6.3 Analysis

-a comparison between how far a component has moved compared to the solvent in thin layer chromatography

-the time taken for a component to travel from the inlet to the detector in a gas chromatograph

-it is fixed in place -it can be a liquid (e.g. in some gas chromatography systems where the mixture components have different attractions to each phase ) -it can also be a solid (e.g. in thin layer chromatography where the components of the mixture are absorbed by different amounts)

-moves in a definite direction -e.g. an inert gas in gas chromatography (GC) or a liquid solvent in thin layer chromatography (TLC)

-by each chemical in a mixture having a different attraction to each phase -e.g. a chemical that is very attracted to the mobile phase but not the stationary phase will travel a long way up, but a chemical that is very attracted to the stationary phase will not travel far

-to analyse organic compounds E.g. to check the purity of a sample or to determine the extent of a chemical reaction

-a thin piece of inert material -e.g. glass covered with an absorbent chemical such as aluminium oxide

-usually an organic solvent -the solvent will move in one direction vertically up the plate and develop the chromatogram

-as the lid reduces the rate at which the solvent is absorbed and allows for a better separation

Rf value= distance moved by component ——————————————————- distance moved by solvent

-how many chemicals make up the mixture

By either: -using data tables that list Rf values for a wide variety of chemicals -or control spots can be run on the same TLC plate and a direct comparison can be made

-the Rf values are different if the phases are changed (e.g if a different solvent is used) so it is important to use the correct table for the mobile and stationary phases in your experiment.

-similar Rf values

-chemicals that a very attracted to the mobile phase may not be separated using this method

-to separate volatile components in a mixture

-so that the separate parts of the mixture can undergo further analysis

-a solid or liquid coating on a coiled tube -this coating is normally a hydrocarbon with a high boiling point

-an unreactive carrier gas such as helium or nitrogen

-a chart of absorption against time -where the x-axis is retention time

-this value can be compared to known values to identify the component as each component will take a different amount of time to travel through the column and reach the detector -be careful as retention times for the same chemical will be different when different phases are used so use the correct data table

-retention time-can be compared to known values to identify the component -each peak represents a different substance each substance has a different retention time -the area under the absorption peak tells us the amount of each substance or percentage of a component in a mixture, the larger the area the more substance .

i) D (the larger the relative size of the peak, the greater the quantity of that substance present) ii) B and C (the peak sizes are equal) iii) D (the larger the retention time, the greater the interaction of that component with the stationary phase)

i) D (the larger the relative size of the peak, the greater the quantity of that substance present) ii) B and C (the peak sizes are equal) iii) D (the larger the retention time, the greater the interaction of that component with the stationary phase)