Dependence of Effective Peak Capacity in Comprehensive Two-Dimensional Separations on the Distribution of Peak Capacity between the Two Dimensions

Joe M. Davis*
Department of Chemistry and Biochemistry, Southern Illinois University Carbondale, Carbondale, Illinois 62901
Dwight R. Stoll
Department of Chemistry, Gustavus Adolphus College, Saint Peter, Minnesota 56082
Peter W. Carr
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455
Anal. Chem., 2008, 80 (21), pp 8122–8134
DOI: 10.1021/ac800933z
Publication Date (Web): October 8, 2008
Copyright © 2008 American Chemical Society
* To whom correspondence should be addressed. Current address: 733 Schloss St., Wrightsville Beach, NC 28480. Telephone: 910 398 5654. E-mail: chimicajmd@ec.rr.com.

Abstract

One of the basic tenets of comprehensive two-dimensional chromatography is that the total peak capacity is simply the product of the first- and second-dimension peak capacities. As formulated, the total peak capacity does not depend on the relative values of the individual dimensions but only on the product of the two. This concept is tested here for the experimentally realistic situation wherein the first-dimension separation is undersampled. We first propose that a relationship exists between the number of observed peaks in a two-dimensional separation and the effective peak capacity. We then show here for a range of reasonable total peak capacities (500−4000) and various contributions of peak capacity in each dimension (10−150) that the number of observed peaks is only slightly dependent on the relative contributions over a reasonable and realistic range in sampling times (equal to the first-dimension peak standard deviation, multiplied by 0.2−16). Most of this work was carried out under the assumption of totally uncorrelated retention times. For uncorrelated separations, the small deviations from the product rule are due to the “edge effect” of statistical overlap theory and a recently introduced factor that corrects for the broadening of first-dimension peaks by undersampling them. They predict that relatively more peaks will be observed when the ratio of the first- to the second-dimension peak capacity is much less than unity. Additional complications are observed when first- and second-dimension retention times show some correlation, but again the effects are small. In both cases, deviations from the product rule are measured by the relative standard deviations of the number of observed peaks, which are typically 10 or less. Thus, although the basic tenet of two-dimensional chromatography is not exact when the first dimension is undersampled, the deviations from the product rule are sufficiently small as to be unimportant in practical work. Our results show that practitioners have a high degree of flexibility in designing and optimizing experimental comprehensive two-dimensional separations.

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History

  • Published In Issue November 01, 2008
  • Article ASAPOctober 08, 2008
  • Received: May 6, 2008
    Accepted: August 12, 2008

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