In Gas Chromatography, 1-Propanol had a longer retention time acetone. Why is this?

Answer 1

In gas chromatography, the sample is injected into a long, narrow column. They are swept through the column by an inert gas to a detector, which emits an electrical signal when it senses the presence of a molecule. Different compounds pass through the column at different rates... thus, one compound will arrive at the detector at a different time than another. The rate at which a given compound travels through the column depends on two things
1. Molecular weight
2. Affinity for the mobile phase

In this case, 1-propanol has a slightly higher molecular weight than acetone. This tends to make it travel more slowly, giving it a higher retention time. It also seems likely that 1-propanol is adsorbing more strongly onto the column materials, thus hindering its progress through the column.

Answer 2

completely depends on the column your using.