Who wants to get into TLC?

[teonanacatl]

what about standed solvent mixes for each compound? that way rf should be the same. nice idea i was going to use other plant material that i new contained the same compound lol, that way i could line them up and test with reaction agent to see if they are both alkaloids etc.

[Fractalhead]

Firstly, even when different experimenters try to use the same solvent system in different laboratories, absolute Rf values can be quite variable since it is difficult to reproduce all the other factors that affect absolute Rf such as condition of the plates (eg. level of dryness), saturation level of the atmosphere inside the development chamber, temperature etc. Even when measures have been taken to control these parameters, absolute Rfs can be quite variable. What is usually more helpful is looking at the relative distances travelled by different spots and comparing these to the relative values of Rf reported in the literature in which many standards have been run alongside one another in the same lab under exactly the same conditions. This info can help you pinpoint the compound of interest in a complex plant extract so that you can then use that extract as a kind of standard to look for the same compound in a completely different mixture coming from another plant.

This approach is easiest when the typical pattern of spots obtained from a given species has been well mapped and validated with the use of standards (eg. HBWR or P. harmala) but more difficult when no such map is available and you can only get a single Rf for the compound without much to compare it to.