Any labelling on the plate to show the original position of the drop must also be in pencil. Anything I draw as pure white allows the background colour of the page to show through.Ī pencil line is drawn near the bottom of the plate and a small drop of a solution of the dye mixture is placed on it. I'm forced to show it as off-white because of the way I construct the diagrams. Note: The chromatography plate will in fact be pure white - not pale grey. We'll start with a very simple case - just trying to show that a particular dye is in fact a mixture of simpler dyes. The mobile phase is a suitable liquid solvent or mixture of solvents. The stationary phase for thin layer chromatography also often contains a substance which fluoresces in UV light - for reasons you will see later. The silica gel (or the alumina) is the stationary phase. Thin layer chromatography is done exactly as it says - using a thin, uniform layer of silica gel or alumina coated onto a piece of glass, metal or rigid plastic.
We'll look at the reasons for this further down the page. Different components travel at different rates. The mobile phase flows through the stationary phase and carries the components of the mixture with it. They all have a stationary phase (a solid, or a liquid supported on a solid) and a mobile phase (a liquid or a gas). All forms of chromatography work on the same principle. Some similar problems are discussed on the page about paper chromatography, but I am unwilling to do the same thing on this page which is intended as a fairly gentle introduction to chromatography.Ĭhromatography is used to separate mixtures of substances into their components. The reality is more complicated and the explanation will vary depending on what sort of solvent or solvent mixture you are using. Note: I'm taking a simple view of the way that thin layer chromatography works in terms of adsorption (see below) which should be adequate for students doing courses for 16 - 18 year olds. Although if you are a beginner you may be more familiar with paper chromatography, thin layer chromatography is equally easy to describe and more straightforward to explain. This page is an introduction to chromatography using thin layer chromatography as an example.