PRESSURE-TUNABLE GC COLUMNS WITH ELECTRONIC PRESSURE CONTROL

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