A Method to Externally Adjust the Column Length in Gas Chromatography Using a Water Stationary Phase

A novel method for externally adjusting the column length during gas chromatography (GC) operation is introduced. The technique employs the controlled dehydration of a water stationary phase off a stainless-steel capillary column wall, which is then removed by the carrier gas. By halting the dehydration process (i.e. through adding water to the system) at specified times, partial column (i.e. coating) lengths are created as desired. For instance, since the phase is removed in a ‘peeling’ motion from inlet to outlet, then dehydrating 1/2 of the water coating away results in a 1/2 coated column remaining. This, in turn, acts analogous to a 1/2 column length in separations. In this way, direct and effective reduction in analyte retention time results from shortening column length. Adjustable lengths from 3/4 down to 1/10 of a full column are demonstrated. Good stability in maintaining new column lengths is realized, as analyte retention times vary by only about 1% RSD for most lengths and temperatures examined. Through calibration, column length can be predictably adjusted using system dehydration time, with changes being performed in a few minutes. Results indicate that this method could be useful for adjusting column length in-situ to accommodate various samples during GC operation.