The separation column consists of two parts : a stripper column and an analysis column. These are usually two identical columns, with different lengths. The goal is to prevent a prolonged analysis, which is normally caused by the necessity of waiting for elution of the highest boiling compound. Therefore the time is set for the slowest eluting compound of interest to get through the column. After this time the flow in the stripper column is reversed by switching the 10-port-valve. All higher boiling compounds will not reach the detector.