Column selectivity programming and fast temperature programming for high-speed GC analysis of purgeable organic compounds

High-speed gas chromatograms are obtained by the use of relatively short le ngths of capillary column operated at relatively large carrier gas how rate s. This approach is difficult for more complex mixtures because of the redu ced peak capacity available with shorter columns. A solution to this proble m is the use of tunable column ensembles consisting of the series (tandem) combination of a polar and a nonpolar column. By adjusting the pressure at the junction point between the columns, the selectivity of the ensemble can be adjusted within the limits imposed by the individual columns, For mixtu res representing a relatively large boiling point range and containing more than similar to 20 components, high-speed, isothermal separations are less effective. These limitations are significantly reduced by combining fast t emperature programming with selectivity programming. Selectivity programmin g is obtained by changing the pressure at the column junction point one or more times during the course of an analysis. In the work described here, th e column ensemble temperature and the junction pressure are initially set t o give a high-quality separation of the earliest eluting components. After these components have eluted, a linear temperature ramp of similar to 35 de grees C/min is initiated. As the temperature increases, the pressure is adj usted to change the selectivity and thus facilitate the separation of group s of components as they migrate through the column ensemble. Using this app roach, a mixture of 30 purgeable organic compounds is separated in less tha n 2.5 min.