Simultaneous temperature and holdup time ratio optimization for tandem column tunable selectivity with high-speed GC

Analysis time for high-speed, capillary column GC is reduced by the use of a pressure-tunable tandem combination of a nonpolar poly(methylsiloxane) (DB-5) column and a polar trifluoropropyl poly(methylsiloxane) (Rtx-200) column operated isothermally at an optimized oven temperature. By adjusting the pressure at the midpoint between the two columns, the residence times of all sample components are adjusted to give the maximum resolution of the critical component pair. The result is a two-dimensional optimization where the column temperature and the midpoint pressure were adjusted to give the shortest possible analysis time. A previously defined relative resolution function, which requires only empirical capacity factor data for the target compounds, is used as the dependent variable in the optimization algorithm. The resulting three-dimensional resolution map is projected parallel to the relative resolution axis in order to obtain a useful two-dimensional display from which the optimal operating conditions can be determined.