faculty

Professor of Chemistry
Ph.D., University of Wisconsin

High Speed Analytical Separations

Phone: (734) 764-7373
E-mail: rdsacks@umich.edu

Research Group

Gas chromatography (GC) is the most widely used analytical technique for the speciation and quantification of organic compounds. Strategies, instruments and procedures are being developed for increasing the speed of capillary gas chromatography by a factor of a hundred or more. This would make gas chromatography far more useful for chemical process monitoring, general laboratory applications and environmental monitoring. Completely automated instruments that are capable of generating 10,000 chromatograms in a 24-hour period are used to implement strategies and procedures for high-speed chemical analysis. Low pressure gas chromatography is used as a means of improving the performance of capillary columns. High-speed gas flow switching techniques are used to implement on-column sample preparation and clean-up procedures and to multiplex several columns into one detector. Tunable selectivity strategies employing series coupled ensembles of two or more capillary columns with different selectivities are being studied for high-speed applications. An important recent project has been the development of cryofocusing inlet systems which use steep thermal gradients along a capillary metal tube to cryofocus a dilute vapor sample into a small condensed-phase plug which is then revaporized by rapidly heating the metal tube. The resulting narrow vapor plug us introduced into a capillary separation column. When this inlet system is combined with relatively short capillary columns operated at unusually high carrier gas flow rates, up to ten components can be separated in less than two seconds.

Other projects involve the use of pressure tunable selectivity for shifting peaks from congested regions of a chromatogram to open regions. The ability to move peaks locally within a chromatogram greatly reduces the peak capacity required for a separation and thus can result in 100-fold or greater reductions in analysis time. Tunable selectivity is achieved by the use of series-coupled columns of different selectivity and adjustable junction-point pressure. These multiphase separations are very powerful, and models and optimization strategies are under development for facilitating their application to environmental and process monitoring. A model under current development uses a vector representation in a multidimensional retention space to des-cribe the separation of each component pairs in a complex mixture. Projections of the complete ensemble of all such vectors for a mixture allows for the prediction of conditions which will minimize separation time. Other optimization strategies also are under development.

REPRESENTATIVE PUBLICATIONS

1. Whiting, J; Sacks, R. "Selectivity Enhancement for High-Speed GC Analysis of Volatile Organic Compounds with Portable Instruments designed for Vacuum-Outlet and Atmospheric-pressure Inlet Operation Using Air as the Carrier Gas, Anal. Chem. 2002, 74, 246.
2. Smith, H.; Sacks, R., Vector Model for Window-Diagram Optimization of Tunable Column Ensembles for High-Speed GC, J. Microcol. Sep. 2002, 14, in press.
3. Veriotti, T.; Sacks, R.; "High-Speed GC and GC/Time-of-Flight MS of Lemon and Lime Oil Samples," Anal. Chem. 2001, 73, 4395.
4. Veriotti, T.; Sacks, R.; "High-Speed GC and GC/MS with a Series-Coupled Column Ensemble Using Stop-Flow Operation,Ó Anal. Chem., 2001, 73, 3045.
5. McGuigan, M.; Sacks, R.; "Band Trajectory Model for Temperature-Programmed Series-Coupled Column Ensembles with Pressure-Tunable Selectivity,Ó Anal. Chem. 2001, 73, 3112.