[arwa]

What is the bset way to purification by using Column chromatography  technique? by leave the solvent flow Continuous or by add the solvent with keep the slovent in the column until the mixture reactants seprate to layers then take each layer directly?

[Yggdrasil]

It seems like there may be some misunderstanding of how column chromatography works.  Column chromatography works because different molecules travel at different rates through the column material.  Column chromatography utilizes these different rates of travel in order to separate compounds.

As an analogy consider a foot race.  A race can be considered a type of chromatography to separate slow runners from fast runners.  Consider two groups of runners with different speeds.    Lets say that the blue track team runs with an average speed of 20 km/h while the red track team runs with an average speed of 10 km/h.  At first everyone is lined up on the starting line and the blue and red runners are mixed together.  However, once they start running, the blue team will slowly gain a lead over the red team.  If we take, for example, a 10km race, blue team will finish in an average time of 30 min while the red team will finish in 60 min.  Therefore, the "chromatography" has separated the two teams.

However, if you don't start the race, the runners will all stay mixed together at the starting line.  Separation occurs only when the runners are moving.  Similarly, a column will not separate a mixture if the chemicals are just sitting in the column.  Solvent must be flowing thorugh the column in order for the molecules to be separated from each other.