Pressure-Tunable GC Columns with Electronic Pressure Control

High-precision selectivity tuning is achieved by the use of a series-coupled (tandem) ensemble of a nonpolar and a polar capillary GC column with adjustable pressure at the junction point between the columns. Changing the junction pressure results in a differential change in the holdup times for the two columns. This results in a change in the fractional contribution that each column makes to the overall separation selectivity. An electronic pressure controller is used to obtain greater control and improved tuning precision. With an available tuning range extending from less than 0.60 to greater than 0.85 for the fractional contribution of the nonpolar column, 37 unique, digitally selectable elution patterns are obtained. High-precision tuning is required since fractional contribution changes as small as 0.5% can significantly degrade resolution. With this system, resolution increments of 0.2 or less are achieved for typical critical component pairs.