How to calculate GC chromatography column length?

Restek EZGC Method Converter and Flow Calculator

Determining the GC column length is important during the initial setup of the column or after maintenance column trimming so that the electronic pneumatic control of the carrier gas flow is accurate. Otherwise, you may see more flow coming into the detector than you think (especially problematic in MS as you can lose sensitivity) or you may see elution order changes in your chromatography.

With the EZGC Method Converter and Flow Calculator, calculating the GC column length is easy (or EZ!), simply by performing a dwell time determination. The residence time can be determined by split air (GC-MS), methane (GC-FID), or methylene chloride headspace (GC-ECD), the time it takes for an unattached compound to cross the GC column from the inlet to the detector, and the "retention time" should be noted.

In the latter case, make sure the furnace temperature is at least 250°C as the GC-ECD will show some retention of methylene chloride at lower column temperatures. Do not overload the column with compound, ie the vertex must be symmetrical for an accurate determination. Start by entering the nominal value for the length (eg 30m) in your GC control software, enter a stream, and then set the dwell time. Usually the average “holding time” of three analyzes is taken.


















The rest of the process is shown in the figures below. Note that I'm using the Downloaded version with "spinner" for easy adjustment of the column length, but for the web-based version it will work as well by entering the column length values instead of the "spin".