Determining the length of your GC capillary column is essential for accurate control of carrier gas flow rate. Just because you purchased a 30 m column, does not mean that your column is exactly 30 meters long; in fact, columns will typically have a little extra tubing. But ultimately, it is not the physical length tha matters as much as the total volume of the column. Since columns can have slight variations in internal diameter, what we really want to find is the “effective length” of the column, which accounts for these variations. The easiest way to do this is by injecting a non-retained compound and seeing how long it takes to elute from the column. This is known as the “holdup time” or “dead time”.
Once we find a “holdup time”, how do we actually go about calculating column length? Check out the following short webinar to see how you can use Restek’s EZGC Method Translator and Flow Calculator to do exactly this: