1. Boiling temperature and polarity of the compound
The boiling temperature of a compound is often related to its polarity. The more polar a molecule the higher its boiling temperature and sol the less time it spends in the gas phase. This will cause a higer retention time as it will take longer for the compound to be pushed along the column by the gas phase.
When the polarity of the stationary phase and compound are similar, the retention time increases. This occurs because the compound has a greater interaction with the stationary phase. Remember, like interacts with like. Selection of stationary phase will influence the retention time of the component compounds. Polar compounds have longer retention times on polar stationary phases than less polar molecules and shorter retention times on non-polar columns at the same temperature.
Very high column temperatures result in very short retention times and poor separation due to the fact that all components mainly stay in the gas phase and interact little with the stationary phase. In order for good separation to occur the components need to be able to interact with the stationary phase. If the compounds do not interact with the stationary phase, their retention times will decrease and will fluctuate around the same value.
4. Flow rate of the carrier gas
A high flow rate reduces retention times, as well as causing poor separation. Again, this is because the component molecules have little time to interact with the stationary phase as they are quickly pushed through the column.
5. Column length
A longer column generally increases retention times but improves the separation.
6. Amount of material injected
Amount of material, really has no impact on retention time. If too much of the sample is injected, the peaks show a significant tailing, instead of symmetric shape.