Pressure-tunable column ensemble

FIGURE 5.19 Pressure-tunable column ensemble. Columns Ca and Cb use different stationary phases. Electronic pressure controller PC is used to adjust the carrier gas pressure at the column junction point. Detector Dj monitors the final chromatogram from the column ensemble, and D2 monitors a small fraction of the effluent from Ca. Carrier gas is provided at points CG. 

FIGURE 5.21 High-speed isothermal separation of a 20-component mixture using a pressure-tunable column ensemble. The plots of band position versus time were obtained from the retention factors for the mixture components on the two separate colimms along with the column dimensions and the inlet, outlet and junction point pressures. A window diagram was used to determine the junction point pressure for the complete separation of the first 14 components. Compounds are 1, n-pentane 2, methyl alcohol 3, 2,2-dimethylbntane 4, 1,1,1-trichloroethane 5, cyclopentane 6, w-hexane 7, w-propyl alcohol 8, cyclohexane 9, benzene 10, n-heptane 11, l,2-dichloropropane 12, toluene 13, n-bntyl alcohol 14, w-octane 15, 2-hexyl alcohol 16, n-pentyl alcohol 17, ethylbenzene 18, m-xylene 19, w-nonane 20, o-xylene. 

The limitation of tunable and programmable selectivity with tandem capillary columns using electronic pressure control at the column junction point is that changing the junction point pressure results in a change in the ensemble elution pattern for the entire mixture or a subgroup of the mixture, and under optimal conditions, any pressure change used to enhance the resolution of one component pair will degrade the resolution of another component pair. 

---