Tunable selectivity strategies for high-speed gas chromatography.

Column bifurcation and tunable selectivity were developed for high-speed gas chromatography. The separation of eleven VOCs (volatile organic compounds) in fifteen seconds is demonstrated using high-speed gas chromatography on serially linked capillary columns with different stationary phases. When carrier gas pressure at the junction of the tandem columns is adjusted, the carrier gas flow rates change in the two columns, resulting in components spending different amounts of time in contact with the stationary phases. Pressure changes result in a new overall selectivity, which is intermediate between the selectivity of each of the tandem columns individually. Adjusting the selectivity of a separation can shift apart the pair of components which were least resolved. A linear tuning model which predicts the retention of components was developed and tested. Window diagrams to predict the optimum tuning pressure were developed. A window diagram is a computer generated model which predicts the separation over a range of tandem column lengths or tuning pressures. Previous work with window diagrams used relative retention to predict resolution which was shown to be inadequate. A new function was developed which was shown to have better predictive power for resolution than relative retention, especially at low capacity factor values. Using temperature as an added tuning parameter resulted in the separation of fifteen VOCs in under twenty seconds on tandem columns. Data were collected to predict the resolution at any temperature and tuning pressure. Three-dimensional window diagrams were produced to describe the optimization of the two tuning parameters, temperature and tuning pressure. Temperature was also shown to have an effect on the overall analysis time. Three-dimensional triangular coordinate window diagrams were produced to predict the optimum column lengths of three columns in tandem. The best possible resolution of fifteen VOCs on the three tandem columns was demonstrated in about one hundred seconds. Column bifurcation, a technique which selectively switches components onto a tandem column, was also developed. This technique separated twenty-one VOCs in under forty-five seconds. The utility of column bifurcation was shown with window diagrams.PhDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/103900/1/9423132.pdfDescription of 9423132.pdf : Restricted to UM users only