6.3.1 Chromatography and Qualitative Analysis

used to separate individual components from a mixture of substances - e.g. for analysis of drugs, plastics, air samples, flavourings and forensics

• stationary • mobile

• does not move • usually a solid • or liquid supported on a solid

• does move • usually a liquid or gas

thin layer chromatography

quick and inexpensive, and is able to indicate how many components are in a mixture

a plastic sheet or glass coated with a thin layer of a solid, adsorbent substance, e.g. silica gel

the adsorbent, e.g. silica gel

the process by which the solid silica holds the different substances in the mixture to its surface

• the different components in the mixture have different affinities for the adsorbent, and bind with differing strengths to its surface • so the components separate due to the relative adsorptions of the substances with the stationary phase

1) add a base line on the TLC plate using a pencil, about 1cm from one end 2) use a capillary tube to add a small spot of a sample to the base line 3) add solvent to a beaker, about 0.5cm depth and add a lid on top, e.g. using a watch glass 4) place your TLC plate in the solvent, making sure the solvent doesn’t go above the base line, and add the lid 5) allow the solvent to rise until it is near the top, and then remove the plate and mark the solvent font straight away using a pencil, then allow to dry 6) if any spots are visible, mark them with a pencil. could also use UV lamp to see those invisible to the naked eye, or spray on dyes/chemicals to show the spots too

retention factor

can be compared to known Rf values, which have already been recorded - MAKE SURE values compared to also used the SAME solvent system and SAME adsorbent

distance moved by component/distance moves by solvent font

• run TLC of sample alongside the pure sample • see if the same component is present

separating and identifying volatile organic compounds in a mixture

a high boiling liquid adsorbed onto an inert, solid support

the inert carrier gas, e.g. helium or neon

gas chromatogram

the liquid stationary phase adsorbed onto the solid support

1) a small amount of the volatile mixture is injected into the apparatus 2) the mobile carrier gas carries the components through the capillary column 3) the components slow down as the interact with the liquid stationary phase inside the column - the more soluble the component is in the liquid - the slower it moves - means that the components are separated, relative to their solubility 4) each component reaches the detector at different times depending on their interactions with the stationary phase - the compound retained in the column for the shortest time - has the lowest retention time - so is detected first

the time taken for each component to travel through the column

as a peak

• the retention time = IDENTIFY THE COMPONENT • the peak integrations(area) = CONCENTRATION OF COMPONENTS