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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: jaques on April 17, 2009, 08:52:26 pm

Title: Thin layer chromotography
Post by: jaques on April 17, 2009, 08:52:26 pm: Can anyone explain thin layer chromotography? I can't understand what the example is saying in the heineman textbook about the plate and the sample, i haven't a clue of what they are tryin to say.
If someone could help it would really be appreciated :)
Title: Re: Thin layer chromotography
Post by: TrueTears on April 17, 2009, 08:59:56 pm: Basically in TLC, you have a stationary phase such as : Glass/metal sheet covered in a thin layer of absorbent material e.g. Silica gel, $Al_2O_3$ where different components in the sample can adsorb to. Then you also have a mobile phase which would separate the components of a mixture along a stationary phase.

You place the sample on what is known as the 'origin' and wait for the different components to separate along the stationary phase.

The $R_f$ value is equal to $\frac{\mbox{distance of component from the origin}}{\mbox{distance of the solvent front from the origin}}$ (the solvent front is the furthest place where the mobile phase 'climbs' up to) (Note: the $R_f$ value will always be smaller or may equal to 1)

The $R_f$ value can be varied according to:

•   Differing polarities of components in a mixture and hence differing solubilities
•   Separation of the mixture by components adsorbing onto the stationary phase, and desorbing into the mobile phase where it will be swept along the stationary phase.
•   Greater desorption implies a greater distance moved along the stationary phase.
Title: Re: Thin layer chromotography
Post by: Dark Horse on April 18, 2009, 01:04:17 pm: Its just like paper chromatography, except it is more sensitive, precise and can analyse less polar substances.