Guard columns are typically from 0.5 to 10 meters long. Although there are no definitive lengths that are good for all samples, the following guidelines can be used.
If the sample matrix is relatively "clean" (a small concentration of non-volatile compounds) and the solutes are active, the guard column should be 0.5 meter to 1 meter in length. If the sample matrix is dirty, the guard column should be longer (to collect the nonvolatile compounds). Five to ten meters help simplify system maintenance. With use a guard columns saturates and it becomes necessary to replace it. The longer guard column allows the user to simply cut off the first meter or so and reinstall it into the injector instead of replacing the entire guard column