Question

column chromatography

Why do you begin with a nonpolar solvent and continually increase polarity instead of the other way around?

. Are the factors controlling the movement of the compounds the same for TLC as they are for column chromatography? Briefly, why or why not?

. what would you change to make for a more efficient separation.

Answer 1

- Polar compounds will interact with the silica more strongly than non-polar ones so will come off the column, or elute, after non-polar compounds. When a sample contains compounds with similar polarity, the separation between then can be small and recovering all of your clean sample can become a challenge.

- not same for TLC and coloum chromatography

Thin layer chromatography (TLC) is a chromatographic technique used to separate the components of a mixture using a thin stationary phase supported by an inert backing. It may be performed on the analytical scale as a means of monitoring the progress of a reaction, or on the preparative scale to purify small amounts of a compound. TLC is an analytical tool widely used because of its simplicity, relative low cost, high sensitivity, and speed of separation.TLC functions on the same principle as all chromatography: a compound will have different affinities for the mobile and stationary phases, and this affects the speed at which it migrates. The goal of TLC is to obtain well defined, well separated spots.

Column chromatography in chemistry is a method used to purify individual chemical compounds from mixtures of compounds. It is often used for preparative applications on scales from micrograms up to kilograms. The main advantage of column chromatography is the relatively low cost and disposability of the stationary phase used in the process. The latter prevents cross-contamination and stationary phase degradation due to recycling.

-To get a good separation between your product and any impurities and, where possible, to use as little solvent as possible, the key is to test potential solvent systems before setting up your column. To do this, you will need to run thin layer chromatography (TLC) using glass or aluminium sheets coated with silica