Ebook: Multidimensional Liquid Chromatography Separations

PhD diss., University of Tennessee, 2010. – 160 p.
Many mixtures important to research consist of hundreds or even thousands of individual components of interest. These types of mixtures are far too complex to separate by a single chromatographic dimension in any reasonable amount of time. However, if a multidimensional approach is used, where a complex mixture is separated by an initial dimension, simpler fractions of that separation are collected and each of those fractions are analyzed individually, highly complex mixtures can be resolved in relatively short amounts of time. This dissertation serves as a guide to multidimensional chromatography, in particular, two-dimension liquid chromatography. There are many aspects of multidimensional separations that have been investigated to show its aspects, drawbacks and potential ability to separate highly complex mixtures. Measurements for the performance of multidimensional chromatography, the effects of the first and subsequent dimensions and the approaches to pairing dimensions are shown with experimental examples. Fundamental and practical features of multidimensional chromatography are explained as well as theoretical discussions on current and future multidimensional chromatography performance. Experimentally, very high peak capacities were obtained (ca. 7000) and an algorithm to predict how to best optimize a two-dimensional separation based on the time used and performance was created for designing experiments.As the scientific community continues to evolve and become interested in highly complex mixtures, multidimensional chromatography will be the main resource to separate such mixtures in acceptable amounts of time. From the research presented here, the fundamentals have been examined and demonstrations were given on how to prepare, optimize and execute multidimensional separations. The two main factors in multidimensional chromatography are undoubtedly the peak capacity and the price for which delivering a high peak capacity is paid, time. When an analyst understands peak capacity and its meaning, the choices for MDLC become much easier. From choosing the appropriate scheme, on-line, stop-and-go or off-line, to optimizing each part of the separation to achieve a certain goal, the choices become logical when the boundary setup conditions are defined.
A detailed expression of how multidimensional liquid chromatography separations should be optimized was given. The derived equations should help in understanding and optimizing MDLC methods. Many parameters must be considered simultaneously during optimization and that the separations in the first- and the seconddimensions must be optimized together. The optimization process must be carefully thought out because the method leaves little room for empirical adjustments.
Finally, the on-line scheme of 2DLC will probably never permit the achievement of peak capacities in excess of 10 000; however, this limit still leaves considerable room to practitioners. Current on-line methods rarely, if ever exceed peak capacities of 1000, which is a considerable difference. Moving onward, the theoretical outlines and experimental results previously provided should exist as strong base for development. When MDLC is extended beyond two dimensions, the proposed optimization methods should be used to minimize the aggregate time used, maximize peak capacity (and peak capacity production) and achieve lofty separation goals under less taxing chromatographic conditions. Furthermore, when analysis requires much higher peak capacities, the utility of stop-and-go and off-line MDLC should make reaching those goals quite easy. In which case, peak capacities reaching 20 000 to 100 000 will be realistic in 30 hours or less as column and instrument technology improves.