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Longitudinal on-column thermal modulation for comprehensive two-dimensional liquid chromatography Mari E. Creese, Mathew J. Creese, Joe P Foley, Hernan J. Cortes, Emily F. Hilder, Robert A. Shellie, and Michael C. Breadmore Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b03279 • Publication Date (Web): 05 Dec 2016 Downloaded from http://pubs.acs.org on December 7, 2016
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Analytical Chemistry
Longitudinal on-column thermal modulation for comprehensive twodimensional liquid chromatography. Mari E. Creese†, Mathew J. Creese◊, Joe P. Foley†, ‡, Hernan J. Cortes||, Emily F. Hilder†, ∫, Robert A. Shellie†, §, Michael C. Breadmore†* †
Australian Centre for Research on Separation Science, School of Physical Sciences, University of Tasmania, Private Bag 75, Hobart, Tasmania 7001, Australia ‡ Department of Chemistry, Drexel University, 3141 Chestnut Street, Philadelphia 19104, United States ◊ Allison Laboratories Pty Ltd, Sandy Bay, Tasmania 7005, Australia § Trajan Scientific and Medical, 7 Argent Place, Ringwood, Victoria 3134, Australia ||HJ Cortes Consulting LLC, Midland, Michigan 48642, United States ∫Future Industries Institute, University of South Australia, GPO Box 2471, Adelaide, South Australia 5001, Australia Corresponding author: Michael Breadmore, email:
[email protected]; fax: +61 3 6226 2858 ABSTRACT: Longitudinal on-column thermal modulation for comprehensive two-dimensional liquid chromatography is introduced. Modulation optimization involved a systematic investigation of heat transfer, analyte retention and migration velocity at a range of temperatures. Longitudinal on-column thermal modulation was realized using a set of alkylphenones and compared to a conventional valve-modulator employing sample loops. The thermal modulator showed a reduced modulation-induced pressure impact than valve modulation, resulting in reduced baseline perturbation by a factor of 6; yielding a 6-14-fold improvement in signalto-noise. A red wine sample was analyzed to demonstrate the potential of the longitudinal on-column thermal modulator for separation of a complex sample. Discrete peaks in the second dimension using the thermal modulator showed 30-55 % narrower peaks than the valve modulator. The results shown herein demonstrate the benefits of an active focusing modulator such as reduced detection limits and increased total peak capacity.
KEYWORDS Longitudinal thermal modulation, low thermal mass (LTM) resistive heating, online comprehensive two-dimensional liquid chromatography. Modulation is the core process in any comprehensive twodimensional chromatographic separation. The modulator consecutively and systematically collects analytes as they are eluted from the first dimension column and delivers them to the second dimension column1. There are many modulation possibilities for comprehensive two-dimensional gas chromatography (GC × GC): resistive heating of painted zones of modulator capillary2, rotational movement of a slotted heater3,4, longitudinal movement of a cold trap5-7, cryogen jets with or without the combination of a hot jet8, and resistive heating with or without a cryogen trap9-11, and more8. In contrast, comprehensive two-dimensional liquid chromatography (LC × LC) has not been demonstrated in online-mode without use of switching valves. LC × LC using switching valves may be performed with or without trap columns12-16. A trap column offers a focusing mechanism, however, re-equilibration of the trap column is not always reached and band compression efficiency is reduced throughout the analysis unless the mobile phase strength of the second dimension gradient greatly exceeds that of the first dimension gradient, or if an equilibration step is accounted for in the modulation period16. Further, switching valves have negative effects on the 2D system17 such as pressure pulses (
