Question

2. An unknown compound was analyzed using thin layer chromatography, its constituted of two components (A and B) as shown in the TLC (Silica coated stationary phase; Chloroform and Ethyl acetate as mobile phase). The mixture was then loaded onto column with silica as the stationary phase and the same solvent system was used. (2 points) Column Chromatography TLC time A В Predict the order of elution of the compounds (A and B). which one would be eluted first/last and how would you use the solvents to elute the compound a. b. Show the progress in the column as well with the passage of time. Comment on the interaction of compounds with the stationary phase. с.

Answer 1

Thin layer chromatography (TLC) is used to check the purity of the compounds. In TLC technique the compound under study will be spotted on a solid support stationary phase (usually silical gel). This spot is then eluted in a mobile phase (mixture of organic solvents) In normal phase ILC, the polar components present in the compound will have greater interactions with stationary phase and they travel less distance on the TLC plate in comparison with the non polar components that travel longer distance The mobile phase used will be a mixture of two solvents one polar solvent and one non polar solvent. The reason for using a mixture of solvents is to have better separation or elution of the compound under study If one use only non polar solvent only if the compound only have polar groups the elution will not be good. If one use only polar solvent only if the compound only have non polar groups the elution will not be good. Hence to get ideal separation, the mobile phase should have a mixture of solvents, TLC In the given TLC analysis the solvent mixture used is chloroform (non polar solvent) ethyl acetate (polar solvent) mixture. a. Predict the order of elution of the compounds (A and B). which one would be eluted first/last and how would you use the solvents to elute the compound. From the given TLC plate, it is clear that A spot travelled more distance than the B spot This suggests that A is non polar and B is polar and hence the order of elution of the compounds is A compound will come elute first from the column followed by polar compound B. b. Show the progress in the column as well with the passage of time. Column Chromatography With the passgate of time, the non polar compound A elute (travel) more distance in the column than the polar compound B as shown here. - compound B time o compound A C. Comment on the interaction of compounds with the stationary phase. The polar compound B will have more interactions with stationary phase and hence it travel less distance than the non polar compound A.which have less interactions with stationary phase