
Distance moved by solvent
Investigating the activity of dehydrogenase in chloroplast
• In photosystem 1, NADP is the oxidising agent in that it accepts electrons and is therefore reduced
• The reaction is catalysed by dehydrogenase enzyme
• The activity of the reaction can be determined by the adding a redox indicator dye to extract the chloroplasts
• The dye accepts electrons just like the NADP and gets reduced by the dehydrogenase in the chloroplast
• As the dye gets reduced there will be a colour change e.g. dye DCPIP changes from blue to colourless when reduced
• The rate of dehydrogenase activity is measured by the colour change of the dye, for example the DCPIP changing to colourless. A colorimeter is used to measure the absorbance of a solution where a coloured solution will absorb more light than a colourless one.