Question

A student using dichloromethane as the solvent runs a chromatography column and elutes with a 10:1...

A student using dichloromethane as the solvent runs a chromatography column and elutes with a 10:1 ratio of hexane/ethyl acetate. The student found that all the mixture came off the column at nearly the same time. What mistake did the student make in running the column?

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