A)You perform column chromatography on a mixture of reaction products which show

Question

A)You perform column chromatography on a mixture of reaction products which show two spots on TLC. However, under the column conditions you chose those two compounds do not separate. One can alter a number of factors in order to improve the resolution of components by column chromatography. For each of the factors listed, separation can be improved by either by increasing or decreasing the factor. For each, describe how changes in sample size or interactions between components and the chromatography medium are altered by increasing or decreasing the factor so that resolution will be improved. 1) Column Diameter 2) Column length 3) Sample Volume 4) Sample Concentration 5) Loading Time 6) Flow Rate B) Based on your answer to a, consider the changes five classmates made to column conditions and decide who was most likely, and the next most likely, to separate the compounds you could not by making all of those changes. For each, list all conditions which improved resolution.

Explanation / Answer

1) Column Diameter: increasing the diameter of the column will improve separation. This increase while keeping the volume of the sample the same will cause the sample to be concentrated in a more narrow band in comparison to the total volume of the column.

2) Column Length: Increase the column length results in an improved separation. This is because the solute will interact with the adsorbent more, creating a better resolution.

3) Sample Volume: Reducing the sample volume produces an improved separation because the sample is a smaller fraction of the column volume.

4) Sample Concentration: Increasing concentration results in an improved separation. this causes the band to be tighter and diffuse less.

5) Loading time: The decrease in loading time will result in improved separation.

6) Flow Rate: Decreasing flow rate increases separation. This allows the solute to have enough time to interact with adsorbent and eluting solvent.

Mike is the most likely to separate compounds. All of the conditions he has chosen will improve the separation. Bonnie is the next most likely to improve the separation. Four of the factors improve resolution (increase column diameter, increase column length, increase concentration of sample, and decrease flow rate).

Lee only had the decrease in volume loaded, increase in concentration of loaded sample, and decrease in flow rate improve the separation.

Dan only had increase in column diameter.

Robin only has increase in column length, decrease in time to load sample, and decrease in flow rate.

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